Funding for this research was provided by:
National Natural Science Foundation of China (71561024)
The key projects of Natural Science Foundation of Gansu province of China (18JR3RA084)
Article History
Received: 30 January 2019
Accepted: 17 May 2019
First Online: 28 May 2019
Competing interests
: The authors declare that they do not have any competing interests in this manuscript.
: The authors confirm that the work described has not been published before (except in the form of an abstract or as part of a published lecture, review, or thesis), that its publication has been approved by all co-authors.