DOI is a digital object identifier. DOI established by American Publishers Association (AAP) is relatively mature in technology. Mainly aimed at how to effectively protect and manage intellectual property rights under the Internet environment. There is only one DOI per paper. As long as this article is included in SCI, you can find the corresponding DOI, and when your paper is hired, you will be given a DOI, so the reference you used has not been officially published, but you can find the DOI on the Internet and quote it.