Funding for this research was provided by:
Health and Family Planning Commission of Sichuan Province (18PJ042)
Text and Data Mining valid from 2020-01-14
Received: 2 August 2019
Accepted: 23 December 2019
First Online: 14 January 2020
Compliance with Ethical Standards
: Scientific Research Project of Sichuan Provincial Health and Family Planning Commission (18PJ042).