Environmental regulation and corporate environmental performance: A bibliometric analysis

: Under the concept of green development, enterprises will face more environmental constraints. Whether government environmental regulation (ER) can effectively promote corporate environmental performance (CEP) has not yet been unified among scholars, and few studies have conducted bibliometric analysis on ER and CEP. Based on the above, this study has three purposes: first, to fill the research gap by analyzing and visualizing 72 articles on ER and CEP through Biblioshiny and VOSviewer; second, to help scholars easily understand the research development and quickly find promising research directions; and lastly, to enable the government and corporate managers gain a more comprehensive view of ER’s impacts on CEP, which can assist in policy making and business management. The research found that: (a) the number of articles and citations in the field is on the rise. China is the most academically influential country in terms of publications, citations, and collaborations. Journal of Cleaner Production is the top-ranked journal. Ramanathan R, Testa F, and Zhang Y are the top three authors. Environmental management, sustainability, and China are the most popular keywords. Collaboration between authors, institutions, and countries is relatively weak and isolated. (b) ER and CEP have three emerging clusters: Climate Change, FDI, as well as Environmental Awareness, and three core clusters: Environmental Management, Data Envelopment Analysis, and Economic Analysis. The evolution of themes shows a trend from decentralized to centralized and then back to decentralized. (c) Future research can take the Regulatory Framework, Green Technological Innovation, and Environmental Management System as breaking points


Introduction
The trending subjects of business today differ greatly from the past.Previously there was too much focus on profits with much business literature focusing on the drivers of economic performance, which can lead to a neglect of the environment (Ngo, 2021).Research studies have shown that more than three thousand international corporations cause over two trillion dollars in negative social and environmental impacts each year (Dai et al., 2021;Sutherland et al., 2016).The problem of environmental pollution has attracted increasingly widespread attention, and problems such as air pollution, wastewater discharges, and climate warming need to be urgently solved (An et al., 2022).Therefore, realizing a double-win situation between environmental protection and economic development is a hot issue in the modern scientific community, and also a conflict that countries around the world are desperate to resolve (Peng et al., 2020;Y. Zhang et al., 2022).Enterprises in modern society should concentrate not only on economic achievement but also on environmental performance.
Some scholars believe that social culture, government regulation, and technological progress contribute significantly to the implementation of green management by enterprises, and government environmental regulation (ER), in particular, is considered a key driver (Esfahbodi et al., 2017;Xu et al., 2013).ER refers to the continuous and centralized supervision by the government of behaviors of economic entities, mostly enterprises, through the establishment of laws and regulations, in order to constrain enterprises from damaging the natural environment in their operations (Dong et al., 2011;Tan, 2016).Regarding the relationship between ER and corporate environmental performance (CEP), there are mainly three views expressed by scholars.First, ER has a positive impact on CEP (Dong et al., 2014;Y. Zhang et al., 2022;Zhuo, 2023), represented by the "Porter hypothesis".This hypothesis argues that ER will stimulate companies to innovate, and the economic benefits of such innovation will not only generate an "innovation compensation effect" to offset the increased costs of environmental pollution control but also generate a "first mover advantage" effect, which will lead firms to adjust their strategic layout and solve the pollution problem at source (Porter, 1991).According to this theory, ER can significantly motivate firms to improve their environmental performance, but there is some controversy in the academic community (Saeed et al., 2018).The second argument is that ER negatively affects CEP (Niesten et al., 2017).The traditional view of the "compliance cost effect" proposes that ER generates a green paradox (Liu et al., 2020), which can be understood as the funds used for technological innovation are taken up by the cost of environmental management.This makes it impossible for enterprises to profit from technological research and development, which leads to long-term interests being jeopardized and is not conducive to improving productivity (Albrizio et al., 2017;Jaffe et al., 1995).Hence, ER reduces productivity (J.Zhang, 2016) which in turn weakens CEP.Finally, there is a third academic viewpoint of uncertainty.R. Li and Ramanathan (2018) concluded that the relationship between control-based as well as market-based ERs and CEP is non-linear and positive, while the relationship between informal ER and CEP is not significant.
There are very few literature review articles on the topic of ER and CEP.First, Aragón-Correa et al. (2020) provided an in-depth analytical review of literature on the relationship between different regulatory pressures and corporate environmental strategy and performance, which is the most relevant qualitative review article on ER and CEP.However, it was published in 2020, and the review covers publications up to 2019, nearly four years ago.Therefore, it remains to be seen what the latest scientific progress within the field has been.Second, Dechezleprêtre et al. (2019) qualitatively reviewed all the literature including both economic and environmental performance, and from a small number of articles dealing with ER, sorted out that ER tends to improve environmental performance without weakening economic performance.However, because the number of articles is limited, this result cannot be easily generalized (Dechezleprêtre et al., 2019).Finally, apart from all the qualitative reviews mentioned above, the abstracts or keywords of some bibliometric analysis articles may address ER or CEP but tend to focus on other elements as well, all of which are of low relevance.For example, the literature review on green innovation, environmental and financial performance includes ER as a keyword (Borsatto and Bazani, 2023).Another example is the bibliometric analysis written by M. Li et al. (2022) on ER and green technology innovation (GTI) via CiteSpace software, where the abstract refers to performance as one of its three main research areas.These bibliometric articles do not relate well to ER and CEP and usually employ different analysis and visualization tools than this paper.In summary, qualitative review articles are the most relevant to this topic but with a research scope of only up to 2019; while quantitative bibliometric articles are relatively numerous and published in recent years, they have a lower relevance.Therefore, the quantitative bibliometric analysis and qualitative review of core articles on the latest research of ER and CEP in this paper will fill the gap.In addition, this paper is of great significance in enabling business managers, governments, and scholars to be well informed of the relationship between ER and CEP, which will facilitate business management, policy making and quick access to research.
The main objective of this study is to sort out and summarize the literature in ER and CEP through bibliometrics, systematically analyze the core elements, research trends, and knowledge structure of selected literature in this field, and present the findings to scholars in the form of visualization diagrams.To be specific, this paper primarily addresses the following six research questions (RQs): RQ1: What is the current status of publication on ER and CEP? RQ2: What are the top journals, publications, key words, authors, and most relevant institutions about ER and CEP?
RQ3: What is the degree of research collaboration concerning ER and CEP? RQ4: What are the "hot spots" in ER and CEP and how about their evolution over time?
RQ5: What is the intellectual structure between ER and CEP? RQ6: What are the future potential directions and avenues in ER and CEP research?
The rest of the paper is arranged as follows.Section 2 describes the research methodology.Section 3 conducts the bibliometric analysis and derives results, Section 4 summarizes and discusses the bibliometric findings, and Section 5 gives conclusions.

