  Momentum-space derivatives of matrix elements can be related to their
coordinate-space moments through the Fourier transform. We derive these
expressions as a function of momentum transfer $Q^2$ for asymptotic in/out
states consisting of a single hadron. We calculate corrections to the finite
volume moments by studying the spatial dependence of the lattice correlation
functions. This method permits the computation of not only the values of matrix
elements at momenta accessible on the lattice, but also the momentum-space
derivatives, providing {\it a priori} information about the $Q^2$ dependence of
form factors. As a specific application we use the method, at a single lattice
spacing and with unphysically heavy quarks, to directly obtain the slope of the
isovector form factor at various $Q^2$, whence the isovector charge radius. The
method has potential application in the calculation of any hadronic matrix
element with momentum transfer, including those relevant to hadronic weak
decays.
