Perhaps you should try some spelling variations:
"societal effect model" » "societal effects model", "social effects model", "society effects model", "societal effect models", "societal effects models"
"social effect model" » "social effects model", "special effect model", "local effect model", "social effect models", "social effects models"
"social needs model" » "special needs model", "social norms model", "social needs more"
"social net model" » "social news model", "social na model"

Try widening your search to All Fields.

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: (((("social net model") OR ("social needs model"))) OR ((("social effect model") OR ("societal effect model")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"social net model\") OR (\"social needs model\"))) or (((\"social effect model\") or (\"societal effect model\"))))".
• Removing quotes may allow a broader search: (((( social net model ) OR ( social needs model ))) or ((( social effect model ) or ( societal effect model )))).
• Adding a wildcard symbol may retrieve word variants: (((("social net model") OR ("social needs model"))) or ((("social effect model") or ("societal effect model"))))*.