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 poor performance evidence." » "improving sector performance evidence.", "improving power performance evidence.", "improving food performance evidence.", "improving peer performance evidence."

You may be able to get more results by adjusting your search query.

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