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.
The font size of each country's name represents the number of publication in the country. Different colors inside the circle represent different time intervals. The thickness of the straight connecting line represents the collaborative intensity between countries.
