Funding for this research was provided by:
Social Science Foundation of Shandong Province (17CCXJ19)
National Natural Science Foundation of China (71722007, 61573210)
Article History
First Online: 8 October 2018
Compliance with ethical standards
:
: All authors declare that they have no conflict of interest.
: This article does not contain any studies with animals performed by any of the authors.
: Informed consent was obtained from all individual participants included in the study.