Funding for this research was provided by:
National Planning Office of Philosophy and Social Science (14CSH063)
Text and Data Mining valid from 2019-04-17
Accepted: 8 April 2019
First Online: 17 April 2019
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was approved by the Institutional Review Board of Shandong University.
: Informed consent was obtained from all individual participants included in the study.