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."
"export price integration theory." » "export price integration through.", "export price information theory.", "export price innovation theory.", "export service integration theory.", "export price indexation theory.", "export die integration theory.", "export prices integration theory.", "import prices 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 ("export price integration theory."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("import trade integration theory.") OR ("export price integration theory.")).
• Removing quotes may allow a broader search: (( import trade integration theory. ) or ( export price integration theory. )).
• Adding a wildcard symbol may retrieve word variants: (("import trade integration theory.") or ("export price integration theory."))*.