Perhaps you should try some spelling variations:
"improve maternal performance series." » "improve materials performance series.", "improve external performance series.", "improve national performance series.", "improve maternal performance studies.", "improve maternal performance size.", "improve water performance series."
"improving maternal performance reports." » "improving materials performance reports.", "improving external performance reports.", "improving national performance reports.", "improving water performance reports.", "improving maternal performance report."

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