Perhaps you should try some spelling variations:
"improve maternal performance evidence." » "improve materials performance evidence.", "improve external performance evidence.", "improve national performance evidence.", "improving maternal performance evidence.", "improve water performance evidence."
"improving human performance contract." » "improving human performance contracts.", "improving loan performance contract.", "improving thermal performance contract.", "improving chain performance contract."

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