Perhaps you should try some spelling variations:
"particle and nuclear optical" » "particle and nuclear option", "particle and nuclear medical", "particle and nonlinear optical"
"particle and nuclear physics" » "particle and nuclear physical"

Try widening your search to All Fields.

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: (("particle and nuclear optical") OR ("particle and nuclear physics")).
• Removing quotes may allow a broader search: (( particle and nuclear optical ) or ( particle and nuclear physics )).
• Adding a wildcard symbol may retrieve word variants: (("particle and nuclear optical") or ("particle and nuclear physics"))*.