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   541602篇
  免费   9238篇
  国内免费   3013篇
电工技术   9812篇
技术理论   5篇
综合类   1705篇
化学工业   84419篇
金属工艺   20992篇
机械仪表   15704篇
建筑科学   13643篇
矿业工程   3109篇
能源动力   12542篇
轻工业   50181篇
水利工程   5833篇
石油天然气   10830篇
武器工业   291篇
无线电   58241篇
一般工业技术   104804篇
冶金工业   101473篇
原子能技术   11791篇
自动化技术   48478篇
  2021年   5408篇
  2020年   4016篇
  2019年   4812篇
  2018年   8304篇
  2017年   8180篇
  2016年   8862篇
  2015年   6338篇
  2014年   9916篇
  2013年   25177篇
  2012年   16240篇
  2011年   20742篇
  2010年   16456篇
  2009年   17778篇
  2008年   18928篇
  2007年   18943篇
  2006年   16184篇
  2005年   14478篇
  2004年   13661篇
  2003年   13041篇
  2002年   12728篇
  2001年   12468篇
  2000年   11743篇
  1999年   12201篇
  1998年   29718篇
  1997年   21255篇
  1996年   16212篇
  1995年   12214篇
  1994年   10838篇
  1993年   10827篇
  1992年   7908篇
  1991年   7559篇
  1990年   7479篇
  1989年   7424篇
  1988年   6902篇
  1987年   6100篇
  1986年   6123篇
  1985年   6826篇
  1984年   6461篇
  1983年   5938篇
  1982年   5424篇
  1981年   5721篇
  1980年   5427篇
  1979年   5316篇
  1978年   5284篇
  1977年   5837篇
  1976年   7935篇
  1975年   4573篇
  1974年   4357篇
  1973年   4392篇
  1972年   3712篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
21.
A technique using a lifting scheme is presented for constructing compactly supported wavelets whose coefficients are composed of free variables locating in an interval. An efficient approach-based wavelet for image compression is developed by selecting the coefficients of the 9-7 wavelet filter and associated lifting scheme. Furthermore, the rationalised coefficients wavelet filter that can be implemented with simple integer arithmetic is achieved and its characteristic is close to the well known original irrational coefficients 9-7 wavelet filters developed by A. Cohen et al. (Commun. Pure Appl. Maths., vol.45, no.1, p.485-560, 1992). To reduce the computational cost of image coding applications further, an acceleration technique is proposed for the lifting steps. Software and hardware simulations show that the new method has very low complexity, and simultaneously preserves the high quality of the compressed image.  相似文献   
22.
23.
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   
24.
Lateral scattering of retrograde well implants is shown to have an effect on the threshold voltage of nearby devices. The threshold voltage of both NMOSFETs and PMOSFETs increases in magnitude for conventional retrograde wells, but for triple-well isolated NMOSFETs the threshold voltage decreases for narrow devices near the edge of the well. Electrical data, SIMS, and SUPREM4 simulations are shown that elucidate the phenomenon.  相似文献   
25.
A common computing-core representation of the discrete cosine transform and discrete sine transform is derived and a reduced-complexity algorithm is developed for computation of the proposed computing-core. A parallel architecture based on the principle of distributed arithmetic is designed further for the computation of these transforms using the common-core algorithm. The proposed scheme not only leads to a systolic-like regular and modular hardware for computing these transforms, but also offers significant improvement in area-time efficiency over the existing structures. The structure proposed here is devoid of complicated input/output mapping and does not involve any complex control. Unlike the convolution-based structures, it does not restrict the transform length to be a prime or multiple of prime and can be utilized as a reusable core for cost-effective, memory-efficient, high-throughput implementation of either of these transforms  相似文献   
26.
This paper presents a hand-held microsystem based on new fully integrated magnetoresistive biochips for biomolecular recognition (DNA hybridization, antibody antigen interaction, etc.). Magnetoresistive chip surfaces are chemically treated, enabling the immobilization of probe biomolecules such as DNA or antibodies. Fluid handling is also integrated in the biochip. The proposed microsystem not only integrates the biochip, which is an array of 16times16 magnetoresistive sensors, but it also provides all the electronic circuitry for addressing and reading out each transducer. The proposed architecture and circuits were specifically designed for achieving a compact, programmable and portable microsystem. The microsystem also integrates a hand-held analyzer connected through a wireless channel. A prototype of the system was already developed and detection of magnetic nanoparticles was obtained. This indicates that the system may be used for magnetic label based bioassays  相似文献   
27.
Rigorous analytic expressions for radiation resistance R Σ of an electric dipole are obtained for three mutually orthogonal orientations of the dipole’s axis with respect to a plane metal screen or right-angle corner of infinite dimensions. Radiation resistance R Σ of the dipole oriented arbitrarily in space is calculated and analyzed as a function of the distance from the screen.  相似文献   
28.
We report for the first time optical signal-to-noise penalties which lead to performance degradations in single-fiber long-reach optical access networks when compared to identical dual-fiber systems. A simplified architecture, with reduced optical amplifier count compared to previous work, for single-fiber operation of a symmetrical 10-Gb/s, 1024-way split, 110-km long-reach optical access network is presented and demonstrated. In addition, a possible solution to remove the optical signal-to-noise penalty is suggested  相似文献   
29.
A multi-level attention framework for tracking and segmentation of humans and objects under complex occlusions is investigated, featuring an effective probabilistic appearance-based technique for pixel reclassification during object grouping and splitting. A novel ’spatial-depth affinity metric’ is introduced in the conventional likelihood function, utilising information of both spatial locations of pixels and dynamic depth ordering of the component objects in grouping. Depth ordering estimation is achieved through a combination of top-down and bottom-up approach. Experiments on some realworld difficult scenarios of low quality and highly compressed videos demonstrate the very promising results achieved.  相似文献   
30.
This paper proposes some novel techniques to accommodate users with different rate requirements in a wideband code-division multiple-access system employing orthogonal variable spreading factor codes. Two simple static code assignment strategies are first considered, and an improvement based on multicode assignment. Then the new idea of tree partitioning is introduced and used to devise a dynamic code reassignment algorithm. The behavior of these different techniques is experimentally investigated, in terms of call blocking probability and number of required reassignments. The tree partitioning method exhibits very good performances.  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