This paper aims to provide a comprehensive understanding of the evolution of major research themes and trends in e-learning research. A co-word analysis is applied for the analysis of the 21,656 keywords collected from 7214 articles published in 10 journals in the field of e-learning from the years 1999 to 2018. Specifically, a cluster analysis, social network analysis, strategic diagram, and graph theory were applied in the analysis for two time periods: 1999–2008 and 2009–2018. The study detects the bridging, popular, and core topics in e-learning research for the two periods. The research results indicate that e-learning research has undergone a health evolution over the past two decades. There is a temporal continuity of e-learning research because some research topics have kept their continuity over the studied 20 years. Meanwhile, the research traditions in the e-learning field are also continuously evolving with the development of new technologies. The results also offer useful hints on the future direction of how the field may evolve.

中文翻译：

---

E-learning领域的研究趋势和研究主题演变的可视化：1999-2018

本文旨在全面了解电子学习研究的主要研究主题和趋势的演变。对1999年至2018年电子学习领域10种期刊发表的7214篇文章中收集的21656个关键词进行了共词分析。 具体而言，聚类分析、社交网络分析、战略图和图论应用于两个时间段的分析：1999-2008 和 2009-2018。该研究检测了两个时期电子学习研究中的桥梁、流行和核心主题。研究结果表明，电子学习研究在过去二十年中经历了健康演变。电子学习研究具有时间连续性，因为某些研究主题在研究的 20 年中一直保持其连续性。同时，随着新技术的发展，电子学习领域的研究传统也在不断发展。结果还为该领域如何发展的未来方向提供了有用的提示。