PubMed.gov - PubMed comprises more than 29 million citations for biomedical literature from MEDLINE, life science journals, and online books. Citations may include links to full-text content from PubMed Central and publisher web sites.
ResearchGate - Access scientific knowledge, and make your research visible
Biohunter - Biohunter is a one-stop portal for literature search, batch-download PDFs and reference manager
PubPharm - PubPharm is a search plattform tailored for pharmaeceutical researchers.
Hubmed - An alternative interface to the PubMed medical literature database.
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.