全文获取类型
收费全文 | 497745篇 |
免费 | 44171篇 |
国内免费 | 24749篇 |
专业分类
电工技术 | 33692篇 |
技术理论 | 76篇 |
综合类 | 58485篇 |
化学工业 | 61654篇 |
金属工艺 | 20275篇 |
机械仪表 | 28209篇 |
建筑科学 | 64963篇 |
矿业工程 | 26740篇 |
能源动力 | 19681篇 |
轻工业 | 30775篇 |
水利工程 | 27870篇 |
石油天然气 | 24985篇 |
武器工业 | 5756篇 |
无线电 | 31207篇 |
一般工业技术 | 36864篇 |
冶金工业 | 27451篇 |
原子能技术 | 5228篇 |
自动化技术 | 62754篇 |
出版年
2024年 | 1754篇 |
2023年 | 5599篇 |
2022年 | 10936篇 |
2021年 | 13683篇 |
2020年 | 13678篇 |
2019年 | 11228篇 |
2018年 | 10688篇 |
2017年 | 13210篇 |
2016年 | 15795篇 |
2015年 | 17150篇 |
2014年 | 30621篇 |
2013年 | 28163篇 |
2012年 | 34246篇 |
2011年 | 37329篇 |
2010年 | 28379篇 |
2009年 | 29310篇 |
2008年 | 27184篇 |
2007年 | 34283篇 |
2006年 | 31927篇 |
2005年 | 27992篇 |
2004年 | 23619篇 |
2003年 | 20912篇 |
2002年 | 17185篇 |
2001年 | 14455篇 |
2000年 | 12269篇 |
1999年 | 9836篇 |
1998年 | 7396篇 |
1997年 | 6455篇 |
1996年 | 5742篇 |
1995年 | 4841篇 |
1994年 | 4197篇 |
1993年 | 3116篇 |
1992年 | 2689篇 |
1991年 | 1924篇 |
1990年 | 1712篇 |
1989年 | 1497篇 |
1988年 | 1097篇 |
1987年 | 767篇 |
1986年 | 594篇 |
1985年 | 532篇 |
1984年 | 478篇 |
1983年 | 360篇 |
1982年 | 286篇 |
1981年 | 238篇 |
1980年 | 198篇 |
1979年 | 150篇 |
1978年 | 83篇 |
1977年 | 91篇 |
1975年 | 72篇 |
1959年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 243 毫秒
991.
River ice jams are a common occurrence on northern rivers, and their formation can present a severe flood risk to nearby communities. As more and more river regulation projects are developed to provide an alternative to fossil fuels for electrical power-generating capacity, our need to understand the mechanisms associated with ice jam formation under variable flow conditions becomes more vital. This is because, at present, hydropeaking operations are often severely curtailed during the ice-affected seasons due to concerns that sudden flow fluctuations might instigate ice jams and associated flooding. Here, an experimental investigation explores the effects of rapid increases in discharge on ice jam formation and evolution. It is found that the thickness of ice jams formed under highly dynamic flow conditions tend to be slightly thinner than those formed during steady carrier flows for comparable discharges. Also, despite the highly dynamic nature of these consolidation events, the resulting ice thicknesses appear reasonably well approximated by steady flow theory. 相似文献
992.
Emergency department status boards: user-evolved artefacts for inter- and intra-group coordination 总被引:1,自引:1,他引:0
Robert L. Wears Shawna J. Perry Stephanie Wilson Julia Galliers James Fone 《Cognition, Technology & Work》2007,9(3):163-170
Large, easily viewed status boards are commonly used in some healthcare settings such as emergency departments, operating
theaters, intensive care units, and inpatient wards. Because these artefacts were developed by front-line users, and have
little to no supervisory or regulatory control, they offer valuable insights into the theories of work and hazard held by
those users. Although the status boards case were locally developed over many years for within-group coordination, they have
also become useful for between-group coordination across organizational boundaries. In this paper, we compare and contrast
the use of such status boards in two disparate settings: a US emergency department, and a UK pediatric ward, and note striking
similarities in their form and usage, despite the large differences in setting. 相似文献
993.
