Freely available and open access sources
Google Scholar - search records and full text of study materials across multiple disciplines
OpenAIRE - platform for open publishing of documents and scientific data generated within the European Commission's 7th Framework Programme for Research
Journals
Repositories and digital libraries
The Directory of Open Access Repositories - directory of institutional repositories with freely available content from all over the world
Repository66 - map of institutional repositories around the world with freely available content.
Registry of Open Access Repositories - search records from institutional and disciplinary repositories
Národní úložiště šedé literatury - technically oriented sources from Czech Republic, especially from Czech universities and the Academy of Science
arXiv - disciplinary repository for mathematics, physics, technology and engineering; has over 700,000 documents
RePEc - digital library maintained by volunteers that is focused on economics
Digital Mathematic Library - a collection of freely available documents from Czech Republic focused on mathematics; offers both record and full text
GitHub - source codes repository
Books
Catalogues a information gateways - bibliographic references searching
Norms, patents
EIZ