Perhaps you should try some spelling variations:
"nonlinear potential theory" » "nonlinear material theory", "nonlinear properties theory"
"nonlinear matrix theory" » "nonlinear material theory", "linear matrix theory", "nonlinear media theory"
"nonlinear partial theory" » "nonlinear particle theory", "nonlinear spatial theory", "nonlinear particles theory"

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