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   92141篇
  免费   13999篇
  国内免费   201篇
电工技术   1579篇
综合类   99篇
化学工业   26684篇
金属工艺   2405篇
机械仪表   3753篇
建筑科学   2885篇
矿业工程   55篇
能源动力   2919篇
轻工业   10577篇
水利工程   530篇
石油天然气   255篇
武器工业   1篇
无线电   15625篇
一般工业技术   21029篇
冶金工业   6387篇
原子能技术   633篇
自动化技术   10925篇
  2023年   533篇
  2022年   846篇
  2021年   1596篇
  2020年   2262篇
  2019年   3835篇
  2018年   4130篇
  2017年   4387篇
  2016年   5095篇
  2015年   4803篇
  2014年   5483篇
  2013年   7975篇
  2012年   5615篇
  2011年   6033篇
  2010年   5354篇
  2009年   5431篇
  2008年   4775篇
  2007年   4226篇
  2006年   3754篇
  2005年   3179篇
  2004年   3066篇
  2003年   2887篇
  2002年   2793篇
  2001年   2297篇
  2000年   2199篇
  1999年   1600篇
  1998年   2259篇
  1997年   1485篇
  1996年   1231篇
  1995年   981篇
  1994年   744篇
  1993年   706篇
  1992年   503篇
  1991年   509篇
  1990年   432篇
  1989年   407篇
  1988年   328篇
  1987年   280篇
  1986年   264篇
  1985年   237篇
  1984年   204篇
  1983年   155篇
  1982年   154篇
  1981年   132篇
  1980年   132篇
  1979年   104篇
  1978年   96篇
  1977年   124篇
  1976年   161篇
  1975年   81篇
  1974年   75篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
In a high-resolution flat panel system, a conventional interface that directly connects a liquid crystal display (LCD) controller to a flat panel cannot overcome the problems of excess EMI (electromagnetic interference) and power caused by full-swing transmission signals in parallel lines. This paper presents a high-speed digital video interface system implemented with a low-cost standard CMOS (complimentary metal-oxide-semiconductor) technology that can mitigate EMI and power problems in high-resolution flat panel display systems. The combined architecture of the high-speed, small number of parallel lines and low-voltage swing serial interface can support resolutions from VGA (640×480 pixels) up to XGA (1024×768 pixels) with significant power improvement and drastic EMI reduction. To support high-speed, low-voltage swing signaling and overcome channel-to-channel skew problems, a robust data recovery system is required. The proposed digital phase-locked loop enables robust skew-insensitive data recovery of up to 1.04 GBd  相似文献   
992.
Fast DCT algorithm with fewer multiplication stages   总被引:1,自引:0,他引:1  
A novel fast DCT scheme with reduced multiplication stages and fewer additions and multiplications is proposed. The proposed algorithm is structured so that most multiplications tend to be performed at the final stage, which reduces the propagation error that could occur in the fixed-point computation. Minimisation of the multiplication stages can further decrease the error  相似文献   
993.
Motion based object tracking with mobile camera   总被引:4,自引:0,他引:4  
An efficient algorithm which detects and tracks a moving object is proposed. The global motion energy caused by camera movement is eliminated by finding the maximal matching position with the cross-correlation value between two consecutive frames using the spiral scanning technique. The region of a moving object is segmented exactly by combining the results of the temporal derivatives and edge map from one image, and the actual centroid of the moving object is determined as the mid-point of the cumulative distribution of the projection profile of the region  相似文献   
994.
The new generation of engineering professionals needs to know not only the scientific and engineering principles, but also have extensive knowledge about arts, literature, and social sciences. They need far-reaching vision for the future in order to understand grand challenges on the technical-level, the system-level, and the social aspects of topics that are of importance to the modern society. One solution is to emphasize fundamental courses such as mathematics and physics with new interpretation to correlate with real-world applications. It is important to include system-oriented topics in the curriculum so that students know how to apply the basic principles, The key focus should be placed on analysis and design skills, and effective communication is essential to address any large-scale problems  相似文献   
995.
Thermooptic 2×2 switches based on low-loss fluorinated polymer waveguides have been demonstrated. For the waveguide possessing a low-loss around the 1.55-μm wavelength, crosslinkable fluorinated poly(arylene ethers) (FPAE) is developed as a core material and perfluorocyclobutane (PFCB) is used as a cladding material. To enhance the fabrication tolerance and to achieve a low switching power, asymmetric X-junctions with a Mach-Zehnder interferometer are exploited for the polymeric waveguide switches. An inverted rib waveguide structure is fabricated by filling up the etched groove on a lower cladding with the core polymer. The switch exhibits a crosstalk of less than -20 dB, a switching power of 10 mW, and an insertion loss of 4.5 dB  相似文献   
996.
Simons  R.N. Lee  R.Q. 《Electronics letters》1998,34(24):2287-2289
A new impedance matching technique for tapered slot antennas using a dielectric transformer is presented. The technique is demonstrated by measuring the input impedance, VSWR and the gain of a Vivaldi antenna (VA). Measured results at Ka-band frequencies are presented and discussed  相似文献   
997.
Robust backward adaptive formant prediction for speech coder   总被引:1,自引:0,他引:1  
Lee  I. Gibson  J.D. 《Electronics letters》1998,34(24):2314-2315
To improve the error performance of speech coders, an adaptation method for the backward adapted formant predictor is proposed. The filtered residual signal is used instead of the reconstructed output signal as the input to an adaptation of the formant predictor. The performance of the filtered-residual driven adaption method in the noise free channel is as good as that of conventional output driven adaptation. Moreover, the new adaptation method maintains the same robustness to channel errors as residual driven adaptation  相似文献   
998.
A frequency tunable active leaky-wave scanning antenna using Gunn-diode voltage control oscillator (VCO) as source is developed. The frequency tuning controlled by changing either the varactor diode dc bias or the Gunn diode dc bias is demonstrated. The measured scanning angle of active antenna is close to 15 degree as the Gunn VCO frequency tuned from 12.58GHz to 12.98GHz. To excite the first higher order mode of the microstrip leaky-wave antenna is fed asymmetrically. The dominant mode excitation has been successfully suppressed by adding a sequence of covered wire in the middle line of the microstrip leaky wave antenna. This is a prototype of frequency scanning antenna using two terminal device, which can be easily scaled up to millimeter wave frequency region.  相似文献   
999.
We searched numerically dielectric-loaded cylindrical waveguide configurations with an injected electron beam in which the growth rate of the cyclotron-Cherenkov instability surpassed that of the Cherenkov instability, and found such a configuration. This configuration consists of a metallic core and an outer metallic cylinder with a dielectric liner on the inner surface. In order to investigate experimentally radiation due to the cyclotron-Cherenkov instability, we designed and assembled an experimental device using the computational results. We studied beam propagation in the dielectric-loaded coaxial waveguide and microwave radiation due to the cyclotron-Cherenkov instability and the Cherenkov instability.  相似文献   
1000.
The current approaches in Object-Oriented Analysis have limitations on modeling complex real world systems because they require priori knowledge about objects and their interactions before applying them. This may be practical in small systems and systems with clear domain knowledge, but not in large real world systems with unclear domain knowledge. Our approach uses a stepwise refinement technique in a top-down manner to the Object-Oriented Analysis stage with the application of use cases. This approach is especially good for new areas where we do not know all the information in advance. We present the approach with an example of its application to the B-ISDN service modeling and distributed systems.  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