Funding for this research was provided by:
National Natural Science Foundation of China (81270589)
Natural Science Foundation of Heilongjiang Province (H2017032)
Text and Data Mining valid from 2019-11-04
Received: 3 October 2019
Accepted: 1 November 2019
First Online: 4 November 2019
Compliance with ethical standards
: The authors declare that they have no competing interests.
: This study protocol was discussed and approved by the Medical Ethics Committee of the First Affiliated Hospital of Harbin Medical University who waived the need for patient informed consent for this retrospective analysis.