Perhaps you should try some spelling variations:
"evidence synthese" » "evidence synthesis", "evidence scheme", "evidence sentence"
"evidence systems" » "science systems", "evidence synthesis", "reference systems"
"valence systems" » "value systems", "defence systems", "science systems"

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: (((("evidence systems") OR ("valence systems"))) OR ("evidence synthese")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"evidence systems\") OR (\"valence systems\"))) or (\"evidence synthese\"))".
• Removing quotes may allow a broader search: (((( evidence systems ) OR ( valence systems ))) or ( evidence synthese )).
• Adding a wildcard symbol may retrieve word variants: (((("evidence systems") OR ("valence systems"))) or ("evidence synthese"))*.