How to find just the dups

I'm new to sql.. and I have not been able to find in the books I have the answer to this question.

How do you code a select statement to pull out just the duplicate rows, based on just one field, which is not the primary key.

SELECT nombre_cliente,count(*)
FROM clientes
GROUP BY nombre_cliente
HAVING COUNT(*)>1

This will display rows which are having duplicates

select distinct * from emp a
where a.rowid < (select max(b.rowid) from emp b where b.empno = a.empno)