Perhaps you should try some spelling variations:
"nonlinear material theory" » "nonlinear materials theory", "nonlinear matrix theory", "nonlinear media theory"
"nonlinear particle theory" » "collinear particles theory", "linear particle theory", "nonlinear price theory"
"nonlinear partial theory" » "nonlinear spatial theory", "nonlinear particles theory", "nonlinear partial tears"

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