Funding for this research was provided by:
National Natural Science Foundation of China (31622002, 41506163)
Text and Data Mining valid from 2018-02-27
Received: 29 November 2017
Revised: 30 January 2018
Accepted: 1 February 2018
First Online: 27 February 2018
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: This article does not contain any studies with human participants performed by any of the authors.