Clarification in like command

hi everybody

i am a beginner in sql.. i need a clarification

                    
sqlcommand com=new sqlcommand("Select * from Registration where UserName like %@UserName%",con)                    
com.parameters.add("@UserName",sqldbtype.varchar,128).value='d';                    
sqlDataAdapter adp=new sqlDataAdapter(com);                    
Datattable dt=new Datatable();                    
adp.fill(dt);                    
return dt;                    

but i am not getting the value..how to pass parameter in like command