Use the CRAAP Test
Currency - Is it timely?
Relevance - Useful for your purposes?
Authority - Who? What is the source?
Accuracy - References to back it up?
Purpose - Why? Is there a bias?
More detailed information on the CRAAP Test
Physics and Interdisciplinary Databases
The following databases feature good coverage of physics in general.
Medical Physics Database
Geophysics Database
Astronomy Databases
Particle Physics Database