Perhaps you should try some spelling variations:
"improving rural performance series." » "improving rural performance studies.", "improving rural performance size.", "improving euract performance series.", "improving larval performance series.", "improving pupil performance series."
"improving model performance series." » "improving model performance studies.", "improving model performance size.", "improving social performance series.", "improving pupil performance series.", "improvement model performance series.", "improving budget performance series.", "improving gender performance series."

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