Perhaps you should try some spelling variations:
"airport sector integration theory." » "airport sector integration through.", "airport sector information theory.", "airport sector integration report.", "airport social integration theory.", "export sector integration theory.", "port sector integration theory.", "transport sector integration theory."
"support group integration study." » "support grid integration study.", "support run integration study.", "support through integration study.", "support from integration study.", "support grant integration study."

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: (("airport sector integration theory.") OR ("support group integration study."))~.
• Removing quotes may allow a broader search: (( airport sector integration theory. ) or ( support group integration study. ))~.
• Adding a wildcard symbol may retrieve word variants: (("airport sector integration theory.") or ("support group integration study."))*.