Funding for this research was provided by:
National Office for Philosophy and Social Sciences (20VYJ039)
Innovative Research Group Project of the National Natural Science Foundation of China (71921003)
Major Project of the National Social Science Fund of China (19ZDA149)
Received: 20 October 2020
Accepted: 19 February 2021
First Online: 2 March 2021
: Not applicable.
: Not applicable. This analysis is based on search engine data at prefectural level, and no individual information is required.
: The authors declare that they have no competing interests.