Perhaps you should try some spelling variations:
"nonlinear particle theory" » "collinear particles theory", "linear particle theory", "nonlinear price theory"
"nonlinear partial theory" » "nonlinear spatial theory", "nonlinear particles theory", "nonlinear partial memory"

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