All SCI journals are ranked according to their impact factors, and the top 5% are the first region, the top 20% are the second region, the top 50% are the third region, and the rest are fourth area.

Or let's put it this way: Generally, SCI papers are divided into four areas, the first area is the top international journals, the second area is the second, and the third and fourth areas are general SCI journals.

Scientific Citation Index (SCI) is a citation database established by eugene garfield of institute for scientific information (ISI) in Philadelphia, USA on 1957. SCI (Science Citation Index), EI (Engineering Index) and ISTP (Science and Technology Conference Index) are three world-famous retrieval systems for scientific documents, which are internationally recognized as the main retrieval tools for scientific statistics and scientific evaluation.

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Scientific citation index is based on Bradford's literature dispersion theory and E. Garfield's citation analysis theory. It evaluates and studies academic journals and scientific research achievements in many aspects by counting the cited frequency of 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. Therefore, SCI is an internationally recognized scientific and technological literature retrieval tool worthy of reference.