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

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 external performance reports."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"improve maternal performance series.\") OR (\"improving external performance reports.\"))".
• Removing quotes may allow a broader search: (( improve maternal performance series. ) OR ( improving external performance reports. )).
• Adding a wildcard symbol may retrieve word variants: (("improve maternal performance series.") OR ("improving external performance reports."))*.