Perhaps you should try some spelling variations:
"improving thermal performance series." » "improving thermal performance studies.", "improving thermal performance size.", "improving external performance series.", "improving animal performance series.", "improving erm performance series."
"improving annual performance evidence." » "improving fiscal performance evidence.", "improving social performance evidence.", "improving financial performance evidence.", "improving animal performance evidence.", "improving sexual performance evidence.", "improving antenatal performance evidence."

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