Funding for this research was provided by:
National Natural Science Foundation of China (11371221,11571207)
the Tai'shan Scholar Engineering Construction Fund of Shandong Province of China
Text and Data Mining valid from 2018-07-17
Received: 2 December 2017
Accepted: 20 May 2018
First Online: 17 July 2018
: The authors declare that they have no competing interests.