Perhaps you should try some spelling variations:
"improving maternal performance risk." » "improving materials performance risk.", "improving external performance risk.", "improving national performance risk.", "improve maternal performance risk.", "improving water performance risk.", "improving maternal performance 2019."
"improving general performance series." » "improving federal performance series.", "improving senegal performance series.", "improving gendered performance series.", "improving general performance studies.", "improving general performance size.", "improving central performance series.", "improving energy 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 general performance series.") or ("improving maternal performance risk."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving general performance series.") OR ("improving maternal performance risk.")).
• Removing quotes may allow a broader search: (( improving general performance series. ) or ( improving maternal performance risk. )).
• Adding a wildcard symbol may retrieve word variants: (("improving general performance series.") or ("improving maternal performance risk."))*.