Perhaps you should try some spelling variations:
"improving basic performance series." » "improving basic performance studies.", "improving basic performance size.", "improving based performance series.", "improving music performance series.", "improving baseline performance series.", "improving air performance series.", "improve basic performance series."
"improving past performance evidence." » "improving plant performance evidence.", "improving port performance evidence.", "improving transit performance evidence.", "improving fast performance evidence.", "improving post 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 basic performance series.") or ("improving past performance evidence."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving basic performance series.") OR ("improving past performance evidence.")).
• Removing quotes may allow a broader search: (( improving basic performance series. ) or ( improving past performance evidence. )).
• Adding a wildcard symbol may retrieve word variants: (("improving basic performance series.") or ("improving past performance evidence."))*.