全文获取类型
收费全文 | 427672篇 |
免费 | 6779篇 |
国内免费 | 1424篇 |
专业分类
电工技术 | 7892篇 |
综合类 | 369篇 |
化学工业 | 64842篇 |
金属工艺 | 14669篇 |
机械仪表 | 12187篇 |
建筑科学 | 12455篇 |
矿业工程 | 971篇 |
能源动力 | 11635篇 |
轻工业 | 45062篇 |
水利工程 | 3437篇 |
石油天然气 | 1899篇 |
武器工业 | 13篇 |
无线电 | 56585篇 |
一般工业技术 | 79279篇 |
冶金工业 | 77727篇 |
原子能技术 | 5669篇 |
自动化技术 | 41184篇 |
出版年
2021年 | 2916篇 |
2019年 | 2663篇 |
2018年 | 4139篇 |
2017年 | 4212篇 |
2016年 | 4492篇 |
2015年 | 3696篇 |
2014年 | 6139篇 |
2013年 | 20310篇 |
2012年 | 10867篇 |
2011年 | 15592篇 |
2010年 | 11938篇 |
2009年 | 13586篇 |
2008年 | 14659篇 |
2007年 | 14973篇 |
2006年 | 13385篇 |
2005年 | 12555篇 |
2004年 | 12041篇 |
2003年 | 11694篇 |
2002年 | 11316篇 |
2001年 | 11398篇 |
2000年 | 10516篇 |
1999年 | 11036篇 |
1998年 | 24289篇 |
1997年 | 17826篇 |
1996年 | 14171篇 |
1995年 | 11214篇 |
1994年 | 9991篇 |
1993年 | 9565篇 |
1992年 | 7337篇 |
1991年 | 6919篇 |
1990年 | 6590篇 |
1989年 | 6273篇 |
1988年 | 5996篇 |
1987年 | 5017篇 |
1986年 | 4957篇 |
1985年 | 6125篇 |
1984年 | 5752篇 |
1983年 | 4975篇 |
1982年 | 4628篇 |
1981年 | 4584篇 |
1980年 | 4324篇 |
1979年 | 4210篇 |
1978年 | 3875篇 |
1977年 | 4648篇 |
1976年 | 6225篇 |
1975年 | 3215篇 |
1974年 | 3103篇 |
1973年 | 2985篇 |
1972年 | 2388篇 |
1971年 | 2048篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Jeong-Soo Lee Yang-Kyu Choi Daewon Ha Balasubramanian S. Tsu-Jae King Bokor J. 《Electron Device Letters, IEEE》2003,24(3):186-188
The hydrogen annealing process has been used to improve surface roughness of the Si-fin in CMOS FinFETs for the first time. Hydrogen annealing was performed after Si-fin etch and before gate oxidation. As a result, increased saturation current with a lowered threshold voltage and a decreased low-frequency noise level over the entire range of drain current have been attained. The low-frequency noise characteristics indicate that the oxide trap density is reduced by a factor of 3 due to annealing. These results suggest that hydrogen annealing is very effective for improving device performance and for attaining a high-quality surface of the etched Si-fin. 相似文献
122.
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
123.
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
124.
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
125.
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
126.
Starting from a microscopic Hamiltonian defined on a semi-infinite cubic lattice, and employing a mean-field approximation, the surface parameters relevant for wetting in confined ternary mixtures are derived. These are found in terms of the microscopic coupling constants, and yield a physical interpretation of their origins. In comparison with the standard expression for the surface free-energy density, several new terms arising from the derivation are identified. The influence of the surface parameters on a predicted unbinding transition in a mixture of oil, water, and amphiphile demonstrate that existing results are robust to the addition of the extra surface terms. 相似文献
127.
An introduction to Web Services 总被引:1,自引:0,他引:1
Paul Muschamp 《BT Technology Journal》2004,22(1):9-18
This paper provides an introduction to Web Services. A brief history of Web Services is given, leading into an overview of
the key Web Services technologies. The paper describes the way in which the IT industry has embraced Web Services and the
uses to which the technologies are currently being applied. It concludes with a view of the role of both the key developers
and standards bodies in the creation of Web Services and discusses the ways in which this process needs to be supported in
order for Web Services to evolve.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
128.
The perceived locations of paired auditory images, simulating direct sounds and their echoes, have been recently studied in budgerigars (Melopsittacus undulatus; M. L. Dent & R. J. Dooling, 2003a, 2003b). In this article, the authors extend those experiments to include measurements of the precedence effect using a discrimination paradigm in two additional bird species: canaries (Serinus canaria) and zebra finches (Taeniopygia guttata). Although time courses of summing localization, localization dominance, and echo thresholds were similar across all species, budgerigars had slightly higher overall levels of discrimination. The results from these experiments add further support that the precedence effect in birds is similar to that found in other animals and that the ability to suppress echoes that might degrade localization and auditory object perception may be a general property of the vertebrate auditory system. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
129.
Thomas S. Lowry John C. Bright Murray E. Close Christina A. Robb Paul A. White Stewart G. Cameron 《国际水资源开发杂志》2003,19(4):579-592
The primary objective of this project is to identify gaps, whether real or perceived, that hinder effective groundwater management in New Zealand. These gaps show as gaps in information, gaps in implementation, gaps in technological and management tools, and gaps in understanding of fundamental processes. The secondary objective is to propose a management strategy to close the identified gaps. Several methods are used to meet these objectives: surveys distributed to selected staff in each regional council; the review of various written reports; the analysis of land-use databases; and private consultation within each regional council. Results show that groundwater management in New Zealand is generally reactionary with the main gaps being in strategic planning and national guidelines. Most gaps appear to be predominantly information and implementation issues. In some cases there are gaps in the understanding of fundamental processes within an aquifer system, including the long-term effects of land-use on groundwater quality. An adaptive management approach is suggested as a means of closing these gaps. 相似文献
130.