SCI is a scientific citation index and a database run by ISI, an American intelligence agency. In fact, similar to Google's search engine, the purpose is to facilitate researchers to find the literature in this research field.

However, after NTU introduced SCI into China as an evaluation of scientific research work, the number of SCI papers is now regarded as an important standard for national scientific research assessment. The SCI articles you ask mean that the published articles have been retrieved by SCI database, and to do this, we need to invest in the journals included in SCI. After the article is hired and published, it will be searched by SCI database within three months. It should be noted that SCI only includes periodicals, and conference articles will not be included. There is another special database, ISTP Conference ISI. Some conferences will recommend the best papers to be published in SCI journals. If published in a journal, it can of course be retrieved by SCI in the end.

Core journals are the list of domestic journals published by Peking University, belonging to core journals, and there are many core journals.

First-class journals are the most prestigious and authoritative domestic magazines in every field. Generally, there are 3-4 magazines in every field, and doctoral supervisors in Tsinghua and Peking University can publish 2-3 articles on them continuously every year, all of which belong to giant cows. Of course, there are some magazines that claim to be first-class journals, but people in all fields know that the most authoritative magazines are those.

If published, each magazine has its own requirements, from content to format. You need to check the submission guide on the magazine website.

As for the impact factor, ISI will calculate the number of citations of articles in included journals every year, and the number of citations/published articles is the impact factor of journals. If the impact factor is large, it means that the results published in journals are used by many researchers, which will promote the development and prosperity of this field and the journals will be better and more authoritative. ISI calculates and publishes the latest list of influencing factors every year, which is called cited report.

If you need SCI for graduate students, you'd better learn more from your brothers and sisters to see if your field is easy to publish, what research you usually do and what magazines you publish. I hope my answer can answer your question. If you answer, remember to adopt it.