The theoretical basis of SCI is Bradford's literature diffusion law theory and Garfield's citation analysis theory. SCI evaluates and studies academic journals and scientific research achievements from various aspects by counting the frequency of cited papers, so as to judge the performance of scientific research output of a country or region, scientific research units and individuals and reflect its international academic level.
SCI ranks journals and papers with its unique citation approach and comprehensive scientific data, and then obtains quantitative indicators such as impact factors, citation frequency, real-time index and so on. The high citation frequency shows that this paper has had a great influence in its research field.
Because the papers included in SCI are mainly in the basic research field of natural science, SCI indicators are mainly suitable for evaluating the achievements of basic research, and the main achievements of basic research are academic papers. The contents of periodicals collected by SCI mainly involve basic scientific research fields such as mathematics, science, chemistry, agriculture, forestry, medicine and biology.