全文获取类型
收费全文 | 428111篇 |
免费 | 6344篇 |
国内免费 | 1427篇 |
专业分类
电工技术 | 7892篇 |
综合类 | 369篇 |
化学工业 | 64843篇 |
金属工艺 | 14671篇 |
机械仪表 | 12187篇 |
建筑科学 | 12456篇 |
矿业工程 | 972篇 |
能源动力 | 11635篇 |
轻工业 | 45061篇 |
水利工程 | 3437篇 |
石油天然气 | 1898篇 |
武器工业 | 13篇 |
无线电 | 56585篇 |
一般工业技术 | 79283篇 |
冶金工业 | 77725篇 |
原子能技术 | 5670篇 |
自动化技术 | 41185篇 |
出版年
2021年 | 2919篇 |
2019年 | 2662篇 |
2018年 | 4140篇 |
2017年 | 4213篇 |
2016年 | 4493篇 |
2015年 | 3696篇 |
2014年 | 6139篇 |
2013年 | 20311篇 |
2012年 | 10867篇 |
2011年 | 15592篇 |
2010年 | 11938篇 |
2009年 | 13587篇 |
2008年 | 14660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 | 11035篇 |
1998年 | 24289篇 |
1997年 | 17826篇 |
1996年 | 14172篇 |
1995年 | 11213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 | 4958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 | 3874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
61.
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
62.
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
63.
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
64.
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
65.
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
66.
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
67.
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
68.
69.
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
70.
Martin F. Falcone F. Bonache J. Marques R. Sorolla M. 《Microwave and Wireless Components Letters, IEEE》2003,13(12):511-513
A novel compact stop band filter consisting of a 50 /spl Omega/ coplanar waveguide (CPW) with split ring resonators (SRRs) etched in the back side of the substrate is presented. By aligning SRRs with the slots, a high inductive coupling between line and rings is achieved, with the result of a sharp and narrow rejection band in the vicinity of the resonant frequency of the rings. In order to widen the stop band of the filter, several ring pairs tuned at equally spaced frequencies within the desired gap are cascaded. The frequency response measured in the fabricated prototype device exhibits pronounced slopes at either side of the stop band and near 0 dBs insertion loss outside that band. Since SRR dimensions are much smaller than signal wavelength, the proposed filters are extremely compact and can be used to reject frequency parasitics in CPW structures by simply patterning properly tuned SRRs in the back side metal. Additional advantages are easy fabrication and compatibility with MMIC or PCB technology. 相似文献