Funding for this research was provided by:
National Natural Science Foundation of China (71320107005)
Text and Data Mining valid from 2018-12-01
Received: 15 November 2018
Accepted: 20 November 2018
First Online: 13 December 2018
: The author declares that he has no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.