Perhaps you should try some spelling variations:
"improving human performance series." » "improving human performance metrics.", "improving human performance reviews.", "improving human performance review.", "improving loan performance series.", "improving company performance series.", "improving animal performance series.", "improving urban performance series.", "improving rural performance series."
"improving thermal performance series." » "improving thermal performance metrics.", "improving thermal performance reviews.", "improving thermal performance review.", "improving maternal performance series.", "improving rural 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 human performance series.") or ("improving thermal performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving human performance series.") OR ("improving thermal performance series.")).
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