These databases contain peer-reviewed journals, technical reports, conference proceedings, and several other forms of credible, scholarly literature.
Locating these types of articles can be tricky, but here are a couple of engineering-related databases that can be helpful.
These databases are mostly for older technical reports and archives.
What's a preprint? A preprint is a version of a paper that precedes formal peer review and publication in a peer-reviewed scholarly or scientific journal.