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   476782篇
  免费   5633篇
  国内免费   1575篇
电工技术   9221篇
综合类   516篇
化学工业   68379篇
金属工艺   18250篇
机械仪表   14793篇
建筑科学   11481篇
矿业工程   1837篇
能源动力   12711篇
轻工业   39963篇
水利工程   4431篇
石油天然气   6540篇
武器工业   80篇
无线电   63228篇
一般工业技术   92252篇
冶金工业   90412篇
原子能技术   9518篇
自动化技术   40378篇
  2021年   3885篇
  2020年   2895篇
  2019年   3643篇
  2018年   6220篇
  2017年   6311篇
  2016年   6608篇
  2015年   4233篇
  2014年   7407篇
  2013年   21318篇
  2012年   11749篇
  2011年   16166篇
  2010年   12842篇
  2009年   14575篇
  2008年   15606篇
  2007年   15488篇
  2006年   13956篇
  2005年   12507篇
  2004年   12110篇
  2003年   12215篇
  2002年   11424篇
  2001年   11850篇
  2000年   11189篇
  1999年   11736篇
  1998年   29043篇
  1997年   20403篇
  1996年   15787篇
  1995年   12146篇
  1994年   10813篇
  1993年   10702篇
  1992年   7967篇
  1991年   7576篇
  1990年   7320篇
  1989年   6891篇
  1988年   6655篇
  1987年   5777篇
  1986年   5609篇
  1985年   6378篇
  1984年   5902篇
  1983年   5476篇
  1982年   5135篇
  1981年   5082篇
  1980年   4876篇
  1979年   4646篇
  1978年   4309篇
  1977年   5206篇
  1976年   6784篇
  1975年   3863篇
  1974年   3776篇
  1973年   3773篇
  1972年   3130篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Crosstalk between microstrip transmission lines   总被引:1,自引:0,他引:1  
Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Classical coupled transmission line theory is used for uniform lines, and potential and induced EMF methods are used for crosstalk between nonuniform lines. It is shown that the potential method is equivalent to classical coupled transmission line theory for the case of uniform lines. An experiment was performed for uniform coupled microstrip lines for frequencies from 50 MHz to 5 GHz, and good agreement between theory and measurement was obtained for both near- and far-end crosstalk  相似文献   
62.
Efficient numerical solution techniques have been developed and used to examine the electromagnetic fields that can be developed in the working volume of the CW Ellipticus antenna operated at frequencies from 100 kHz to 1 GHz. An exponentially tapered transition section is designed to obtain the desired illumination pattern in the working volume. The input transition section is needed for impedance matching and to drive efficiently the Ellipticus antenna. A parametric study is performed to ascertain the performance of the Ellipticus antenna for frequencies up to 1 GHz  相似文献   
63.
We present a microscopic interpretation of electronic noise in semiconductor materials and two-terminal devices. The theory is based on Monte Carlo simulations of the carrier motion self-consistently coupled with a Poisson solver. Current and voltage noise operations are applied and their respective representations discussed. As application we consider the cases of homogeneous materials, resistors, n+nn + structures, and Schottky-barrier diodes. Phenomena associated with coupling between fluctuations in carrier velocity and self-consistent electric field are quantitatively investigated for the first time. At increasing applied fields hot-carrier effects are found to be of relevant importance in all the cases considered here. As a general result, noise spectroscopy is found to be a source of valuable information to investigate and characterize transport properties of semiconductor materials and devices  相似文献   
64.
65.
Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal  相似文献   
66.
We report here a series of observations-most of which the reader can experience directly-showing that distinct components of patterned visual stimuli (orthogonal lines of a different hue) vary in perception as sets. Although less frequent and often less complete, these perceptual fluctuations in normal viewing are otherwise similar to the binocular rivalry experienced when incompatible scenes are presented dichoptically.  相似文献   
67.
Subcellular localization directed by specific A kinase anchoring proteins (AKAPs) is a mechanism for compartmentalization of cAMP-dependent protein kinase (PKA). Using a two-hybrid screen, a novel AKAP was isolated. Because it interacts with both the type I and type II regulatory subunits, it was defined as a dual specific AKAP or D-AKAP1. Here we report the cloning and characterization of another novel cDNA isolated from that screen. This new member of the D-AKAP family, D-AKAP2, also binds both types of regulatory subunits. A message of 5 kb pairs was detected for D-AKAP2 in all embryonic stages and in all adult tissues tested. In brain, skeletal muscle, kidney, and testis, a 10-kb mRNA was identified. In testis, several small mRNAs were observed. Therefore, D-AKAP2 represents a novel family of proteins. cDNA cloning from a mouse testis library identified the full length D-AKAP2. It is composed of 372 amino acids which includes the R binding fragment, residues 333-372, at its C-terminus. Based on coprecipitation assays, the R binding domain interacts with the N-terminal dimerization domain of RIalpha and RIIalpha. A putative RGS domain was identified near the N-terminal region of D-AKAP2. The presence of this domain raises the intriguing possibility that D-AKAP2 may interact with a Galpha protein thus providing a link between the signaling machinery at the plasma membrane and the downstream kinase.  相似文献   
68.
A case of endometrioid carcinoma arising from endometriosis of the sigmoid colon is reported. The patient had been treated with unopposed continuous estrogen injection for twenty years after bilateral salpingo-oophorectomy because of severe endometriosis. The pathology, pertinent literature and implications of the present case are discussed.  相似文献   
69.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9  相似文献   
70.
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