【简答题】真空中有一根半径为r的无限长直圆柱形导线,其轴线OO'沿铅垂方向.沿轴线方向通有电流I,电流均匀分布于横截面内,在距轴线3r处有一个电荷量为-e的电子,沿平行于OO'轴方向以速度v向下运动,如图所示.求电子所受的磁场力.
【单选题】More and more shops use the paper bags to take the place of the ones.
【判断题】半径为R的无限长直圆柱面导体,沿圆柱面轴向通有恒定电流I ,电流均匀分布。以r 表示场点到圆柱面轴线的距离,则圆柱面外磁感应强度大小为
【判断题】半径为R的无限长直圆柱面导体,沿圆柱面轴向通有恒定电流I ,电流均匀分布。以r 表示场点到圆柱面轴线的距离,则圆柱面内磁感应强度大小为
【判断题】从赤道处出发,沿着一定的方位角出发的大地线,一定不会回到原来的点
【单选题】在乳腺癌和前列腺癌常见。患者对化疗或放疗有较好的治疗反应,治疗后6个月内临床上有改善,但骨显像似有恶化的表现(最明显在治疗后3个月),称之为
【简答题】Online shopping is becoming more
and more popular for a number of reasons; prices are often lower online and
you don’t have to queue up in busy shops.
【简答题】Online shopping is becoming more and more popular for a number of reasons; prices are often lower online and you don’t have to queue up in busy shops.
【单选题】With Christmas ______, more and more people come to shops to buy gifts.