Funding for this research was provided by:
National Natural Science Foundation of China (91639107)
Text and Data Mining valid from 2019-11-13
Received: 15 July 2019
Accepted: 15 October 2019
First Online: 13 November 2019
Ethics approval and consent to participate
: Not applicable.
: All authors read and approved the final manuscript.
: The authors declare that they have no competing interests.