Perhaps you should try some spelling variations:
"special effective model" » "specific effective model", "special effects model", "special effect model"
"social effective model" » "social affective model", "local effective model", "socio effective model"
"social effects model" » "special effects model", "social aspects model", "social effects models", "social effect models"
"social exact model" » "social effect model", "social etats model", "social et 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 exact model") OR ((((("social effective model") OR ("special effective model"))) OR ("social effects model")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"social exact model\") or (((((\"social effective model\") OR (\"special effective model\"))) or (\"social effects model\"))))".
• Removing quotes may allow a broader search: (( social exact model ) or ((((( social effective model ) OR ( special effective model ))) or ( social effects model )))).
• Adding a wildcard symbol may retrieve word variants: (("social exact model") or ((((("social effective model") OR ("special effective model"))) or ("social effects model"))))*.