Perhaps you should try some spelling variations:
operational research » international research
educational research » education research
operation research » education research

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: ((((operation research) OR (((operational research) OR (educational research))))) OR (operations research))/decision theory.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((operation research) or (((operational research) OR (educational research))))) or (operations research))/decision theory".
• Adding a wildcard symbol may retrieve word variants: ((((operation research) or (((operational research) OR (educational research))))) or (operations research))/decision theory*.