Perhaps you should try some spelling variations:
"import trade integration theory." » "import trade integration through.", "import trade information theory.", "import trade innovation theory.", "export trade integration theory.", "import price integration theory.", "import taxes integration theory."
"import policy integration theory." » "import policy integration through.", "import policy information theory.", "import policy innovation theory.", "import political integration theory.", "import policy international theory.", "import policy intervention theory.", "important policy integration theory.", "import price integration theory."

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

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