title: Letter: Organic structure characterization by natural-abundance nitrogen-15 nuclear magnetic resonance spectroscopy. Penicillin and cephalosporin derivatives.
mesh_terms: D002511:Cephalosporins; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D010406:Penicillins
chemical_list: D002511:Cephalosporins; D010406:Penicillins