Perhaps you should try some spelling variations:
"cooperational systems" » "operational systems", "cooperation systems", "conversational systems"
"operation systems" » "operations systems", "operation system", "operational systems"
"operations system" » "operations systems", "operation system", "operational 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: (((("operation systems") OR ("cooperational systems"))) OR ("operations system"))*.
• Removing quotes may allow a broader search: (((( operation systems ) or ( cooperational systems ))) or ( operations system ))*.