-- If you want to display the system generated partitions as part of the CREATE TABLE DDL, then set the EXPORT parameter of the dbms_metadata to true.
-- The default behavior of "DBMS_METADATA.GET_DDL" is that it does not show Interval Partitions created by the system for interval partitioned tables and indexes.
-- In the case of Interval Partitioning, New Partitions are created automatically when corresponding row is inserted. This newly created partition information will be displayed in "DBA_TAB_PARTITIONS" dictionary view. However when the DDL is queried using function "DBMS_METADATA.GET_DDL", then this information is not shown.
Demo: (Following was tested on the Oracle 12c, and it should be valid for Oracle 11g too.)