Abundances in planetary nebulae near the galactic centre - I. Abundance determinationsM. A. Ratag, S. R. Pottasch, M. Dennefeld and J. MenziesAstron. Astrophys. Suppl. Ser., 126 2 (1997) 297-310DOI: https://doi.org/10.1051/aas:1997390