Funding for this research was provided by:
National Natural Science Foundation of China (41201256)
Text and Data Mining valid from 2018-05-08
Received: 31 October 2017
Accepted: 30 April 2018
First Online: 8 May 2018
Ethics approval and consent to participate
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.