Class A journals include: Peking University Library (Peking University Core and Chinese Core Journals), Chinese Social Sciences Citation Index (CSSCI) of Nanjing University, China Science and Technology Core Journals of China Institute of Science and Technology Information, China Humanities and Social Sciences Core Journals of Chinese Academy of Social Sciences Document Information Center, China Science Citation Database (CSCD) Source Journals of Chinese Academy of Social Sciences Document Information Center, and China Humanities and Social Sciences Core Journals of China Academy of Social Sciences.

1. Legal journals include informal journals and official journals: informal journals refer to those approved by the administrative department for internal communication and are generally not publicly distributed.

2. Official periodicals are approved by the State Press and Publication Administration and the State Science and Technology Commission within the agreed number, incorporated into the domestic unified serial number (the domestic unified serial number is also CN, and ISSN is an international serial number to help retrieve the serial number of publications), and can be published publicly.

3. There are four kinds of illegal periodicals: publications printed without the approval of the press and publication department; Overseas publications illegally imported without the approval of the General Administration of Press and Publication; Forging publications printed in the name of others; Buy and sell publications with ISBN, serial number and version number. Legal journals have regular CN numbers and ISSN numbers except official journals, while illegal journals have no serial numbers or use false serial numbers. Therefore, when searching for published periodicals, you must look up the serial number on the regular website to avoid being cheated.