Perhaps you should try some spelling variations:
"supply trade integration theories." » "supply trade integration theorems.", "supply trade integrationstheorie 2.", "supply trade integration theory.", "supply case integration theories."
"support migrant integration services." » "support migrant integrating services.", "support migrant integrated services.", "support migrant insemination services.", "support market integration services.", "support migrants integration services.", "support grant integration services.", "supporting migrants integration services."

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (("supply trade integration theories.") or ("support migrant integration services."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("supply trade integration theories.") OR ("support migrant integration services.")).
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