Funding for this research was provided by:
National Natural Science Foundation of China (61504073)
A Project of Shandong Province Higher Educational Science and Technology Program (J18KA011)
Text and Data Mining valid from 2019-02-06
Received: 17 October 2018
Accepted: 27 January 2019
First Online: 6 February 2019
: The authors declare that they have no competing interests.
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