Perhaps you should try some spelling variations:
"improving rural performance series." » "improving rural performance metrics.", "improving rural performance reviews.", "improving rural performance review.", "improving pupil performance series.", "improving overall performance series.", "improving fiscal performance series.", "improving urban performance series.", "improving social performance series."
"improving thermal performance series." » "improving thermal performance metrics.", "improving thermal performance reviews.", "improving thermal performance review.", "improving maternal performance series.", "improving human performance series.", "improving mental performance series."

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (("improving rural performance series.") or ("improving thermal performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving rural performance series.") OR ("improving thermal performance series.")).
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