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   1606979篇
  免费   26447篇
  国内免费   7152篇
电工技术   35431篇
综合类   6648篇
化学工业   277502篇
金属工艺   66536篇
机械仪表   47308篇
建筑科学   48384篇
矿业工程   11980篇
能源动力   50540篇
轻工业   125000篇
水利工程   16407篇
石油天然气   38450篇
武器工业   202篇
无线电   200806篇
一般工业技术   303082篇
冶金工业   202499篇
原子能技术   34705篇
自动化技术   175098篇
  2021年   15670篇
  2020年   11994篇
  2019年   14768篇
  2018年   19258篇
  2017年   19079篇
  2016年   23118篇
  2015年   17683篇
  2014年   28827篇
  2013年   88209篇
  2012年   38590篇
  2011年   54087篇
  2010年   46310篇
  2009年   54027篇
  2008年   49437篇
  2007年   47601篇
  2006年   47101篇
  2005年   43032篇
  2004年   44090篇
  2003年   43741篇
  2002年   42348篇
  2001年   39204篇
  2000年   37308篇
  1999年   36905篇
  1998年   56831篇
  1997年   46472篇
  1996年   40066篇
  1995年   33605篇
  1994年   31044篇
  1993年   30867篇
  1992年   27034篇
  1991年   24265篇
  1990年   24530篇
  1989年   23576篇
  1988年   22124篇
  1987年   20356篇
  1986年   19765篇
  1985年   23057篇
  1984年   22827篇
  1983年   20797篇
  1982年   19597篇
  1981年   19697篇
  1980年   18341篇
  1979年   18834篇
  1978年   18046篇
  1977年   18355篇
  1976年   20164篇
  1975年   16246篇
  1974年   15749篇
  1973年   15868篇
  1972年   13284篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
K. M. Granstr  m 《Drying Technology》2003,21(7):1197-1214
This paper describes a novel method to measure emission from dryers. The method resolves the known difficulties caused by diffuse emissions, and also solves the problems associated with high moisture content of the drying medium. The basic idea is to use water vapor to determine the exhaust flow, while a dry ice trap is used both to preconcentrate emitted VOCs and to determine the moisture content of the drying medium.  相似文献   
952.
High efficient LED structures covering the spectral range of 1.6–2.4 μm have been developed on the basis of GaSb and its solid solutions. The electroluminescent characteristics and their temperature and current dependences have been studied. The radiative and nonradiative recombination mechanisms and their effect on the quantum efficiency have been investigated. A quantum efficiency of 40–60% has been obtained in the quasi-steady mode at room temperature. A short-pulse optical power of 170 mW was reached. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 8, 2003, pp. 996–1009. Original Russian Text Copyright ? 2003 by Stoyanov, Zhurtanov, Astakhova, Imenkov, Yakovlev.  相似文献   
953.
Long-range prediction of the mobile-radio fading envelope is an enabling technology for many fading compensation approaches. Because the fading envelope is well modeled as a bandlimited process, it has special predictability properties. In this paper, we find a linear predictor that is optimal in the mean-square sense when the predictor impulse response is energy constrained. This solution may be used to determine the minimum mean squared error of a prediction based on past values that are corrupted with estimation errors.  相似文献   
954.
An extremal self-dual doubly-even binary (n,k,d) code has a minimum weight d=4/spl lfloor/n/24/spl rfloor/+4. Of such codes with length divisible by 24, the Golay code is the only (24,12,8) code, the extended quadratic residue code is the only known (48,24,12) code, and there is no known (72,36,16) code. One may partition the search for a (48,24,12) self-dual doubly-even code into three cases. A previous search assuming one of the cases found only the extended quadratic residue code. We examine the remaining two cases. Separate searches assuming each of the remaining cases found no codes and thus the extended quadratic residue code is the only doubly-even self-dual (48,24,12) code.  相似文献   
955.
956.
PNNI-based control plane for automatically switched optical networks   总被引:1,自引:0,他引:1  
Much effort has been spent on the definition of control plane protocols for automatically switched optical networks (ASON). Most of the proposals brought into the standardization for an International Telecommunications Union-Telecommunication Sector, Internet Engineering Task Force, and Optical Internetworking Forum are based on Internet protocol concepts. One such proposal is the generalized multi-protocol label switching (GMPLS), an extension of the MPLS traffic engineering control plane model that includes nonpacket switched technologies (time, wavelength, and fiber switching). Recently, the potential use of private network-network interface (PNNI) in ASONs has been discussed as an alternative proposal by the standardization bodies. The goal of this paper is to appropriately adapt asynchronous transfer mode into an optical PNNI (O-PNNI) protocol that can be used as the control plane of ASONs. The paper also provides a critical viewpoint on the potential usage of either O-PNNI or GMPLS control plane and analyzes the pros and cons of each. The methodology adopted toward devising O-PNNI hinges on reviewing PNNI along with ASON recommendations in order to determine the set of PNNI features that require adaptation. Having identified these features we engineer and present appropriate solutions relating to routing, signaling and addressing aspects.  相似文献   
957.
It is shown that, for the spectrum analysis of digital quasi-periodic signals, one must use a procedure based on approximating the sequence of data readouts by a first-order trigonometric polynomial with a varying frequency of its harmonic functions.  相似文献   
958.
The authors present an experimental real-time GSM terminal detector, to be installed in a restricted area. The detector triggers terminal signaling, which can be captured.  相似文献   
959.
Accurate and reliable decision making in oncological prognosis can help in the planning of suitable surgery and therapy, and generally, improve patient management through the different stages of the disease. In recent years, several prognostic markers have been used as indicators of disease progression in oncology. However, the rapid increase in the discovery of novel prognostic markers resulting from the development in medical technology, has dictated the need for developing reliable methods for extracting clinically significant markers where complex and nonlinear interactions between these markers naturally exist. The aim of this paper is to investigate the fuzzy k-nearest neighbor (FK-NN) classifier as a fuzzy logic method that provides a certainty degree for prognostic decision and assessment of the markers, and to compare it with: 1) logistic regression as a statistical method and 2) multilayer feedforward backpropagation neural networks an artificial neural-network tool, the latter two techniques having been widely used for oncological prognosis. In order to achieve this aim, breast and prostate cancer data sets are considered as benchmarks for this analysis. The overall results obtained indicate that the FK-NN-based method yields the highest predictive accuracy, and that it has produced a more reliable prognostic marker model than both the statistical and artificial neural-network-based methods.  相似文献   
960.
Several kinds of waveguide components such as curved waveguide bends, arbitrary angle waveguide bends and T-junctions have been analyzed with boundary element method in this paper. A new discretization method for the boundary element method to solve the waveguide discontinuities has been given. The numerical results obtained agree well with the experimental results and numerical results in other literature. Especially, the scattering characteristics of Forded E-, H-plane T-junctions in 3mm band have been analyzed using boundary element method and the calculation results are presented.  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