Funding for this research was provided by:
National Natural Science Foundation of China (41601353, 61801384, 61503300)
Scientific Research Plan of Education Department of Shaanxi Province (17JK0789)
Text and Data Mining valid from 2019-02-22
Received: 21 January 2018
Accepted: 28 January 2019
First Online: 22 February 2019
: The authors declare that they have no competing interests.
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