Funding for this research was provided by:
National Natural Science Foundation of China (61702389)
Yanta Scholars Foundation of Xian University of Finance and Economics
Social Science Foundation of Hebei Province (HB18GL036)
Text and Data Mining valid from 2019-02-13
First Online: 13 February 2019
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: This article does not contain any studies with human participants or animals performed by any of the authors.