Perhaps you should try some spelling variations:
international services » international service, international reserves, integration services
numerical mathematics » general mathematics
international series » international serious, international serials, international aerien

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 series) OR (international services)) of ((((numerical mathematics) OR (industrial mathematics))) OR (numerische mathematik)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((international series) or (international services)) of ((((numerical mathematics) OR (industrial mathematics))) or (numerische mathematik))".
• Adding a wildcard symbol may retrieve word variants: ((international series) or (international services)) of ((((numerical mathematics) OR (industrial mathematics))) or (numerische mathematik))*.