英语美文精选
英语美文精选
经典美文是中华民族文化的精粹,凝聚着前人的智慧、蕴含着丰富的情感、营造着优美的意境。小编精心收集了初中英语美文，供大家欣赏学习!
初中英语美文篇1
Nitinol
Nitinol is one of the most extraordinary metals to be discovered this century: A simple alloy ofnickel and titanium, nitinol has some perplexing properties. A metal with a memory, it can bemade to remember any shape into which it is fashioned, returning to that shape whenever it isheated.
For example, a piece of nitinol wire bent to form a circle that is then heated and quenched willremember this shape. It may then be bent or crumpled, but on reheating, will violentlyuntwist, reforming its original shape. This remarkable ability is called Shape Memory Effect(SME); other alloys, such as brasses, are known to possess it to a limited extent. No one fullyunderstands SME,and nitinol remains particularly perplexing, for, whenever it performs thispeculiar feat, it appears to be breaking the laws of thermodynamics by springing back intoshape with greater force than was used to deform it in the first place.
But not only is nitinol capable of remembering, it also has the ability to "learn". If the heating-cooling-crumpling-reheating process is carried out sufficiently often, and the metal is alwayscrumpled in exactly the same way, the nitinol will not only remember its original shape, butgradually it learns to remember its crumpled form as well, and will begin to return to the samecrumpled shape every time it is cooled. Eventually, the metal will crumple and uncrumple, totallyunaided, in response to changes in temperature and without any sign of metal fatigue.
Engineers have produced prototype engines that are driven by the force of nitinol springingfrom one shape to another as it alternately encounters hot and cold water. The energy fromthese remarkable engines is, however, not entirely free: heat energy is required to producethe temperature differences needed to run the engine. But the optimum temperatures atwhich the metal reacts can be controlled by altering the proportions of nickel to titanium; somealloys will even perform at room temperature. The necessary temperature range betweenthe warm and the cold can be as little as twelve degrees centigrade.
镍钛合金
学习啦在线学习网 镍钛诺是这个世纪所发现的最不寻常的金属之一，作为镍和钛的简单的一种合金，镍钛诺具有一些令人惊叹的特征。 这是一种有记忆力的金属，人们可以使它记住它被塑成的任何形状，并在加热后恢复这一形状。 比如，一节镍钛诺线圈在加热冷却后会记住圆圈这形状。 随后它可能被弯折成其它形状，但一旦再次加热，就会迅速地自动恢复成最初的圆圈状。 这种不寻常的能力被称为形状记忆效果(SME)。 其它一些合金如黄铜在一定程度上也具有这种特性。 目前人们对 SME 这一特性尚缺乏透彻的认识，而镍钛诺尤其使人惊奇，因为每当它展现这一惊人的功能时，似乎都违背了热力学原理。 因为它在恢复原有形状时所释放的力比人们使它变形所施加的力大得多。 镍钛诺不仅有记忆力，还能"学习"。如果加热-冷却-弯曲-再加热这一过程重复一定次数，且每次冷却后它都被丝毫不差地弯成同一形状，它不仅可以记住最初的形状，还能逐渐记住它被弯成的形状，并开始在每次冷却时恢复这一形状。
最终，它会自动地随温度变化而弯曲和恢复这些形状，并且没有任何疲劳迹象。 工程师们已制造出一些发动机样机，利用镍钛合金在交替遇热水和冷水时迅速改变形状所产生的力做推动力。 然而这些神奇的发动机工作时并非完全不耗能，因为必须有热能来制造温差才能使机器运转。 但人们可以通过改变合金中镍钛的比例来控制使它反应的最佳温度。 有的镍钛合金甚至能在室温下做出反应，冷暖之间的最小温差只有 12℃。
初中英语美文篇2
Museums
From Boston to Los Angeles, from New York City to Chicago to Dallas, museums are eitherplanning, building, or wrapping up wholesale expansion programs. These programs alreadyhave radically altered facades and floor plans or are expected to do so in the not-too-distantfuture.
学习啦在线学习网 In New York City alone, six major institutions have spread up and out into the air space andneighborhoods around them or are preparing to do so.
学习啦在线学习网 The reasons for this confluence of activity are complex,but one factor is a considerationeverywhere -- space. With collections expanding, with the needs and functions of museumschanging, empty space has become a very precious commodity.
Probably nowhere in the country is this more true than at the Philadelphia Museum of Art, whichhas needed additional space for decades and which received its last significant facelift ten yearsago. Because of the space crunch, the Art Museum has become increasingly cautious inconsidering acquisitions and donations of art, in some cases passing up opportunities tostrengthen its collections.