Bibliometric analysis procedure
In this study, a comprehensive and detailed bibliometric workflow on publications in the field of ER and CEP was carried out according to the five steps recommended by H. Li et al. (2023) and Lei et al. (2022), as shown in Figure 1. Figure 1.Five main steps in the bibliometric analysis process.

Scheme of study
The main research objective of this study is to conduct a bibliometric review of the literature in ER and CEP.By using software such as Biblioshiny, VOSviewer, and Microsoft Excel, this paper attempts to answer and contribute to the six questions posed in the introduction section.The first objective is to clarify the current state of literature in ER and CEP through descriptive, quantitative, and three-field analysis.The second objective of the study is to contribute to the identification of core journals, articles, authors, keywords, and other aspects of the field using Biblioshiny and Microsoft Excel.Specifically, for influential sources and core authors we use H-Index, total citations (TC), and annual net publications (NP) to identify them (Arslan et al., 2022).In addition, Bradford's law is used to tri-categorize major journals.Zone 1 is the most active one, and Zone 2 is the intermediately active region, while Region 3 has virtually zero output compared to Zones 1 and 2 (Bashir, 2022).In the keyword analysis, author keywords and keywords plus were utilized for the analysis respectively.Third, collaboration network diagrams by Biblioshiny are used to visualize research collaborations among authors, institutions, and countries.Then, Biblioshiny is used to map themes and themes' evolution to identify hot topics and their evolutionary processes (Bashir et al., 2021).The fifth objective explores the intellectual structure of ER and CEP in the past and present through co-citation analysis based on cited references and bibliographic coupling analysis on citing literature in VOSviewer (Phan Tan, 2022).Finally, based on the analyses and findings of the first five objectives, potential future research agendas are explored in conjunction with the keyword co-occurrence analysis in VOSviewer (Donthu et al., 2021).
There are several bibliometric tools, and the Biblioshiny and VOSViewer software were adopted for the following reasons.Firstly, Biblioshiny has the advantage of enabling non-coders to process bibliographic data with the R-package (Ullah et al., 2022), which is suitable for basic statistics analysis (Aria and Cuccurullo, 2017;Gu et al., 2021).Secondly, VOSViewer allows the construction of network maps in a highly user-friendly and easy-to-analyze way (Van Eck and Waltman, 2010), visualizing the relationships among selected items vividly and thus making them easier to comprehend and interpret (Gu et al., 2021).In addition, VOSviewer has useful features such as overlay visualization and density visualization, making it an excellent choice for visual mapping (Bosi et al., 2022).Therefore, in this paper, except for using VOSviewer for co-citation analysis, bibliographic coupling analysis, keyword cooccurrence analysis, and plotting the corresponding maps, the rest of the analyses are achieved by Biblioshiny.

Data collection
The data collection part of the bibliometric analysis was divided into two parts.The first is the selection of databases from which the literature is obtained.This paper uses the Scopus database to select relevant literature due to the following reasons.First, the Scopus database has been well accepted by a large number of scholars due to its broader, more inclusive, and comprehensive range of available publications (Caviggioli and Ughetto, 2019;Pham-Duc et al., 2023;Pranckutė, 2021).It is the largest "peer-reviewed" database worldwide (Karagiannopoulou et al., 2023), offering more citation records and more flexible and convenient data processing services (Aznar-Sánchez et al., 2019;Lima and Bonetti, 2020).Second, it also labels each publication included in its collection with author biographies and institutional affiliations, enabling a more user-friendly literature analysis process (Mongeon and Paul-Hus, 2016).Finally, it also has two major advantages over the Web of Science (WOS) database.On the one hand, Scopus makes it easier to extract data, whereas exporting more than 500 publications using WOS entails manual work (Gao et al., 2021); on the other hand, Scopus databases cover a wider range of publications in the business and management areas (Aksnes and Sivertsen, 2019;Farrukh et al., 2022).
The second part is screening the exported data.The final search query is "TITLE-ABS-KEY ("environment* regulation*" AND ("environment* performance" OR "green performance")) AND (LIMIT-TO (DOCTYPE, "ar")) AND (LIMIT-TO (SUBJAREA, "busi")) AND (LIMIT-TO (LANGUAGE, "english"))".For efficiency, we limited the search to English-language publications.Though conference papers, books, and book chapters can all provide valued perspectives to some extent, only journal articles were selected for this paper.This is because firstly, journal articles must undergo a rigorous peer review process and thus have a higher level of quality assurance (Harsanto and Firmansyah, 2023); secondly, journals usually have wellestablished citations, which are more scholarly influential (Setiawan et al., 2023); and thirdly, journal articles are usually in a standardized format (Green and Cookson, 2012) and can provide comprehensive bibliographic data (Oliveira et al., 2019).The query was run on 23 August 2023 in the Scopus database.Initially, a total of 213 publications related to ER and CEP were retrieved.We then manually analyzed 213 documents according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, which are a set of proposals aimed at improving the clarity, completeness, reproducibility, and quality of systematic review and meta-analysis studies (Page et al., 2021).141 out of 213 publications were excluded, which are 2 duplicate articles, 32 articles in unrelated fields such as environmental science and ecology, industrial and systems engineering, and architectural engineering, and 107 articles in related fields but with less relevance (ER and CEP are mentioned only in the background or suggestion parts of the abstracts).Our final sample consisted of 72 articles from 34 journals that examined the relationship between ER and CEP from 2002 to 2023.

Data analysis and results
As stated earlier, the major analytical tools utilized to conduct big data analysis of 72 journal articles and draw conclusions were Biblioshiny software and VOSviewer software.Additionally, the Biblioshiny based on the R package and the JAVA-based VOSviewer differ from other bibliometric analysis tools in bibliometric features.
Table 1 shows the descriptive data using Biblioshiny for articles on ER and CEP, with a focus on research cooperation rather than single-author publications.

