首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   36099篇
  免费   2403篇
  国内免费   907篇
电工技术   2051篇
综合类   2331篇
化学工业   3718篇
金属工艺   3281篇
机械仪表   2632篇
建筑科学   4034篇
矿业工程   733篇
能源动力   721篇
轻工业   3441篇
水利工程   451篇
石油天然气   2152篇
武器工业   333篇
无线电   2717篇
一般工业技术   4430篇
冶金工业   1107篇
原子能技术   223篇
自动化技术   5054篇
  2025年   257篇
  2024年   780篇
  2023年   649篇
  2022年   700篇
  2021年   891篇
  2020年   1034篇
  2019年   810篇
  2018年   787篇
  2017年   1027篇
  2016年   1087篇
  2015年   1295篇
  2014年   2122篇
  2013年   1873篇
  2012年   2575篇
  2011年   2564篇
  2010年   2076篇
  2009年   2018篇
  2008年   1932篇
  2007年   2231篇
  2006年   2002篇
  2005年   1732篇
  2004年   1412篇
  2003年   1262篇
  2002年   1112篇
  2001年   948篇
  2000年   790篇
  1999年   638篇
  1998年   542篇
  1997年   410篇
  1996年   358篇
  1995年   312篇
  1994年   239篇
  1993年   164篇
  1992年   153篇
  1991年   120篇
  1990年   102篇
  1989年   62篇
  1988年   43篇
  1987年   29篇
  1986年   23篇
  1985年   33篇
  1984年   28篇
  1983年   32篇
  1982年   29篇
  1981年   7篇
  1980年   7篇
  1979年   9篇
  1978年   10篇
  1965年   17篇
  1962年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Grey box identification refers to the practice of identifying dynamical systems in model structures exploiting partial prior information. This contribution reviews a method for stochastic grey box identification and surveys experiences and lessons of applying it to a number of industrial processes. Issues to be addressed include advantages and costs of introducing stochastics into the model, the question of what contribution must be expected from the model designer as opposed to what can be formalized in computer algorithms, and an outlook on future plans to resolve present shortcomings.  相似文献   
2.
3.
We have recently developed an optical contactless method for testing the quality of solder joints during accelerated thermal cycling ageing processes.1 The method was based upon the measurement of the dynamic thermal behaviour of the joint to short bursts of Joule heating. It has proved to be efficient in revealing the formation of cracks at the lead-solder interface. We present a method to evaluate ageing at a much earlier stage in the cycling process. We have observed in earlier work,1 that before cracks appear, structural changes occur in the solder at the lead-solder interface. The thermal response of the solder joint is recorded over time to a Peltier heat perturbation produced by flowing a current pulse through the interface where structural changes occur. The key point in this method is to discriminate the Peltier effect from the Joule thermal response because both effects generate heat. The variation of the early Peltier response in the thermal cycling ageing tests is seen as a quantitative signature of the structural changes in the lead-solder interface.  相似文献   
4.
A new principle and arrangement for directly determining the angle of incidence of an optical beam on an object are proposed and demonstrated. The novelty of the approach lies in the realization of a ‘smart object’, which extracts a portion of the incident beam's power into an optical waveguide attached to the object's surface or embedded in its body for converting the angle of incidence into the position of a guided beam with finite lateral extent. This ‘integrated optical light pointer’ beam is accomplished by means of creating additional degrees of freedom on the target in two different ways. While a first type is based on introducing spatial variations of the waveguide thickness, a second type makes use of a chirp of the grating periodicity. The feasibility for practical applications has been experimentally demonstrated by a direct comparison with a commercial high-resolution encoder, resulting in an r.m.s. error of <30′'. Measurements have been performed for chips fabricated based on replicated polycarbonate substrates and with no external optics, showing the great potential of this approach for realizing low-cost yet high-performance miniature goniometers.  相似文献   
5.
Power devices with high capability have been developed. 8‐kV/3.5‐kA‐class light‐triggered thyristors have the highest capability among power devices. These devices are used in the Kii Channel HVDC transmission system in Japan. In this paper, we report the extracted problems of conventional testing methods of 8‐kV/3.5‐kA‐class light‐triggered thyristors among manufacturers, and the proposed unified testing methods on the basis of element characteristics and operating conditions in the Kii Channel HVDC system. Furthermore, we propose a figure of merit for power devices for the practical use, and try to extract elements used at the Kii Channel HVDC system with small margins and low withstand capabilities. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 61–70, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10024  相似文献   
6.
The average diet in most developing countries is predominantly cereal based. Wheat, rice and millets are major staple foods. Although these diets are sufficient in iron, their low bioavailability is one of the most significant factors for iron deficiency anaemia. Traditional techniques like fermentation show promise in improving iron bioavailability. In vitro ionizable iron was estimated in 31 different combinations of rice, wheat, sorghum, black gram, bengal gram, green gram and coriander in five replicates with or without, fermentation in steamed products. Results indicate that in general cereal pulse combination and fermentation significantly ( P <0.05) increase the per cent ape of ionizable iron. Combination effects dominated in rice whilst fermentation dominated in sorghum. There was a significant reduction ( P <0.05) in phytate phosphorus on fermentation but no loss of tannin.  相似文献   
7.
8.
The Office Document Architecture (ODA) is an International Standard which is developed by TC 97/sc 18 of the International Organization for Standardization (ISO) in close collaboration with CCITT's Study Group VIII and with ECMA. This paper describes the current state of a formal specification of the ODA document structures by mathematical means and its use for conformance specification and conformance testing.  相似文献   
9.
Bovine spongiform encephalopathy (BSE), or ‘mad cow disease’, is one of several transmissable spongiform encephalopathies (TSEs) known to affect certain mammals and is spread through the ingestion of infected animal tissue. It is believed that the inadvertent contamination of meat and bone meal (MBM) with infected animal tissue and the subsequent use of this material as a feed supplement contributed to the spread of the disease in cattle. As a result, the use of processed animal proteins (PAPs) in animal feeds is regulated in many parts of the world. Although feed testing is the only definitive means to certify compliance, regulatory compliance often relies solely on paper certification. Recently, rapid methods have become available that can be used by regulators to determine compliance during routine inspections. We describe a rapid, immunochromatographic strip test that can detect 0.1% MBM in animal feed. The test takes 15 min to perform and large numbers of samples can be screened for PAPs simultaneously.  相似文献   
10.
A test chamber has been developed in order to provide a small and simple emission testing facility capable of testing construction products in a climate where the important climatic parameters such as temperature, ventilation rate and air velocity can be varied independently around typical indoor values. The test chamber CLIMPAQ is made of panes of window glass. Other main surface materials are stainless steel and eloxated aluminium. The chamber has a volume of 50.9 litres and is designed to meet the requirements for quantifying air pollution. In this investigation human subjects acted as air pollution judges, and chemical characterization of the air pollution was carried out. Carpet, linoleum, wall paint and seal- ant were tested simultaneously in the CLIMPAQ and in four other chambers ranging from a full-scale chamber of 28 m3 to a field and laboratory emission cell of 3.5· 10?5m3. Product ranking is the same in all chambers for the sensory measurements. Emission rates based on sensory measurements differ for all products less than 100 % except for tests in a 3-litre chamber where emission rates were higher. Chemical measurements differ up to approximately 10 times for the same product in different chambers. Deviations appear to be the result of different environmental parameters in the various chambers. Low air concentrations or high specific ventilation rates seem to increase emissions, while differences in air velocities and sink properties may also be the cause of differences in emission rates.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号