Perhaps you should try some spelling variations:
"cooperation systems" » "cooperating systems", "operation systems", "cogeneration systems", "cooperative systems", "teleoperation systems"
"cooperation system" » "cooperative system", "operation system", "teleoperation system"
"operations systems" » "operations system", "operational systems", "operating systems"

Try widening your search to All Fields.

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: (((("cooperation systems") OR ((("cooperation system") OR ("cooperative systems"))))) OR ("operations systems")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"cooperation systems\") or (((\"cooperation system\") OR (\"cooperative systems\"))))) or (\"operations systems\"))".
• Removing quotes may allow a broader search: (((( cooperation systems ) or ((( cooperation system ) OR ( cooperative systems ))))) or ( operations systems )).
• Adding a wildcard symbol may retrieve word variants: (((("cooperation systems") or ((("cooperation system") OR ("cooperative systems"))))) or ("operations systems"))*.