Funding for this research was provided by:
National Natural Science Foundation of China (81703459)
Text and Data Mining valid from 2019-02-08
Received: 6 December 2018
Revised: 13 January 2019
Accepted: 18 January 2019
First Online: 8 February 2019
Compliance with ethical standards
: No research was conducted using human participants or animals of any kind.
: No data, text, or theories by others are presented as if they were the authors’ own.
: The authors declare that they have no conflict of interest.