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   142754篇
  免费   11265篇
  国内免费   6743篇
电工技术   8020篇
技术理论   7篇
综合类   11239篇
化学工业   23346篇
金属工艺   7721篇
机械仪表   9177篇
建筑科学   10039篇
矿业工程   4010篇
能源动力   4079篇
轻工业   10977篇
水利工程   2441篇
石油天然气   7989篇
武器工业   998篇
无线电   15962篇
一般工业技术   16617篇
冶金工业   6892篇
原子能技术   1713篇
自动化技术   19535篇
  2024年   513篇
  2023年   1984篇
  2022年   3507篇
  2021年   4898篇
  2020年   3765篇
  2019年   3359篇
  2018年   3788篇
  2017年   4220篇
  2016年   3803篇
  2015年   5115篇
  2014年   6706篇
  2013年   8203篇
  2012年   9035篇
  2011年   9910篇
  2010年   8977篇
  2009年   8684篇
  2008年   8595篇
  2007年   8271篇
  2006年   8245篇
  2005年   7159篇
  2004年   5374篇
  2003年   4872篇
  2002年   5224篇
  2001年   4549篇
  2000年   3777篇
  1999年   3463篇
  1998年   2671篇
  1997年   2185篇
  1996年   2091篇
  1995年   1774篇
  1994年   1393篇
  1993年   1043篇
  1992年   802篇
  1991年   624篇
  1990年   491篇
  1989年   359篇
  1988年   330篇
  1987年   219篇
  1986年   151篇
  1985年   147篇
  1984年   105篇
  1983年   71篇
  1982年   61篇
  1981年   49篇
  1980年   43篇
  1979年   27篇
  1978年   11篇
  1977年   19篇
  1976年   23篇
  1975年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Based on the optimal fusion estimation algorithm weighted by scalars in the linear minimum variance sense, a distributed optimal fusion Kalman filter weighted by scalars is presented for discrete‐time stochastic singular systems with multiple sensors and correlated noises. A cross‐covariance matrix of filtering errors between any two sensors is derived. When the noise statistical information is unknown, a distributed identification approach is presented based on correlation functions and the weighted average method. Further, a distributed self‐tuning fusion filter is given, which includes two stage fusions where the first‐stage fusion is used to identify the noise covariance and the second‐stage fusion is used to obtain the fusion state filter. A simulation verifies the effectiveness of the proposed algorithm. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
22.
The strengths of two graphite/epoxy notched laminate systems with a softening strip were investigated. The softening strip was created by replacing the 0°-graphite/epoxy plies by a glass/epoxy composite. Experimental results indicated that the use of softening strips could significantly increase the laminate strength. Analysis was performed with finite elements developed using the classical laminated plate theory and was shown to be adequate. A simple point-stress failure criterion was used to predict the strength of notched laminates with softening strips and the result was found to be satisfactory.  相似文献   
23.
For pt.I see IEEE Trans. Neural Networks, vol.1, p.167-78 (1990). Parallel, self-organizing, hierarchical neural networks (PSHNNs) involve a number of stages with error detection at the end of each stage, i.e., rejection of error-causing vectors, which are then fed into the next stage after a nonlinear transformation. The stages operate in parallel during testing. Statistical properties and the mechanisms of vector rejection of the PSHNN are discussed in comparison to the maximum likelihood method and the backpropagation network. The PSHNN is highly fault tolerant and robust against errors in the weight values due to the adjustment of the error detection bounds to compensate errors in the weight values. These properties are exploited to develop architectures for programmable implementations in which the programmable parts are reduced to on-off or bipolar switching operations for bulk computations and attenuators for pointwise operations  相似文献   
24.
This paper presents a method of obtaining transmission network equivalents from the network's response to a pulse excitation signal. The proposed method is based on modal decomposition representation for the large-scale interconnected system. In this framework we use Prony analysis to identify the network function of the system and to decompose the large system into a parallel combination of simple first-order systems. As a result the network function of the transmission network can be identified easily, and a Thevenin-type of discrete-time filter model can be generated. It can reproduce the driving-point impedance characteristic of the network. Furthermore, the proposed model can be implemented into the EMTP in a direct manner. The simulation results with the full system representation and the developed equivalent system showed a good agreement  相似文献   
25.
There is no good method to measure the shape and the strain distributions of a structure changing with time. We have previously proposed the Fourier transform grid method (FTGM) to measure the three-dimensional shape and surface strain distributions of stationary objects by analysing the two-dimensional grating images recorded with two cameras. In the stereoscopic method, it is very important to determine the accurate geometric parameters of the camera system. In this paper, the positions and the directions of cameras are accurately determined using the FTGM applied to images of a reference object on which a two-dimensional grating is drawn. Applications for analysing shape and strain distributions of vibrating rubber plates and a moving human skin are shown.  相似文献   
26.
The aim of this study was to design a modified atmosphere package for a mixed vegetable salad consisting of 75 g of cut carrot, 55 g of cut cucumber, 20 g of sliced garlic and 50 g of whole green pepper. Respiration data of all the components were combined with film permeability data to predict package atmospheres and design optimal packages for experimental testing for improved shelf-life of the produce. The optimal package avoided minimum O2 and maximum CO2 tolerance limits, and chilling injury temperatures for any component. A pouch form package made of 27 mm low density polyethylene developed a modified atmosphere of 2.0–2.1% O2 and 5.5–5.7% CO2, which was beneficial for all components and provided better quality retention than other test packages.  相似文献   
27.
We present a method to obtain complete information of femtosecond pulses. By measuring triple-optical autocorrelation directly with third-harmonic generation, without spectral information, a temporal pulse shape can be obtained by analytical calculation without direction-of-time ambiguity. Combining the resulting optical pulse shape with its corresponding optical spectrum, the exact phase and color variations in time can all be recovered with a Gerchberg-Saxton algorithm through an iterative calculation with an O(n) complexity.  相似文献   
28.
支气管上皮靶细胞形态学参数对计算受氡子体照射的支气管的剂量是很重要的。本文介绍利用奥尔新兰-PAS 染色的外科切除人肺组织切片,测量基底细胞粘液细胞和的胞核深度与数目。结果表明,叶、段和小支气管的粘液细胞核深度分别为相应节段基底细胞的61%、69%和73%;此三节段粘液细胞的数目分别为基底细胞的53%、29%和28%,平均为37%。  相似文献   
29.
30.
如果我们这个企业能生产长生不老的药品,那么,全世界的钱都会集中到我们的企业来。所以,我们现在需要什么?我们需要新项目,我们需要新产品,这些都要依靠科技进步。  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