Perhaps you should try some spelling variations:
"collinear particles theory" » "collider particle theory", "colloidal particles theory", "colliding particles theory", "collinear particles through", "collinear partials theory", "colline particles theory", "collidar particles theory"
"nonlinear material theory" » "nonlinear materials theory", "nonlinear matrix theory", "nonlinear media theory"
"nonlinear spatial theory" » "nonlinear spectral theory", "nonlinear static theory", "nonlinear initial theory", "nonlinear special theory", "nonlinear social theory", "nonlinear spatial memory"
"linear particle theory" » "linear partial theory", "line particle theory", "lidar particle theory"
"nonlinear partial theory" » "nonlinear partial tears", "nonlinear partial theta", "nonlinear parts 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 partial theory") OR ("nonlinear spatial theory"))) OR ((("linear particle theory") OR ("collinear particles theory"))))) OR ("nonlinear material theory")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((((\"nonlinear partial theory\") OR (\"nonlinear spatial theory\"))) or (((\"linear particle theory\") or (\"collinear particles theory\"))))) or (\"nonlinear material theory\"))".
• Removing quotes may allow a broader search: (((((( nonlinear partial theory ) OR ( nonlinear spatial theory ))) or ((( linear particle theory ) or ( collinear particles theory ))))) or ( nonlinear material theory )).
• Adding a wildcard symbol may retrieve word variants: (((((("nonlinear partial theory") OR ("nonlinear spatial theory"))) or ((("linear particle theory") or ("collinear particles theory"))))) or ("nonlinear material theory"))*.