  We consider an electronic spin, such as a nitrogen-vacancy (NV) center in
diamond, weakly coupled to a large number (bath) of nuclear spins, and
subjected to the Rabi driving with a periodically alternating phase (multiple
rotary echo). We show that by switching the driving phase synchronously with
the precession of a given nuclear spin, the interaction to this spin is
selectively enhanced, while the rest of the bath remains decoupled. The
enhancement is of resonant character. The key feature of the suggested scheme
is that the width of the resonance is adjustable, and can be greatly decreased
by increasing the driving strength. Thus, the resonance can be significantly
narrowed, by a factor of 10--100 in comparison with the existing detection
methods. Significant improvement in selectivity is explained analytically and
confirmed by direct numerical many-spin simulations. The method can be applied
to a wide range of solid-state systems.
