  We present heat capacity measurements of the upper critical fields of
single-crystal NdFeAsO1-xFx. In zero-magnetic field a clear step in the heat
capacity is observed at Tc = 47K . In fields applied perpendicular to the
FeAs-layers the step broadens significantly whereas for the in-plane
orientation the field effects are small. This behavior is reminiscent of the
CuO2-high-Tc superconductors and is a manifestation of pronounced fluctuation
effects. Using an entropy conserving construction we determine the transition
temperatures in applied fields and the upper critical field slopes of dHc2,a =
-0.72 T/K and dHc2,ab = -3.1 T/K. Zero-temperature coherence lengths of xiab =
3.7 nm and xic = 0.9 nm and a modest superconducting anisotropy of gamma ~ 4
can be deduced in a single-band model.
