Perhaps you should try some spelling variations:
"particle and nonlinear physical" » "particle and nonlinear physics", "particle and nonlinear chemical", "particle and nonlinear optical"
"particle and nuclear material" » "particle and nuclear materials", "particle and nuclear matrix", "particle and nuclear matter"

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