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   68705篇
  免费   7485篇
  国内免费   3311篇
电工技术   6810篇
技术理论   6篇
综合类   9129篇
化学工业   2627篇
金属工艺   1250篇
机械仪表   4356篇
建筑科学   5475篇
矿业工程   2773篇
能源动力   1844篇
轻工业   8203篇
水利工程   2868篇
石油天然气   4814篇
武器工业   1277篇
无线电   4409篇
一般工业技术   3955篇
冶金工业   1678篇
原子能技术   364篇
自动化技术   17663篇
  2025年   513篇
  2024年   1469篇
  2023年   1474篇
  2022年   1935篇
  2021年   2202篇
  2020年   2566篇
  2019年   2216篇
  2018年   2080篇
  2017年   2223篇
  2016年   2664篇
  2015年   2749篇
  2014年   4144篇
  2013年   4044篇
  2012年   4874篇
  2011年   5141篇
  2010年   3828篇
  2009年   3968篇
  2008年   3823篇
  2007年   4578篇
  2006年   4033篇
  2005年   3501篇
  2004年   2814篇
  2003年   2429篇
  2002年   1869篇
  2001年   1610篇
  2000年   1331篇
  1999年   1080篇
  1998年   851篇
  1997年   687篇
  1996年   569篇
  1995年   479篇
  1994年   371篇
  1993年   284篇
  1992年   219篇
  1991年   164篇
  1990年   122篇
  1989年   143篇
  1988年   66篇
  1987年   52篇
  1986年   36篇
  1985年   27篇
  1984年   34篇
  1983年   38篇
  1982年   20篇
  1981年   17篇
  1979年   16篇
  1978年   10篇
  1977年   15篇
  1964年   14篇
  1959年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
This paper presents different approaches which enable a data base management system to obtain a plausible fuzzy estimate for an attribute value of an item for which the information is not explicitly stored in the data base. This can be made either by a kind of analogical reasoning from information about particular items or by means of expert rules which specify the (fuzzy) sets of possible values of the attribute under consideration, for various classes of items. Another kind of expert rules enables the system to compute an estimate from the attribute value of another item provided that, in other respects, this latter item sufficiently resembles the item, the value of which we are interested in; then these expert rules are used either for controlling the analogical reasoning process or for enlarging the scope of application of the first kind of expert rules. The different approaches are discussed in the framework of possibility theory.  相似文献   
3.
Meeting time and cost objectives in complex projects involves specific problems and risks. An attempt is made to analyse the components of total cost increase of a project caused by time delay. An outline is given as to how these considerations can be used to estimate cost increases in investors' decision situations as well as to ascertain fair contractual penalties and claims for compensation and for the evaluation of justified project acceleration costs.  相似文献   
4.
5.
In recent years, the Asia-Pacific region has experienced several financial setbacks, including speculative attacks in 1998 and the SARS outbreak in 2003. Financial stresses of this nature are unanticipated, and not all of the dangers can be predicted by the examination of market information and macroeconomic indicators. The Early Warning System (EWS) that has been adopted by the International Monetary Fund may not be able to predict future financial crises for all possible scenarios, because shocks come in many different forms. To supplement the EWS, this paper proposes a data mining framework to measure the resilience of an economy. The resilience framework does not predict a crisis, but rather assesses the current state of health of an economy and its ability to withstand a financial shock should one occur. The framework is based on a feedback system consisting of two stages. The first stage assigns a resilience score to each economy based on a fuzzy logic scoring scheme that is built on the ambiguous reasoning of experts. The second stage uses the classification tree approach to estimate thresholds for each economic indicator, and examines the quality of the fuzzy score. The result from the second stage is then passed back to the first stage as feedback. The final result is obtained when the feedback system reaches its equilibrium state. The proposed resilience framework is applied to the external-sector and the public-sector economies of several countries to illustrate its applicability.  相似文献   
6.
Biphasic and nth-order models were tested as to their usefulness to fit experimental inactivation data of Bacillus licheniformis α-amylase, immobilized on glass beads, and were discussed with respect to their suitability to characterize the considered enzymic system as a time—temperature integrator (TTI) to evaluate heat processes. Both isothermal and non-isothermal inactivation experiments were carried out. Model (kinetic) parameters (rate constant k, activation energy EA and reaction order n) were estimated using a non-linear regression procedure. The results obtained, especially the activation energy of about 293 kJ mole–1, indicated a potential use of this system as a TTI for heating processes in the temperature range of 96–108°C.  相似文献   
7.
The proposed new color-difference formula of CIE TC 129, which is a modified version of CIELAB, was tested with a recently published data set of textile pass/fail judgments. Goodness of fit is improved, if the parameter of lightness is set near 2, and if, additionally, a weight function for lightness is defined that reduces the weight of a lightness difference with lightness level in relation to chroma or hue scaling. © 1994 John Wiley & Sons, Inc.  相似文献   
8.
Power system control equipment needs higher sensitivity and operational reliability. Advanced voltage control equipment is needed for reducing the frequency of tap changes and improving the characteristics (the relationship between the actual voltage and reference voltage) of the voltage to meet today's power system requirements. However, these objectives are in a trade-off relationship. Studies of voltage control derived from a knowledge base suitable for electric power systems can satisfy these objectives using fuzzy inference. Compared with corresponding conventional equipment, the new equipment improved the deviation of 30 min average voltage of 30 percent. This paper describes the design concept of new voltage control equipment using fuzzy inference. In addition, field test results are described along with rules of fuzzy inference, membership functions, and the deviation of 30 min average voltage through detailed simulation.  相似文献   
9.
10.
Samples of chicken meat from spent laying hens were obtained by four different methods: (1) manual deboning of whole carcasses; (2) manual deboning of skinned carcasses; (3) mechanical deboning of whole carcasses; and (4) mechanical deboning of skinned carcasses. The meat was packaged, frozen and stored at ?18 °C for up to 3 months. Functional properties studied were pH, emulsifying capacity (EC) and water‐holding capacity (WHC) and, in addition, pigment concentration was investigated. Sensory properties included aroma, colour, texture and overall acceptability, as judged by a trained panel using a nine‐point hedonic scale. Removal of the skin prior to deboning by either method gave significantly higher values (P < 0.05) for EC, while WHC values were not significantly different among the experimental treatments, despite higher pH values for mechanically‐deboned meat, with and without skin. Pigment concentrations were highest in meat from Treatment 4 and lowest for Treatment 1, but values for both methods of deboning were affected by the presence of skin. There were no significant differences between treatments for any of the sensory properties studied. Changes occurring in the meat during frozen storage are described.  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