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."
"supply china information theory." » "supply china's information theory.", "supply chief information theory.", "supply child information theory.", "supply chains information theory.", "supply chain information theory."

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