题目内容
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Through microscopes people can see objects that are ______to the naked eyes.
A．invisible
B．invincible
C．incredible
D．impassable
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更多“Through microscopes people can see objects that are ______to the naked eyes.A．invisibleB．i”相关的问题
Scientists ______that bacteria through microscopes for many years．
A．studied
B．have studied
C．had studied
D．have seen studied
Each advance in microscopic technique has provided scientists with new perspectives on the function of living organisms and the nature of matter itself. The invention of the visible-light microscope late in the sixteenth century introduced a previously unknown realm of single celled plants and animals. In the twentieth century, electron microscope have provided direct views of viruses and minuscule surface structures. Now another type of microscope, one that utilizes X rays rather than light or electrons, offers a different way of examining tiny de tails; it should extend human perception still farther into the natural world.
The dream of building an X-ray microscope dates to 1895; its development, however, was virtually halted in the 1940's because the development of the electron microscope was progressing rapidly. During the 1940's, electron microscopes routinely achieved resolution better than that possible with a visible-light microscope, while the performance of X-ray microscopes resisted improvement. In recent years, however, interest in X-ray microscopes has revived, largely because of advances such as the development of new sources of X-ray illumination. As a result, the brightness available today is millions, of times that of X-ray tubes, which, for most of the century, were the only avail able sources of soft X-rays.
The new X-ray microscopes considerably improve on the resolution provided by optical microscopes. They can also be used to map the distribution of certain chemical elements. Some can form. pictures in extremely short times; others hold the promise of special capabilities such as three-dimensional imaging. Unlike conventional electron microscopy, X-ray microscopy enables specimens to be kept in air and in water, which means that biological samples can be studied under conditions similar to their natural state. The illumination used, so-called soft X rays in the wavelength range of twenty to forty angstroms (an angstrom is one ten-billionth of a meter), is also sufficiently penetrating to, image intact biological cells in many cases. Because of the wavelength of the X rays used, soft X-ray microscopes will never match the highest resolution possible with electron microscopes. Rather, their special properties will make possible investigations that will complement those performed with light-and-electron-based instruments.
What does the passage mainly discuss？
A．The detail seen through a microscope.
B．Sources of illumination for microscopes.
C．A new kind of microscope.
D．Outdated microscopic techniques.
A．They will probably replace electron microscopes altogether.
B．They will eventually he much cheaper to produce than they are now.
C．They will provide information not available from other kinds of microscopes.
D．They will eventually change the illumination range that they now use.
It is universally known that microscopes make small things appear larger than______.
A．really are
B．are really
C．are they really
D．they really are
Without microscopes and other modern ______, attempts to teach science were futile.
A．utilities
B．equipment
C．costume
D．products
A、Ionization potential of hydrogen called zero loss peak
B、Plasmon loss peak called zero loss peak
C、Energy of primary electron beam taken as zero loss peak
D、Fermi level of sample taken as the reference, zero loss peak
It is implied in the first paragraph______.
A．cells or even molecules can be magnified by a microscope
B．a molecule is as small as a cell
C．telescopes and microscopes are similar; they both magnify small things
D．telly is a Greek word
Why did it take so long to develop the X-ray microscope？
A．Funds for research were insufficient.
B．The source of illumination was not bright enough until recently.
C．Materials used to manufacture X-ray tubes were difficult to obtain.
D．X-ray microscopes were too complicated to operate.
Why does the author mention "blemish," in paragraph 4？
A．To suggest that sunspots are flaws on the surface of the sun.
B．To illustrate that the sun is thought to have a face.
C．To emphasize that sunspots are indicative of illness.
D．To explain that microscopes are strong enough to see sunspots.
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