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

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 review."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"improving rural performance series.\") OR (\"improving thermal performance review.\"))*".
• Removing quotes may allow a broader search: (( improving rural performance series. ) OR ( improving thermal performance review. ))*.