Perhaps you should try some spelling variations:
"improving maternal performance evidence." » "improving national performance evidence.", "improving thermal performance evidence.", "improving lanterns performance evidence.", "improve maternal performance evidence.", "improving water performance evidence."
"improving rural performance series." » "improving rural performance metrics.", "improving rural performance reviews.", "improving rural performance review.", "improving pupil performance series.", "improving thermal performance series.", "improving overall performance series.", "improving urban performance series.", "improving social 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 maternal performance evidence."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving rural performance series.") OR ("improving maternal performance evidence.")).
• Removing quotes may allow a broader search: (( improving rural performance series. ) or ( improving maternal performance evidence. )).
• Adding a wildcard symbol may retrieve word variants: (("improving rural performance series.") or ("improving maternal performance evidence."))*.