题目内容
计算字段是指根据一个或多个表中的一个或多个字段并使用_________建立的 _________。
查看答案
搜索结果不匹配？点我反馈
更多问题
TapeStore: A NEW TAPE SIORAGE SYSTEMTapeStore is a new kind of tape storage system which can store up to 6,000 computer tapes. No other tape storage system can hold as many computer tapes as TapeStore. The tapes look exactly like video cassettes. Many hundreds of data files can be stored on each tape, up to a maximum of 500 million bytes of data. If you stored the same amount of information on paper, you would need nearly 4.5 billion printed pages.The machine is a tall black box with a mechanical arm. The machine is 2.5 metres high and 3.0 metres wide. This is how it works. Each tape has a code printed on it. YOU feed the code number into TapaStore, which then looks for the code. As soon as TapaStore locates the cede, the arm reaches in and pulls out the tape.The system is very fast. It takes the mechanical arm about 10 seconds to find the tape it is looking for. The machine then searches the tape to extract the required file, and this take less than a minute. A human technician would have to locate and remove the tape by hand; and could take at least an hour to find the right file on the tape.Some of the world’s biggest companies, including banks, insurance companies, airlines, telephone companies, utilities and computer centres, have bought the system. They like it particularly because the system guarantees the security of their data.TapeStore was originally developed in Canada and is now being marketed world-wide. In Europe alone, 750 have already been installed at a cost of 480,000 dollars each. The TapeStare system is popular with big companies because（）
As evidence that the Earth’s atmosphere is warming continues to accumulate, scientists are making slow progress toward an answer to the big question raised by the evidence: (89) How much of the warming is due to human activity and how much to natural causes The UN Intergovernmental Panel on Climate Change, (90) the group of scientists widely considered the most authoritative voice on the subject, has already concluded that there is a "discernible human influence" on the global climate. Now the panel is deep into another of its periodic full-scale scientific assessments of global climate change. (91) Some experts on the problem say the human imprint on climate is becoming clearer, and may even have been the dominant factor in the global warming of recent decades. Not everyone agrees and virtually all experts say that in any case, a reliable estimate of the human imprint’s magnitude still remains some distance off. A number of influences, both natural and manmade, cause the planet’s temperature to vary. The natural ones include changes in solar radiation, and sulfate droplets called aerosols cast aloft by erupting volcanoes, which coo] the atmosphere by reflecting sunlight. (92) The human influence stems mostly from emissions of waste industrial gases like carbon dioxide, which trap heat in the atmosphere, and sulfate aerosols(硫酸盐悬浮颗粒)from industrial smokestacks. (93) Human factors appeared to be playing a part, but no judgment has been made on whether that part was big, small or in between.
Questions 68-73 are based on the following passage. Normally a student must attend a certain number of courses in order to graduate, and each course which he attends gives him a credit which he may count towards a degree. In many American universities the total work for a degree consists of thirty-six courses each lasting for one semester. A typical course consists of three classes per week for fifteen weeks; while attending a university a student will probably attend four or five courses during each semester. Normally a student would expect to take four years attending two semesters each year. It is possible to spread the period of work for the degree over a longer period. It is also possible for a student to move between one university and another during his degree course, though this is not in fact done as a regular practice. For every course that he follows a student is given a grade, which is recorded, and the record is available for the student to show to prospective employers. All this imposes a constant pressure and strain of work, but in spite of this some students still find time for great activity in student affairs. Elections to positions in student organizations arouse much enthusiasm. The effective work of maintaining discipline is usually performed by students who advise the academic authorities. Any student who is thought to have broken the rules, for example, by cheating has to appear before a student court. With the enormous number of students, the operation of the system does involve a certain amount of activity. A student who has held one of these positions of authority is much respected and it will be of benefit to him later in his career. ______ A student who holds a position in student organization is sure to succeed in his future career.
What’s the probable relationship between the man and the woman
微信支付 
支付宝支付