Funding for this research was provided by:
Hebei Province Science and Technology Support Program (16277720D)
Text and Data Mining valid from 2019-03-11
Received: 17 January 2019
Accepted: 21 February 2019
First Online: 11 March 2019
Compliance with ethical standards
: All authors declare that they have no conflict of interest.
: This study was appoved by ethical committee of Qinhuangdao First hospital (2016D005).
: All participants provided informed consent prior to their participation.