Funding for this research was provided by:
National Natural Science Foundation of China (81571843, No. 41201090)
Text and Data Mining valid from 2018-05-11
Received: 30 August 2017
Accepted: 24 April 2018
First Online: 11 May 2018
Ethics approval and consent to participate
: Not applicable.
: The authors declare that they have no competing interests.