Perhaps you should try some spelling variations:
"import duty integration schemes." » "import duty integration schengen.", "import duty irrigation schemes.", "import duty integration regimes.", "import dutch integration schemes.", "import data integration schemes.", "import why integration schemes.", "import duties integration schemes."
"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."

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