Funding for this research was provided by:
National Natural Science Foundation of China (11671227)
the Natural Science Foundation of Shandong Province (ZR2019MA034)
Text and Data Mining valid from 2019-09-10
Received: 17 May 2019
Accepted: 9 August 2019
First Online: 10 September 2019
: The authors declare that there is no conflict of interests regarding the publication of this paper.