Unpaywall

https://unpaywall.org/

Locate legally available open access articles in thousands of journals.

Get the Chrome extension.

CORE

https://core.ac.uk/

The world's largest collection of open access research papers.

Semantic Scholar

https://www.semanticscholar.org/

Search for scientific articles.

PLOS

https://plos.org/

Open access journals include: PLOS One (all science areas, also social sciences and humanities),

PLOS Biology, PLOS Genetics, PLOS Medicine, PLOS Pathogens.

Elsevier Open Access Journals

https://www.elsevier.com/about/open-science/open-access/open-access-journals

Many science areas.

Google Scholar

https://scholar.google.com/

Articles in many research areas. Many are full text (search for PDF). Use the date filter to search for recent articles.

Wiley Open Access Journals

https://authorservices.wiley.com/open-research/open-access/browse-journals.html

Science journals.

Oxford University Press Open Access Journals

https://academic.oup.com/journals/pages/open_access

Science journals.