Funding for this research was provided by:
National Natural Science Foundation of China (81372439)
Text and Data Mining valid from 2018-06-15
Received: 9 January 2018
Accepted: 4 June 2018
First Online: 15 June 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.