Funding for this research was provided by:
National Natural Science Foundation of China (51506112)
Tsinghua University Initiative Scientific Research Program (20161080094)
Text and Data Mining valid from 2019-06-29
Received: 7 April 2019
Accepted: 7 June 2019
First Online: 29 June 2019
Ethics approval and consent to participate
: Not applicable.
: Authors agreed to publish this article.
: The authors declare that they have no competing interests.