Volume analysis of publications, countries, and journals
In this part, a simple quantitative analysis of publications, countries, and journals related to the ER and CEP fields will be carried out using Biblioshiny, in addition, MS Excel was used for visualization in Figure 2.
As shown in Figure 2, we first investigate the trend of annual publications and citations about the topic of ER and CEP since 2002.The trend of articles and citations per year remained roughly consistent, both showing waves based on an overall upward trend, with four peaks occurring successively and respectively.In terms of annual publications, 2004, 2013, 2018, and 2022 were more productive, with peaks emerging, while 2007, 2016, and 2020 hit rock bottom.The same applies to annual citations, with summits in 2004, 2011, 2018, and 2021, and troughs in 2007, 2015, and 2020.This suggests that scholars' attention to this field has shown an increasing and periodic trend and the topics are more innovative.Next, the statistical analysis is further broken down into individual countries and ranked according to total publications, total citations, and SJR, as shown in Table 2. SCImago Journal & Country Rank (SJR) is a public website portal based on the Scopus database that provides free bibliometric information on different countries and a large number of specialized journals (Harsanto and Firmansyah, 2023).Its Country Rankings form a comprehensive assessment of the overall impact and relevance of scientific research in different countries.In Table 2, China, the United Kingdom, the United States, Italy, Canada, Spain, and Australia are included in both the publication and citation rankings.France, Ghana, and the Netherlands, on the other hand, feature only in the publication rankings, while Austria, Belgium, and Korea occur only in the citation rankings.Further, it can be found that the top ten countries in terms of publications and citations are also relatively close to each other in terms of SJR and do not fluctuate much within the top ten.The number of publications of Ghana is ranked 9th in ER and CEP, well ahead of its SJR ranking, which is its area of specialization.Austria and Belgium rank in the top ten in terms of citations in ER and CEP, but their SJR rankings are outside the twentieth place, suggesting that they have a large influence advantage in ER and CEP.

Core aspects of ER and CEP literature
Next, in this part, the influential aspects of the selected 72 pieces of literature article will be analyzed separately, such as the influential research journals, core publications, trending keywords, top authors, and most relevant affiliations.All relevant analyses in this part are performed using Biblioshiny software and MS Excel

Influential journals and publications
Source impact and Bradford's law were applied in this section to assess the influence of academic journals on ER and CEP literature.According to the indexes, total publications, and citations, Table 3 lists the top 10 influential journals in this field, while Table 4 presents a different journal ranking of Zone 1 and Zone 2 based on Bradford's law, indicating higher research impact classified into Zone 1. Note(s): H-Index (h) = number of publications (h) with h citations or more, G-Index = number of papers that have accumulated g 2 number of citations, M-Index = H-Index per active year, TC = total citations, NP = number of publications, PY_Start = start of the publication year.Journal of Cleaner Production is the most influential journal in the field, focusing on the impact of different ERs on CEP, the moderating effect of ER on relationships relating to CEP, the influence of ER on sustainable development, etc.The key articles in the journal with high citations (see Table 5) on ER and CEP are presented as follows.First, "Is environmental regulation effective in China?Evidence from city-level panel data" empirically analyzed 283 Chinese cities' panel data and four environmental quality indicators from 2003 to 2010 using a first-order difference GMM model (Hao et al., 2018).It was found that current ER does not meet the objective of reducing pollution.Furthermore, ER is effective only when foreign direct (FDI) investment is controlled.Second, drawing on panel data of Chinese listed companies from 2011 to 2017, Cao et al. (2021) revealed that digital finance greatly benefits China's energyenvironmental performance.In addition, the positive impact of digital finance on energy-environmental performance is strengthened under conditions such as financial and environmental regulation by the Chinese government, and in regions with immature credit and capital markets.Third, R. Li and Ramanathan (2018) categorized ER into three types: command-and-control regulations, market-based regulations, and informal ones, in order to investigate the linear relationship between different ER and CEP, as well as the potential nonlinear relationship.It is found that there is a nonlinear positive relationship between command-and-control and market-based regulations, and CEP, whereas neither linear nor non-linear relationships were statistically significant in the case of informal regulations (R. Li and Ramanathan, 2018).Last, by examining Chinese companies in the pulp and paper industry in Shandong Province for the period 2001-2008, Y. Wang et al. (2011) ) discovered that, with stricter environmental regulation, indicators such as water efficiency, energy efficiency, and environmental efficiency (except for carbon dioxide emissions and energy consumption) have improved significantly, and the industry's overall environmental performance has become more sustainable.
Business Strategy and The Environment is the second leading journal, covering studies on the impact of ER in the forms of environmental labeling certification (ELC) or European Union Emission Trading Scheme (EU ETS) on CEP and the effect of ER on CEP in the context of outward foreign direct investment (OFDI).Typical articles on ER and CEP in this journal include the following.Firstly, using Chinese companies as research objects Long et al. (2023) found that OFDI improves CEP.In addition, in their research CEP is further improved when OFDI is hosted in developed countries with stricter environmental regulations and where the national cultures focused on long-term development (Long et al., 2023).Secondly, He et al. (2022) took a sample of Chinese A-share listed companies in the manufacturing industry over the period of 2008 to 2016 and discovered that environmental labeling certification (ELC) enhances CEP while having no influence on financial performance.Lastly, using a sample of listed companies that have been penalized by the U.S. government for violating environmental regulations, Shevchenko (2021) found that being subject to environmental penalties is not linked to improved CEP.On the contrary, these penalties even lead to further deterioration of CEP (Shevchenko, 2021).
International Journal of Production Economics is followed by the third rank in this field, in which the published articles mainly study the influence of ER in terms of carbon tax or ecological civilization regulation on CEP, the moderating role of environmentally friendly product innovation on the relationship between ER and CEP, etc. "The moderating effect of environmental dynamism on green product innovation and performance" is the third most cited research article, see Table 5.It employs a questionnaire survey to investigate the relationship between ER and the performance of listed companies in China and the moderating role of green product innovation in it.Furthermore, the article also examines the relationship between environmental production innovation and corporate performance along with the moderating role of green dynamics (Chan et al., 2016).
Then, the yearly scientific output of the top five research journals can be seen in  Next, this paper counts the top 10 articles in ER and CEP and their impact.Table 5 provides statistics on global citations, a metric that reflects the overall citation trend of an article worldwide (Lei et al., 2022)."Environmental policy, innovation and performance: New insights on the porter hypothesis" by Lanoie et al. (2011) is the most globally cited study in the field.It tests the implications of different versions of the Porter hypothesis by analyzing data on environmental policy, R&D, environmental performance, and business performance from a sample of about 4,200 factories in seven OECD countries (Lanoie et al., 2011).The second-ranked publication by Clarkson et al. (2004) discovered that environmental investments by low-polluting firms that over-comply with current ER result in incremental economic benefits, whereas high-polluting firms that meet only minimal environmental requirements do not.The study by R. Wang et al. (2018) drew from panel data and insight interviews that CEP exhibits an inverted U-shape as the control over environmental behavior is decentralized from the central government to the administrative level.There is also a positive moderation of this relationship by the stringency of ER and a negative moderation of environmental supervision capacity (R. Wang et al., 2018).Yu et al. (2017) validated the relationship between environmental pressures, namely ER and stakeholder pressures, and firm performance, along with the environmental innovation strategy as a mediator and marketing capabilities as a moderator, using primary data from 121 UK manufacturers and secondary data about financial performance.Lastly, Dong et al. (2014) performed a regression analysis on 245 Chinese firms and found that both eco-innovation and ER can significantly affect CEP and competitiveness, whereas firm size and the enforcement of ER only exert a strong effect on CEP.The other top ten articles in Table 4 are summarized in detail in the previous section 4.2.1 Core research journals.

