Funding for this research was provided by:
National Natural Science Foundation of China (81773296)
Natural Science Foundation of Shandong Province (ZR2015HM064)
Article History
Received: 20 October 2018
Revised: 27 January 2019
Accepted: 19 February 2019
First Online: 27 February 2019
Compliance with ethical standards
:
: The authors declare that they have no conflict of interest.
: Questionnaires were distributed to participants who agreed to participate in the study after being informed of it. This study was approved by the Institutional Review Board of the authors’ institutes and was performed in accordance with the ethical standards of the institution and the 1964 Declaration of Helsinki and its later amendments.