Perhaps you should try some spelling variations:
"import duty integration theories." » "import duty integration theory.", "import duty integration through.", "import duty integration efforts.", "import data integration theories.", "import south integration theories.", "import deep integration theories.", "import duties integration theories."
"supply trade integration series." » "supply trade integrating services.", "supply trade integration schemes.", "supply trade integration social.", "supply side integration series.", "supply case integration series."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("supply trade integration series.") OR ("import duty integration theories."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"supply trade integration series.\") OR (\"import duty integration theories.\"))".
• Removing quotes may allow a broader search: (( supply trade integration series. ) OR ( import duty integration theories. )).
• Adding a wildcard symbol may retrieve word variants: (("supply trade integration series.") OR ("import duty integration theories."))*.