Perhaps you should try some spelling variations:
"biochemical characterization" » "chemical characterization", "mechanical characterization", "material characterization"
"optical characterization" » "chemical characterization", "material characterization", "functional characterization"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("optical characterization") OR ("biochemical characterization")).
• Removing quotes may allow a broader search: (( optical characterization ) or ( biochemical characterization )).
• Adding a wildcard symbol may retrieve word variants: (("optical characterization") or ("biochemical characterization"))*.