Keywords
Table 6 illustrates the most frequently used terms in the literature related to ER and CEP, which is further manually filtered based on the statistical results of Biblioshiny software.Words with low relevance to ER and CEP, such as China, and duplicate words, such as environmental regulations, were excluded, displaying only highly relevant non-repeated words to the topic.For keywords plus, besides the topic terms CEP and ER, the most frequently occurring words are environmental management with a high frequency of 40 times, followed by commerce, sustainable development, environmental economics, and so on.The most common keywords used by the authors are sustainability, followed by economic performance, data envelopment analysis, etc.All of these keywords are related to ER and CEP and to a certain extent demonstrate the relationship between these two variables.According to related literature (Arslan et al., 2022;H. Li et al., 2023), the word cloud created in the paper is based on the frequent occurrence of keywords plus, see Figure 5, where larger words mean more frequent usage.Keyword Plus goes beyond author-supplied keywords, which is determined using a unique algorithm designed to enhance the power of cited reference searching and broaden the scope of search results (Garfield and Sher, 1993).From Figure 5, Commerce and sustainable development appear most frequently because the subject regulated by ER is the business behavior of companies, which seek better environmental performance to achieve sustainable development.Furthermore, the terms China, environmental economics, environmental protection, and efficiency have received special attention from scholars, and these studies aim to explore the initiatives and effectiveness of China, as the largest developing country, in the process of balancing economic development and environmental governance issues.Some of the literature also studied keywords such as environmental policy, environmental legislation, emission control, and innovation, focusing environmental performance on emission reduction and improving environmental problems through relevant policy legislation and innovation.In short, all the keywords in Figure 5 have been studied in the context of ER and CEP, and researchers can use them as a reference in the future to select the niche areas of interest for their research.

Top authors and relevant affiliations
To take the research further, it was investigated which researchers and research organizations contribute the most to the literature on ER and CEP.The top ten authors are initially reported on the basis of h-index, total citations, and total publications, as shown in Table 7.The h-index (h) denotes that a researcher has h articles that have been cited at least h times, and is an indicator of both productivity and citation impact (Dhiaf et al., 2021).From the table, Ramanathan R has played the most pivotal role in the field by focusing on the effects of different ERs, environmental pressures, and organizational stresses on environmental performance, respectively (R. Li and Ramanathan, 2018;Ramanathan et al., 2014;Yu et al., 2017).Zhang Y has been a rising star in this field in the past two years, ranking second, mainly studying the two major influences on environmental performance, ER & media attention, the environmental performance of carbon emission policies, and the impact of different ERs on energy environmental performance, etc. (H.Li and Zhang, 2022;Y. Zhang et al., 2022;Y. Zhang and Song, 2021).Testa F, a predecessor in the field, is ranked third as his research was mainly conducted 10 years ago.Although the total number of citations is slightly higher, his articles are lagging in terms of timeliness.He mainly empirically studied the impact of different environmental regulations, such as Integrated Pollution Prevention Control regulation and Environmental Agreement (EA), on performance in some European Union (EU) countries and also conducted case studies (Gusmerotti et al., 2012;Testa et al., 2012Testa et al., , 2014)).Next, the performance of each research institute is further analyzed in Figure 7, as most scholars tend not to be stand-alone, but rely on the resources provided by their institutes for research innovation.In the field of ER and CEP, as indicated in the figure, the Sant'anna School of Advanced Studies dominates.It is followed by Central South University and Jiangsu University in a tie for second place.Hunan University, Rennes School of Business, University of Pisa, and University of Zaragoza are tied for third.The analysis shows that the influential affiliations in this field are relatively decentralized and also points potential directions for seeking strong alliances between academic institutions.

Research collaboration analysis
This section turns its attention to the situation of research synergies and analyzes them with respect to three dimensions: author collaboration network, institutional collaboration network, and national/regional collaboration map.This is because fostering collaboration among different scholars, different institutions, and various countries/regions will contribute not only to solving the ongoing challenges in ER and CEP but also to uncovering the shortcomings of existing literature and generating new sparks.Collaborative network analysis demonstrates networks of cooperation among authors, institutions, and countries aimed at contributing to the evolution of knowledge in a particular research domain (Rocio et al., 2023).All of the related analyses in this part are conducted with Biblioshiny software.
Figure 8 illustrates the collaborative network diagram between authors, and it can be noticed that the scholars are divided into a total of 11 clusters, with no connection among the clusters.The orange group, led by Testa F, has the most members of six authors and is more closely interconnected, followed by the pink and green groups.The red and blue clusters also have a large number of members, but the links between members are more singular.The remaining six groups have very few members, two or three, and have a homogenous association. Figure 9 demonstrates the inter-institutional collaborative network, with the institutions concerned divided into 8 clusters in total, and again there is no connection across the clusters.The red-colored cluster, with Nanjing University as its core, has the largest members, consisting of four institutions, with closer links within its members.The remaining five clusters all have two members.In addition, interinstitutional cooperation is often limited to the same country or even the same province or city, and transnational institutional cooperation needs to be further strengthened.

