The Spin Structure of Nucleons and Deep Inelastic Scatterings

Based on a simple model which is compatible with the idea of the static quark model and the parton model, the polarized structure functions of proton and deuteron, two-spin asymmetries of $\pi ^0$ in polarized $pp$ reactions and inelastic $J/\psi$ productions in polarized lepton-proton collisions are analyzed. In particular, an important role of polarized gluon distributions is pointed out.