Perhaps you should try some spelling variations:
observational clues » observational aspects, observational results, observational techniques
observation content » observation consistent, observational context, observation concepts
observation concept » observation concepts, conservation concept, observation conceptual

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: ((observational clues) OR (((observation content) OR (observation concept)))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((observational clues) or (((observation content) OR (observation concept))))".
• Adding a wildcard symbol may retrieve word variants: ((observational clues) or (((observation content) OR (observation concept))))*.