Funding for this research was provided by:
National Natural Science Foundation of China (11571296)
Natural Science Foundation of Shandong Province of China (ZR2017MA036)
Text and Data Mining valid from 2019-07-26
Received: 16 May 2019
Accepted: 18 July 2019
First Online: 26 July 2019
: The author declares that there is no conflict of interests regarding the publication of this paper.