  We present the first analysis of cosmic shear measured in DES Y3 that employs
the entire range of angular scales in the data. To achieve this, we build upon
recent advances in the theoretical modelling of weak lensing provided by a
combination of $N$-body simulations, physical models of baryonic processes, and
neural networks. Specifically, we use BACCOemu to model the linear and
nonlinear matter power spectrum including baryonic physics, allowing us to
robustly exploit scales smaller than those used by the DES Collaboration. We
show that the additional data produce cosmological parameters that are tighter
but consistent with those obtained from larger scales, while also constraining
the distribution of baryons. In particular, we measure the mass scale at which
haloes have lost half of their gas, $\log\,M_{\rm
c}=14.38^{+0.60}_{-0.56}\log(h^{-1}{\rm M_{ \odot}})$, and a parameter that
quantifies the weighted amplitudes of the present-day matter inhomogeneities,
$S_8=0.799^{+0.023}_{-0.015}$. Our constraint on $S_8$ is statistically
compatible with that inferred from the Planck satellite's data at the
$0.9\sigma$ level. We find instead a $1.4\sigma$ shift in comparison to that
from the official DES Y3 cosmic shear, because of different choices in the
modelling of intrinsic alignment, non-linearities, baryons, and lensing shear
ratios. We conclude that small scales in cosmic shear data contain valuable
astrophysical and cosmological information and thus should be included in
standard analyses.
