Perhaps you should try some spelling variations:
"improving firms performance series." » "improving firms performance studies.", "improving firms performance size.", "improving firm performance series.", "improving firm performances series.", "improving funds performance series.", "improving farmers performance series.", "importing firms performance series.", "improving air performance series."
"improving human performance measures." » "improving loan performance measures.", "improving thermal performance measures.", "improving chain performance measures."

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 measures.") OR ("improving firms performance series."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"improving human performance measures.\") OR (\"improving firms performance series.\"))".
• Removing quotes may allow a broader search: (( improving human performance measures. ) OR ( improving firms performance series. )).
• Adding a wildcard symbol may retrieve word variants: (("improving human performance measures.") OR ("improving firms performance series."))*.