Perhaps you should try some spelling variations:
"cooperation systems" » "cooperation system", "cooperative systems", "cooperating systems"
"operations systems" » "operational systems", "operating systems", "operation system", "operation systems"
"operations system" » "operation system", "operational system", "operating 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: (("cooperation systems") OR ((("operations systems") OR ("operations system")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"cooperation systems\") or (((\"operations systems\") OR (\"operations system\"))))".
• Removing quotes may allow a broader search: (( cooperation systems ) or ((( operations systems ) OR ( operations system )))).
• Adding a wildcard symbol may retrieve word variants: (("cooperation systems") or ((("operations systems") OR ("operations system"))))*.