Analytical expressions for collinear parton distributions are presented. The valence and non-singlet quark parts obey the Gross-Llewellyn-Smith and Gottfried sum rules and momentum conservation for the singlet quark and gluon densities is taken into account. Several phenomenological parameters are extracted from combined fit to precision data on the proton structure function F2(x,Q2) collected by the BCDMS, H1 and ZEUS Collaborations, comprising a total of 933 points from 5 data sets.

A model for nuclear medium modification of parton densities is also presented. The approach is based on the global analysis of available deep inelastic scattering data for different nuclear targets within the rescaling model combined with taking into account the effects of Fermi motion. By fitting the rescaling parameters to experimental data on the ratio F2A(x,Q2)/F2B(x,Q2) for several nuclear targets A and B, we obtain predictions for nuclear parton distributions, even for unmeasured nuclei.