全文获取类型
收费全文 | 338719篇 |
免费 | 30816篇 |
国内免费 | 16580篇 |
专业分类
电工技术 | 22305篇 |
技术理论 | 30篇 |
综合类 | 31930篇 |
化学工业 | 46266篇 |
金属工艺 | 19574篇 |
机械仪表 | 20399篇 |
建筑科学 | 42079篇 |
矿业工程 | 18630篇 |
能源动力 | 14967篇 |
轻工业 | 23583篇 |
水利工程 | 14283篇 |
石油天然气 | 21449篇 |
武器工业 | 4430篇 |
无线电 | 22827篇 |
一般工业技术 | 29092篇 |
冶金工业 | 18278篇 |
原子能技术 | 3681篇 |
自动化技术 | 32312篇 |
出版年
2024年 | 1591篇 |
2023年 | 4612篇 |
2022年 | 8761篇 |
2021年 | 11150篇 |
2020年 | 11281篇 |
2019年 | 8712篇 |
2018年 | 8215篇 |
2017年 | 10482篇 |
2016年 | 12025篇 |
2015年 | 12871篇 |
2014年 | 22202篇 |
2013年 | 20656篇 |
2012年 | 24737篇 |
2011年 | 26948篇 |
2010年 | 19511篇 |
2009年 | 19797篇 |
2008年 | 17872篇 |
2007年 | 22138篇 |
2006年 | 20354篇 |
2005年 | 17335篇 |
2004年 | 14846篇 |
2003年 | 12657篇 |
2002年 | 10534篇 |
2001年 | 8853篇 |
2000年 | 7488篇 |
1999年 | 5939篇 |
1998年 | 4478篇 |
1997年 | 3898篇 |
1996年 | 3238篇 |
1995年 | 2674篇 |
1994年 | 2300篇 |
1993年 | 1565篇 |
1992年 | 1359篇 |
1991年 | 1028篇 |
1990年 | 855篇 |
1989年 | 716篇 |
1988年 | 454篇 |
1987年 | 329篇 |
1986年 | 272篇 |
1985年 | 286篇 |
1984年 | 209篇 |
1983年 | 170篇 |
1982年 | 114篇 |
1981年 | 103篇 |
1980年 | 118篇 |
1979年 | 75篇 |
1978年 | 26篇 |
1977年 | 33篇 |
1976年 | 21篇 |
1959年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A. F. Kurbatskii 《High Temperature》2004,42(1):79-87
The difference in the turbulent diffusion between the active (heat) and passive (mass) scalars in a thermally stably stratified medium is investigated. The axisymmetric problem is treated on the formation of a turbulent circulation flow above a heated disk and on the turbulent diffusion of a passive scalar (impurity) from a continuous surface source in a stably stratified medium. The results indicate that the thermal stratification causes appreciable differences in the coefficients of turbulent transfer between the active (heat) and passive (mass) scalars. This means that the assumption of the identity of the coefficient of turbulent diffusion of heat and mass, employed in conventional models of turbulence, produces significant errors in estimating the heat and mass transfer in a thermally stably stratified medium. 相似文献
102.
D. Roy 《International journal for numerical methods in engineering》2004,61(5):764-790
Sample pathwise numerical integration of noise-driven engineering dynamical systems cannot generally be performed beyond a limited level of accuracy, especially when the noise processes are modelled using (filtered) white noises. Recently, a locally transversal linearization (LTL) strategy has been proposed by the author (Proc Roy Soc London A 2001; 457 :539–566) for direct integration of deterministic and stochastic non-linear dynamical systems. The present effort is focussed on a host of extensions along with detailed theoretical error analyses of the linearization approach, especially as applied to problems in non-linear stochastic engineering dynamics. Thus, to begin with, estimates of local and global error orders in the basic LTL scheme are obtained separately for the displacement and velocity vectors when the system is driven either by a set of additive noises or by an arbitrary combination of (independently evolving) additive and multiplicative noises. Following this, a new family of higher-order LTL schemes is proposed in order to improve upon the basic LTL method and the associated error orders are established. A stepwise implementation of the lower- and higher-order versions of the LTL method, along with certain computational aspects, is also outlined. The proposed schemes are numerically illustrated, to a limited extent, for a single degree-of-freedom (SDOF) and a two degree-of-freedom (TDOF) non-linear engineering systems under additive and/or multiplicative white noise excitations. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
103.
