Funding for this research was provided by:
“Double-First Class” Think Tank Program of China University of Mining and Technology (2018WHCC01)
Text and Data Mining valid from 2020-05-06
Received: 27 January 2020
Accepted: 27 April 2020
First Online: 6 May 2020
Ethics approval and consent to participate
: Not applicable.
: All authors agreed to publish the paper.
: The authors declare that they have no competing interests.