According to the impact factor division of JCR journals published annually by the American Institute of Information, the \x0d\ periods of SCI of the same discipline are sorted according to the impact factors from high to low. The top 5% journals with discipline impact factors are those in An 1 region, the top 20% journals with discipline impact factors \x0d\ are those in An2 region, and the top 50% journals in three regions are those in An3 region. After \x0d\50% subject influence factor, the journals in An4 area are in turn; The core journals included in EI are those in the An5 area, and the papers published in the corresponding journals in the above areas are called An 1, An2, An3, An4 and An5 respectively.