Perhaps you should try some spelling variations:
"support trade integration theories." » "support trade integration theory.", "support trade integration through.", "support trade integration efforts.", "export trade integration theories.", "support grant integration theories.", "import trade integration theories."
"support a interaction theories." » "support a interaction terms.", "support a interaction term.", "support a integration theory.", "support _ interaction theories.", "support tax interaction theories.", "support _ interactions theories."

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

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