Funding for this research was provided by:
National Natural Science Foundation of China (81260325)
Text and Data Mining valid from 2019-09-10
Received: 28 June 2019
Accepted: 29 August 2019
First Online: 10 September 2019
Ethics approval and consent to participate
: Not applicable.
: All authors have read the manuscript and approved the final version.
: The authors declare that they have no competing interests.