[EN] (+)-TRANS-ISOMERS OF (1-PHOSPHONOMETHOXY-2-ALKYLCYCLOPROPYL) METHYL NUCLEOSIDE DERIVATIVES, PROCESS FOR THE PREPARATION OF STEREOISOMERS THEREOF, AND USE OF ANTIVIRAL AGENTS THEREOF [FR] TRANS-ISOMERES (+) DE DERIVES DE NUCLEOSIDE ( 1-PHOSPHONOMETHOXY-2-ALKYLCYCLOPROPYL)METHYLE, PROCESSUS DE PREPARATION DE STEREO-ISOMERES DE CEUX-CI ET UTILISATION D'AGENTS ANTIVIRAUX A BASE CEUX-CI