Perhaps you should try some spelling variations:
"improving maternal performance series." » "improving materials performance series.", "improving external performance series.", "improving national performance series.", "improve maternal performance series.", "improving water performance series.", "improving maternal performance studies.", "improving maternal performance size."
"improving thermal performance risk." » "improving external performance risk.", "improving animal performance risk.", "improving erm performance risk.", "improving thermal performance 2019."

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