In the references, "DOI" is the abbreviation of "DigitalObjectUniqueIdentifier", which is translated into "digital object identifier" in Chinese. This is a non-profit standard for identifying online electronic resources, which is managed and operated by IDF (International DOI Foundation), a non-profit organization established by American Publishers Association (AAP) on 1998. The main function of DOI is to provide a unique identification for network electronic resources, so that users can locate specific electronic resources quickly and accurately. In the academic field, DOI is often used to identify academic papers, so that when this paper is cited, readers can directly link to the full text of this paper through DOI.