Perhaps you should try some spelling variations:
nonlinear potential » nonlinear partial, nonlinear material, nonlinear properties
particles theory » particles through
partial theory » spatial theory, partial memory, 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 potential theory ) OR ( nonlinear ((((partial theory) OR (particle theory))) OR (particles theory)) )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( nonlinear potential theory ) or ( nonlinear ((((partial theory) OR (particle theory))) or (particles theory)) ))".
• Adding a wildcard symbol may retrieve word variants: (( nonlinear potential theory ) or ( nonlinear ((((partial theory) OR (particle theory))) or (particles theory)) ))*.