Free Databases

National System of Dissemination and Open Access to Information
Scientific Database of SID University Jihad (Full-Text Persian Articles)
Comprehensive Humanities Portal (Full Text English Articles)
All Articles Text Database
Online book archives and audiovisual resources
Archives of journals full text journal articles (Highware)
Online Journals of Chemistry
Directory of Open Access Journals (DOAJ)
Directory of open access books
Full-text database of books and articles in various Libgen formats (PDF, E-Pub, DJV)
American Digital Public Library (All Text Database, Photos, Video & Audio)
All article texts and miscellaneous materials
All Text Database of Latin Thesis 
All Text Database of Latin Thesis 
All Text Database of Latin Thesis 
Full-text articles
Database ArXiv in the field of mathematics, physics, computer science, electronic engineering and statistics resources
Conference Papers in Physics, Energy and Related Fields  (Stanford University)
Social Sciences Research Network
Gothenburg Project (e-book)
O'Reilly Project (e-book)
Online Book Access (Penn Libraries)
Biomedical Digital Archives
Books published by National Academies (Official Publishing Website)
Economic Archive (HEARTH: Home Economics Archive: Research, Tradition, History 1850-1925)
Search Engine Pdf 
Wikipedia Books
Where is doc?
Public access to research papers (sci-hub)
Internet Archive (non-profit library of millions of free books, movies, software, music, websites)