Copy complete structure of a table in Oracle without using Backup
select dbms_metadata.get_ddl('TABLE','SCHEMANAME','TABLENAME') DDL from dual;


TABLE is the type of object (you can also extract INDEX, VIEW, FUNCTION, PROCEDURE etc)

or:

create table t1 as
( select * from t2 where 3=4 );


dbms_metadata.get_ddl is the way to go, as it preserves various aspects that a CTAS query doesn't.