Perhaps you should try some spelling variations:
observational economy » observational astronomy, observational cohort, observational cinema
operational concepts » computational concepts, foundational concepts, operational costs
observation concepts » observation concept, observational concepts, conservation concepts

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 economy) OR (observations astronomical))) OR (((((operational concepts) OR (relational concept))) OR (observation concepts))))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((observational economy) or (observations astronomical))) or (((((operational concepts) OR (relational concept))) or (observation concepts))))*".