【单选题】对一个作简谐振动的物体,下面哪种说法是正确的
A.
物体处在运动正方向的端点时,速度和加速度都达到最大值
B.
物体位于平衡位置且向负方向运动时,速度和加速度都为
C.
物体位于平衡位置且向正方向运动时,速度最大,加速度为零
D.
物体处在负方向的端点时,速度最大,加速度为零
【单选题】Viruses cause many human infections such as hepatitis, encephalitis, and the “ common cold. ” Which one of the following is a common trait of all these viruses?
A.
They are small, circular DNA molecules that enter bacteria and replicate outside the host genome.
B.
Upon infecting eukaryotic cells, they are called phages.
C.
All the common cold viruses contain both DNA and RNA genomes.
D.
In order to reproduce, they must use the infected cell ’ s DNA, RNA, and protein-synthesizing machinery.
E.
Upon becoming infectious, they are called plasmids.
【单选题】对一个作简谐振动的物体,下面哪种说法是正确的
A.
物体处在运动正方向的端点时,速度和加速度都达到最大值
B.
物体位于平衡位置且向负方向运动时,速度和加速度都为零
C.
物体位于平衡位置且向正方向运动时,速度最大,加速度为零
D.
物体处在负方向的端点时,速度最大,加速度为零
【单选题】对一个作简谐振动的物体,下面哪种说法是正确的
A.
( A )物体处在运动正方向的端点时,速度和加速度都达到最大值;
B.
( B )物体位于平衡位置且向正方向运动时,速度最大,加速度为零;
C.
( C )物体位于平衡位置且向负方向运动时,速度和加速度都为零;
D.
( D )物体处在运动负方向的端点时,速度最大,加速度为零。
【判断题】目前在型腔加工中应用最多的电极材料是石墨和紫铜。
【单选题】A runner ’ s muscles use glucose as a source of energy. Muscle contains glycogen stores that are degraded into glucose 1-phosphate via glycogen phosphorylase, which is an allosteric enzyme. Assume tha...
A.
A Vmax of 25 U/mg enzyme and a Km,app of 0.2 mM
B.
A Vmax of 15 U/mg enzyme with a Km,app of 2.0 mM
C.
A Vmax of 25 U/mg enzyme with a Km,app of 2.0 mM
D.
A Vmax of 50 U/mg enzyme with a Km,app of 5.0 mM
E.
A Vmax of 50 U/mg enzyme with a Km,app of 10.0 mM
【单选题】对一个作简谐振动的物体,下面哪种说法是正确的是
A.
物体处在运动正方向的端点时,速度和加速度都达到最大值
B.
物体位于平衡位置且向负方向运动时,速度和加速度都为零
C.
物体位于平衡位置且向正方向运动时,速度最大,加速度为零
D.
物体处在负方向的端点时,速度最大,加速度为零