Perhaps you should try some spelling variations:
"improving firm performance studies." » "improving firm performance audits.", "improving firm performance audit.", "improving firm performance standards.", "improving firms performance studies.", "improving air performance studies.", "improving erm performance studies."
"improving urban performance series." » "improving urban performance size.", "improving bank performance series.", "improving loan performance series.", "improving human performance series."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("improving urban performance series.") OR ("improving firm performance studies."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"improving urban performance series.\") OR (\"improving firm performance studies.\"))".
• Removing quotes may allow a broader search: (( improving urban performance series. ) OR ( improving firm performance studies. )).
• Adding a wildcard symbol may retrieve word variants: (("improving urban performance series.") OR ("improving firm performance studies."))*.