6. Let $[x]$ denote the greatest integer not exceeding the real number $x$ (for example, $[3.14]=3, [0]=0, [-3.14]=-4$). If

a positive integer $x$ satisfies $x-[\sqrt{x}]^{2}=9$, then $x$ is called a "good number". Then, among the 2014 positive integers from $1$ to $2014$, the number of good numbers is ( ).
(A) 36
(B) 40
(C) 44
(D) 48
6. B.

Let $[\sqrt{x}]=n$. Then $x=n^{2}+9$.
Thus $n \leqslant \sqrt{n^{2}+9}<n+1 \Rightarrow n \geqslant 5$.
Also, $n^{2}+9 \leqslant 2014 \Rightarrow n \leqslant 44$.
Therefore, $5 \leqslant n \leqslant 44$.
Hence, there are 40 values of $n$ that satisfy the condition, which means there are 40 good numbers.