Zhang, X.
Liu, Z.
Funding for this research was provided by:
the National Natural Science Foundation of China (31501342)
the Specialized Research Fund for the Doctoral Program of Yan’an University (YDBK2017-26)
Article History
Received: 11 September 2017
Revised: 11 February 2018
Accepted: 9 May 2018
First Online: 21 May 2018
Compliance with ethical standards
:
: The authors declare that they have no conflict of interest.