PubMed: PubMed is a free resource supporting the search and retrieval of biomedical and life sciences literature with the aim of improving health–both globally and personally.
The PubMed database contains more than 30 million citations and abstracts of biomedical literature. It does not include full-text journal articles; however, links to the full text are often present when available from other sources, such as the publisher's website or PubMed Central (PMC). (Description from PubMed site)
Science Direct: Open access journal articles covering multiple subjects in science (account creation may be necessary)
PLOS ONE: Full-text open access articles covering multiple subject areas
Chochrane Library: A collection of systematic reviews and other synthesized research evidence created with the goal of informing health decision making
**Preprints and unpublished work has not been peer reviewed.**
National Library of Medicine Clinical Trials Database: Collection of up-to-date clinical trials from around the world
Biorxiv: Unpublished preprints of articles in life sciences
Medrxiv: Unpublished preprints of articles in the medical, clinical, and health sciences
Here is the direct link for you: MAKE A REQUEST
GOOGLE TIP
Google: "article title" open access pdf
Sometimes you will find the preprint, or the author has chosen to make their article public.
NEW and in BETA
UNPAYWALL - Search for your article here if it's behind a paywall. You may get access to it this way. If you still can't find it, put in the interlibrary loan.