Perhaps you should try some spelling variations:
"improving sector performance series." » "improving sector performance studies.", "improving sector performance size.", "improve sector performance series.", "improving eco performance series.", "improving sewer performance series."
"improving human performance evidence." » "improving loan performance evidence.", "improving thermal performance evidence.", "improving chain performance evidence."

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

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