Funding for this research was provided by:
National Natural Science Foundation of China (81371861)
Text and Data Mining valid from 2018-04-09
Received: 24 December 2017
Revised: 30 January 2018
Accepted: 30 January 2018
First Online: 9 April 2018
Compliance with Ethical Standards
: The authors declare that they have no conflict of interest.
: This research did not require ethical approval.
: This research did not require informed consent.