Perhaps you should try some spelling variations:
nonlinear particles » collinear particles, nonlinear partial, nonlinear vortices
nonlinear material » nonlinear materials, nonlinear matrix, nonlinear partial
particles theory » particles through
material theory » materials theory
spatial theory » special theory, social theory, spatial 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 ((spatial theory) OR (particle theory)) ) OR ( nonlinear particles theory ))) OR ( nonlinear material theory )).
• Adding a wildcard symbol may retrieve word variants: (((( nonlinear ((spatial theory) or (particle theory)) ) or ( nonlinear particles theory ))) or ( nonlinear material theory ))*.