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

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 ("operation system"))) OR ("operations systems"))*.
• Removing quotes may allow a broader search: (((( cooperation systems ) or ( operation system ))) or ( operations systems ))*.