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   690231篇
  免费   7343篇
  国内免费   1174篇
电工技术   12317篇
综合类   525篇
化学工业   109525篇
金属工艺   30542篇
机械仪表   22506篇
建筑科学   15192篇
矿业工程   6005篇
能源动力   16884篇
轻工业   51731篇
水利工程   9034篇
石油天然气   20029篇
武器工业   48篇
无线电   70235篇
一般工业技术   146760篇
冶金工业   112407篇
原子能技术   18895篇
自动化技术   56113篇
  2021年   6629篇
  2019年   6298篇
  2018年   11245篇
  2017年   11416篇
  2016年   11960篇
  2015年   7328篇
  2014年   12501篇
  2013年   31252篇
  2012年   19017篇
  2011年   25302篇
  2010年   20318篇
  2009年   22712篇
  2008年   23015篇
  2007年   22578篇
  2006年   19411篇
  2005年   17505篇
  2004年   16783篇
  2003年   16450篇
  2002年   15921篇
  2001年   15381篇
  2000年   14817篇
  1999年   14337篇
  1998年   32103篇
  1997年   23526篇
  1996年   18299篇
  1995年   14148篇
  1994年   12958篇
  1993年   12687篇
  1992年   9987篇
  1991年   9816篇
  1990年   9686篇
  1989年   9380篇
  1988年   9029篇
  1987年   8335篇
  1986年   8066篇
  1985年   9024篇
  1984年   8298篇
  1983年   8027篇
  1982年   7287篇
  1981年   7440篇
  1980年   7187篇
  1979年   7406篇
  1978年   7385篇
  1977年   8043篇
  1976年   9718篇
  1975年   6669篇
  1974年   6579篇
  1973年   6646篇
  1972年   5820篇
  1971年   5399篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
An analysis is made of the characteristic features and problems of the optimal processing of the results of measurements in the case of a random observation function utilizing a nonlinear Kalman filter. A method is proposed for increasing the convergence domain of the filter with additional processing of measurements in the frequency domain.  相似文献   
62.
水电站运行过程中河床变形会使河底高程逐渐降低。从而导致下游流量特性曲线下降以及水电站水头增大。水头增大使水电站气蚀特性发生变化,导致动力设备的正常工作条件受到破坏。并对其运行安全性和效率造成不利影响。以卡马河的沃特金水电站为例,阐述了河床变形对水电站动力设备工作条件的影响。  相似文献   
63.
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications.  相似文献   
64.
65.
Current features are considered in the calculation of carrying capacities for constructions in engineering plant (EP). Methods and algorithms are described for EP calculations with comprehensive incorporation of the effects from technological and working defects on the behavior of structures under standard and emergency conditions. __________ Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 8, pp. 38–40, August, 2006.  相似文献   
66.
We have developed a narrow-band controller in the MHz range, based on a field-programmable gate array. It is used to control the probe beam intensity in frequency-modulated spectroscopy experiments with an acoustooptic modulator. The residual amplitude modulation at the modulation frequency (2.5 MHz) is reduced by 50 dB. The first-harmonic detection of the signals is operated in saturation spectroscopy of I/sub 2/ at 514.5 nm and 501.7 nm. A reduction of the background noise and a large increase in the signal-to-noise ratio are obtained.  相似文献   
67.
Phase equilibria involving spinel solid solutions, delafossite, and hematite in the Fe–Cu–O system are studied by emf measurements in solid-electrolyte galvanic cells. The results demonstrate that, above 1250 K, Fe3O4 and CuFe2O4 form a continuous series of solid solutions. At lower temperatures, the solid solution disproportionates with the formation of delafossite and Fe2O3, and two spinel solid solutions appear: one based on Fe3O4 and the other based on Cu2FeO4. The compositions of the spinel phases in equilibrium with delafossite and Fe2O3 are determined in the range 1100–1250 K.  相似文献   
68.
Relations for determining a motive force in a complex model of mass transfer as applied to concurrent, countercurrent, and cross motion of the vapor and liquid phases have been introduced. These forces have been compared for different forms of organization of the flow, and their comparison with similar quantities from the known Murphree and Hausen models is presented.  相似文献   
69.
70.
First-order polarization-mode dispersion (PMD) compensation by means of a polarization controller and a differential delay line is not sufficient to guarantee error-free transmission for 40-Gb/s channels when higher order effects severely increase signal distortion. Higher order mitigation is possible by cascading more than one first-order block. However, only two-stage or three-stage devices remain simple enough to be actually controlled. The performance of such higher order PMD compensators is evaluated by means of numerical simulations. Two different feedback signals have been used, demonstrating that first-order and higher order PMD distortion of nonreturn-to-zero (NRZ) pulses at 40 Gb/s can be strongly mitigated for instantaneous values of the differential group delay (DGD) up to the bit slot, when the compensator is properly controlled.  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