The authors have developed a technique to determine the electron spin polarization in a single GaAs quantum well by combining resistance-detected (RD) nuclear magnetic resonance (NMR) with conventional NMR. We use this method to study the unpolarized-polarized spin transition at filling factor ν=2∕3 for small and large currents. The formation of domains with these two polarizations at the transition was observed spectroscopically. Domains with full, partial, or no polarization were also uncovered at ν=3∕5 and 4∕7. An anomalous NMR line shape around filling factor ν=1∕3, 1, and 2∕3 was measured. This pecularity of the NMR line is probably not due to skyrmions, as previously reported for ν=1.