Perhaps you should try some spelling variations:
"improving crop performance series." » "improving crop performance studies.", "improving crop performance size.", "improving group performance series.", "improving top performance series.", "improving do performance series.", "improving co performance series.", "improving pro performance series.", "improving macro performance series."
"improving can performance risks." » "improving can performance risk.", "improving chain performance risks.", "improving loan performance risks.", "improving human performance risks.", "improving care performance risks.", "improving a performance risks.", "improving co performance risks."

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (("improving can performance risks.") or ("improving crop performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving can performance risks.") OR ("improving crop performance series.")).
• Removing quotes may allow a broader search: (( improving can performance risks. ) or ( improving crop performance series. )).
• Adding a wildcard symbol may retrieve word variants: (("improving can performance risks.") or ("improving crop performance series."))*.