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.
Flow diagram of study search (n, number of articles; CNKI, China National Knowledge Infrastructure Database; WanFang, the WanFang Database; VIP, the Chinese Scientific Journals Full-Text Database; SinoMed, the Chinese Biomedical Literature Database).
