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   762011篇
  免费   8630篇
  国内免费   2236篇
电工技术   13416篇
综合类   548篇
化学工业   115049篇
金属工艺   32760篇
机械仪表   24855篇
建筑科学   16708篇
矿业工程   5401篇
能源动力   19249篇
轻工业   56832篇
水利工程   8698篇
石油天然气   18495篇
武器工业   40篇
无线电   85647篇
一般工业技术   158244篇
冶金工业   134426篇
原子能技术   18735篇
自动化技术   63774篇
  2021年   6787篇
  2020年   5256篇
  2019年   6565篇
  2018年   11505篇
  2017年   11671篇
  2016年   12580篇
  2015年   7776篇
  2014年   13067篇
  2013年   35451篇
  2012年   20710篇
  2011年   27878篇
  2010年   22228篇
  2009年   25031篇
  2008年   25713篇
  2007年   25304篇
  2006年   22312篇
  2005年   20074篇
  2004年   19352篇
  2003年   19095篇
  2002年   18015篇
  2001年   18133篇
  2000年   17022篇
  1999年   17482篇
  1998年   41609篇
  1997年   29468篇
  1996年   22460篇
  1995年   17072篇
  1994年   15107篇
  1993年   15219篇
  1992年   11290篇
  1991年   10848篇
  1990年   10811篇
  1989年   10248篇
  1988年   9907篇
  1987年   8737篇
  1986年   8473篇
  1985年   9679篇
  1984年   8985篇
  1983年   8263篇
  1982年   7661篇
  1981年   7819篇
  1980年   7474篇
  1979年   7438篇
  1978年   7398篇
  1977年   8165篇
  1976年   10118篇
  1975年   6544篇
  1974年   6391篇
  1973年   6539篇
  1972年   5519篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Conclusions 1. Use of dewatering systems based on voidless drainage is most effective when dewatering slightly permeable soils in regions with a deep seasonal frost. 2. Two-story drainage with the upper and lower stories spaced 30 m apart accelerates the discharge of gravitational water from the arable layer. Results of observations on two-story drainage in experimental-production sections indicated that it discharges 2 – 3.8 times more water than systematic tubular drainage with an interdrain spacing of 10 m and a 0.2-m thick three-dimensional filter of a sandy-gravelly mixture. 3. It is recommended to use crushed stone and porous-clay gravel with a fineness of 10 – 20 mm as a filler. In that case, protection of the drain filler is, as a rule, required only from the intrusion of soil from above during construction in cohesive soils with a plasticity indexW p≥7. 4. seepage rate in a voidless drain should be lower than the scouring velocity for the soil in which the voidless drainage is placed. In the opposite case, it is necessary to lower the grade of the drains or select a filler gradation such that the seepage rate in the drain be lower than the scouring velocity. Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 8, pp. 41–43, August, 1998.  相似文献   
102.
Approaches to using visual language in a cultural context can be placed on a continuum, with global (universal) on one end and culture-focused on the other. Each approach reveals contrasting assumptions about three central design issues: perception, aesthetics and pragmatics. The global approach is characterized by attempts to invent an objective, universal visual language or to define such a language through perceptual principles and empirical research. The culture-focused perspective is founded on the principle that visual communication is intimately bound to experience and hence can function only within a given cultural context, to which designers must be sensitive. While the modernist, universal approach has been losing ground to the postmodern, culture-focused approach, the two complement each other in a variety of ways and, depending on the rhetorical situation, offer pragmatic benefits and drawbacks  相似文献   
103.
Implementing a neural network on a digital or mixed analog and digital chip yields the quantization of the synaptic weights dynamics. This paper addresses this topic in the case of Kohonen's self-organizing maps. We first study qualitatively how the quantization affects the convergence and the properties, and deduce from this analysis the way to choose the parameters of the network (adaptation gain and neighborhood). We show that a spatially decreasing neighborhood function is far more preferable than the usually rectangular neighborhood function, because of the weight quantization. Based on these results, an analog nonlinear network, integrated in a standard CMOS technology, and implementing this spatially decreasing neighborhood function is then presented. It can be used in a mixed analog and digital circuit implementation.  相似文献   
104.
Genetic evolution of the topology and weight distribution of neuralnetworks   总被引:52,自引:0,他引:52  
This paper proposes a system based on a parallel genetic algorithm with enhanced encoding and operational abilities. The system, used to evolve feedforward artificial neural networks, has been applied to two widely different problem areas: Boolean function learning and robot control. It is shown that the good results obtained in both cases are due to two factors: first, the enhanced exploration abilities provided by the search-space reducing evolution of both coding granularity and network topology, and, second, the enhanced exploitational abilities due to a recently proposed cooperative local optimizing genetic operator.  相似文献   
105.
106.
107.
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 95–112, March–April, 1994.  相似文献   
108.
Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 172–176, May–June, 1994  相似文献   
109.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period  相似文献   
110.
An experimental and theoretical analysis of the nonlinear coupling mechanism between the two solitary pulses circulating in a two-color femtosecond laser is presented. Two operation regimes; synchronized; and nonsynchronized; and a hysteresis of the transition between the two regimes are clearly observed; while independent modelocking and tunability of the output pulse trains is found in both regimes. Pulses in the range from 15 to 100 fs are synchronized with a timing jitter below 2 fs. The combined effects of cross-phase modulation and negative group velocity dispersion are shown to be responsible for the strong pulse correlation in the synchronized regime. Our experimental observations are in agreement with numerical simulations, thus confirming the theoretical model  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