  Analyzing the noise in the momentum profiles of single realizations of
one-dimensional Bose gases, we present the experimental measurement of the full
momentum-space density correlations $\langle \delta n_p \delta n_{p'}\rangle$,
which are related to the two-body momentum correlation function. Our data span
the weakly interacting region of the phase diagram, going from the the ideal
Bose gas regime to the quasicondensate regime. We show experimentally that the
bunching phenomenon, which manifests itself as super-Poissonian local
fluctuations in momentum space, is present in all regimes. The quasicondensate
regime is however characterized by the presence of negative correlations
between different momenta, in contrast to Bogolyubov theory for Bose
condensates, predicting positive correlations between opposite momenta. Our
data are in good agreement with {\it ab-initio} calculations.
