Funding for this research was provided by:
National Natural Science Foundation of China (81220108007)
Natural Science Foundation of Beijing Municipality (4122018, 7174282)
Text and Data Mining valid from 2019-02-01
Received: 26 September 2018
Accepted: 21 January 2019
First Online: 1 February 2019
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the national research committee.
: For this type of study formal consent is not required.