Perhaps you should try some spelling variations:
"psychological studies" » "ecological studies", "morphological studies", "psychological theories"
"psychological stress" » "psychological distress"
"psychological tests" » "psychological testing", "psychological aspects", "psychological theory"

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("psychological studies") OR ("psychological stress"))) OR ("psychological tests")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"psychological studies\") OR (\"psychological stress\"))) or (\"psychological tests\"))".
• Removing quotes may allow a broader search: (((( psychological studies ) OR ( psychological stress ))) or ( psychological tests )).
• Adding a wildcard symbol may retrieve word variants: (((("psychological studies") OR ("psychological stress"))) or ("psychological tests"))*.