【判断题】齿轮采用低碳钢时:工艺过程:锻造→正火→齿形加工→渗碳→淬火低温回火→喷丸→校正花键孔→磨齿 。 常用材料;20Cr、20CrMnTi、20MnB
【单选题】C Many young people want to be pop stars. Pop stars are rich. Many people think they are leading a happy and easy life. In fact, they have very hard lives. They spend much of their time on travel. Som...
【单选题】下列说法正确的是( )
C.
Na和Cs属于第ⅠA族元素,Cs失电子能力比Na的强
D.
P和As属于第ⅤA族元素,H 3 PO 4 酸性比H 3 AsO 4 的弱
【单选题】下列不属于 FileInputStream输入流的read()成员函数的是
A.
int read(byte b[],int offset,int len);
【单选题】下列说法正确的是( )
C.
Na和Cs属于第ⅠA族元素,Cs失电子能力比Na的强
D.
HClO 4 、H 2 SO 4 、H 3 PO 4 的酸性依次增强
【单选题】Many stars overhead are _______ to the naked eye.