Perhaps you should try some spelling variations:
"improving voluntary performance series." » "improving country performance series.", "improving entry performance series.", "improving industry performance series.", "improving voluntary performance studies.", "improving voluntary performance size."
"improving loan performance series." » "improving loan performance studies.", "improving loan performance size.", "improving local performance series.", "improving land performance series.", "improving lead performance series."

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