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