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宁德检查卵巢去哪好平安健康

2020年01月20日 10:38:25|来源:国际在线|编辑:服务问答
Natures Helicopters自然界的直升机Most birds flap their wings up and down, but hummingbirds move their wings in a figure-eight pattern. With each flap they twist their wings one-hundred-eighty degrees so that they create a downward thrust on both the forward and backward strokes.大多数的鸟是上下拍打翅膀飞行,但蜂鸟不一样,它是以八字形移动翅膀。蜂鸟每次拍打翅膀都会旋转180度,以便为前后的拍打创造一个推力。If each loop of the wings is of the same strength, they hover. They can go forward, backwards, or sideways by tilting their wings in the direction they want to go. Kind of like a helicopter.Exactly.如果每次翅膀旋转的力度一样,蜂鸟就会盘旋在空中。它们只要往想去的方向倾斜翅膀,就可以前进,后退,或横向移动。就像直升机一样。是的。In order to hover, hummingbirds have to be really strong. Their wing muscles are thirty percent of their total weight. When a small hummingbird hovers it flaps its wings about eighty times per second.要盘旋在空中,蜂鸟必须得很强壮。它们翅膀的肌肉重量占身体整个体重的三分之一。一只小蜂鸟盘旋在空中时,翅膀的震动频率约为每秒80次。Hummingbirds have to eat close to fifty percent of their weight in food everyday to keep up their strength. They eat things that are packed with calories and produce lots of reusable energy, like seeds, nuts, fruit, and nectar.蜂鸟每天吃的东西是它们体重的二分之一,这样才能维持体力。它们吃的东西都是高热量食物,能产生大量可重复使用的能量,像种子,坚果,水果和花蜜。 /201301/219192

Survival Of The Sluggish缓慢的生存Silkworms have been bred over thousands of years to behave quite unlike their caterpillar cousins in the wild. Thats because people purposely breed silkworms to fit this job description:蚕这种动物已经被人类豢养了上千年,这使得它们的行为远远异于野外的毛毛虫同类们。因为人类故意培养蚕,使得他们能够适应这样的工作岗位:WANTED–Superlative silk producers. Benefits include housing, unlimited food and protection from all predators. Wanderlust greatly discouraged. No opportunity for travel.诚聘:招优秀的产丝工。福利包括住房、包吃包喝、不受天敌威胁。不欢迎旅游迷。没有出差机会。Obviously, what makes a good silk producer in captivity is very different from what helps a caterpillar survive in the wild. Commercial silkworms are dynamos at silk production, and compared to their wild relatives, rather sluggish about everything else.很明显,造就人工饲养的产丝能手的条件跟让野生毛毛虫在野外生存的能力会非常不同。跟它们的野生同类相比,商用蚕在产丝方面是能手,但在其他任何方面的行动都很迟缓。Outdoors, you’ve probably seen caterpillars crawling to find food or hide from birds, but commercial silkworm caterpillars hardly move. For silk production, theyre kept on open trays because theyre content to stay put, as long as they have a steady supply of mulberry leaves. Even when they reach the moth stage, commercial silkworms are surprisingly immobile. Wild moths fly to evade predators and to lay their eggs in different areas. However, commercial silkworm moths havent needed to do these things for thousands of years. Theyve completely lost the ability to fly, even though they still have wings!在户外,你可能见过毛毛虫爬来爬去寻找食物或躲避鸟类,但是商用蚕幼虫很少活动。为了产丝,这些蚕就被放在敞口的匾上,因为只要有充足的桑叶供应,它们就 会满足于一动不动地呆着。即使商用蚕蜕变成蛾子,它们的活动力也惊人地弱。野生的蛾子会到处飞,以躲避天敌并且把卵产在不同的地方。但是,从上千年前开 始,商用蚕的蛾子就不用做这些事情了。即使它们仍然有翅膀,它们也已对完全丧失了飞行的能力。Heres another difference. In the wild, moths are often very particular about where theyll lay eggs. This ensures that baby caterpillars can chomp their favorite leaves as soon as they hatch. Commercial silkworm moths have lost that instinct too. Theyll even lay eggs on a sheet of paper, where its easy for humans to keep track of them.还有一处不同。野外的蛾子通常对产卵地点很挑剔。这可以保它们的幼虫一孵化就能吃到喜欢吃的树叶。商用蚕的蛾子连这种本能也丧失了。它们甚至会在纸张上产卵,对于人类来说可以很方便的找到它们。 /201206/188090

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