Perhaps you should try some spelling variations:
"improving external performance series." » "improving emotional performance series.", "improving materials performance series.", "improving thermal performance series.", "improving maternal performance series.", "improving central performance series.", "improving federal performance series.", "improving external performance studies.", "improving external performance size."
"improving road performance risk." » "improving board performance risk.", "improving good performance risk.", "improving bond performance risk.", "improving road performance 2019.", "improving food performance risk.", "improving rural performance risk."

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 external performance series.") or ("improving road performance risk."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving external performance series.") OR ("improving road performance risk.")).
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• Adding a wildcard symbol may retrieve word variants: (("improving external performance series.") or ("improving road performance risk."))*.