Perhaps you should try some spelling variations:
"import duty integration theories." » "import duty integration theorems.", "import duty integrationstheorie 2.", "import duty integration theory.", "import dutch integration theories.", "import data integration theories.", "import why integration theories.", "import duties integration theories."
"supply factor integration series." » "supply facto integration series.", "supply sector integration series.", "supply actor interaction series.", "supply factor integration services.", "supply factor interaction series.", "supply factor integration server.", "supply factors integration series."

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

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