Perhaps you should try some spelling variations:
depressive disorders » depressive disorder
2.2 etiology » 12.2 etiology, 1.2 etiology, 2.1 etiology
2f etiology » 21 etiology, 28 etiology, 2.1 etiology
22 etiology » 12 etiology, 21 etiology, 28 etiology

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: %depressive disorders %((2f etiology) OR (((22 etiology) OR (2.2 etiology))))%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%depressive disorders %((2f etiology) or (((22 etiology) OR (2.2 etiology))))%22".
• Adding a wildcard symbol may retrieve word variants: %depressive disorders %((2f etiology) or (((22 etiology) OR (2.2 etiology))))%22*.