Perhaps you should try some spelling variations:
"supply grid irrigation schemes." » "supply grid irrigation scheme.", "supply grid irrigation systems.", "supply grain irrigation schemes.", "supply drip irrigation schemes.", "supply gray irrigation schemes.", "supply crowd irrigation schemes.", "supply great irrigation schemes.", "support grid irrigation schemes."
"survey global integration theory." » "survey regional integration theory.", "survey global integration through.", "survey global information theory.", "survey global innovation theory.", "turkey global integration theory.", "survives global integration theory.", "sur global integration theory."

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• If you are trying to use Boolean operators, they must be ALL CAPS: (("supply grid irrigation schemes.") OR ("survey global integration theory."))~.
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