Funding for this research was provided by:
National International Science and Technology Cooperation Project (2015DFA 30440)
Text and Data Mining valid from 2019-01-18
Received: 17 November 2018
Accepted: 4 January 2019
First Online: 18 January 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 institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards, and the requirement for informed consent was waived for this retrospective study.