Therefore, the first zone, the second zone and the third zone of SCI papers refer to the classification of journals into different grades according to factors such as impact factors and cited amount, among which the journals in the first zone represent high-level journals with the highest influence, while the journals in the third zone are low-level journals.

CR2 is an SCI journal of engineering technology in the third district of China Academy of Sciences. The first, second, third and fourth districts are the divisions of sci journals. There are two kinds of sci journals, one is jcr, and the other is Chinese Academy of Sciences. These two divisions are very similar, both of which are divided into four areas, and the criteria of division are also the influencing factors of periodicals.

The first, second, third and fourth districts are the divisions of sci journals. Sci journals have two branches, one is jcr branch and the other is Chinese Academy of Sciences branch. These two zones are very similar, both of which are divided into four zones.

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.

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.

According to the periodicals in SCI (Science Index) database, the regional classification of SCI papers can be divided into 1 zone, zone 2 and zone 3. This classification is based on the academic reputation and influence of journals.