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

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