Thematic map
As a further extension of the systematic literature review, this section analyzes the hot topics in ER and CEP and their evolution over the last two decades by means of thematic maps and thematic evolution diagrams through Biblioshiny.
To assess the significance of themes and the development of their creation, the themes of selected 72 documents in this paper were grouped into a strategic map through the Biblioshiny software, see Figure 12 Thematic Map.The value of the selected themes is measured by the horizontal axis indicator of relevance (centrality), and the growth of the themes is measured by the Y-axis indicator of the development degree, i.e., density (Arslan et al., 2022).For the purpose of drawing conclusions, the min cluster frequency and number of labels were limited to five and three, respectively.Figure 12 is delineated into four categories of themes, and the detailed information of each cluster is shown in Table 8.The lower left portion of the coordinate chart implies that both the relevance and development degrees are low, so it depicts emerging or declining themes in the field of study.Four clusters in the figure fall into this region, and only the Surveys Cluster is classified as a declining theme because most of the articles under this theme were published 10 years ago and nothing relevant has been published in the last three years.Highlighted in the lower right are basic themes, which are less dense but more central.Topics clusters such as Environmental Economics, Emission Control, and Environmental Policy, for example, fall into this category and require more academic attention.Next, the upper left section shows themes with high density and low centrality.This means that they are developed and isolated and are segmented themes, i.e., Industrial Performance, Innovation, Ecology, etc. Subsequent scholars could avoid these segmented topics and choose other unstudied niches when conducting their research, having obtained better essay innovativeness.Finally, the research themes with higher density and centrality are the motor themes located in the upper right part, which are crucial in the scientific literature, such as Data Envelopment Analysis, Environmental Management, and Economic Analysis.Therefore, this paper suggests that scholars who want to delve deeper into the field of ER and CEP should carefully study these literature to build a good foundation.The above analysis will help readers to identify basic dynamics of the existing literature in ER and CEP.

Thematic evolution
Furthermore, this paper investigates the evolution of themes in the ER and CEP domains by Biblioshiny, see Figure 13.We categorized the literature using keywords plus, with 2014 and 2019 as time points and finally generated Figure 13 with the help of the R package.The year 2014 was chosen because environmental regulation and supervision became particularly stringent from 2015 onwards, while 2019 was picked because of the global outbreak of the COVID-19 epidemic from 2020 onwards, both of which will have a huge impact on ER and CEP research (Chowdhury et al., 2023).The evolution of themes is implemented through three phases: phase 1 (2002-2014), phase 2 (2015-2019), and phase 3 (2020-2023).Overall, the evolution of the themes has taken the form of decentralization-centralization-decentralization, reflecting the continuous integration and changes in the fields of ER and CEP.
The most popular topics in the first phase were environmental protection and environmental management, followed by company size and efficiency.Regarding environment protection and environmental management, Clarkson et al. (2004) classified firms into low-polluting ones that excessively comply with ERs and highpolluting ones that only fulfill the minimum environmental requirements, and then verified the impact of different enterprises' environmental capital expenditures on their incremental economic performance.Lanoie et al. (2011) empirically discovered that ER stimulates firms' environmental innovation behavior and that flexible environmental policies facilitated corporate innovation more than prescriptive regulations to some extent.In addition, Dong et al. (2014) further validated the effects of different types of eco-innovation, firm size, ER, and its implementation on CEP and competitiveness.For efficiency, Y. Wang et al. (2011) examined whether stricter ERs can promote both environment and economic performance in terms of eco-efficiency (i.e., water, energy, and environmental efficiency).
By the second phase, the themes showed a trend of concentration.As the topic of environmental management matured and generalized, all of the popular topics from phase one were encompassed by it.Environmental economics followed as the second most popular and largest emerging topic in this phase.With regard to environmental management in phase II, studies have focused on the impacts of different types of ERs (R. Li and Ramanathan, 2018), corporate green product innovation (Chan et al., 2016), and supervision by different state administrative agencies (R. Wang et al., 2018) on CEP.As for environmental economics, researches mainly focused on the relationship between CEP and financial performance in the context of increasing ERs (Delmas et al., 2015), as well as the relationship between environmental pressures (from regulators & stakeholders, respectively) and performance (Yu et al., 2017).On greenhouse gases (GHGs), Delmas et al. (2015).measured CEP in terms of GHG emissions and then verified the impact of CEP on short-and long-term financial performance.Niesten et al. (2017) found that eco-innovation not only reduces GHG emissions but also helps companies cut down on the negative impacts of ER on CEP.
Lastly, since 2020 (Phase III), environmental management has shown a new subdirection of sustainable development on the basis of Phase II and also cross-studied with environmental economics.Environmental economics has also been subdivided into performance assessment.With respect to sustainable development, Lazzini et al. (2021) found that regulation in the form of the European Union Emissions Trading Scheme (EU ETS) can promote sustainability in enterprises, but that the economic crisis may counteract that effect.Defining sustainable development through disclosure effectiveness, Zhou et al. (2023) found that there is a positive link between CEP and the readability of corporate environmental disclosures (CEDs), especially in the case of poor profitability, stringent ER, and high media attention.On performance assessment, Long et al. (2023) explored the OFDI on domestic CEP and the role played by ERs and national culture.He et al. (2022) examined the impact of Environmental Labeling Certification (ELC), as a voluntary ER, on corporate environmental and financial performance.In terms of environmental economics, Shevchenko (2021) observed that financial penalties not only fail to promote the environmental performance of firms violating ERs but even have the opposite effect of worsening it.In contrast, Ma et al. (2021) argued that a higher frequency of government inspections can improve CEP in the short run, and the long-term effect can be achieved by combining the frequency of inspections and the severity of penalties.In relation to environmental management, L. Wang et al. (2023) discussed in detail the factors affecting the implementation of ISO14001 and its impact on different corporate performances.Yu et al. (2021) focused on the different patterns of environmental management in family firms and their impact on CEP.For economic analysis, M.

Intellectual structure analysis
To gain an understanding of the previous and present development of the fundamental research themes, this section will use co-citation analysis and bibliographic coupling analysis in VOSviewer to further sort out the knowledge structure in the ER and CEP research areas.

