Funding for this research was provided by:
National Natural Science Foundation of China (81572209)
Text and Data Mining valid from 2018-05-24
Received: 11 November 2017
Accepted: 5 April 2018
First Online: 24 May 2018
Compliance with ethical standards
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of study, formal consent is not required.
: The authors declare that they have no conflict of interest.