We present results on the production of hadrons in collisions of 400-GeV/c protons with beryllium, copper, and tungsten nuclei. The data cover the region from 5.6 to 8.0 GeV/c in the transverse momentum of the final-state hadron and from 73/sup 0/ to 102/sup 0/ in the proton-nucleon center-of-momentum frame production angle theta/sup */. The restriction of the data to values of x/sub T/ (x/sub T/ = 2p/sub T// ..sqrt..s ) greater than 0.4 enriches the sample with hard collisions of valence quarks. Asymmetries about theta/sup */ = 90/sup 0/ reflect the presence of neutrons in the target nuclei. The variation of the atomic-weight dependence parameter ..cap alpha.. with production angle is discussed in the context of the phenomenology of nucleonic structure within nuclei. We also extrapolate our measurements to a ''deuteron'' target to minimize nuclear effects and compare the result to QCD calculations.