Co-citation analysis
Co-citation analysis presumes that publications that are frequently co-referenced are similar in themes (Donthu et al., 2021).In a co-citation network, when two papers appear simultaneously in the references of a third paper, then the first two papers are linked together (Singhania et al., 2023).It is a scientific mapping analysis technique that is primarily used to reveal the development of knowledge structure in a particular field, the connections between co-cited references, and thematic clusters (Donthu et al., 2021;Sardana and Singhania, 2022).It focuses solely on the highly cited publications with two major benefits; one is to discover the most influential publications and the other is to locate thematic clusters from cited publications (Donthu et al., 2021).
Figure 14 is the network diagram of the co-citation analysis, which was generated by the VOSviewer software, with the unit of analysis being cited references and the counting method being full count.Among the 4602 cited references, 10 articles reached the minimum threshold of being co-cited at least 4 times each.The choice of having the threshold at least 4 times is mainly the result of a trade-off between the meaningfulness of the analysis and the robustness of the results (Khan et al., 2022).On the one hand, a lower threshold, e.g., 1 time, yields a richer set of potential connections among sub-themes (Janssens et al., 2020), whilst, on the other hand, a higher threshold ensures that the co-citation relationship is statistically significant, such as 5 times or more (Wan et al., 2023).Therefore, after testing, 4 times were finally chosen in this paper for the analysis.The size of the circular nodes in the figure indicates the number of co-citations of a given article, and the thickness of the line expresses the intensity of the citational relationships (Phan Tan, 2022).Different colors represent different subject clusters.Author information is labeled on each node.Based on Figure 14, we can identify three different colored clusters and then analyze the content of these co-cited references in each cluster to organize three different themes they represent, as presented in Table 9.
The authors carefully read the typical references in each cluster, summarized the themes, and made the following findings: first, the three clusters are evenly matched and of comparable size as can be seen from the charts.Second, all three clusters reflect to some extent the highly dense and highly centered motor theme of environmental management.Cluster 1, represented by the red color, focuses on the relationship between natural resource-based firms and the environment (Hart, 1995), the concept of environmental competitive advantage (Porter and Van Der Linde, 1995), and the relationship between executive compensation and CEP (Berrone and Gomez-Mejia, 2009), all of which are either motivational themes or basic themes of environmental policy.The green cluster focuses on the topic of the relationship between stakeholder pressures on the organization and their environmental management activities (Delmas and Toffel, 2004;Henriques and Sadorsky, 1996;Kassinis and Vafeas, 2006), covering the dynamics theme and the niche theme of corporate strategy.Finally, the third blue cluster describes the impact of environmental policies and standards on companies (Khanna and Damon, 1999;King et al., 2005), and also introduces relevant psychometric theory (Nunnally and Bernstein, 1994), while covering the motivational theme, the basic theme, and the niche theme.
Stakeholders' institutional pressures, environmental management practices, environmentally responsive firm Kassinis & Vafeas (2006), Henriques & Sadorsky (1996), Delmas & Toffel (2004) 3. Blue EPA's voluntary 33/50 program, toxic releases and economic performance, strategic motives of individual actors, ISO 14001 management standard Nunnally & Bernstein (1994), King et al. (2005), Khanna & Damon (1999) In summary, it can be seen that co-citation analysis examines the relationship between cited articles and helps scholars understand the development of the past underlying themes in ER and CEP (Donthu et al., 2021).This is because, on the one hand, the three major thematic clusters were derived from co-cited publications more than ten years ago; on the other hand, the co-citation analysis only centered on highly cited articles and excluded recent or niche publications from the clusters.Therefore, it is necessary to conduct further bibliographic coupling analysis to explore the topical clusters of recent and niche publications and improve the knowledge structure of ER and CEP (Donthu et al., 2021).

Bibliographic coupling analysis
Bibliographic coupling is also a common scientific mapping technique, as opposed to co-citation (Chhtrapati et al., 2023).It assumes that the contents of the two articles are similar if they share the same reference (Donthu et al., 2021;Kessler, 1963).The bibliographic coupling analysis allows for the classification of articles with shared references, i.e., citing publications rather than cited publications, into different thematic clusters (Donthu et al., 2021;Zupic and Čater, 2014).Thus, unlike the co-citation analysis in the previous section, recent or niche articles can obtain visibility through bibliographic coupling analysis to reflect the current status of the research field (Donthu et al., 2021).This leads to its two main benefits, namely that it can be used to discover broader or even niche thematic clusters, and that it can reveal the latest research developments in each field (Donthu et al., 2021).
The bibliographic coupling visualization shown in Figure 15 was generated via the VOSviewer software, with the unit of analysis being document and the counting method being full count.Out of 72 documents, 60 reached the minimum threshold of at least 4 citations per document.Similar to the co-citation analysis, four times were chosen as the threshold while weighing the meaningfulness of the analysis and the robustness of the results (Janssens et al., 2020;Khan et al., 2022;Wan et al., 2023).Each bubble in the graph represents an article, and its size indicates the number of citations per article.In general, the closer the position of the two articles in the figure, the stronger the bibliographic coupling-based relationship between them (Chhtrapati et al., 2023).Different colors represent different topics and literature information is labeled on each bubble.Based on Figure 15, we can identify seven clusters and then analyze the content of main literature in each category to organize the different themes they represent, as shown in Table 10.Gusmerotti et al. (2012) Based on the results of previous co-citation and bibliographic coupling analyses, this section further summarizes the similarities and dissimilarities between theme clusters under the two analyses, presented in Table 11.It can be seen that the first and third themes in the co-citation analysis are similar to the first and seventh themes in the bibliographic coupling analysis, respectively.The second theme in the co-citation analysis was linked to the second and sixth themes in the bibliographic coupling analysis.These topics are all motor or basic themes that have been the focus of research in ER and CEP from the past to the present.Also, there are three emerging themes at the current stage, all of which are derived from the bibliographic coupling analysis of the existing citing publications, and are hot topics in the current literature that deserve the attention of scholars.The moderating or mediating influence of innovation on ER and CEP The influence of ER on the relationship between CEP and other variables, such as OFDI, chief sustainability officer (CSO), and green initiatives The impact of a particular regulation European Union Emissions Trading System (EU ETS) on CEP