陈继初 《湖南冶金职业技术学院学报》2003,(4)
会计政策选择类型在理论上大体可分为机会主义型和效率(或有效契约)型。会计政策选择具有效率性,但也为经理人员的机会主义行为打开了大门。在我国,由于企业缺乏一系列有效的激励约束机制,会计政策选择的机会主义仍然严重。为此,必须建立适合我国企业有效的激励约束机制。 相似文献
104.
105.
Christos Bouras Agisilaos Konidaris 《International Journal of Communication Systems》2005,18(2):119-142
Redundant data transfers over the Web, can be mainly attributed to the repeated transfers of unchanged data. Web caches and Web proxies are some of the solutions that have been proposed, to deal with the issue of redundant data transfers. In this paper we focus on the efficient estimation and reduction of redundant data transfers over the Web. We first prove that a vast amount of redundant data is transferred in Web pages that are considered to carry fresh data. We show this by following an approach based on Web page fragmentation and manipulation. Web pages are broken down to fragments, based on specific criteria. We then deal with these fragments as independent constructors of the Web page and study their change patterns independently and in the context of the whole Web page. After the fragmentation process, we propose solutions for dealing with redundant data transfers. This paper has been based on our previous work on ‘Web Components’ but also on related work by other researchers. It utilises a proxy based, client/server architecture, and imposes changes to the algorithms executed on the Proxy server and on clients. We show that our proposed solution can considerably reduce the amount of redundant data transferred on the Web. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
106.
107.
建立垂直管吸收器管内泡式吸收过程中传热传质的数学物理模型,对其泡式吸收过程进行数值研究,获得泡式吸收方式的一些传热传质特性,为吸收器的优化设计提供一定理论指导。 相似文献
108.
Comments on the article "A house divided? The psychology of red and blue America" by D. C. Seyle and M. L. Newman (see record 2006-11202-001). Seyle and Newman concluded that the red and blue metaphor is inaccurate and proposed a purple America strategy to better convey that the majority of people do not align themselves with political extremes. There is interdisciplinary agreement on this. Although not cited by Seyle and Newman, the findings by Professor Fiorina of Stanford University were reported by the APA Monitor on Psychology in its coverage of the 2005 APA State Leadership Conference (Murray Law, 2005). In contrast to their social psychological analysis, Seyle and Newman were incorrect in concluding that "[a]s psychologists, we are not in a position to change either the elements of the American political system that may spur this conflict or even the decisions made by pundits, politicians, and reporters about the terms they choose to use in political discussion" (p. 579). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
109.
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
110.
Compared to other fields of engineering, in mechanical engineering, the Discrete Element Method (DEM) is not yet a well known
method. Nevertheless, there is a variety of simulation problems where the method has obvious advantages due to its meshless
nature. For problems where several free bodies can collide and break after having been largely deformed, the DEM is the method
of choice. Neighborhood search and collision detection between bodies as well as the separation of large solids into smaller
particles are naturally incorporated in the method. The main DEM algorithm consists of a relatively simple loop that basically
contains the three substeps contact detection, force computation and integration. However, there exists a large variety of
different algorithms to choose the substeps to compose the optimal method for a given problem. In this contribution, we describe
the dynamics of particle systems together with appropriate numerical integration schemes and give an overview over different
types of particle interactions that can be composed to adapt the method to fit to a given simulation problem. Surface triangulations
are used to model complicated, non-convex bodies in contact with particle systems. The capabilities of the method are finally
demonstrated by means of application examples.
Commemorative Contribution. 相似文献