Typically, the string length of a 3/4 violin is longer than that of a 1/2 violin, so the E string for a 1/2 violin may be too short for a 3/4 violin.
However, some 3/4 violins may have a shorter string length that is similar to that of a 1/2 violin, in which case the E string for a 1/2 violin may fit.