Perhaps you should try some spelling variations:
"improving human performance reviews." » "improving human performance review.", "improving human performance reports.", "improving human performance risks.", "improving loan performance reviews.", "improving chain performance reviews."
"Improving thermal performance series." » "Improving thermal performance studies.", "Improving thermal performance size."
improving thermal » improving external, improving animal, improving erm

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