Perhaps you should try some spelling variations:
"social exact model" » "social effect model", "social etats model", "social email model"
"social bots model" » "social robots model", "social robot model", "social cots model", "social potts model", "social costs model"
"social net model" » "social news model", "social na model", "social needs model", "social nset model", "social njet model", "social net modele"
"social et model" » "social en model", "social e model", "social etats model", "social set model", "social jet model", "social et modele"

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