I just checked the "China Science and Technology Paper Statistics Source Journal" (i.e. the core science and technology journals). There is no "Modern Electronic Technology" in the 2007 edition, and there is no "Chinese Core Journal Catalog (2008 Edition)". this magazine.
There are currently 7 core journal (or source journal) selection systems in China: Peking University Library’s “Chinese Core Journals”, Nanjing University’s “Chinese Social Sciences Citation Index (CSSCI) Source Journals”, China Science and Technology "Chinese Scientific and Technological Paper Statistical Source Journal" (also known as "Chinese Science and Technology Core Journal") of the Institute of Information, "Chinese Core Journal of Humanities and Social Sciences" of the Documentation Information Center of the Chinese Academy of Social Sciences, "Chinese Science Citation Database (CSCD)" of the Documentation and Information Center of the Chinese Academy of Sciences Source Journals", the "Chinese Journal of Humanities and Social Sciences Core Journals" of the Chinese Journal of Humanities and Social Sciences, and the "Chinese Core Journal Selection Database" under construction by Wanfang Data Co., Ltd.
Therefore, core journals are only a general term, and different units and systems use different standards.