用NA表示阿伏德罗常数，下列叙述正确的是（ ）A．标准状况下，22.4LH2O含有的分子数为1NAB．常温常压下,1.06g Na2CO3含有的Na+离子数为0.02 NA
相对分子质量由小到大排列的X、Y、Z三种气体单质，组成这三种单质的元素分别位于不同的短周期。在一定条件下，X与Y化合生成M；X与Z化合生成N；M能
人们能否正确认识世界和改造世界，从主观因素来讲，关键就在于( ) A．获得的认识是否正确B．能否坚持从实际出发，使主观符合客观 C．是否坚持了
我国雅砻江水电开发受季节影响较大，针对“丰枯不均”的现象，开发时应注意 A.统一管理，科学调度 B. 疏浚河道
There are two types of people in the world. Although they have equal degree of health and wealth and other comforts of life, one becomes happy and the other becomes unhappy. This arises from the d
In 1971, Arthur P. Mullaney, of Randolph, Massachusetts, came up with a great idea. He asked his neighbors to give up cigarettes for a day and donate the money they would have spent for cigarettes to
将0.0000025用科学记数法表示为 A．2.5×10－5 B．2.5×10－6 C．0.25×10－5 D．0.25×10－6
在杨氏双缝干涉实验装置的双缝后面各放置一个偏振片，若两个偏振片的透振方向相互垂直，则（ )A.光屏上仍有干涉条纹，但亮条纹的亮度减小B.
