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   733120篇
  免费   8395篇
  国内免费   1693篇
电工技术   12975篇
综合类   670篇
化学工业   110558篇
金属工艺   34256篇
机械仪表   24256篇
建筑科学   16498篇
矿业工程   5339篇
能源动力   17562篇
轻工业   53950篇
水利工程   8814篇
石油天然气   18387篇
武器工业   50篇
无线电   76410篇
一般工业技术   154186篇
冶金工业   128180篇
原子能技术   18045篇
自动化技术   63072篇
  2021年   6697篇
  2020年   4908篇
  2019年   6375篇
  2018年   15211篇
  2017年   15375篇
  2016年   14369篇
  2015年   7849篇
  2014年   12812篇
  2013年   31112篇
  2012年   20781篇
  2011年   30056篇
  2010年   24611篇
  2009年   26248篇
  2008年   26905篇
  2007年   27462篇
  2006年   19743篇
  2005年   19450篇
  2004年   18382篇
  2003年   18085篇
  2002年   16612篇
  2001年   16273篇
  2000年   15350篇
  1999年   15492篇
  1998年   37717篇
  1997年   26938篇
  1996年   20553篇
  1995年   15653篇
  1994年   13767篇
  1993年   13637篇
  1992年   10175篇
  1991年   9785篇
  1990年   9742篇
  1989年   9389篇
  1988年   8765篇
  1987年   8050篇
  1986年   7854篇
  1985年   8621篇
  1984年   8159篇
  1983年   7416篇
  1982年   6948篇
  1981年   7119篇
  1980年   6865篇
  1979年   6902篇
  1978年   6878篇
  1977年   7783篇
  1976年   9764篇
  1975年   6064篇
  1974年   5909篇
  1973年   5985篇
  1972年   5117篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
Photodiodes designed to be sensitive in the region 0.5–1.7 μm and obtained by vacuum magnetron sputtering of the ITO (SnO2 + In2O3) layer on the surface of the Hg3In2Te6 single crystal are studied. The electrical characteristics, measured at 265–333 K, indicate that the mechanism of charge transport in the diodes under study is thermionic. The current-voltage characteristic and its temperature variations are described quantitatively based on the energy diagram and the found parameters of the heterojunction. Original Russian Text ? L.A. Kosyachenko, I.M. Rarenko, E.F. Sklyarchuk, I.I. German, Sun Weiguo, 2006, published in Fizika i Tekhnika Poluprovodnikov, 2006, Vol. 40, No. 5, pp. 568–571.  相似文献   
962.
The maximum-likelihood technique is applied to determine the coordinates of moving targets in a three-dimensional bistatic forward-scattering radar. The potential accuracy of the coordinates’ determination is estimated. Simulation results are presented.  相似文献   
963.
A diagnostic array has been developed for studying the operating modes of the divertor in the ITER tokamak-reactor using the Thomson scattering technique. The aim of this study is to measure the spatial profiles of the electron temperature and density. The structure of the diagnostic setup was selected on the basis of a classical diagnostic geometry and the high-resolution LIDAR system, which provide access to different regions of the divertor plasma. A severe radiation environment, limited access to the plasma in the ITER divertor, and a high-dust environment (the divertor plate erosion material) in the divertor volume pose many problems for performing diagnostics under unique conditions having no analogs in the tokamaks that are now in operation. Different methods for protecting optical surfaces from plasma-enriched deposition are proposed and analyzed. The efficiency of these methods has been demonstrated in bench tests. The concept of laser and detector systems and diffraction polychromators capable of operating at different electron temperatures with a lower limit of 1 eV, has been justified and approved.  相似文献   
964.
Lean philosophy: implementation in a forging company   总被引:2,自引:2,他引:0  
This research addresses the implementation of lean philosophy in a forging company with a focus on radial forging production flow lines. Here, the prime motive is to evolve and test several strategies to eliminate waste on the shop floor. In this research, a systematic approach is suggested for the implementation of lean principles. This paper describes an application of value stream mapping (VSM). Consequently, the present and future states of value stream maps are constructed to improve the production process by identifying waste and its sources. Furthermore, Taguchi’s method of design of experiments is pursued here to minimize the forging defects produced due to imperfect operating conditions. A noticeable reduction in set-up time and work-in-process (WIP) inventory level is substantiated. Finally, we conclude with a discussion of managerial implications and the future scope of research.  相似文献   
965.
Emission characteristics of an electron-beam-pumped Cd(Zn)Se/ZnMgSSe semiconductor laser are studied. The laser’s active region consists of a set of ten equidistant ZnSe quantum wells containing fractional-monolayer CdSe quantum-dot inserts and a waveguide formed by a short-period superlattice with the net thickness of ~0.65 μm. Lasing occurs at room temperature at a wavelength of 542 nm. Pulsed power as high as 12 W per cavity face and an unprecedentedly high efficiency of ~8.5% are attained for the electron-beam energy of 23 keV.  相似文献   
966.
We propose and analyze new finger assignment techniques that are applicable for RAKE receivers in the soft handover (SHO) region. Specifically, extending the results for the case of two-base station (BS), we consider the multi-BS situation, attack the statistics of several correlated generalized selection combining (GSC) stages, and provide closed-form expressions for the statistics of the output signal-to-noise ratio (SNR). By investigating the tradeoff among the error performance, the average number of required path estimations/comparisons, and the SHO overhead, we show through numerical examples that the new schemes offer commensurate performance in comparison with more complicated GSC-based diversity systems while requiring a smaller estimation load and SHO overhead.  相似文献   
967.
By applying a combination of characterisation tools, changes in structural and superconducting properties with nominal Mg non‐stoichiometry in MgxB2 are found. The non‐stoichiometry produces enhanced in‐field critical current densities (Jc's) and upper critical field / irreversibility field (Hc2/Hirr(T)) values. Upper critical fields of ~ 21 T (4.2 K) were obtained in nominal Mg‐deficient samples compared to ~ 17 T (4.2 K) for near‐stoichiometric samples.  相似文献   
968.
969.
It is proposed a rule of total classes of composition systems of discrete frequency signals (CDF-signals) construction in extended Galois fields. It is carried out modeling and research a correlation properties of CDF-signals, and determined their practical attraction.  相似文献   
970.
Different and alternative methods for the preparation of Ni/pillared clays based on impregnation and encapsulation procedures are reported. Several nickel precursors and metal loadings are considered in order to evaluate their influence on the structural, textural and catalytic properties of the resulting solids. The behaviour of the optimum solids as catalysts has been proved in the selective catalytic reduction of nitrogen oxides with propene, and the relevance of the oxidant nature was checked by changing the composition of the oxidant mixture. Of all the factors studied, the nature of the nickel precursors appears as the most important one, owing to the formation of different active nickel species during the synthesis procedure.  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