If the UO doesn't have access to a book or article you can request it from another library. This is a free to use service that can quickly get you the materials you need!
Encompasses a variety of psychology related materials and is run by The American Psychological Association.
Includes: PsycINFO, PsycArticles, and PsycTESTS
Covers biomedical related literature and is run by the National Institute of Health. (Not psychology specific, but includes many relevant studies in the field)
The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-5®) is used by clinicians and researchers to diagnose and classify mental disorders.