Figure 1.
(A) Country co-occurrence network map; (B) author co-occurrence network map; (C) keyword co-occurrence network map; (D) clustering map of keywords.
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.