题目:
由于剪切速率越高,钻井液的网状结构被破坏越严重,网状结构的强度越低,即()越低。
A.表观黏度
B.结构黏度
C.塑性黏度
D.视黏度
答案:
参考答案:B
由于剪切速率越高,钻井液的网状结构被破坏越严重,网状结构的强度越低,即()越低。
A.表观黏度
B.结构黏度
C.塑性黏度
D.视黏度
参考答案:B
下图是小华收集的一份《捷报》图片,它报道的信息与某一战役有关,该战役是
[ ]A.辽沈战役
B.平津战役
C.淮海战役
D.渡江战役
在200 mL含Mg2+、Al3+、NH4+、H+、Cl-等离子的溶液中,逐滴加入5 mol/L的氢氧化钠溶液,所加氢氧化钠溶液的体积(mL)与产生沉淀的物质的量(mol)关系如下图所示,下列叙述正确的是
[ ]A.x与y的差值为0. 01 mol
B.原溶液中c(Cl-) =0. 75 mol/L
C.原溶液的pH=1
D.原溶液中n(Mg2+):n(Al3+)=5:2
下列措施中可以增加袜带密度的()
A.选择高织针数的针筒
B.选择低织针数的针筒
C.将压针三角向上移动
D.将压针三角向下移动
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.
How can researchers in "sleep laboratories" tell that the animals they are observing are asleep or not()
A. They see if the animals respond to light and sound
B. They do this by observing changes in the animals’ brain signals, breathing, heartbeat, and muscle activity
C. They see if the animals’ eyes are closed
D. They can tell this by seeing if the animals lie down or not
科研成果的鉴定形式有()
A.检测鉴定
B.函审鉴定
C.会议鉴定
D.软件鉴定