【单选题】赫尔希和蔡斯通过噬菌体侵染细菌的实验,证明了噬菌体的遗传物质是 [ ]
【单选题】不受年龄结构影响,能够反映整个人群的死亡水平的指标是
【简答题】你想证明某种噬菌体的遗传物质是DNA而不是蛋白质。你设想的一个实验类似于捣碎实验,但遗憾的是这种噬菌体尾巴短,不能用捣碎器使它从细胞壁上脱开。你已知道分离和纯化子代噬菌体的方法。你制备了 32 P和 35 S双标记的噬菌体,感染了细菌,并从感染细菌中收集了子代噬菌体。下面的哪一个结果可作为证据支持你的设想?并说明理由。 ① 35 S不会出现在子代噬菌体中。 ② 32 P总是出现在几个子代的噬菌体中...
【单选题】能够不受年龄结构的影响,反映整个人群死亡水平的指标是( )
【判断题】3 The
moon changes from a new moon to a full moon in around 29 days.
【单选题】In old times, people wondered about the changes of seasons, about the stars, the moon and the sun. They could not explain these things, and so they made up 'why' stories about them. The ancient Greeks...
A.
how the year was divided into four seasons
B.
how Demeter's daughter was saved
C.
why they loved Demeter and hated Hades
D.
why they had a winter season
【简答题】联合国世界旅游组织的总部在西班牙的[填空(1)] 。