Liu, Wei http://orcid.org/0000-0001-8164-071X
Funding for this research was provided by:
Education Department of Shaanxi Province (16JK1184)
Shaanxi Xueqian Normal University (2016YBKJ074)
Article History
Received: 23 August 2017
Revised: 20 October 2017
Accepted: 11 January 2018
First Online: 24 January 2018