已知 $\stackrel{\rightharpoonup }{a}$是平面内的单位向量，若向量 $\stackrel{\rightharpoonup }{b}$满足 $\stackrel{\rightharpoonup }{b}·(\stackrel{\rightharpoonup }{a}-\stackrel{\rightharpoonup }{b})=\stackrel{\rightharpoonup }{0}$, 则 $\left|\stackrel{\rightharpoonup }{b}\right|$的取值范围是.