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   252398篇
  免费   3165篇
  国内免费   857篇
电工技术   4805篇
综合类   193篇
化学工业   35981篇
金属工艺   9505篇
机械仪表   7544篇
建筑科学   6080篇
矿业工程   879篇
能源动力   7223篇
轻工业   21097篇
水利工程   2201篇
石油天然气   3230篇
武器工业   15篇
无线电   34270篇
一般工业技术   49979篇
冶金工业   48572篇
原子能技术   5076篇
自动化技术   19770篇
  2021年   2155篇
  2020年   1558篇
  2019年   1914篇
  2018年   3272篇
  2017年   3309篇
  2016年   3400篇
  2015年   2217篇
  2014年   3954篇
  2013年   11477篇
  2012年   6235篇
  2011年   8575篇
  2010年   6906篇
  2009年   7884篇
  2008年   8404篇
  2007年   8297篇
  2006年   7365篇
  2005年   6503篇
  2004年   6288篇
  2003年   6560篇
  2002年   6039篇
  2001年   6517篇
  2000年   5976篇
  1999年   6390篇
  1998年   16495篇
  1997年   11419篇
  1996年   8803篇
  1995年   6607篇
  1994年   5903篇
  1993年   5849篇
  1992年   4134篇
  1991年   4020篇
  1990年   3858篇
  1989年   3650篇
  1988年   3562篇
  1987年   3017篇
  1986年   2944篇
  1985年   3210篇
  1984年   2929篇
  1983年   2831篇
  1982年   2638篇
  1981年   2543篇
  1980年   2461篇
  1979年   2305篇
  1978年   2108篇
  1977年   2606篇
  1976年   3566篇
  1975年   1765篇
  1974年   1729篇
  1973年   1665篇
  1972年   1466篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
Surveys the field of super resolution (SR) processing for compressed video. The introduction of motion vectors, compression noise, and additional redundancies within the image sequence makes this problem fertile ground for novel processing methods. In conducting this survey, though, we develop and present all techniques within the Bayesian framework. This adds consistency to the presentation and facilitates comparison between the different methods. The article is organized as follows. We define the acquisition system utilized by the surveyed procedures. Then we formulate the HR problem within the Bayesian framework and survey models for the acquisition and compression systems. This requires consideration of both the motion vectors and transform coefficients within the compressed bit stream. We survey models for the original HR image intensities and displacement values. We discuss solutions for the SR problem and provide examples of several approaches.  相似文献   
152.
The In-site of Ba2In2O5 with Brownmillerite structure was partially substituted for Ce4+ ions in order to examine the doping effect on the order-disorder transition. Ba2In2 – x Ce x O5 + x/2 (x = 0.1, 0.2, 0.3, 0.5, 1.0, and 1.5) were prepared by solid state reaction. X-Ray diffraction analyses of these powder samples demonstrated that Ba2In2 – x Ce x O5 + x/2 (x = 0.1 and 0.2) possesses Brownmillerite structure. With increasing content of Ce4+ ion the crystal system of Ba2In2 – x Ce x O5 + x/2 (x = 0.3, 0.5, and 1.0) changed to cubic perovskite structure above the order-disorder transition temperature of Ba2In2O5. Arrhenius plots of the electrical conductivities of Ba2In2 – x Ce x O5 + x/2 (x = 0.2, 0.3, and 1.0) exhibited no discontinuity. These compounds had high transference numbers of oxide ion above 973 k.  相似文献   
153.
The basic methods of verifying continuous automatic belt weighers are described. A comparative analysis of these methods on the basis of experimental studies is made and ways of implementing the results in industry are recommended.  相似文献   
154.
The effect of crystal orientation on the photogeneration of free charge carriers was studied for C60 single crystals in a weak magnetic field. The photoconductivity sharply depends on the orientation of magnetic field with respect to the crystallographic directions, showing a 5–8% increase for seven axes of the C60 crystal.  相似文献   
155.
We propose a standardization procedure that provides a convenient, quantitative and reproducible laboratory-based method for measuring the state of polarization (SOP) fluctuations produced by polarization varying devices. This method is based on the SOP distributions generated by commercial polarization scramblers. We show that these devices generate distributions of the maximum change of the SOP (in a given sample time) that follow Rayleigh statistics, which scale linearly with scrambling frequency and the sample time. We use this procedure to measure the SOP fluctuations in a short length of coiled fiber subject to mechanical perturbations.  相似文献   
156.
A set of poly[N‐oligo(ethylene oxide)yl 4‐vinylpyridinium tosylate] (P4VOEOOTs) has been prepared by spontaneous polymerization of 4‐vinylpyridine. This method gives a grafted polyelectrolyte having a positive charge on every backbone pyridinic moiety. The P4VP15Ts, P4VP164Ts, P4VP350Ts and P4VP750Ts aqueous solution conductivities were determined in the concentration range from 6 × 10?4 to 10?2 M at 25 °C. The variation of the conductivity versus concentration of the investigated system exhibits typical polyelectrolyte behaviour. The polyelectrolyte mobility was found to be dependent on the oligo(ethylene oxide) (OEO) side‐chain length. Manning's rod‐like model fails to describe these results. A simple steric effect is proposed to explain the influence of the OEO length. Copyright © 2003 Society of Chemical Industry  相似文献   
157.
Flotation is a water treatment alternative to sedimentation, and uses small bubbles to remove low-density particles from potable water and wastewater. The effect of zeta potential, bubble size and particle size on removal efficiency of the electro-flotation process was investigated because previous model-simulations indicated that these attributes are critical for high collision efficiency between micro-bubbles and particles. Solutions containing Al3+ as the metal ion were subjected to various conditions. The zeta potentials of bubbles and particles were similar under identical conditions, and their charges were influenced by metal ion concentration and pH. Maximum removal efficiency was 98 and 12% in the presence and absence of flocculation, respectively. Removal efficiency was higher when particle size was similar to bubble size. These results agree with modelling simulations and indicate that collision efficiency is greater when the zeta potential of one is negative and that of the other is positive and when their sizes are similar.  相似文献   
158.
The ORPHEUS dark matter detector consists of 450 g superconducting tin granules with diameters of 28 and 36 μm. The detector has been operating in the shallow site of the underground laboratory in Bern (70 m.w.e). First preliminary results on WIMP detection sensitivity will be presented.  相似文献   
159.
Experimental study on the effect of strain rate on discontinuous flow and mechanical characteristics of the high-nitrogenous steel Kh23AG19F has been performed. Within the range of strain rates from 4.62 · 10-5 to 1.85 · 10 -4 s-1, discontinuous flow, reflected by serration on the tensile diagram, is chiefly determined by intergranular deformation mechanisms. Under strain rates over 1.85 · 10-2 s-1, combined deformation modes prevail, which cause a change in the character of discontinuous flow and transform a serrated tensile diagram into a wavy graph, with the yield stress of steel increased significantly.  相似文献   
160.
The hydrogen content, its depth distribution, and its bonding configuration have been studied in hydrogenated amorphous silicon prepared by plasma-enhanced chemical vapor deposition with hydrogen-diluted silane. Nuclear reaction analysis and infrared spectroscopy were used to determine the total amount of hydrogen and its bonded component, respectively. It has been established that the total concentration of hydrogen does not depend on the film thickness, and has a uniform depth profile. The concentration of bonded hydrogen changes with the film thickness within the measurement accuracy. The data obtained suggest the presence of molecular (non-bonded) hydrogen, uniformly distributed in concentration across the film thickness.  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