Umi no Kenkyu has been published as online journal since 2006 (Vol. 15).
Back number (Vol. 15-)
Vol. 15 | Vol. 16 | Vol. 17 | Vol. 18 | Vol. 19 | Vol. 20 | Vol. 21 | Vol. 22 | Vol. 23 | Vol. 24 | Vol. 25 | Vol. 26 | Vol. 27 | Vol. 28 | Vol. 29 | Vol. 30 | Vol. 31 | Vol. 32 (in Japanese)
Previous issues are all deposited in the CiNii (Citation Information by the National Institute of Informatics) online database and are open to the public.