全文获取类型
收费全文 | 476727篇 |
免费 | 5631篇 |
国内免费 | 1572篇 |
专业分类
电工技术 | 9221篇 |
综合类 | 516篇 |
化学工业 | 68370篇 |
金属工艺 | 18241篇 |
机械仪表 | 14791篇 |
建筑科学 | 11477篇 |
矿业工程 | 1836篇 |
能源动力 | 12709篇 |
轻工业 | 39960篇 |
水利工程 | 4431篇 |
石油天然气 | 6540篇 |
武器工业 | 80篇 |
无线电 | 63223篇 |
一般工业技术 | 92246篇 |
冶金工业 | 90409篇 |
原子能技术 | 9518篇 |
自动化技术 | 40362篇 |
出版年
2021年 | 3882篇 |
2020年 | 2894篇 |
2019年 | 3639篇 |
2018年 | 6214篇 |
2017年 | 6306篇 |
2016年 | 6605篇 |
2015年 | 4232篇 |
2014年 | 7405篇 |
2013年 | 21303篇 |
2012年 | 11744篇 |
2011年 | 16165篇 |
2010年 | 12842篇 |
2009年 | 14572篇 |
2008年 | 15603篇 |
2007年 | 15487篇 |
2006年 | 13956篇 |
2005年 | 12507篇 |
2004年 | 12110篇 |
2003年 | 12214篇 |
2002年 | 11423篇 |
2001年 | 11850篇 |
2000年 | 11189篇 |
1999年 | 11736篇 |
1998年 | 29042篇 |
1997年 | 20403篇 |
1996年 | 15787篇 |
1995年 | 12145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 | 5901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 | 6783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 9 毫秒
81.
K. N. Subramanian J. G. Lee 《Journal of Materials Science: Materials in Electronics》2004,15(4):235-240
Properties of body centered tetragonal tin are highly anisotropic. As a consequence large stresses can develop at the tin grain boundaries due to coefficient of thermal expansion mismatch during temperature excursions. A modeling approach to evaluate the 3D stress states that develop at grain boundaries during thermomechanical fatigue in tin-based solder is presented. Development of significant amounts of stresses in the plane of the grain boundary can cause grain-boundary sliding and surface-relief effects, while those normal to the grain boundary can cause grain-boundary decohesion and cracking. 相似文献
82.
Hambleton P.J. Ng B.K. Plimmer S.A. David J.P.R. Rees G.J. 《Electron Devices, IEEE Transactions on》2003,50(2):347-351
The nonlocal enhancement in the velocities of charge carriers to ionization is shown to outweigh the opposing effects of dead space, increasing the avalanche speed of short avalanche photodiodes (APDs) over the predictions of a conventional local model which ignores both of these effects. The trends in the measured gain-bandwidth product of two short InAlAs APDs reported in the literature support this result. Relatively large speed benefits are predicted to result from further small reductions in the lengths of short multiplication regions. 相似文献
83.
T. Choi J.‐H. Jang C.K. Ullal M.C. LeMieux V.V. Tsukruk E.L. Thomas 《Advanced functional materials》2006,16(10)
The probing of the micromechanical properties within a two‐dimensional polymer structure with sixfold symmetry fabricated via interference lithography reveals a nonuniform spatial distribution in the elastic modulus “imprinted” with an interference pattern in work reported by Tsukruk, Thomas, and co‐workers on p. 1324. The image prepared by M. Lemieux and T. Gorishnyy shows how the interference pattern is formed by three laser beams and is transferred to the solid polymer structure. The elastic and plastic properties within a two‐dimensional polymer (SU8) structure with sixfold symmetry fabricated via interference lithography are presented. There is a nonuniform spatial distribution in the elastic modulus, with a higher elastic modulus obtained for nodes (brightest regions in the laser interference pattern) and a lower elastic modulus for beams (darkest regions in the laser interference pattern) of the photopatterned films. We suggest that such a nonuniformity and unusual plastic behavior are related to the variable material properties “imprinted” by the interference pattern. 相似文献
84.
