题目内容
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[单选题]
Closed-die forging is very widely used for（)production in industry, in which the meta
A.small
B.large scale
C.mass
D.median
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题目内容
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题目内容
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A.small
B.large scale
C.mass
D.median
如果结果不匹配，请 联系老师 获取答案
更多“Closed-die forging is very wid…”相关的问题
A.equipment is expensive
B.large pieces are greater strength
C.less noise
D.less vibration
A.Cutting
B.Forging
C.Grinding
D.Casting
A.Open Die Forgings
B.Impression Die Forgings
C.Precision Forgings
D.Hand Forgings
Testing Times
Researchers are working on ways to reduce the need for animal experiments, but new laws may increase the number of experiments needed.
The current situation
In an ideal world, people would not perform. experiments on animals. For the people, they are expensive. For the animals, they are stressful and often painful.
That ideal world, sadly, is still some way away. People need new drugs and vaccines. They want protection from the toxicity of chemicals. The search for basic scientific answers goes on. Indeed, the European Commission is forging ahead with proposals that will increase the number of animal experiments carried out in the European Union, by requiring toxicity tests on every chemical approved for use within the union's borders in the past 25 years.
Already, the commission has identified 140,000 chemicals that have not yet been tested. It wants 30,000 of these to be examined right away, and plans to spend between ~ 4 billion — 8 billion ($5 billion—10 billion) doing so. The number of animals used for toxicity testing in Europe will thus, experts reckon, quintuple (翻五倍) from just over lm a year to about 5m, unless they are saved by some dramatic advances in non-animal testing technology. At the moment, roughly 10% of European animal tests are for general toxicity, 35% for basic research, 45% for drugs and vaccines, and the remaining 10% a variety of uses such as diagnosing diseases.
Animal experimentation will therefore be around for some time yet. But the search for substitutes continues, and last weekend the Middle European Society for Alternative Methods to Animal Testing met in Linz, Austria, to review progress.
A good place to start finding alternatives for toxicity tests is the liver--the organ responsible for breaking toxic chemicals down into safer molecules that can then be excreted. Two firms, one large and one small, told the meeting how they were using human liver cells removed incidentally during surgery to test various substances for long-term toxic effects.
One way out of the problem
PrimeCyte, the small firm, grows its cells in cultures over a few weeks and doses them regularly with the substance under investigation. The characteristics of the cells are carefully monitored, to look for changes in their microanatomy.
Pfizer, the big firm, also doses its cultures regularly, but rather than studying individual cells in detail, it counts cell numbers. If the number of cells in a culture changes after a sample is added, that suggests the chemical in question is bad for the liver.
In principle, these techniques could be applied to any chemical. In practice, drugs (and, in the case of PrimeCyte, food supplements) are top of the list. But that might change if the commission has its way: those 140,000 screenings look like a lucrative market, although nobody knows whether the new tests will be ready for use by 2009, when the commission proposes that testing should start.
Other tissues, too, can be tested independently of animals. Epithelix, a small firm in Geneva, has developed an artificial version of the lining of the lungs. According to Huang Song, one of Epithelix's researchers, the firm's cultured cells have similar microanatomy to those found in natural lung linings, and respond in the same way to various chemical messengers. Dr. Huang says that they could be used in long-term toxicity tests of airborne chemicals and could also help identify treatments for lung diseases.
The immune system can be mimicked and tested, too. ProBioGen, a company based in Berlin, is developing an artificial human lymph node (淋巴结) which, it reckons, could have prevented the neardisastrous consequences of a drag trial held in Britain three months ago, in which (despite the drag having passed animal tests) six men suffered multiple organ failure and ne
A．Y
B．N
C．NG
A.is
B.are
C.have
D.has
