  We study the cosmological evolution based upon a $D$-dimensional action in
low-energy effective string theory in the presence of second-order curvature
corrections and a modulus scalar field (dilaton or compactification modulus). A
barotropic perfect fluid coupled to the scalar field is also allowed. Phase
space analysis and the stability of asymptotic solutions are performed for a
number of models which include ($i$) fixed scalar field, ($ii$) linear dilaton
in string frame, and ($iii$) logarithmic modulus in Einstein frame. We confront
analytical solutions with observational constraints for deceleration parameter
and show that Gauss-Bonnet gravity (with no matter fields) may not explain the
current acceleration of the universe. We also study the future evolution of the
universe using the GB parametrization and find that big rip singularities can
be avoided even in the presence of a phantom fluid because of the balance
between the fluid and curvature corrections. A non-minimal coupling between the
fluid and the modulus field also opens up the interesting possibility to avoid
big rip regardless of the details of the fluid equation of state.
