Perhaps you should try some spelling variations:
"import duty integration theories." » "import duty integration theorems.", "import duty integrationstheorie 2.", "import duty integration series.", "import dutch integration theories.", "import data integration theories.", "import why integration theories.", "import duties integration theories."
"support chain integration theory." » "support chain integration through.", "support chain information theory.", "support chain innovation theory.", "support can integration theory.", "support chuan integration theory.", "supply chain integration theory."

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 ("support chain integration theory."))~.
• Removing quotes may allow a broader search: (( import duty integration theories. ) or ( support chain integration theory. ))~.
• Adding a wildcard symbol may retrieve word variants: (("import duty integration theories.") or ("support chain integration theory."))*.