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   124964篇
  免费   12885篇
  国内免费   8853篇
电工技术   9802篇
技术理论   4篇
综合类   11998篇
化学工业   17101篇
金属工艺   7912篇
机械仪表   8134篇
建筑科学   8197篇
矿业工程   4080篇
能源动力   3549篇
轻工业   12813篇
水利工程   3287篇
石油天然气   3807篇
武器工业   1474篇
无线电   14740篇
一般工业技术   12310篇
冶金工业   6273篇
原子能技术   2159篇
自动化技术   19062篇
  2024年   684篇
  2023年   1891篇
  2022年   4409篇
  2021年   5656篇
  2020年   4145篇
  2019年   2916篇
  2018年   3224篇
  2017年   3680篇
  2016年   3314篇
  2015年   4815篇
  2014年   6290篇
  2013年   8102篇
  2012年   9233篇
  2011年   9910篇
  2010年   9265篇
  2009年   8999篇
  2008年   9727篇
  2007年   9187篇
  2006年   8022篇
  2005年   6605篇
  2004年   4925篇
  2003年   3701篇
  2002年   3753篇
  2001年   3421篇
  2000年   2576篇
  1999年   1338篇
  1998年   1146篇
  1997年   805篇
  1996年   675篇
  1995年   545篇
  1994年   435篇
  1993年   401篇
  1992年   303篇
  1991年   270篇
  1990年   280篇
  1989年   256篇
  1988年   207篇
  1987年   182篇
  1986年   150篇
  1985年   147篇
  1984年   130篇
  1983年   92篇
  1982年   82篇
  1981年   77篇
  1980年   107篇
  1979年   63篇
  1978年   63篇
  1977年   58篇
  1976年   78篇
  1975年   44篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
加强地方教育立法是我国整个立法工作不可或缺的一部分。文章以广东省为例,对广东省教育法规体系建设的现状和现存的问题进行剖析,并与北京、上海等省市的地方教育立法内容现状进行比较研究,提出广东省教育教育法规体系建设的重点及策略。  相似文献   
92.
It was found that the discontinuity at the end of an impulse will lead to numerical inaccuracy as this discontinuity will result in an extra impulse and thus an extra displacement in the time history analysis. In addition, this extra impulse is proportional to the discontinuity value at the end of the impulse and the size of integration time step. To overcome this difficulty, an effective approach is proposed to reduce the extra impulse and hence the extra displacement. In fact, the novel approach proposed in this paper is to perform a single small time step immediately upon the termination of applied impulse, whereas other time steps can be conducted by using the step size determined from accuracy consideration in period. The feasibility of this approach is analytically explored. Further, analytical results are confirmed by numerical examples. Numerical studies also show that this approach can be applied to other step-by-step integration methods. It seems that to slightly complicate the programming of dynamic analysis codes is the only disadvantage of this approach.  相似文献   
93.
在测定 2 0CrMnTi、4 0MnBH、2 0MnVBH钢淬透性及试样的化学成分基础之上 ,利用计算机采用逐步回归分析方法进行了回归运算 ,得到淬透性与化学成分的关系———回归方程 ,根据回归方程求出了不同窄淬透带规格所对应控制的化学成分范围  相似文献   
94.
Image processing allows the automation of the business transaction, turning “paper factories” into “image factories.” This burgeoning new area of computerization needs new paradigms, theories, and methods to maximize its effectiveness at cutting time and costs. This paper investigates what this new area of computerization can gain from CIM technology. It examines the similarities between the processing of computer images in a paperless business environment and the processing of materials into products in the manufacturing plant. These similarities will allow us to apply mature, well-tested CIM techniques to emerging image factories.  相似文献   
95.
This study investigates the ozonation of CI Reactive Black 5 (RB5) by using the rotating packed bed (RPB) and completely stirred tank reactor (CSTR) as ozone contactors. The RPB, which provides high gravitational force by adjusting the rotational speed, was employed as a novel ozone contactor. The same ozone dosage was separately introduced into either the RPB or the CSTR for the investigation, while the experimental solution was continuously circulated within the apparatus consisting of the RPB and CSTR. The decolorization and mineralization efficiencies of RB5 in the course of ozonation are compared for these two methods. Moreover, the dissolved and off‐gas ozone concentrations were simultaneously monitored for the further analysis. As a result, the ozone mass transfer rate per unit volume of the RPB was significantly higher because of its higher mass transfer coefficient and gas–liquid concentration driving force. Furthermore, ozonation kinetics was found to be independent of the gravitational magnitude of an ozone gas–liquid contactor. Therefore, the results suggest employing RPBs as ozone‐contacting devices with the advantage of volume reduction. The experimental results, which can be used for further modeling of the ozonation process in the RPB, also show the requirement of correct design for the RPB. Consequently, the present study is useful for the understanding of practical application of RPBs. Copyright © 2004 Society of Chemical Industry  相似文献   
96.
Let Ψ be any adaptive sampling algorithm that can run in real time on a tapeless multichannel electrocardiogram (ECG) Holter system. Simple methods which can significantly improve Ψ's fidelity are described and their results are compared in this paper. It is shown that by adding some simple tests to Ψ, the signals reconstructed by Ψ can be improved as much as 5.45 dB. It is also shown that under the same data rate, a good data compressor with slowly sampled input ECG is preferable to a bad data compressor with highly sampled input ECG  相似文献   
97.
Presents a model suitable for computing images of absorption cross sections of thick tissue structures illuminated at near infrared (NIR) wavelengths from tomographic projection data. Image reconstruction is accomplished by solving a system of linear equations derived from transport theory. Reconstruction results using different algebraic solvers are shown for anatomical maps of the breast, derived from magnetic resonance imaging data, containing two simulated pathologies, in which case qualitatively good reconstructions were obtained. Evaluation of magnetic resonance (MR) data to optimize NIR optical tomographic imaging methods and to assess the feasibility of a combined MR-optical measurement scheme is discussed  相似文献   
98.
In this paper, a new multiple negative-differential-resistance (MNDR) device based on a metal-insulator-semiconductor-insulator-metal (MISIM)-like structure with step-compositional InxGa1-x As quantum wells has been fabricated and demonstrated. The interesting MNDR phenomena are found in the current-voltage (I-V) characteristics of this device. At room temperature, the triple switching behaviours and quadruple stable operation states are obtained. In addition, the sixfold switching behaviors and a staircase-shaped I-V characteristic are observed at -105°C. A sequential carrier accumulation at InGaAs subwells and the potential lowering process are used to qualitatively explain the interesting MNDR phenomena. From the experimental results, it is shown that the studied device has good potential in multiple-valued logic applications  相似文献   
99.
从冷却曲线上相变段倾角最小原则出发,研究了新型激冷剂的配比与热分析法检测铸铁成分精度的关系,实验结果表明,能使相变段倾角最小的成分配比,也能提高对铸铁成分的热分析和检测精度。  相似文献   
100.
阐述了国内外羰基镍测定的各种方法以及在工业与环境保护等领域的应用状。  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