It is periodical information retrieved from electronic library and periodical database, which is generally HowNet, Wanfang, etc. After retrieving this periodical, there will be a website in the address bar of the browser, which is a periodical retrieval link.

The general unit is afraid that you will publish fake periodicals or cheat to make fake periodicals, so the published periodicals and papers can be accessed online, so it is necessary to provide periodical retrieval links.