Server Administration :: Unable To See / Insert Chinese Characters In Oracle Database

We are getting problem with the Chinese character set. My current character set is as follows.

PARAMETER VALUE
---------------------------------------------------------------- ----------------------------------------------------------------
NLS_LANGUAGE AMERICAN
NLS_TERRITORY AMERICA
NLS_CURRENCY $
NLS_ISO_CURRENCY AMERICA
NLS_NUMERIC_CHARACTERS .,
[code]....

My column description for the table product is as follows.

PART_NBRVARCHAR2 (30 Byte)
PART_DESCNVARCHAR2 (2000)

when trying to insert Chinese character using the insert command below

insert into product(part_nbr,part_desc,cust_name) values('322341',unistr('功'),'test');

I am getting the value when selecting the same record using the select command

select a.part_nbr,a.part_desc,a.cust_name from product a where a.part_nbr='322341'322341¿test

When I running this command on TOAD

select a.rowid,a.part_nbr,a.part_desc,a.cust_name from product a where a.part_nbr='322341'

and manually editing/inserting '功' character in output from select command above. After that I am able to get the same Chinese character when I am running select next time.