Perhaps you should try some spelling variations:
"improving human performance series." » "improving human performance studies.", "improving human performance size.", "improving loan performance series.", "improving thermal performance series.", "improving chain performance series."
"improving plant performance review." » "improving plant performance risk.", "improving plant performance evidence.", "improving port performance review.", "improving court performance review.", "improving land performance review.", "improving place performance review.", "improved plant performance review."

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

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