Web of Science (WoS) is a website that provides subscription-based access to multiple databases that provide comprehensive citation data for many different academic disciplines. It was originally produced by the Institute for Scientific Information (ISI) and is currently maintained by Clarivate Analytics (previously the Intellectual Property and Science business of Thomson Reuters).
Scopus is a bibliographic and abstract database and a tool for tracking the citation of articles published in scientific publications. The developer and owner of Scopus is Elsevier publishing corporation.
Russian Science Citation Index (RSCI) is a bibliographic database of scientific publications in Russian.ндекс цитирования научных статей.
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