The Transition between Perturbative and Non-Perturbative QCD

We study both polarized and unpolarized proton structure functions in the kinematical region of large Bjorken x and four-momentum transfer of few GeV^2. In this region the phenomenon of parton-hadron duality takes place between the smooth continuation of the deep inelastic scattering curve and the average of the nucleon resonances. We present results on a perturbative-QCD analysis using all recent accurate data with the aim of extracting the infrared behavior of the nucleon structure functions.