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   192036篇
  免费   2507篇
  国内免费   731篇
电工技术   3489篇
综合类   113篇
化学工业   30999篇
金属工艺   8045篇
机械仪表   5418篇
建筑科学   5109篇
矿业工程   968篇
能源动力   5095篇
轻工业   17472篇
水利工程   1824篇
石油天然气   3284篇
武器工业   3篇
无线电   20827篇
一般工业技术   35540篇
冶金工业   36954篇
原子能技术   4451篇
自动化技术   15683篇
  2021年   1483篇
  2019年   1418篇
  2018年   2288篇
  2017年   2265篇
  2016年   2403篇
  2015年   1743篇
  2014年   2960篇
  2013年   8662篇
  2012年   4994篇
  2011年   7004篇
  2010年   5473篇
  2009年   6350篇
  2008年   6452篇
  2007年   6414篇
  2006年   5550篇
  2005年   5132篇
  2004年   4857篇
  2003年   4524篇
  2002年   4487篇
  2001年   4398篇
  2000年   4186篇
  1999年   4334篇
  1998年   10799篇
  1997年   7725篇
  1996年   5976篇
  1995年   4575篇
  1994年   3924篇
  1993年   3908篇
  1992年   2873篇
  1991年   2747篇
  1990年   2639篇
  1989年   2656篇
  1988年   2561篇
  1987年   2349篇
  1986年   2279篇
  1985年   2645篇
  1984年   2428篇
  1983年   2230篇
  1982年   2086篇
  1981年   2156篇
  1980年   2000篇
  1979年   2016篇
  1978年   1980篇
  1977年   2278篇
  1976年   2870篇
  1975年   1747篇
  1974年   1688篇
  1973年   1751篇
  1972年   1442篇
  1971年   1342篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem.  相似文献   
32.
33.
A monitor is proposed based on ultrasonic production when ionizing radiation passes through a medium. The recording element is a 0.2 mm aluminum plate mounted in a ceramic acoustic converter AC in the form of a wedge of thickness 2 mm. The low plate thickness minimizes the beam parameter distortion, while special technology used in the AC provides high sensitivity. The device has been calibrated in the proton beam from the ITEP accelerator at 200 MeV with 2·109–6·1010 particles in a pulse and a pulse length of 70 nsec.  相似文献   
34.
Analogue switch for very low-voltage applications   总被引:2,自引:0,他引:2  
A new analogue switch suitable for operation at very low-voltage supply in a standard CMOS technology is presented. The proposed switch is based on 'quasi-floating-gate' transistors and has a simple and compact structure. For illustrative purposes, two sample-and-hold circuits operating from a single supply voltage close to the threshold voltage of a transistor, and using the proposed technique, are presented. Experimental results obtained from prototypes in a 1.5 /spl mu/m CMOS technology are provided.  相似文献   
35.
A novel technique to form high-K dielectric of HfSiON by doping base oxide with Hf and nitridation with NH/sub 3/, sequentially, is proposed. The HfSiON gate dielectric demonstrates excellent device performances such as only 10% degradation of saturation drain current and almost 45 times of magnitude reduction in gate leakage compared with conventional SiO/sub 2/ gate at the approximately same equivalent oxide thickness. Additionally, negligible flatband voltage shift is achieved with this technique. Time-dependent dielectric breakdown tests indicate that the lifetime of HfSiON is longer than 10 years at V/sub dd/=2 V.  相似文献   
36.
Polycrystalline Cu(In,Ga)Se2 (CIGS) films with various ratios of Cu, In, and Ga were grown by codeposition of all elements in vacuum. The X-ray diffraction study showed that the films are single-phase and possess a chalcopyrite structure with predominant [112] orientation. The films exhibited a mirror smooth surface and had a close-packed structure composed of crystallites with clear faceting and a transverse size of 0.1–0.3 μm. Related surface barrier structures of the (In,Ag)/Cu(In,Ga)Se2 type were obtained and their spectra of the quantum efficiency of photoconversion were studied. The obtained structures can be used for optimization of the CIGS film technology.  相似文献   
37.
A new method has been developed for compressing the matrices that occur in most integral-equation-based computer programs. This method is easy to interface with existing computer programs, and allows them to run significantly faster and with significantly less memory. This method applies not only to electromagnetic and acoustic computation, but also to most programs involving a Green's function or any integral equation with a kernel having some smoothness properties. Our numerical computations, running on a high-end personal computer, have achieved compression ratios of fifty times, and compressed inversion of the matrices fifty times faster than by previous methods. For larger problems, solved on high-performance computers, these ratios would improve to about one thousand to one for larger moment method problems.  相似文献   
38.
The emerging software defined radio technologies will be an enabler for a new generation of dynamic wireless systems. It will also open up the possibility of allocating frequencies in a, more dynamic way than today. From an intersystem-interference point of view, this can cause unforeseen problems to occur due to the increased complexity in such applications. In such applications, a measure indicating whether or not a frequency band is possible to use from an electromagnetic interference point of view, must be found. A simple approach is to use the measured total average interference power within the receiver band. Since the interference impact on modern digital communication systems from an interference signal does not only depend on the power but also on the actual waveform of the interference signal, some kind of quality measure of the average-power approach would be convenient to use. In this paper, we introduce a simple quality measure of the average-power approach so that a rough adjustment for the interference-waveform properties can be done.  相似文献   
39.
This paper provides an overview of the main aspects of modern fluorescence microscopy. It covers the principles of fluorescence and highlights the key discoveries in the history of fluorescence microscopy. The paper also discusses the optics of fluorescence microscopes and examines the various types of detectors. It also discusses the signal and image processing challenges in fluorescence microscopy and highlights some of the present developments and future trends in the field.  相似文献   
40.
This paper presents a simple alternative for an electronic ballast operating in self-sustained oscillating mode with dimming capability for fluorescent lamps. A simple modification in one of the gate drivers side circuit allows the lamp to dim without compromising the simplicity, reliability, and low cost which characterize the self-oscillating electronic ballast (SOEB). A qualitative analysis is presented to explain the behavior of the proposed self-oscillating electronic ballast with dimming feature. In addition, the stability and the key equations for the design are derived using the extended Nyquist criterion and describing function method. Experimental results from two 40-W electronic ballasts are presented to demonstrate the performance and to validate the analysis carried out.  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