Perhaps you should try some spelling variations:
"improving thermal performance series." » "improving thermal performance metrics.", "improving thermal performance reviews.", "improving thermal performance targets.", "improving maternal performance series.", "improving rural performance series.", "improving human performance series."
"improving loan performance review." » "improving loan performance risk.", "improving loan performance evidence.", "improving poor performance review.", "improving bank performance review.", "improving _ performance review.", "improving local performance review.", "improving land performance review.", "improving road performance review."

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