Fatcat, versioned, user-editable catalog of research publications including journal articles, conference proceedings, and datasets
link: https://fatcat.wiki/
Fulltext search index, 25 million research articles and other documents preserved in the Internet Archive
link: https://scholar-qa.archive.org/
Multidisciplinary aggregator of open access research
link: https://core.ac.uk/
Research and publishing network
link: https://www.scienceopen.com/
A multidisciplinary, community-curated directory
link: https://doaj.org/
Search by topic for material related to the field of education
link: https://eric.ed.gov/
Resource in the fields of mathematics and computer science
link: https://arxiv.org/
A collection of papers from the social sciences community
link: https://www.ssrn.com/index.cfm/en/
Publishing seven open access journals
link: https://plos.org/
Directory of Open Access Repositories, using Google Custom Search.
link: https://www.opendoar.org/search.php
(BASE) is operated by the Bielefeld University Library in Germany
link: https://www.base-search.net/
(DLC) Repository is a multidisciplinary journal repository
link: https://dlc.dlib.indiana.edu/dlc/
Highly useful research database for academics in a variety of disciplines
link: https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html
+15K journals
link: https://paperity.org/
Online index of major computer science publications
link: https://dblp.org/
Resource for economic and business studies
link: https://www.econbiz.de/
Open access research from more than 290 peer-reviewed journals in the fields of biology, clinical medicine, and health
link: https://www.biomedcentral.com/
A multidisciplinary search engine
link: https://www.jurn.org/ (down)
Dryad is a digital repository of curated, open access scientific research
link: https://datadryad.org/
400,000 doctoral theses in a variety of disciplines
link: https://ethos.bl.uk/Home.do
From the National Center for Biotechnology Information, research platform in the fields of science and medicine
link: https://pubmed.ncbi.nlm.nih.gov/
Use AI sort through millions of science-related papers based on your search terms
link: https://www.semanticscholar.org/
You can sort by keyword, title, journal, and more and download open access documents directly from the site
link: https://zenodo.org/