1. A method for operating a nuclear magnetic resonance apparatus having means for generating a fundamental magnetic field and means for generating switched unmodulated gradient fields in which an examination subject is disposed, and means for inducing nuclear magnetic resonance in said examination subject by the application of high-frequency pulses and for acquiring nuclear magnetic resonance signals from said examination subject, said method maintaining dynamic equilibrium magnetization in said examination subject for image reconstruction by filtered back-projection and comprising the steps of: selectively exciting a slice of said examination subject by simultaneously applying a slice selection gradient G.sub.z for a duration T and a high-frequency pulse having a flip angle .alpha., 0.degree.&lt;.alpha..ltoreq.90.degree.; simultaneously applying a projection gradient -G.sub.r and a slice selection gradient -G.sub.z to said examination subject for a duration of approximately T/2; applying a projection gradient G.sub.r to said examination subject and reading out the nuclear magnetic resonance signal emitted by said examination subject for a duration of approximately T; applying at least one of a slice selection gradient G.sub.z and a projection gradient -G.sub.r for a duration of approximately T/2; and repeating the above steps N.sub.r times with the direction of the projection gradient being changed by a selected amount for each successive repetition until N.sub.r scans are recorded.