Perhaps you should try some spelling variations:
"improving thermal performance series." » "improving thermal performance studies.", "improving thermal performance size.", "improving external performance series.", "improving animal performance series.", "improving erm performance series."
"improving chain performance risk." » "improving loan performance risk.", "improving managing performance risk.", "improving chain performance 2019.", "improving brain performance risk.", "improving caring performance risk.", "improving air performance risk."

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (("improving thermal performance series.") or ("improving chain performance risk."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving thermal performance series.") OR ("improving chain performance risk.")).
• Removing quotes may allow a broader search: (( improving thermal performance series. ) or ( improving chain performance risk. )).
• Adding a wildcard symbol may retrieve word variants: (("improving thermal performance series.") or ("improving chain performance risk."))*.