1.PrePubMed
http://www.prepubmed.org/



PrePubMed indexes preprints from arXiv q-bio, PeerJ Preprints, bioRxiv, F1000Research, preprints.org, The Winnower, Nature Precedings, and Wellcome Open Research. Articles are not stored on PrePubMed, but you will be linked to the article at the respective site.

2.bioRxiv
https://www.biorxiv.org/

bioRxiv (pronounced "bio-archive") is a free online archive and distribution service for unpublished preprints in the life sciences. It is operated by Cold Spring Harbor Laboratory, a not-for-profit research and educational institution. By posting preprints on bioRxiv, authors are able to make their findings immediately available to the scientific community and receive feedback on draft manuscripts before they are submitted to journals.