题干

某蛋白质由n个肽链组成,氨基酸的平均分子质量为a,该蛋白质所含的氨基酸有 b
3
,则该蛋白质的相对分子质量约为(    )

A:23 ab﹣6b+18n

B:13 ab﹣6b

C:( 13 b﹣a)×18

D:13 ab﹣( 13 b﹣n)×18

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D

同类题2

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蚊子为什么没有被雨滴砸死?

    ①漫步细雨中对于人们来说,或许是浪漫而惬意的,但对体积微小的蚊子,简直是一场灾难。一滴雨的重量可达到蚊子体重的50倍之多,人们所谓的毛毛雨,在蚊子看来,不亚于一辆辆甲壳虫汽车从天而降。但是,在这“甲壳虫汽车雨”中,蚊子却能够毫发无损,这是什么原因呢?

    ②为破解这一谜题,美国佐治亚理工学院的胡立德教授与美国疾控中心合作,对雨中飞舞的蚊子进行了高速摄像,以观察蚊子被雨滴击中瞬间的行为。

    ③通过视频,胡立德教授与他的研究小组分析了雨滴击中蚊子不同部位的各种情况,计算出蚊子被雨滴击中的瞬间所受到的作用力,以及其后随雨滴向下移动的距离。他们发现,蚊子并不像人们可能推测的那样去躲避雨滴,也不会因遭到雨滴的冲击而受伤,秘密之一就在于蚊子体重极轻。

    ④原来,蚊子被雨滴击中时并不进行抵挡,而是与雨滴融为一体,顺应它的趋势落下。如果雨滴击中蚊子的翅膀或腿部,它会向击中的那一侧倾斜,通过“侧身翻滚”的高难度动作,让雨滴从身体一侧滑落,像极一位技巧娴熟的“体操运动员”。当雨滴正中蚊子身体时,它先顺应雨滴强大的推力与之一同下落,随之迅速侧向微调与雨滴分离并恢复飞行。

    ⑤研究者还发现,当雨滴击中栖息于地面的蚊子时,雨滴的速度在瞬间减小为0,这时蚊子就会承受相当于它体重10000倍的力,足以致命。当蚊子在空中被击中并采用“不抵抗”策略时,它受到的冲击力就减小为其体重的1/50至1/300,此时,这雨滴就像一根极细小的羽毛压在了蚊子身上——这是蚊子能够承受的。

    ⑥虽说蚊子柔弱如风中柳絮会被雨滴砸得摇晃不定,但正是由于它体重极轻,雨滴在与蚊子碰撞的过程中几乎没有减速,它的动能也几乎没有转化为能量击打在蚊子身上,而是让蚊子瞬间加速下降,从而化解了高速下降的雨滴带来的巨大冲击。这就像是“以柔克刚”,达到“四两拨千斤”的效果,小小的蚊子还是个太极高手呢!

    ⑦蚊子在雨中安然无恙的另一个秘密,是覆盖它们全身的细毛具有疏水性。这种防水的细毛使得蚊子与打在它身上的雨滴保持分隔状态,从而使蚊子能够迅速摆脱雨滴重新飞起,在雨滴将它们砸落地面造成致命伤害前成功逃生。

    ⑧胡立德教授的这一发现引起了广泛关注。事实上,在应对自然之道上,动物往往有着比人类更丰富的经验,它们在千万年的进化过程中拥有了适应生存环境的生理结构和功能。这可为科学家和工程师提供新的设计思想——比如,如何更好地设计微型飞行器,让它们能像蚊子这类昆虫一样,在雨中轻盈地飞翔。

同类题4

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Five ways to improve creativity

    Creativity is the ability to go beyond traditionally rules, ideas or relationships and create something new through imagination or progressiveness. There are many ways to improve your creative mind.

    Exercise the mind. Exercising your mind is an ideal way to boost creativity. Like the body, the mind needs exercise to work the creative muscles and make them stronger. Exercise your brain by learning new subjects, getting into a debate about politics and talking to other creative and intelligent people. ____

    Be Passionate. One aspect of creativity is passion. ____ Find you internal motivation and follow your passion to improve your creativity.

    Change your routine. ____ To boost your creativity, consider changing one to two elements of your daily routine. If you are working on a certain project, consider stopping one project to work on another project at regular interval throughout the day or week.

    Read. While reading provides many intellectual benefits, reading is also beneficial for boosting creativity, exercising your brain and provide creative inspiration. ____Consider reading about subjects that were previously uninteresting to you. This change in the norm might spark your creative interest.

    ____. Our packed schedules have no room for creative thinking. Take a certain amount of time every day to quiet, refresh and clear the mind while relaxing the body. This quiet .time can consist of a yoga workout, meditation or simply sitting still in a dark and quiet room, in a peaceful garden or on a beautiful beach.

A. Schedule quiet time.

B. It can become weak due to stresses.

C. Creativity is a natural quality.

D. Often, creativity is blocked due to a too-familiar routine.

E. These activities will encourage a flow of creativity.

F. Read as much as possible about several different subjects

G. Typically, students will do well in subjects they are interested in.