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.
(A) Keyword co-occurrence knowledge map. A larger and more centered font corresponds to the number of times a keyword appears. (B) Top 14 keywords with the strongest citation bursts. The color depth represents the strength value of keywords with the strongest citation bursts. Darker color corresponds to a larger strength value.
