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.
Co‐occurrence of keywords. A, The keywords co‐occurrence clustering network. Node size and node colour represent the number of keywords and clusters. Different coloured lines indicate that the two keywords appeared in an article. B, The top 20 keywords with the strongest citation bursts. The red bars indicate that certain keywords are frequently referenced at a certain time
