Funding for this research was provided by:
The National Social Science Fund of China (16BSH086)
Text and Data Mining valid from 2018-09-21
Received: 15 May 2018
Accepted: 13 September 2018
First Online: 21 September 2018
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.