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 board performance evidence." » "improving court performance evidence.", "improving good performance evidence.", "improving based performance evidence.", "improving food performance evidence.", "improving care performance evidence.", "improving blood 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 board performance evidence."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving basic performance series.") OR ("improving board performance evidence.")).
• Removing quotes may allow a broader search: (( improving basic performance series. ) or ( improving board performance evidence. )).
• Adding a wildcard symbol may retrieve word variants: (("improving basic performance series.") or ("improving board performance evidence."))*.