Functioning as a research and publishing network, ScienceOpen offers open access to more than 28 million articles in all areas of science. Although you do need to register to view the full text of the articles, registration is free. The advanced search function is highly detailed, allowing you to find precisely the research you’re looking for.
The Berlin- and Boston-based company was founded in 2013 with the goal to “facilitate open and public communications between academics and to allow ideas to be judged on their merit, regardless of where they come from.”