Funding for this research was provided by:
University Natural Science Research Project of Anhui Province (No. 2016SCXPTTD)
Text and Data Mining valid from 2019-02-15
Received: 29 October 2018
Accepted: 23 January 2019
First Online: 15 February 2019
Compliance with ethical standards
: The author(s) declare that they have no competing interests.