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 bond performance risk." » "improving board performance risk.", "improving fund performance risk.", "improving good performance risk.", "improving bond performance 2019.", "improving blood performance risk.", "improving food performance risk.", "improving beef 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 thermal performance series.") or ("improving bond performance risk."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving thermal performance series.") OR ("improving bond performance risk.")).
• Removing quotes may allow a broader search: (( improving thermal performance series. ) or ( improving bond performance risk. )).
• Adding a wildcard symbol may retrieve word variants: (("improving thermal performance series.") or ("improving bond performance risk."))*.