Funding for this research was provided by:
National Natural Science Foundation of China (81372008)
China Scholarship Council (201608110199)
Text and Data Mining valid from 2018-04-13
Received: 28 November 2017
Accepted: 27 March 2018
First Online: 13 April 2018
Compliance with ethical standards
: The authors declare that they have no competing interests.
: The study was in accordance with the ethical standards of the institutional research committee, the 1964 Helsinki declaration, and its later amendments. For this type of study formal consent is not required.