单选题关于关键酶的叙述哪一项是错误的

单选题能识别终止密码的是

单选题Aristotle believed that the heavens were perfect. If they ever were, they are no longer. The skies above Earth are now littered with the debris (残骸) of dead satellites, bits of old rockets and the odd tool dropped by a spacewalking astronaut. Such is the extent of the detritus that the first accidental collision between two satellites has already taken place. It happened in February 2009, when a defunct (废弃的) Russian Cosmos smashed into a functioning American Iridium, destroying both and creating even more space junk. To stop this sort of thing happening again Vaios Lappas of the University of Surrey, in England, has designed a system that will remove satellites from orbit at the end of their useful lives--and as a bonus will scour part of the sky clean as it does so. Dr. Lappas's satellite-removal system employs a solar sail. As light from the sun hits the sail, it imparts a minuscule but continuous acceleration. When a satellite is first launched, the sail is angled in a way that causes this acceleration to keep the satellite in orbit. (Orbits gradually decay as a result of collisions with the small number of air molecules found even at altitudes normally classified as "outer space". ) Solar sails have yet to be used widely to propel spacecraft in this way--several earlier versions came unstuck when the sails failed to unfurl properly-but doing so is not a novel idea in principle The novelty Dr. Lappas envisages is to change the angle of the sail when the satellite has become defunct. Instead of keeping the derelict craft in orbit, it will, over the course of a couple of years, drag it into the atmosphere and thus to a fiery end. Not only that, but the sail will also act like a handkerchief, mopping up microscopic orbital detritus such as flecks of paint from previous launches. A fleck of paint may not sound dangerous, but if travelling at 27 000kph (17 000mph), as it would be in orbit, it could easily penetrate an astronaut's spacesuit. A prototype of Dr. Lappas's design, called CubeSail, will be launched late next year. It weighs just 3kg and, when folded up, measures 30cm (12 inches) by 10era by 10era. Once unfurled, however, the sail will have an area of 25 square metres. If this prototype, which is paid for by EADS, a European aerospace company, proves successful, solar sails might be added to many future satellites. That would enable them to be removed rapidly from orbit when they became useless and would restore to the skies some measure of Aristotelian perfection.

单选题每种完整蛋白质分子必定具有

单选题关于病毒癌基因论述正确的是

单选题与片段TAGA互补的DNA片段为

单选题A．操纵子B．启动子C．增强子D．沉默子E．衰减子

单选题血浆脂蛋白中空腹12～24小时后血浆中不含

单选题酶竞争性抑制的特点是

单选题糖酵解、有氧氧化和磷酸戊糖途径通过下列哪种中间产物相互联系

单选题肝脏不能利用的物质是

单选题脂肪的主要生理功能是

单选题体内合成卵磷脂时不需要

单选题下列血浆蛋白中，不属于糖蛋白的为

单选题关于加单氧酶系的叙述错误的是

单选题合成卵磷脂时所需的活性碱基是

单选题三羧酸循环和有关的呼吸链反应中能产生ATP最多的步骤是

单选题RNA生物合成过程中，最不稳定的碱基配对为

单选题理论上，哪一种维生素的缺乏会导致血液中丙酮酸的积聚

单选题下列哪种脂肪酶是激素敏感性脂肪酶