Figure 1.
Most frequently used keywords over time, as well as a clustering of the keywords’ citation networks. Network visualization (A), overlay visualization (B), and density visualization (C).
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.