Analisis fungsional ekstrak etanol 70 % akar kelembak (Rheum officinale Baill.) pada sel 3T3 L1 preadiposit dalam media diferensiasi osteogenik = Functional analysis of 70 % ethanol extract of akar kelembak (Rheum officinale Baill.) on 3T3-L1 preadypocite cells cultured in osteogenic differentiation medium