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   1626545篇
  免费   25157篇
  国内免费   7078篇
电工技术   34895篇
综合类   6503篇
化学工业   277152篇
金属工艺   65984篇
机械仪表   46081篇
建筑科学   48633篇
矿业工程   11672篇
能源动力   50576篇
轻工业   127989篇
水利工程   16293篇
石油天然气   38013篇
武器工业   150篇
无线电   199728篇
一般工业技术   302847篇
冶金工业   223073篇
原子能技术   34377篇
自动化技术   174814篇
  2021年   15705篇
  2020年   12074篇
  2019年   14830篇
  2018年   18137篇
  2017年   17499篇
  2016年   22673篇
  2015年   17704篇
  2014年   28956篇
  2013年   88440篇
  2012年   38626篇
  2011年   53062篇
  2010年   45074篇
  2009年   52744篇
  2008年   48890篇
  2007年   46645篇
  2006年   47244篇
  2005年   42428篇
  2004年   44129篇
  2003年   43794篇
  2002年   42437篇
  2001年   39808篇
  2000年   37871篇
  1999年   37958篇
  1998年   63717篇
  1997年   50480篇
  1996年   42752篇
  1995年   35138篇
  1994年   32345篇
  1993年   32246篇
  1992年   27328篇
  1991年   24574篇
  1990年   24777篇
  1989年   23885篇
  1988年   22481篇
  1987年   20574篇
  1986年   20028篇
  1985年   23370篇
  1984年   22948篇
  1983年   20939篇
  1982年   19741篇
  1981年   19947篇
  1980年   18556篇
  1979年   18967篇
  1978年   18171篇
  1977年   18986篇
  1976年   21635篇
  1975年   16295篇
  1974年   15795篇
  1973年   15887篇
  1972年   13375篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
A redundant multivalued logic is proposed for high-speed communication ICs. In this logic, serial binary data are received and converted into parallel redundant multivalued data. Then they are restored into parallel binary data. Because of the multivalued data conversion, this logic makes it possible to achieve higher operating speeds than that of a conventional binary logic. Using this logic, a 1:4 demultiplexer (DEMUX, serial-parallel converter) IC was fabricated using a 0.18-/spl mu/m CMOS process. The IC achieved an operating speed of 10 Gb/s with a supply voltage of only 1.3 V and with power consumption of 38 mW. This logic may achieve CMOS communication ICs with an operating speed several times greater than 10 Gb/s.  相似文献   
93.
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   
94.
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   
95.
Deformation behavior of stoichiometric blends made from poly(styrene-co-styrenesulfonic acid) (SPS) and poly(styrene-co-4-vinylpyridine) (SVP) was investigated by TEM observation of strained thin films. An FTIR investigation revealed that ionic cross-links were formed between the component polymers upon blending due to intermolecular ion-ion interactions, which arose from proton transfer from sulfonic acid groups to pyridine groups. TEM observations indicate that the deformation mode of the blends changed from crazing only to crazing plus shear deformation, with the shear contribution becoming larger, as the ion content in the blends increased. Such changes in deformation mode can be understood as arising from an increase in the ‘effective’ strand density due to the formation of ionic cross-links upon blending. It was also found that the ionic cross-links via pyridinium cation/sulfonate anion ion pairs were more effective in inducing the transition of deformation mode than ionic cross-links via -SO3/Na+ or -SO3/Ca2+ ion pairs.  相似文献   
96.
番禺30-1砂岩强水驱气藏储层非均质性研究   总被引:7,自引:5,他引:2  
针对垂向非均质性严重且边底水能量强的番禺30-1气田面临的潜在开发问题,通过岩心分析及测井二次解释,对其夹层特征及储层非均质性等进行了研究,划分出19个流动单元并定量描述了各流动单元的特征参数,建立了该气田的精细地质模型。综合评价表明,新建的地质模型具有较高的精度,为该气藏合理开发提供了坚实的地质基础。  相似文献   
97.
涡轮搅拌桨反应器混合过程的数值计算   总被引:1,自引:1,他引:0  
利用CFD方法计算单层涡轮反应器搅拌槽内流体混合过程的速度场和浓度场,研究物料在搅拌槽内的混合过程,以及不同监测点对混合时间的影响。结果表明,搅拌槽内物料的混合主要受槽内流体的流动形式所影响;混合时间的长短与监测点位置有关;在搅拌桨的桨叶附近进行监测所得到的混合时间较短,在液面附近进行监测所得的混合时间较长。在实际生产和试验中,应注意对监测点位置的选取。  相似文献   
98.
Reducing CIC filter complexity   总被引:1,自引:0,他引:1  
This paper provides several tricks to reduce the complexity and enhance the usefulness of cascaded integrator-comb (CIC) filters. The first trick shows a way to reduce the number of adders and delay elements in a multi-stage CIC interpolation filter. The result is a multiplierless scheme that performs high-order linear interpolation using CIC filters. The second trick shows a way to eliminate the integrators from CIC decimation filters. The benefit is the elimination of unpleasant data word growth problems.  相似文献   
99.
We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere.  相似文献   
100.
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   
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