Suetsugu T. Kazimierczuk M.K. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(7):1468-1476
Design equations for satisfying the off-nominal operating condition [i.e., only the zero-voltage switching (ZVS) condition] of the Class-E amplifier with a linear shunt capacitance at a duty ratio D=0.5 are derived. A new parameter s (V/s), called the slope of switch voltage when the switch turns on is introduced to obtain an image of the distance from the nominal conditions. By examining off-nominal Class-E operation degree of the design freedom of the Class-E amplifier increases by one. In addition various amplifier parameters such as operating frequency, output power, and load resistance range can be set as design specifications. For example, the peak switch voltage and switch current can be taken into account in the design procedure. Examples of a design procedure of the Class-E amplifier for off-nominal operation are given. The theoretical results were verified with PSpice simulation and experiments. 相似文献
85.
86.
Mobile devices are vulnerable to theft and loss due to their small size and the characteristics of their common usage environment. Since they allow users to work while away from their desk, they are most useful in public locations and while traveling. Unfortunately, this is also where they are most at risk. Existing schemes for securing data either do not protect the device after it is stolen or require bothersome reauthentication. Transient Authentication lifts the burden of authentication from the user by use of a wearable token that constantly attests to the user's presence. When the user departs, the token and device lose contact and the device secures itself. We show how to leverage this authentication framework to secure all the memory and storage locations on a device into which secrets may creep. Our evaluation shows this is done without inconveniencing the user, while imposing a minimal performance overhead 相似文献
87.
Takauchi H. Tamura H. Matsubara S. Kibune M. Doi Y. Chiba T. Anbutsu H. Yamaguchi H. Mori T. Takatsu M. Gotoh K. Sakai T. Yamamura T. 《Solid-State Circuits, IEEE Journal of》2003,38(12):2094-2100
We describe a CMOS multichannel transceiver that transmits and receives 10 Gb/s per channel over balanced copper media. The transceiver consists of two identical 10-Gb/s modules. Each module operates off a single 1.2-V supply and has a single 5-GHz phase-locked loop to supply a reference clock to two transmitter (Tx) channels and two receiver (Rx) channels. To track the input-signal phase, the Rx channel has a clock recovery unit (CRU), which uses a phase-interpolator-based timing generator and digital loop filter. The CRU can adjust the recovered clock phase with a resolution of 1.56 ps. Two sets of two-channel transceiver units were fabricated in 0.11-/spl mu/m CMOS on a single test chip. The transceiver unit size was 1.6 mm /spl times/ 2.6 mm. The Rx sensitivity was 120-mVp-p differential with a 70-ps phase margin for a common-mode voltage ranging from 0.6 to 1.0 V. The evaluated jitter tolerance curve met the OC-192 specification. 相似文献
88.
Web Services Architecture 总被引:1,自引:0,他引:1
K Mockford 《BT Technology Journal》2004,22(1):19-26
The underlying need for Web Services has been demonstrated by their early adoption and rapid evolution during the last few
years. This evolution has resulted in a number of specifications being proposed that at first glance seem independent of one
another. The current immaturity of the base technology and the growing number and diversity of specifications related to Web
Services is sometimes seen as a barrier to developers attempting to combine them to create a working piece of software. For
some, the apparent lack of stability and coherence in the specifications even raises the question of the real long-term viability
and value of the technology. This document puts those specifications into perspective by describing the set of interoperable
XML protocols that are the foundation of building interoperable systems, middleware, and applications.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
89.
In order to ascertain the metastable phase relation in the Cr2O3-Fe2O3 system, the existing phases were investigated by X-ray analysis using samples obtained by heating the coprecipitated powders for 1 h at 600–1000°C. There was a metastable two-phase region of Cr2O3-rich (CC) and Fe2O3-rich (FC) phases below about 940°C. Equilibrium state of 1:1 composition at 600–900°C was considered to be a single phase of the corundum solid solution. The metastable two-phase CC + FC region was suggested to appear probably due to the compositional inhomogeneity in the coprecipitated powders. 相似文献
90.
Mitchell A. Lech M. Kokotoff D.M. Waterhouse R.B. 《Antennas and Propagation, IEEE Transactions on》2003,51(2):249-255
High-performance circular probe-fed stacked patch antenna designs are explored through the use of numerical optimization. New trends are sought to aid understanding and to suggest novel solutions. We describe the optimization technique, present a new design trend relating efficiency and bandwidth to the choice of substrate dielectric, and propose and demonstrate a novel, optimized antenna achieving 33% bandwidth whilst maintaining greater than 80% surface wave efficiency. 相似文献