  Three-dimensional Ising model in zero external field is exactly solved by
operator algebras, similar to the Onsager's approach in two dimensions. The
partition function of the simple cubic crystal imposed by the periodic boundary
condition along two directions and the screw boundary condition along the third
direction is calculated rigorously. In the thermodynamic limit an integral
replaces a sum in the formula of the partition function. The critical
temperatures, at which order-disorder transitions in the infinite crystal occur
along three axis directions, are determined. The analytical expressions for the
internal energy and the specific heat are also presented.
