Yes, you can do it for one session like this:
dbms_system.set_sql_trace_in_session(SID,SerialNb,true);
where you may find SID and SerialNB in v$session:
SELECT SID, SERIAL# SerialNb FROM v$session;
And you also can do it for all sessions like this (under SYS):
alter system set events '10046...