Medical Oxygen a Vital in Covid 19 Pandemic: Production Techniques from Natural to Man-made. Indian Journal of Pure & Applied Physics (IJPAP), [S. l.], v. 60, n. 9, 2023. DOI: 10.56042/ijpap.v60i9.63734. Disponível em: https://or.niscpr.res.in/index.php/IJPAP/article/view/2693. Acesso em: 13 may. 2026.