Perhaps you should try some spelling variations:
observational astronomy » observations astronomical
observational economy » observational cinema, observational errors, observational coding
observational cohort » observational support, observational errors, observational methods
operational concepts » computational concepts, foundational concepts, relational concept
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 (observational cohort))) OR (observational astronomy))) OR (((operational concepts) OR (observation concepts)))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((((observational economy) OR (observational cohort))) or (observational astronomy))) or (((operational concepts) or (observation concepts))))".
• Adding a wildcard symbol may retrieve word variants: ((((((observational economy) OR (observational cohort))) or (observational astronomy))) or (((operational concepts) or (observation concepts))))*.