Perhaps you should try some spelling variations:
international astronomical » international economics, international economic
economique internationale » economics international, economy international, politique internationale
astronomy observational » astronomy observations, astronomical observations, astronomical observation
astronomy observatory » astronomy observations, astronomical observatory

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: ((international astronomical) OR (observations astronomical)) union/union ((((astronomy observational) OR (astronomy observatory))) OR (economique internationale)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((international astronomical) or (observations astronomical)) union/union ((((astronomy observational) OR (astronomy observatory))) or (economique internationale))".
• Adding a wildcard symbol may retrieve word variants: ((international astronomical) or (observations astronomical)) union/union ((((astronomy observational) OR (astronomy observatory))) or (economique internationale))*.