If you want to disable all scheduler jobs definitely and know all the consequences, you may set JOB_QUEUE_PROCESSES to 0 to stop initiating any job process.
Memory
JOB_QUEUE_PROCESSES can be set to 0 temporarily.
SQL> alter system set job_queue_processes=0 scope=memory;
System altered.
Memory and SPFILE :
JOB_QUEUE_PROCESSES can also be set to 0 persistently.
SQL> alter system set job_queue_processes=0 scope=both;
System altered.
RAC :
If the database is a RAC DB, you may set it to zero in all instances.
SQL> alter system set job_queue_processes=0 scope=both sid='*';
System altered.