Funding for this research was provided by:
National Natural Science Foundation of China (51673103)
Postdoctoral Scientific Research Foundation of Qingdao (2016014)
Text and Data Mining valid from 2019-06-25
Received: 19 February 2019
Accepted: 17 June 2019
First Online: 25 June 2019
: The authors declare that they have no competing interests.