Funding for this research was provided by:
Social Science Planning Research Project of Shandong Province (20CGLJ11)
Natural Science Foundation of Shandong Province (ZR2015GM012, ZR2017MG012)
National Natural Science Foundation of China (71772106)
Humanity and Social Science Foundation of Ministry of Education of China (17YJCZH198)
Article History
First Online: 3 August 2020
Compliance with ethical standards
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: The authors declare that they have no conflict of interest.