Funding for this research was provided by:
Natural Science Foundation of Hunan Province (2017JJ1038)
Text and Data Mining valid from 2019-04-05
Received: 28 January 2019
Accepted: 21 March 2019
First Online: 5 April 2019
Compliance with ethical standards
: Ethics approval and consent to participate are not applicable in this study.
: The authors declare that they have no conflict of interest.