1. PNAS articles older than six months have free access
2. Pubmed  PubMed comprises more than 22 million citations for biomedical literature from MEDLINE, life science journals, and online books
3. PLoS a nonprofit publisher 
4. Nature, Most scientific journals are now highly specialized, and Nature is among the few journals that still publish original research articles across a wide range of scientific fields. Paid access
5. Science Paid access
6. Journal of Chemical Education Paid access
7. Journal of Biological Chemistry, articles older than six months have free access
8. Journals from American Society of Microbiology articles older than six months have free access
9. Current Science free access, published in India
10. Resonance free access, published in India
11. Biomed Central free access 
12. Sciencedirect paid access but searchable
13. Pubmed Books free access

A detailed list of references can be seen here.