Funding for this research was provided by:
National Natural Science Foundation of China (21807101, 31722001)
Natural Science Foundation of Shandong Province (JQ201707)
Text and Data Mining valid from 2020-02-01
Received: 15 October 2019
Accepted: 21 January 2020
First Online: 1 February 2020
Ethics approval and consent to participate
: Not applicable.
: All authors read and approved the final manuscript for publication.
: The authors declare that they have no competing interests.