题干

下列所画的数轴中正确的是( )

A:

B:

C:

D:

上一题 下一题 0.0难度 选择题 更新时间:2019-08-22 11:38:35

答案(点此获取答案解析)

D

同类题1

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揭秘“悟空”上天施展神通

    ①12月17日8时12分,我国在酒泉卫星发射中心用长征二号丁运载火箭成功将暗物质粒子探测卫星“悟空”发射升空,卫星顺利进入预定转移轨道。这标志着我国空间科学探测研究迈出重要一步。

    ②“悟空”是目前世界上观测能段范围最宽、能量分辨率最优的暗物质粒子探测卫星,超过国际上所有同类探测器。“悟空”的观测能段是国际空间站“阿尔法磁谱仪”的10倍,能量分辨率比国际同类探测器高3倍以上。

    ③“悟空”的身材比一般的卫星小巧,长宽高只有1.5米、1.5米、1.2米​,像盒银白色的方形蛋糕。而它的“火眼金睛”却可以在茫茫的太空中寻暗物质的踪影。

    ④卫星采用的是以载荷为中心的一体化結构设计。据介绍,“悟空”由四个有效载荷组成,分别是塑闪阵列探测器、硅阵列探测器、BGO能量器和中子探测器。所有探测器及电子设备安装在1个立方米的空间内,技术难度超过了我国目前所有的上天高能探测设备。

    ⑤以《西游记》中的美猴王名字命名的卫星“悟空”,没有携带金箍棒,却带了300多根“水晶棒”。 位于卫星核心部位的BGO能量器包含了300多根纵横交错排列的晶体,每一根都有2厘米见方、60厘米长,是世界上最长的BGO晶体,研制难度非常高。整个卫星中,BGO能量器的重量就占了多半。这些漂亮的“水晶棒”能够测量入射粒子的能量,并且由于电子和质子与晶体发生相互作用,产生类似淋浴喷水形状的簇射,而电子和质子产生的簇射形状不同,因而科学家可以区分出电子和质子。

    ⑥占宇宙95%以上的暗物质和暗能量由万有引力定律证实存在,却从未被直接观测到。暗物质粒子的探测目前是国际科学前沿竞争最为激烈的研究领域。包括我国在内的世界各国正在筹建或实施多个暗物质探测实验项目,其所研究成果可能带来基础科学领域的重大突破。

    ⑦“悟空”将面朝太空,在太空中开展探测任务,接受来自宇宙四面八方的高能电子及高能伽马射线,探寻暗物质存在的证据,研究暗物质特性与空间分布规律。由于暗物质可能存在于任何区域,它头两年将对全天扫描,探测暗物质存在的方位。两年后,根椐全天区探测的分析结果,它将对暗物质最可能出现的区城开展定向观测。

    ⑧寻找暗物质的过程就像与幽灵捉迷藏,天下武功唯快不破,只有仪器越灵敏才越可能有发现。“悟空”就是通过提高能量分辨和空间分辨的本領,降低宇宙射线背景噪音,并且把探测器做得足够大等方法提高灵敏度。

    ⑨中科院国家空间科学中心主任吴季表示,暗物质粒子探测卫星的成功发射和在轨运行将有望推动我国科学家在暗物质探测领域取得重大突破,对促进我国空间科学领域的创新发展具有重大意义。

同类题3

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    Once there lived a poor family in our town. They were so poor that there was almost(几乎)1 in the house but a pot(罐) 2 a broken table. In it there was a little rice. They 3the rice from their neighbour for the coming New Year. On New Year's Eve(除夕夜), the wife already fell asleep, but the husband was 4 in bed, worrying about their life. Suddenly he heard someone breaking into the room.

    “It must be a thief(小偷),” he thought, “5 it doesn't matter. The thief can steal(偷) nothing.”He didn't shout or move. But he kept6over the thief.

    The thief came into the house and was only7 in the rice under the table.

    “But8can I take it away?” the thief thought hard. Then he had an idea. He9 his coat, put it on the ground between the bed and the table and turned around to take the 10 .

    Now the husband knew11the thief would do. He picked up the coat quickly and covered himself with it12the thief turned back.

    The thief took the pot, and poured(倒) the rice onto the coat. Then he began to feel it. But he was13 to find that his coat was gone.

    “Hey,” he shouted out. The14 woke up the wife. She asked her husband, “Did you hear any sound? Maybe there is a thief in the room.”

    “Shut up! (闭嘴)” replied her husband, “15 to sleep. There is no thief in the room.”

    “That's impossible,”the thief shouted loudly, “If there isn't a thief, then, where is my coat?”