Funding for this research was provided by:
National Natural Science Foundation of China (81771884)
Text and Data Mining valid from 2019-11-27
Received: 1 April 2019
Accepted: 11 October 2019
First Online: 27 November 2019
Ethics approval and consent to participate
: No ethics approval was required for this study as it is a systematic analysis using pre-existing, publicly published data.
: Not applicable.
: The authors declare that they have no competing interests.