Perhaps you should try some spelling variations:
"improving thermal performance reviews." » "improving thermal performance review.", "improving thermal performance reports.", "improving thermal performance risks.", "improving external performance reviews.", "improving animal performance reviews.", "improving erm performance reviews."
"improving rural performance series." » "improving rural performance studies.", "improving rural performance size.", "improving euract performance series.", "improving larval performance series.", "improving pupil performance series."

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

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