Potential research directions
This part takes up the analysis of the intellectual network in the previous part, i.e., analyzing previous research through cited literature and studying current research through citing literature, then further reveals future directions of research development in ER and CEP through co-occurring keywords analysis utilizing VOSviewer (Dhiaf et al., 2021;Ohlan et al., 2022).This analysis supposes that there is a thematic relationship between words that frequently occur together, and then network is shown in Figure 16 (Donthu et al., 2021).This graph is generated via VOSviewer, with the unit of analysis being all keywords, and the counting method being full counts, where all keywords with 3 or more co-occurrences were included.Out of 570 keywords, 47 reached this threshold.Each circle in the graph represents a keyword, and the larger the circle, the higher the occurrence frequency of the keyword (Donthu et al., 2021).The links between circles indicate the co-occurrence of keywords, and the thicker the links, the higher the co-occurrence frequency (Donthu et al., 2021).Different colors represent different topic clusters (Donthu et al., 2021).Each circle is labeled with its corresponding key word.
Based on the keyword co-occurrence analysis in Figure 16, there are three findings: first, there are a total of five different clusters in the ER and CEP domains; second, among all co-occurring keywords, apart from the original search terms ER and CEP, environmental management, which belongs to the fourth/yellow cluster, has the highest number of occurrences ( 40) and the highest total connection intensity (240), making it the absolute core term in the field; finally, surprisingly the term environmental management systems, which is one word away from environmental management, also from Cluster 4, appears only 3 times and has the lowest total link strength (8).This means that this phrase has great space for improvement and could be a potential hot topic in the field.Next, the author would further analyze the core and borderline keywords within individual clusters to discover potential future research avenues.Cluster 1 "Performance" (red nodes) has core terms such as economic performance, economic analysis, environmental impacts, and carbon, which have high occurrences as well as high strength of linkage to other themes.The marginal terms are profitability, economic and social effects, taxation, and investments, none of which are linked to keywords in the green cluster.Future research could consider the integration between them to gain innovativeness.Cluster 2 "Regulation" (green) emphasizes ER, China, environmental economics, and environmental legislation.The edge vocabulary innovation is not associated with cluster 3; industrial performance does not co-occur with purple and red clusters; and the term, regulatory frameworks, is the most isolated with only association with the yellow cluster.Future research could start with these terms, especially regulatory frameworks.The blue cluster "Sustainability", or Group III, focuses on keywords such as sustainable development, efficiency, environmental protection, data envelopment analysis, and public policy.The fringe vocabulary is solely pollution control, which does not intersect with the first cluster.Environmental management is the largest node in the fourth (yellow) cluster "Management", generating extensive links with other groups.Surveys and environmental management systems are edge terms, the former being unrelated to the purple and red clusters, and the latter unrelated to the green cluster.The last group "Technology" consists of purple nodes with technological innovation, environmental technology, and emission control as its core words.Green technological innovation as a boundary term has no intersection with the blue group.In summary, scholars can focus on the edge words in the above clusters and make collisions with other clusters with no co-occurrence relationship in order to explore new pathways for research in ER and CEP.
Finally, based on the analysis of the edge terms in each previous cluster combined with the overlay visualization analysis in Figure 17 generated by VOSviewer, the most recent and cutting-edge possible directions of development in ER and CEP are filtered out.According to the legend, it can be seen that the color of the nodes represents the average publication year of relevant literature.The average year spans from 2016-2020 and the color also ranges from purple to blue to yellow.By comparison, it was found that the marginal keywords for each cluster, which are colored yellow in Figure 17, are the regulatory framework and green technological innovation, respectively, with an average year of publication in the literature of 2021.33,followed by environmental management systems (2020.33).They are emerging keywords in the field of ER and CEP, and the existence of unco-occurring clusters deserves scholars to highlight them, find potential research directions, and fill the gap in the literature.As regards green technological innovation, although its bridging role in the relationship between ER and CEP has been studied, the uncertainty of innovation has not been thoroughly researched (M.Wang et al., 2020).In addition, relevant studies have used data from China, and the circumstances of other developing and developed countries remain unknown (Cao et al., 2021).In terms of the relationship among ER, environmental management systems (EMS), and CEP, future research could further consider the contagion effects and regional characteristics of EMS implementation across enterprises, and in addition take into account the impact of EMS on corporate reputation along with their linkages to ER and CEP (L.Wang et al., 2023).The regulatory framework only appears in the index keywords with few mentions in the related literature, which creates more research prospects.Scholars interested in this area may search for relevant information on their own to establish its theoretical framework with ER and CEP.

Discussion of findings
The present study differs significantly from past researches.First, the findings of past studies on the relationship between ER and CEP have not been consistent and unified.Second, past review article on ER and CEP used a qualitative method of analysis and only covered publications up to 2019.Finally, past studies have used the quantitative approach of bibliometric analysis, which tends to have poor thematic relevance, covering only one area of ER or CEP, and does not establish a link between the two.Based on this, this paper uses bibliometric analysis to examine articles quantitatively and qualitatively about ER and CEP from 2002 to 2023, aiming to fill the research gaps in the related fields.
The main objective of this study is to understand the current status of literature, level of research collaboration, hot topics, knowledge structure, and potential directions in the field of ER and CEP through a bibliometric analysis so as to identify research patterns.To this end, a comprehensive literature review of 72 articles retrieved from the Scopus database was performed through Microsoft Excel, Biblioshiny software, and VOSviewer software.In this section, we will summarize the findings and answer the 6 RQs proposed in the introduction section.
The first research question (RQ1) concerns the current status of ER and CEP publications.To answer this question, this paper uses Microsoft Excel and Biblioshiny software to quantitatively analyze publications, countries, and journals and reaches three findings.First, the annual numbers of publications and citations show an upward trend, especially after 2010.Second, China is the country with the most publications and citations in the field, followed by the UK and the US.Finally, articles in this field are most commonly found in the Journal of Cleaner Production, accounting for about one-third of the total.
Regarding the second question (RQ2), this paper analyzes each core aspect of the In terms of research collaboration (RQ3), with the utilization of Biblioshiny, it can be seen by dividing it into authors', institutional, and countries': institutional collaboration is the most fragmented, with no links among the clusters, and mainly collaboration in pairs.Authors' collaboration was the second most fragmented, also with no links between clusters, but half of the groups had more than five members, with close intra-group collaboration.Global collaboration is relatively the strongest, with China leading the way, and there is also collaboration across clusters.
Next, this paper further investigates the hot topics and their evolution concerning ER and CEP (RQ4) through the use of Biblioshiny.It can be seen that there are three emerging topics in the field namely, Climate Change, FDI, and Environmental Awareness, and three motor themes which are Environmental Management, Data Envelopment Analysis, and Economic Analysis.The evolution of the themes shows a trend from decentralized to concentrated to decentralized, indicating that there is potential for further development of the field.
On intellectual structure (RO5), through co-citation analysis based on cited literature and number-coupling analysis based on citing literature, three themes about previous research and one emerging theme on current research in this field are derived using VOSviewer.The three themes are the effects of different kinds of regulation on CEP, the effects of institutional pressures and perceptions on CEP, and environmental policy and CEP.The emerging themes focus on ER and CEP, as well as some special moderating, mediating effects.
The last research question (RQ6) is the potential future direction of the field.By using the keyword co-occurrence network visualization and overlay visualization of VOSviewer, three keywords, regulatory framework, green technological innovation, and environmental management system, were found.They all are borderline terms with fewer connections with other clusters and are involved in publications with an average year of 2020 and beyond, which are emerging keywords at the present time.Therefore, they should be highly valued by scholars, from which new research directions can be found to fill the gaps in the discipline.

