单选题含载脂蛋白B 48 的血浆脂蛋白是

单选题每克下列物质在体内供能最多的是

单选题DNA损伤时，使修复酶反应性增加属于

单选题RNA聚合酶催化转录，其底物是

单选题CO、CN-对呼吸链的抑制点是

单选题患者发生高渗性脱水时，应该（ ）

单选题关于结合胆红素的特点的描述，错误的是

单选题稳定蛋白质分子二级结构的化学键是

单选题DNA复制与转录过程有许多异同点中，描述不正确的是

单选题下列各组氨基酸容易发生磷酸化与脱磷酸的是

单选题A．胆固醇B．直接胆红素C．间接胆红素D．初级胆汁酸E．次级胆汁酸

单选题All animals must rest, but do they really sleep as we know it? The answer to this question seems obvious. If an animal regularly stops its activities and stays quiet and unmoving—if it looks as though it is sleeping—then why not simply assume that it is in fact sleeping? But how can observers be sure that an animal is sleeping? They can watch the animal and notice whether its eyes are open or closed, whether it is active or lying quietly, and whether it responds to light or sound. These factors are important clues, but they often are not enough. Horses and cows, for example, rarely close their eyes, and fish and snakes cannot close them. Yet this does not necessarily mean that they do not sleep. Have you ever seen a cat dozing with an eye partly open? Even humans have occasionally been observed to sleep with one or both eyes partially open. Animals do not necessarily lie down to sleep either. Elephants, for example, often sleep standing up, with their tusks resting in the fork of a tree. Finally, while "sleeping" animals often seem unaware of changes in the sounds and light and other stimuli around them, that does not really prove they are sleeping either. Observations of animal behavior alone cannot fully answer the question of whether or not animals sleep. The answers come from doing experiments in "sleep laboratories" using a machine called the electroencephalograph (EEC). The machine is connected to animals and measures their brain signals, breathing, heartbeat, and muscle activity. The measurements are different when the animals appear to be sleeping than when they appear to be awake. Using the EEC, scientists have confirmed that all birds and mammals studied in laboratories do sleep. There is some evidence that reptiles, such as snakes and turtles, do not truly sleep, although they do have periods of rest each day, in which they are quiet and unmoving. They also have discovered that some animals, like chimpanzees, cats, and moles (who live underground), are good sleepers while others, like sheep, goats, and donkeys, are poor sleepers. Interestingly, the good sleepers are nearly all hunters with resting places that are safe from their enemies. Nearly all the poor sleepers are animals hunted by other animals: they must always be watching for enemies, even when they are resting.

单选题对于磷酸戊糖途径的叙述恰当的是

单选题有关tRNA的叙述，错误的是

单选题不参加脂酸β－氧化的辅因子是

单选题脂酸β-氧化的循环步骤是

单选题体内能量的储存形式是

单选题不参与DNA复制的酶是

单选题获得已知目的DNA序列最常用的方法是

单选题酶的Km值大小主要与