全文获取类型
收费全文 | 43181篇 |
免费 | 5555篇 |
国内免费 | 2241篇 |
专业分类
电工技术 | 2434篇 |
技术理论 | 5篇 |
综合类 | 2909篇 |
化学工业 | 6966篇 |
金属工艺 | 5354篇 |
机械仪表 | 3010篇 |
建筑科学 | 3872篇 |
矿业工程 | 2406篇 |
能源动力 | 1467篇 |
轻工业 | 3856篇 |
水利工程 | 1025篇 |
石油天然气 | 1333篇 |
武器工业 | 336篇 |
无线电 | 3567篇 |
一般工业技术 | 6260篇 |
冶金工业 | 3261篇 |
原子能技术 | 513篇 |
自动化技术 | 2403篇 |
出版年
2024年 | 175篇 |
2023年 | 1081篇 |
2022年 | 1318篇 |
2021年 | 1735篇 |
2020年 | 1841篇 |
2019年 | 1633篇 |
2018年 | 1380篇 |
2017年 | 1654篇 |
2016年 | 1683篇 |
2015年 | 1792篇 |
2014年 | 2709篇 |
2013年 | 2646篇 |
2012年 | 3153篇 |
2011年 | 3100篇 |
2010年 | 2302篇 |
2009年 | 2297篇 |
2008年 | 2023篇 |
2007年 | 2562篇 |
2006年 | 2378篇 |
2005年 | 2147篇 |
2004年 | 1717篇 |
2003年 | 1721篇 |
2002年 | 1409篇 |
2001年 | 1229篇 |
2000年 | 1030篇 |
1999年 | 819篇 |
1998年 | 673篇 |
1997年 | 516篇 |
1996年 | 434篇 |
1995年 | 366篇 |
1994年 | 321篇 |
1993年 | 236篇 |
1992年 | 176篇 |
1991年 | 142篇 |
1990年 | 137篇 |
1989年 | 107篇 |
1988年 | 62篇 |
1987年 | 49篇 |
1986年 | 29篇 |
1985年 | 40篇 |
1984年 | 36篇 |
1983年 | 25篇 |
1982年 | 25篇 |
1981年 | 10篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1959年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
91.
This paper reports the results of current fundamental research at the Department of Process Engineering, University of Miskolc on the processing of clean coal from Mecsek bituminous coal, Southern Hungary. The theoretical possibility of the separation of different petrographic components was proven experimentally and their liberation degree was determined based on the petrographic composition, flotation kinetic study of isolated components (groups of components), scanning electron microscopy and microprobe analyses. The mill with stirred ball media was chosen for the ultra-fine liberation of the coal components. It was revealed that along with the liberation of coal components, their surface oxidation and spontaneous agglomeration, entrapping the mineral impurities take place in ultra-fine grinding. This paper discusses the interfacial phenomena occurring in the ultra-fine grinding process and their influence on the flotation. The concept for the advanced preparation of clean coal was developed, tested and proved. The main steps of this concept are the ultra-fine liberation in the stirred-media mill, the de-agglomeration of flocs spontaneously formed during the ultra-fine grinding and the induced (hydrophobic) flocculation with the following two-step flotation in a flotation column. 相似文献
92.
93.
94.
Depression is a widespread disorder with devastating individual and societal consequences. Although a great deal of research and theory has focused on treatment of acute episodes, progress needs to be made in preventing the emergence of first episodes of the disorder. There has been considerable advancement in understanding psychological vulnerability factors associated with this mood disorder, especially on the basis of cognitive behavioural models and research findings based on this theoretical model. In this paper we review the concept of cognitive vulnerability, with a particular focus on what this body of research work suggests clinically for the prevention of depression. We outline, based on this science, what the effective ingredients of a prevention program could be. We also discuss some of the pragmatic aspects of developing an effective prevention program for depression. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
95.
96.
97.
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
98.
P.-Y. CHANG J.-M. YANG H. SEO H. T. HAHN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(12):1158-1171
The off‐axis fatigue cracking behaviour of notched fibre metal laminates under constant amplitude loading conditions was investigated experimentally and numerically. It was found that the off‐axis fatigue crack initiation life decreased as the off‐axis angles increased. This indicated that the off‐axis laminates raised the applied stress level in the aluminium (Al) layer and subsequently resulted in earlier cracking in the Al layer. The off‐axis fatigue crack initiation lives of notched fibre metal laminates were predicted using lamination theory and an energy‐based critical plane fatigue damage analysis from the literature. After a crack initiated in the Al layer, it was observed that the crack path angles of the off‐axis specimens were neither perpendicular to the fibre nor to the loading direction. A finite‐element model was established for predicting the crack path angles. 相似文献
99.
Crack closure in fibre metal laminates 总被引:1,自引:0,他引:1
H.M. PLOKKER R.C. ALDERLIESTEN R. BENEDICTUS 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(7):608-620
GLARE is a fibre metal laminate (FML) built up of alternating layers of S2-glass/FM94 prepreg and aluminium 2024-T3. The excellent fatigue behaviour of GLARE can be described with a recently published analytical prediction model. This model is based on linear elastic fracture mechanics and the assumption that a similar stress state in the aluminium layers of GLARE and monolithic aluminium result in the same crack growth behaviour. It therefore describes the crack growth with an effective stress intensity factor (SIF) range at the crack tip in the aluminium layers, including the effect of internal residual stress as result of curing and the stiffness differences between the individual layers. In that model, an empirical relation is used to calculate the effective SIF range, which had been determined without sufficiently investigating the effect of crack closure. This paper presents the research performed on crack closure in GLARE. It is assumed that crack closure in FMLs is determined by the actual stress cycles in the metal layers and that it can be described with the available relations for monolithic aluminium published in the literature. Fatigue crack growth experiments have been performed on GLARE specimens in which crack growth rates and crack opening stresses have been recorded. The prediction model incorporating the crack closure relation for aluminium 2024-T3 obtained from the literature has been validated with the test results. It is concluded that crack growth in GLARE can be correlated with the effective SIF range at the crack tip in the aluminium layers, if it is determined with the crack closure relation for aluminium 2024-T3 based on actual stresses in the aluminium layers. 相似文献
100.
应用比较几何的方法研究了完备非紧且具有特定曲率条件的黎曼流形,证明了在一定Pinching条件限制下,流形具有有限拓扑型或者微分同胚于R^n。 相似文献