CrossRef - (formerly styled CrossRef) is an official Digital Object Identifier (DOI) Registration Agency of the International DOI Foundation. It is run by the Publishers International Linking Association Inc. (PILA) and was launched in early 2000 as a cooperative effort among publishers to enable persistent cross-publisher citation linking in online academic journals
Index Copernicus (Poland)- International scientometric base. (Index Copernicus Journals Master List). This website includes indexing, ranking and abstracting journals, and is a platform for scientific collaboration and joint research projects.
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. Google Scholar index includes most peer-reviewed online journals of Europe and America's largest scholarly publishers. This product provides the citation indexing features. While Google does not publish the size of Google Scholar's index, third-party researchers estimated it to contain roughly 160 million documents.
Vernadsky National Library of Ukraineis the main academic library and main scientific information centre in Ukraine, one of the world's largest (top twenty) national libraries.
Ulrich's Periodicals Directory - subscription catalog of American publishing Bowker, is the largest database that describes the global flow of periodicals in all subject areas