Perhaps you should try some spelling variations:
"improving crop performance metrics." » "improving crop performance measures.", "improving group performance metrics.", "improving top performance metrics.", "improving do performance metrics.", "improving co performance metrics.", "improving pro performance metrics.", "improving macro performance metrics."
"improving peer performance series." » "improving peer performance studies.", "improving peer performance size.", "improving power performance series.", "improving poor performance series.", "improving der performance series.", "improving gender performance series.", "improving air performance series.", "improving energy 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 peer performance series.") or ("improving crop performance metrics."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving peer performance series.") OR ("improving crop performance metrics.")).
• Removing quotes may allow a broader search: (( improving peer performance series. ) or ( improving crop performance metrics. )).
• Adding a wildcard symbol may retrieve word variants: (("improving peer performance series.") or ("improving crop performance metrics."))*.