Perhaps you should try some spelling variations:
"particle and nonlinear optical" » "particle and nonlinear optics"
"particle and nuclear medical" » "particle and nuclear medicine", "particle and nuclear material"

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