Perhaps you should try some spelling variations:
"support trade integration theories." » "support trade integration theory.", "support trade integration through.", "support trade integration efforts.", "export trade integration theories.", "support grant integration theories.", "import trade integration theories."
"support european integration theories." » "support european integration theory.", "support european integration through.", "support european integration efforts.", "support europe integration theories."

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("support trade integration theories.") or ("support european integration theories."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("support trade integration theories.") OR ("support european integration theories.")).
• Removing quotes may allow a broader search: (( support trade integration theories. ) or ( support european integration theories. )).
• Adding a wildcard symbol may retrieve word variants: (("support trade integration theories.") or ("support european integration theories."))*.