Georgios D. Styliaras Georgios K. Tsolis Chris M. Papaterpos 《International Journal on Digital Libraries》2007,8(1):61-78
In this paper, AssetCollector is presented, which is a system for managing collections of cultural assets. AssetCollector
covers the needs of collection curators towards defining, populating and searching a collection in a flexible way, while supporting
them in generating reports based on the collection’s assets and reusing them in order to build web sites and CD-ROMs. In order
to support the above functionality, the system provides the content structuring subsystem, the content input subsystem, the
search subsystem and the report subsystem. The use of the subsystems is straightforward and requires no technical skills from
the curators. AssetCollector has been successfully applied for organizing various collections of cultural assets in Greece,
such as archaeological sites, museums and published books. In the future, an evaluation procedure is planned in order to further
refine the use of the system according to the targeted users’ needs. Furthermore, more import and export facilities will be
provided, which will make the system compliant with widely accepted standards. 相似文献
994.
Jules Sadefo Kamdem 《Computing and Visualization in Science》2007,10(4):197-210
In this paper, we generalize the Linear VaR method from portfolios with normally distributed risk factors to portfolios with
mixture of elliptically distributed ones. We treat both the Expected Shortfall and the Value-at-Risk of such portfolios. Special
attention is given to the particular case of a mixture of multivariate t-distributions.
This is a part of J. SADEFO-KAMDEM PhD Thesis[12] of the Université de Reims, France . It has been presented at the workshop
on modelling and computation in Financial Engineering at Bad Herrenalb, Germany May 6-8, 2003. The author is an associate
professor at the Department of mathematics, université d’Evry Val d’Essonne. 相似文献
995.
Discussed in this paper is the Cartesian stiffness matrix, which recently has received special attention within the robotics
research community. Stiffness is a fundamental concept in mechanics; its representation in mechanical systems whose potential
energy is describable by a finite set of generalized coordinates takes the form of a square matrix that is known to be, moreover,
symmetric and positive-definite or, at least, semi-definite. We attempt to elucidate in this paper the notion of “asymmetric
stiffness matrices”. In doing so, we show that to qualify for a stiffness matrix, the matrix should be symmetric and either
positive semi-definite or positive-definite. We derive the conditions under which a matrix mapping small-amplitude displacement
screws into elastic wrenches fails to be symmetric. From the discussion, it should be apparent that the asymmetric matrix
thus derived cannot be, properly speaking, a stiffness matrix. The concept is illustrated with an example. 相似文献
996.
Hitsman Brian; Borrelli Belinda; McChargue Dennis E.; Spring Bonnie; Niaura Raymond 《Canadian Metallurgical Quarterly》2003,71(4):657
The authors conducted a meta-analysis of published studies to (a) evaluate the premise that a history of major depression is associated with failure to quit smoking and (b) identify factors that moderate the relationship between history of depression and cessation outcome. Fifteen studies met the selection requirements and were coded for various study methodology and treatment characteristics. DSTAT was used to calculate individual study effect sizes, determine the mean effect size across studies. and test for moderator effects. No differences in either short-term (≤ 3 months) or long-term abstinence rates (≥ 6 months) were observed between smokers positive versus negative for history of depression. Lifetime history of major depression does not appear to be an independent risk factor for cessation failure in smoking cessation treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
997.
998.
基于Matlab/Simulink的机械工程控制系统仿真 总被引:6,自引:1,他引:5
通过列举一些实例 ,分析了Matlab/Simulink软件在机械工程控制系统仿真中的应用 ,能够简化编程 ,取得了很好的效果。 相似文献
999.
中国硬质合金工业现状及发展趋势 总被引:7,自引:2,他引:5
简要总结了中国硬质合金工业所取得的成就及与国外先进水平比较存在的差距,并对国内外硬质合金市场和技术发展趋势进行了分析。 相似文献
1000.
《中国科学E辑(英文版)》2005,(Z2)
All image systems cause a blurring of the scene radiance field during image acquisi- tion. Accurate characterization of this blurring is referred to as the modulation transfer function (MTF)[1]. The MTF is a fundamental imaging system design specification and system quality metric often used in remote sensing. It results from the cumulative effects of the instrumental optics (diffraction, aberrations, focusing error), integration on a pho- tosensitive surface, charge diffusion along the arra… 相似文献