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 thermal performance series.", "improving company performance series.", "improving urban performance series.", "improving rural performance series."
"improving mental performance evidence." » "improving senegal performance evidence.", "improving annual performance evidence.", "improving entry performance evidence.", "improving maternal performance evidence.", "improving social performance evidence.", "improving rural performance evidence."

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 mental performance evidence."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving human performance series.") OR ("improving mental performance evidence.")).
• Removing quotes may allow a broader search: (( improving human performance series. ) or ( improving mental performance evidence. )).
• Adding a wildcard symbol may retrieve word variants: (("improving human performance series.") or ("improving mental performance evidence."))*.