Text and Data Mining valid from 2019-11-26
Received: 18 July 2019
Accepted: 21 November 2019
First Online: 26 November 2019
Compliance with ethical standards
: The authors declare no conflicts of interest to disclose.
: This article does not contain any studies with human participants performed by any of the authors. It has been approved by the Medical Ethics Committee of the Affiliated Hospital of Qingdao University.