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.
Timeline visualization of co-occurring author keywords network. In the map, each author keyword is displayed along with the year in which it first appeared. Each node represents an author keyword. Co-occurrences of author keywords are represented by the links. The node’s size is proportional to the frequency with which an author keyword occurs.
