Perhaps you should try some spelling variations:
"improving human performance series." » "improving human performance studies.", "improving human performance size.", "improving loan performance series.", "improving thermal performance series.", "improving chain performance series."
"improving road performance series." » "improving road performance studies.", "improving road performance size.", "improving board performance series.", "improving good performance series.", "improving bond performance series.", "improving food performance series.", "improving rural 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 human performance series.") or ("improving road performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving human performance series.") OR ("improving road performance series.")).
• Removing quotes may allow a broader search: (( improving human performance series. ) or ( improving road performance series. )).
• Adding a wildcard symbol may retrieve word variants: (("improving human performance series.") or ("improving road performance series."))*.