Perhaps you should try some spelling variations:
"nonlinear potential theory" » "nonlinear partial theory", "nonlinear properties theory"
"nonlinear material theory" » "nonlinear materials theory", "nonlinear matrix theory", "nonlinear partial theory"

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"nonlinear potential theory\") OR (\"nonlinear material theory\"))".
• Removing quotes may allow a broader search: (( nonlinear potential theory ) OR ( nonlinear material theory )).
• Adding a wildcard symbol may retrieve word variants: (("nonlinear potential theory") OR ("nonlinear material theory"))*.