Google Scholar is a freely accessible web search engine that indexes the full text or metadata of scholarly literature across an array of publishing formats and disciplines. Released in beta in November 2004, the Google Scholar index includes most peer-reviewed online academic journals and books, conference papers, theses and dissertations, preprints, abstracts, technical reports, and other scholarly literature, including court opinions and patents. While Google does not publish the size of Google Scholar's database, scientometric researchers estimated it to contain roughly 389 million documents including articles, citations and patents making it the world's largest academic search engine in January 2018. Previously, the size was estimated at 160 million documents as of May 2014. An earlier statistical estimate published in PLOS ONE using a Mark and recapture method estimated approximately 80–90% coverage of all articles published in English with an estimate of 100 million. This estimate also determined how many documents were freely available on the web.
For more information : Google Scholar
DOAJ (Directory of Open Access Journals)
The DOAJ (Directory of Open Access Journals) was launched in 2003 at Lund University, Sweden, with 300 open access journals. Today, the independent database contains ca. 12000 open access journals covering all areas of science, technology, medicine, social science and humanities.
For more information : DOAJ
The growing interest in the ICI Journals Master List database, the number of applications and the number of journals which had not met the criteria required for the indexation, have inspired us to create a global database of scientific journals the ICI World of Journals. The ICI Journals Master List remains the indexing database of scientific journals which have undergone the process of multiparametric evaluation. The ICI World of Journals gathers information regarding scientific journals from various sources. Thus, we share comprehensive information regarding the scope of journals' activity, editorial offices and articles published by the scientific journals. International journals from all over the world may register in the ICI World of Journals - a dedicated system has been made available to manage the Journal's Passport.
For more information : Index Copernicus
The dblp computer science bibliography provides open bibliographic information on major computer science journals and proceedings. Originally created at the University of Trier in 1993, dblp is now operated and further developed by Schloss Dagstuhl.
For more information : dblp