Conclusions
In recent years, there has been a rapid growth of articles about ER and CEP.This paper attempts to fill the research gap of bibliometric analysis on ER and CEP by analyzing and visualizing 72 articles in the field through Biblioshiny and VOSviewer.This research also contributes to helping scholars easily understand the research development and quickly find promising research directions in ER and CEP.In addition, the study enables the government and corporate managers to gain a more comprehensive view of ER's impacts on CEP, which can assist in policy making and business management.To accomplish the above three purposes, this firstly study provides a quantitative and qualitative analysis of relevant publications, countries, and journals to provide a basic understanding of the field at the temporal and spatial levels using Microsoft Excel and Biblioshiny.Second, this paper identifies the core journals, influential articles, keywords, core authors, and relevant institutions in the field with MS Excel and Biblioshiny, all of which will help future scholars gain a deeper understanding of ER and CEP research.Next, this study reveals collaboration among authors, institutions, and countries through Biblioshiny software, providing guidelines for scholars to work together.Fourth, this paper identifies hot topics in the field and their evolutions also by Biblioshiny software.Fifth, with the use of VOSviewer this research provides scholars with insights into the knowledge structure of ER and CEP.
Finally, this paper explores potential promising research orientations in ER and CEP utilizing VOSviewer, pointing scholars to research outlets and providing new perspectives.In conclusion, this paper argues that although research in ER and CEP has developed rapidly since 2002, it still has great potential for future research.
This research makes both theoretical and practical contributions.First, by providing a comprehensive and systematic overview of ER and CEP literature, this paper identifies knowledge structures and four major categories of research themes in the field.Second, this paper assists researchers in obtaining information about core publications, keywords, authoritative journals, and institutions in ER and CEP, so that they, especially newcomers, can accelerate their research progress.Thirdly, researchers in the field of ER and CEP can utilize the results of this study to identify promising areas for future research.
Nonetheless, there are some limitations.First, the source of the documents analyzed in this research is only the Scopus database.Searching in different databases (such as Web of Science, Google Scholar, etc.) would have made the study more convincing.Secondly, this study only analyzed articles written in English, and other non-English written articles could not be systematically evaluated.Thirdly, the bibliometric tools employed in this paper are Biblioshiny and VOSviewer, supplemented by Microsoft Excel.Other software that may be better suited for certain analyses was not considered.Therefore, future studies could obtain samples based on multiple databases by eliminating duplicates to draw more comprehensive and generalized research conclusions.In addition, future research could also explore other software for bibliometric visualization such as CiteSpace, Bib excel, and Gephi.

Figure 2 .
Figure 2. Annual publications and citations trend.

Figure 3
Figure3presents a deeper insight into the relationship among keyword plus, academic journals, and countries with the largest production concerning the topic of ER and CEP.It can be found that past research in this area has mainly focused on aspects such as environmental management, environmental regulations, environmental performance, sustainable development, and environmental economics, and has been largely published in the Journal of Cleaner Production, with the largest outputs of literature coming from China, UK, Italy, and USA in line with the previous analysis.

Figure 3 .
Figure 3. Three field analyses of ER and CEP.

Figure 4 .
The major source of ER and CEP literature is Journal of Cleaner Production.Business Strategy and the Environment and Corporate Social Responsibility and Environmental Management both played significant roles in the development of literature recently, especially the past three years.International Journal of Production Economics has steadily produced related articles in this field since 2013.The above analyses not only provide an understanding of research trends and limitations of ER and CEP but also promote policy reforms to better environmental performance further.

Figure 4 .
Figure 4. Publication trend per year in top 5 journals.

Figure 6
Figure 6 portrays the development of occurrences of keywords plus in related literature over time.As can be seen from the figure, the top ten keywords all started their initial development around 2011.Among them, ER, CEP, and environmental management are the most popular keywords among authors and have the strongest momentum, rising sharply; the rest of the terms enjoy relatively weaker popularity and have developed relatively gradually, with a slow and steady rise, such as sustainable development and environmental economics.

Figure 10
Figure10shows the network of cooperation between countries/regions.It can be found that China Australia, the United Kingdom, and the Hong Kong region of China have carried out the largest number of joint research programs, while academic cooperation between China and the USA has also achieved major scientific results.Precisely, China plays the most important role in scientific research activities compared to other countries and regions.

Figure 11
Figure11shows the cooperation in ER and CEP between 2002-2023 for each country.The intensity of the shades of blue denotes how many articles have been published, and the thickness of the red line shows the extent of cooperation between countries.The figure shows that China is at high levels both in terms of publications and the scale of cooperation, followed by the UK, France, and the USA.
Wang et al. (2020) developed a Steckelberg game-theoretic model to analyze the impacts of different decision-making approaches and regulations on corporate economic performance and waste discharge.Chelly et al. (2022) compared the impacts of progressive carbon tax strategies on supply chain management, profits, and CEP through four multi-period technology choice models.

Figure 16 .
Figure 16.Co-occurrence analysis of keyword network visualization.
ER and CEP literature, likewise using Microsoft Excel and Biblioshiny.As found in the first question, the Journal of Cleaner Production is the most influential journal in the field, followed by Business Strategy and The Environment and International Journal of Production Economics.Environmental Policy, Innovation and Performance: New Insights on the Porter Hypothesis is the most globally cited core article.Environmental management, sustainable development, and China are the most frequently used keywords.Regarding authors and institutions, Ramanathan R, Testa F, and Zhang Y are ranked among the top three in the field, while Sant'ana School of Advanced Studies is ranked first far ahead of other institutions.

Table 2 .
Countries with the most publications and citations.

Table 3 .
Top 10 journals according to source impact.

Table 5 .
Most globally cited articles.

Table 8 .
Themes and keywords of the thematic map.

Table 11 .
The comparison of co-citation and bibliographic coupling.