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.", "improving maternal performance series.", "improve water performance series."
"improving human performance review." » "improving human performance risk.", "improving human performance evidence.", "improving loan performance review.", "improving thermal performance review.", "improving chain performance review."

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