全文获取类型
收费全文 | 621874篇 |
免费 | 8043篇 |
国内免费 | 2494篇 |
专业分类
电工技术 | 11231篇 |
综合类 | 880篇 |
化学工业 | 92654篇 |
金属工艺 | 22867篇 |
机械仪表 | 18104篇 |
建筑科学 | 16192篇 |
矿业工程 | 2622篇 |
能源动力 | 16076篇 |
轻工业 | 58145篇 |
水利工程 | 6160篇 |
石油天然气 | 7419篇 |
武器工业 | 56篇 |
无线电 | 77570篇 |
一般工业技术 | 118674篇 |
冶金工业 | 115765篇 |
原子能技术 | 11865篇 |
自动化技术 | 56131篇 |
出版年
2021年 | 4429篇 |
2019年 | 4108篇 |
2018年 | 6734篇 |
2017年 | 6868篇 |
2016年 | 7330篇 |
2015年 | 5430篇 |
2014年 | 9047篇 |
2013年 | 28252篇 |
2012年 | 15378篇 |
2011年 | 21815篇 |
2010年 | 16859篇 |
2009年 | 19287篇 |
2008年 | 20387篇 |
2007年 | 20732篇 |
2006年 | 18290篇 |
2005年 | 16992篇 |
2004年 | 16816篇 |
2003年 | 16449篇 |
2002年 | 15875篇 |
2001年 | 15890篇 |
2000年 | 14788篇 |
1999年 | 15488篇 |
1998年 | 36199篇 |
1997年 | 26246篇 |
1996年 | 20373篇 |
1995年 | 15901篇 |
1994年 | 14103篇 |
1993年 | 13831篇 |
1992年 | 10221篇 |
1991年 | 9819篇 |
1990年 | 9368篇 |
1989年 | 9077篇 |
1988年 | 8598篇 |
1987年 | 7507篇 |
1986年 | 7502篇 |
1985年 | 8802篇 |
1984年 | 8196篇 |
1983年 | 7279篇 |
1982年 | 6830篇 |
1981年 | 6829篇 |
1980年 | 6562篇 |
1979年 | 6324篇 |
1978年 | 6054篇 |
1977年 | 7081篇 |
1976年 | 9514篇 |
1975年 | 5146篇 |
1974年 | 4969篇 |
1973年 | 4893篇 |
1972年 | 4051篇 |
1971年 | 3544篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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
92.
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
93.
必须利用水库多蓄水,另外再通过回灌把水蓄在含水层中供缺水时使用。城市废水也是一种重要水资源,但.必须加强规划和管理以防止造成对健康的负面影响,用于灌溉时则应防止污染地下水。长期以来地下水不仅受到非点源污染,还因对其开采超过回灌导致含水层减少。在灌区,地下水位必须通过排水或抽水系统加以控制,以防止水涝和土壤盐碱化。含盐的水排出后必须妥善处置。缺水的国家可以通过从其他国家进口大部分粮食和电力来节水,这往往比开发本国的水资源划算。本地水源就可用于更具社会、生态或经济回报的用途.或以备不时之需。 相似文献
94.
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
95.
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
96.
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
97.
98.
99.
100.
Sheldon H. Jacobson Julie L. Virta Jon M. Bowman John E. Kobza John J. Nestor 《IIE Transactions》2003,35(3):259-269
Aviation security protects vital national interests, as well as passengers and aircraft. Key components of an aviation security system include baggage and passenger screening devices and operations. Determining how and where to assign (deploy) such devices can be quite challenging. Moreover, even after such systems are in place, it can be difficult to measure their effectiveness. This paper describes how discrete optimization models can be used to address these questions, based on three performance measures that quantify the effectiveness of airport baggage screening security device systems. These models are used to solve for optimal airport baggage screening security device deployments considering the number of passengers on a set of flights who have not been cleared using a security risk assessment system in use by the Federal Aviation Administration (i.e., passengers whose baggage is subjected to screening), the number of flights in this set, and the size of the aircraft for such flights. Several examples are provided to illustrate these results, including an example that uses data available from the Official Airline Guide. 相似文献