PsyArXiv allows scholars to post documents such as working papers, unpublished work, and articles under review (preprints), making them accessible to other researchers and to the public at no cost.
This search engine can help you "home in on key publications, citation, and results..." on your topic. Once you hone in an article, there are automatic recommendations to other related citations, sorted by influence. It is mostly focused on computer science and neuroscience topics.
Preprint server for biology, contains articles that are unpublished but uploaded to this database to make their findings immediately available and receive feedback before submission to journals.