Deaccessing --or selling off -- works of art has taken on new importance because of themuseum's space problems. And increasingly, curators have been forced to juggle gallery space,rotating one masterpiece into public view while another is sent to storage.
Despite the clear need for additional gallery and storage space, however, "the museum hasno plan, no plan to break out of its envelope in the next fifteen years," according toPhiladelphia Museum of Art's president.
博物馆
学习啦在线学习网 从波士顿到洛杉机，从纽约到芝加哥、到达拉斯，所有的博物馆或者正在筹划、建造或者正在完成大规模的扩建计划。 这些计划或者已经根本性地改变了博物馆门面与展厅的设计，或者预期在不久的将来会这样做。 单单在纽约市，六个主要机构或者已经向空中和周围扩展，或者正准备这样做。大家一致行动的原因是复杂多样的，但其中的一个因素是普遍 考虑的空间问题。 随着收藏品的增多，也随着博物馆的需要和功能的变化，空间已经变成了一项非常珍贵的商品。在我国，也许没有任何其他地方比费城艺术博物馆更符合这个事实。
这个博物馆几十年来一直需要额外的空间，十年前进行了最后一次重大的翻新。 由于空间紧缺，该艺术博物馆在考虑购买与受赠艺术品已越来越谨慎，有时甚至放弃增强艺术收藏的机会。由于博物馆的空间问题，将艺术品脱手或者说卖掉已经有了新的重要意义。 博物馆馆长们被迫巧妙轮换利用陈列馆的空间，轮流着把一些艺术杰作向公众展出，而把另一些送入存储室中。虽然对额外的陈列室和存储室空间需要很明显，但据费城艺术博物馆经理讲： "博物馆还没有在未来十五年打破这个束缚的计划。"
初中英语美文篇3
Muscles and Human
Body It is in the joints of the human body that movements of the bones take place.Themovement itself is caused by the pull of sheets and cords of very tough tissue called muscle.Muscle tissue has the special ability to shorten itself so that the bone on which it pulls has tomove. When muscle tissue shortens, it also bunches up. Muscle tissue covers the body insheets and bands that lie between the skin and the skeleton.
The bones are the framework of the body, but the muscles fill out the body shape. Mostmuscles extend from one bone to another. When the muscle between the bones shortens, onebone has to move. The point where the muscle is fastened to the unmoving bone is called theorigin of the muscle, whereas the point where the muscle is not fastened to the bone that is tobe moved is called the insertion. Sometimes the muscle is not attached directly to the bone butto a tough, nonstretchable cord, or tendon, that is attached to the bone. Muscles do not push;they can only pull. To bend the arm at the elbow, the muscle at the front of the upper armhas to shorten and bunch up. To unbend the arm other muscles in the back of the arm haveto shorten.
These two sets of muscles - the front and the back - are said to act in opposition to eachother. When one set is working, the other set is usually relaxed. But there are times whenboth of them work. Sometimes muscles are called upon to do more than simply pull in onedirection. They may have to perform a turning motion. To be able to do this, the muscle mustbe attached to the bone at an angle. By pulling, the muscle can cause the bone to pivot. A fewmuscles have special functions. The diaphragm, for example, forces the lungs to take in air. Thispart of breathing is not primarily a bone moving operation.
肌肉和人体
骨骼运动发生在人体的关节部位。这种运动是由称为肌肉的片状或条状的强韧组织拖动而引起的。 肌肉组织有一种特殊的收缩能力，可以带动与之相连的骨骼。 肌肉在收缩的同时，也会聚成团。肌肉以条状或片状形式布满全身，存在于皮肤与骨架之间。 骨骼是身体的支架，而肌肉则构成了人的体形。 大多数肌肉接两块骨头，但当肌肉收缩时只有一块骨头运动。 肌肉与不动骨相连的一端叫肌起端，与动骨相连的一端叫附着端。 有些肌肉不与骨骼直接相连，而是连着附在骨骼上的不能收缩的带状组织或腱上。 肌肉不能推动而只能拉动骨骼。 要从肘部弯曲手臂，就要收缩上臂正面的肌肉。 要伸直手臂，背面的肌肉就得收缩。 这两组肌肉，正面的和背面的，称为相反运动肌肉。 当一组工作时，另一组就休息。 但有时它们也一起工作。 有时我们要求肌肉不仅仅做简单的单向拖动。 它们需要转动。 但只有当肌肉与骨骼形成一定角度时，它们才能转动，从而拖动骨骼绕某个轴旋转。 有几块肌肉的作用较特殊，例如隔膜肌。 它带动肺部吸入空气。 呼吸基本上不是骨骼运动带动的。
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