Fig. 2

Co-citation references network and corresponding clustering visualization generated by CiteSpace. Note: A node represents a cited reference. The network is organized by the betweenness centrality of every node. The size of a node is proportional to its betweenness centrality. A node with high betweenness centrality is usually one that connects two or more clusters or lies at the core within a cluster, and the correspondent cited literature has a significant impact on the local network. The highlighted lines represent the evolution and connections among different clusters