题干

如图为神经肌肉接点示意图.下列有关兴奋传递的叙述,正确的是(  )

A:兴奋传到①时,引起①处Na+通道打开,Na+涌出

B:兴奋传到①时,乙酰胆碱以主动转运方式分泌

C:②属于组织液,其中的O2含量不影响兴奋的传递

D:②处的乙酰胆碱与③处的相应受体结合,可引起肌膜产生电位变化

上一题 下一题 0.0难度 选择题 更新时间:2018-01-28 04:00:07

答案(点此获取答案解析)

D

同类题3

阅读理解

    Radar is an electronic device that detects planes, ships, coastlines, landmarks, and even storm clouds. The name radar comes from the first letters of the words radio direction and ranging. As the human eye uses light waves to see, radar “sees” with radio waves. Without radar, planes could not land safely in bad weather and ships could not move safely in thick fog____

    In the 1800s it was discovered that radio waves could be reflected from objects. But scientists did not make great advances in radar research until the 1930s, when the world was threatened by war____ It has been used widely in almost every conflict since then.

    Echoes make it possible for radar to work. When a beam of radio waves is sent out, it strikes on an object and returns an echo. This echo is picked up by radar and recorded on a screen similar to television screen. On the screen an observer sees a flash, or a blip, that shows the direction and distance of the object.____

    Airport control towers use radar to guide planes in for safe landings. Almost all large ships depend on radar to prevent collisions with icebergs or other ships____Weather forecasters “see” the size, direction, and speed of storms on radar screens. Astronomers can even use radar to measure accurately the distance to the moon. Thus, the device has generated major advancements.

    ____Huge radar antennas have been installed all over the United States. They guard us against possible enemy attacks. We have ballistic—missiles (战略导弹)warning systems that can alert us to attacks when missiles are more than 1,000 miles away. Other radar systems warn us against enemy aircraft and even spying space satellites.

A. Police track speeders in radar-equipped cars.

B. These measurements are now highly accurate.

C. The device can be used in a wide range of fields.

D. It is therefore especially valuable to shippers and travelers.

E. During World War II many countries used radar effectively.

F. Today radar is used by commercial airliners and weather forecasters.

G. Strengthening national defense is one of radar's most important functions.

同类题5

阅读下面的文字,完成后面的题。

笛声化作民族魂

乔忠延

    昆明甬道街边的聂耳故居很平常,三间土木结构的房屋,好在是座两层楼。严格地讲,这不是聂家的祖业,是房东杨家的房产。聂耳就出生于这里。他童年在这里度过,直到十八岁振翅远飞。

    进入院落,悠扬的音韵便萦绕在耳畔。不过,那并不是《义勇军进行曲》的旋律,而是竹笛吹出的稚嫩音韵。对这笛音,小学课本中有篇文章曾有还原,“悠扬的笛声飘扬在林间小路上,许多行人被吸引了,都站在细雨中静静地听他吹笛子。”确实,聂耳能把笛子吹得优美迷人,但是,那其实是后来的事,是聂耳勤奋地拜师学习提高技艺的结晶。先前并不是这样,他吹出的声音不悠扬,也不婉转,甚至有些刺耳。教聂耳吹笛子的师傅姓邱,名字如同姓杨的房东一般,没人记得。可是,若是没有他的启蒙教导,就不会有后来响亮于神州大地的聂耳。而且,这位邱师傅还不是音乐教师,只是一位木工。吹笛子是他做木工活儿歇息时的业余爱好。

    勤奋好学,让聂耳叩开了通向音乐的门扉。不止如此,勤奋好学也让他叩开了通向知识的门扉。聂耳上学不久后,父亲便去世了,家庭陷入困境,连他的学费也没有着落。母亲卖掉心爱的八音钟才凑够学费,可还缺书钱。在学校里,聂耳长知识,长思想,随着个头的增高,眼界也更加开阔了。他看到祖国积弱积贫,时刻梦想着国家能富裕强大。他把满腔热情寄托于变革,为之呼吁奔走,并鼓动同学和自己一道呼吁奔走。然而,时局能忍受弱贫保守,却容忍不下激进变革,聂耳被列入另册,难以在昆明再待下去,只有告别昆明。

    离开昆明后,聂耳飘零到上海,靠在商号当伙计维持一日三餐。还是音乐,改变了聂耳的境遇。有一天,他看到《申报》刊出联华影业公司音乐歌舞学校招收学员的广告,身上沉睡的音乐细胞马上被激活了,便去报考。担任主考的音乐家黎锦晖,一眼看出聂耳身上潜在的音乐天赋,因此录取了他。成为歌剧社的一员后,聂耳如鱼得水,他担任首席小提琴手,但是只要是歌剧社需要的事,他都主动干。时不时还上场演出,要么扮演卖臭豆腐的小贩,要么扮演一身乌黑的煤矿工人。他才华横溢,活泼可爱,大伙儿见他耳朵大,就亲切地叫他“耳朵先生”。叫着叫着,干脆就叫成了“聂耳”——事实上,聂耳的原名是聂守信,此后称聂耳才名副其实。

    就在此时,“九一八”事变发生了。日寇侵犯,东北沦陷。聂耳不再只想着歌唱,他要呐喊!他结识了作家、诗人田汉,参加了革命音乐组织,开始为电影和戏剧创作主题曲和插曲:《大路》《开路先锋》《码头工人之歌》《毕业歌》……聂耳创作了一首又一首明快激昂的歌曲,他要用歌声惊醒沉睡的雄狮,用歌声点燃焚烧侵略者的烽火!

    聂耳的激情在蕴积!聂耳的怒火在燃烧!

    1935年,一部以宣传抗日救亡为主题的电影《风云儿女》开拍了。这是一部电影,更是呼唤共同抗日的呐喊。剧组在呐喊,聂耳也加入了呐喊——聂耳的呐喊声化作了这部电影主题曲《义勇军进行曲》的旋律。

    “起来!不愿做奴隶的人们!把我们的血肉筑成我们新的长城!中华民族到了最危险的时候,每个人被迫着发出最后的吼声。起来!起来!起来!我们万众—一心,冒着敌人的炮火,前进!冒着敌人的炮火,前进!前进!前进、进!”

    创作于中华民族危难关头的《义勇军进行曲》,田汉作词,聂耳作曲,唱出了抗日救亡时代万众的心声,表现出中华民族勇往直前、不屈不挠的战斗精神,后来更成为国歌,散发出永恒的魅力。曾经,这浑厚昂扬的旋律,激愤着国人,奋起抗战、抗战,把侵略者赶出国门。如今,这浑厚昂扬的旋律,又激励着国人,奋起建设、建设,把华夏神州建设得更加繁荣富强。

    站在昆明甬道街聂耳故居里,听那悠扬的稚嫩笛音。那笛音,经过千锤百炼,最终怒吼出的,是民族魂,中华韵!(有删改)

相关链接:1935年2月,田汉被国民党逮捕入狱,由他创作剧本的影片《风云儿女》开拍。当时,聂耳准备去日本,得知影片《风云儿女》有首主题歌要写。聂耳看过歌词后,立即要求由他进行谱曲。果然,没过多久他就从日本寄回《义勇军进行曲》的歌谱。不幸的是,1935 年7月中下旬,《义勇军进行曲》在银幕上首次响起时,聂耳已溺亡于日本,年仅23岁。