Perhaps you should try some spelling variations:
"improving central performance evidence." » "improving control performance evidence.", "improving general performance evidence.", "improving contract performance evidence.", "improving mental performance evidence.", "improving federal performance evidence.", "improving neural performance evidence."
"improving rural performance series." » "improving rural performance studies.", "improving rural performance size.", "improving euract performance series.", "improving larval performance series.", "improving pupil performance series."

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

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