  We reanalyze the experimental NMC data on the nonsinglet structure function
$F_2^p-F_2^n$ and E866 data on the nucleon sea asymmetry $\bar{d}/\bar{u}$
using the truncated moments approach elaborated in our previous papers. With
help of the special truncated sum one can overcome the problem of the
unavoidable experimental restrictions on the Bjorken $x$ and effectively study
the fundamental sum rules for the parton distributions and structure functions.
Using only the data from the measured region of $x$, we obtain the Gottfried
sum $\int_0^1 F_2^{ns}/x\, dx$ and the integrated nucleon sea asymmetry
$\int_0^1 (\bar{d}-\bar{u})\, dx$. We compare our results with the reported
experimental values and with the predictions obtained for different global
parametrizations for the parton distributions. We also discuss the discrepancy
between the NMC and E866 results on $\int_0^1 (\bar{d}-\bar{u})\, dx$. We
demonstrate that this discrepancy can be resolved by taking into account the
higher-twist effects.
