Funding for this research was provided by:
National Natural Science Foundation of China (11501082)
Natural Science Foundation of Shandong Province (No.ZR2013GL001, No.ZR2015AL016, No.ZR2016FM37, No.ZR2015FL006)
Dezhou soft science research plan project (NO.43 (2013))
Text and Data Mining valid from 2017-12-19
Received: 20 August 2017
Revised: 27 November 2017
Accepted: 30 November 2017
First Online: 19 December 2017
Compliance with ethical standards
: All authors have no conflict of interest in this paper.
: This article does not contain any studies with human participants or animals performed by any of the authors.