Subject Specific:
See also the subject specific databases in the fields to which your work is applied, e.g. biology, physics, etc.
Publisher Specific:
These are limited to one or two publishers. Be mindful of what you may be missing!
Multidisciplinary:
Database of articles in peer-reviewed journals, magazines, and news sources with full-text journal coverage for nearly all academic areas of study.
For access to e-books, online journals, databases:
See also the preprint servers in the fields to which your work is applied, e.g: biology.