| Oriens Christianus. Hefte Für die Kunde Des Christlichen Orients | | 0340-6407 |
| Oriens-occidens (cahiers Du Centre D’histoire Des Sciences et Des Philosophies Arabes et Médiévales) | | 1284-2060 |
| Orient - Deutsche Zeitschrift für Politik und Wirtschaft des Orients | ORIENT - DEUTSCHE ZEITSCHRIFT FÜR POLITIK UND WIRTSCHAFT DES ORIENTS | 0030-5227 |
| Oriental Art | | 0030-5278 |
| Oriental Insects | ORIENT INSECTS | 0030-5316 |
| Oriental Journal of Chemistry | ORIENTAL JOURNAL OF CHEMISTRY | 0970-020X |
| Oriental Pharmacy and Experimental Medicine | ORIENTAL PHARMACY AND EXPERIMENTAL MEDICINE | 1598-2386 |
| Oriental Studies | ORIENTAL STUDIES | 2619-0990 |
| Orientalia (rome) | | 0030-5367 |
| Orientalia Christiana Cracoviensia | | 2081-1330 |
| Orientalia Christiana Periodica | | 0030-5375 |
| Orientalia Suecana. An International Journal of Indological, Iranian, Semitic and Turkic Studies | | 0078-6578 |
| Orientation Scolaire et Professionnelle | ORIENTATION SCOLAIRE ET PROFESSIONNELLE | 0249-6739 |
| Orientations | | 0030-5448 |
| Oriente Moderno | ORIENTE MODERNO | 0030-5472 |
| ORIGINI. Preistoria e Protostoria delle civiltà antiche | | 0474-6805 |
| Origins of Life and Evolution of Biospheres | ORIGINS LIFE EVOL B | 0169-6149 |
| Origins of Life and Evolution of the Biosphere | | |
| Orillas | ORILLAS | 2280-4390 |
| ORL-head and neck nursing : official journal of the Society of Otorhinolaryngology and Head-Neck Nurses | ORL-HEAD AND NECK NURSING : OFFICIAL JOURNAL OF THE SOCIETY OF OTORHINOLARYNGOLOGY AND HEAD-NECK NURSES | 1064-3842 |
| ORL-Journal for Oto-Rhino-Laryngology Head and Neck Surgery | ORL J OTO-RHINO-LARY | 0301-1569 |
| ORNAC journal | ORNAC JOURNAL | 1927-6141 |
| Ornamental Horticulture | ORNAMENTAL HORTICULTURE | 2447-536X |
| Ornis Fennica | ORNIS FENNICA | 0030-5685 |
| Ornis Hungarica | ORNIS HUNGARICA | 1215-1610 |
| Ornis Norvegica | ORNIS NORVEGICA | 1502-0878 |
| Ornis Polonica | | 2081-9706 |
| Ornis Svecica | ORNIS SVECICA | 1102-6812 |
| Ornithological Science | ORNITHOLOGICAL SCIENCE | 1347-0558 |
| Ornitologia Colombiana | ORNITOLOGIA COLOMBIANA | 1794-0915 |
| Ornitologia Neotropical | ORNITOL NEOTROP | 1075-4377 |
| Orphan Drugs: Research and Reviews | ORPHAN DRUGS: RESEARCH AND REVIEWS | 2230-6161 |
| Orphanet Journal of Rare Diseases | ORPHANET J RARE DIS | 1750-1172 |
| Orpheus | | 0391-5832 |
| Ortho Magazine | ORTHO MAGAZINE | 1262-4586 |
| Orthodontic Waves | ORTHODONTIC WAVES | 1344-0241 |
| Orthodontics & Craniofacial Research | ORTHOD CRANIOFAC RES | 1601-6335 |
| Der Orthopade | ORTHOPADE | 0085-4530 |
| Orthopaedic Journal of Sports Medicine | ORTHOPAEDIC JOURNAL OF SPORTS MEDICINE | 2325-9671 |
| Orthopaedic Nursing | ORTHOP NURS | 0744-6020 |
| Orthopaedic Surgery | ORTHOPAEDIC SURGERY | 1757-7853 |
| Orthopaedics & Traumatology-Surgery & Research | ORTHOP TRAUMATOL-SUR | 1877-0568 |
| Orthopaedics and Trauma | ORTHOPAEDICS AND TRAUMA | 1877-1327 |
| Orthopedic Clinics of North America | ORTHOP CLIN N AM | 0030-5898 |
| Orthopedic Research and Reviews | ORTHOPEDIC RESEARCH AND REVIEWS | 1179-1462 |
| Orthopedic Reviews | ORTHOPEDIC REVIEWS | 2035-8237 |
| Orthopedics | ORTHOPEDICS | 0147-7447 |
| Ortopedia Traumatologia Rehabilitacja | | 1509-3492 |
| Orvosi Hetilap | ORVOSI HETILAP | 0030-6002 |
| Orvostörténeti Közlemények | | 0010-3551 |
