That is to say, there are four websites, which are relatively large, have periodicals, and can also retrieve published papers. These four websites are China Knowledge Network, also known as CNKI, Wanfang Database, VIP Network and Long Yuan Journal Network.

However, SCI was originally only a powerful document retrieval tool. It is different from the conventional method of searching documents by subject or classification, but it sets up a unique "citation index", that is, by collecting the references cited by a document and tracking the cited situation after its publication, we can grasp the context of the research topic and find the relevant research documents quickly.

SCI "Science Citation Index";

SCI) is a citation database founded and published by institute for scientific information (ISI) 196 1, which covers life science, clinical medicine, physical chemistry, agriculture, biology, veterinary medicine, engineering technology and other comprehensive retrieval publications, especially reflecting the academic level of natural science research.

It is the most famous of the three retrieval systems in the world at present, among which life science, medicine, chemistry and physics account for the largest proportion, and the collection scope is the important international journals of that year. In particular, its citation index shows unique scientific reference value and occupies an important position in academic circles. Many countries and regions regard the papers collected and cited by SCI as an important index to evaluate academic level.

Baidu Encyclopedia-Four Search Systems