Funding for this research was provided by:
special foundation of basic science and technology resources survey of ministry of science and technology of China (2017FY101200)
Text and Data Mining valid from 2019-11-20
Received: 3 June 2019
Accepted: 7 November 2019
First Online: 20 November 2019
Ethics approval and consent to participate
: Prior to data collection, this study was approved by the ethics committee from the Chinese Center for Disease Control and Prevention Institute for Environmental Health and Related Product Safety (201606).
: Not applicable
: The authors declare that they have no competing interests.