全文获取类型
收费全文 | 39163篇 |
免费 | 4946篇 |
国内免费 | 1936篇 |
专业分类
电工技术 | 1219篇 |
技术理论 | 8篇 |
综合类 | 2301篇 |
化学工业 | 14810篇 |
金属工艺 | 2798篇 |
机械仪表 | 915篇 |
建筑科学 | 2283篇 |
矿业工程 | 832篇 |
能源动力 | 2393篇 |
轻工业 | 2121篇 |
水利工程 | 290篇 |
石油天然气 | 2184篇 |
武器工业 | 152篇 |
无线电 | 1837篇 |
一般工业技术 | 8218篇 |
冶金工业 | 2796篇 |
原子能技术 | 356篇 |
自动化技术 | 532篇 |
出版年
2024年 | 235篇 |
2023年 | 994篇 |
2022年 | 1420篇 |
2021年 | 1470篇 |
2020年 | 1564篇 |
2019年 | 1468篇 |
2018年 | 1349篇 |
2017年 | 1536篇 |
2016年 | 1639篇 |
2015年 | 1509篇 |
2014年 | 2259篇 |
2013年 | 2411篇 |
2012年 | 2874篇 |
2011年 | 3108篇 |
2010年 | 2294篇 |
2009年 | 2341篇 |
2008年 | 1829篇 |
2007年 | 2316篇 |
2006年 | 2276篇 |
2005年 | 1900篇 |
2004年 | 1610篇 |
2003年 | 1462篇 |
2002年 | 1157篇 |
2001年 | 872篇 |
2000年 | 798篇 |
1999年 | 608篇 |
1998年 | 538篇 |
1997年 | 377篇 |
1996年 | 336篇 |
1995年 | 276篇 |
1994年 | 251篇 |
1993年 | 182篇 |
1992年 | 149篇 |
1991年 | 117篇 |
1990年 | 107篇 |
1989年 | 62篇 |
1988年 | 44篇 |
1987年 | 48篇 |
1986年 | 32篇 |
1985年 | 57篇 |
1984年 | 46篇 |
1983年 | 45篇 |
1982年 | 25篇 |
1981年 | 4篇 |
1980年 | 13篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1963年 | 1篇 |
1959年 | 5篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
101.
本文利用可控平均冷却速度的单向凝固实验炉测定了45号钢在不同平均冷却速度下的冷却曲线,由此得到其在凝固期间的平均冷却速度R,相应地测量了不同平均冷却速度下试样的二次枝晶臂间距S2,通过回归,得到了如下关系式:S2=727R-0.41,并将引式成功地应用于实际生产中。 相似文献
102.
本文对气相表面处理碳纤维的新工艺进行了系统研究。处理后的碳纤维强度、模量不下降,且其表面能、表面化学官能团含量明显增加;表面微晶结构变小,与环氧树脂复合后,层间剪切强度(LLSS)提高47%左右。本文还对复合材料断口的形态结构进行了分析,说明这种表面处理方法能有效改善碳纤维增强环氧树脂复合材料(CFRP)的界面粘结。 相似文献
103.
104.
105.
A theoretical model is presented to describe the effect of ion beam bombardment rate on the formation of tetrahedral amorphous carbon (ta-C) films. The critical ion energy, Ec, corresponding to a 50% sp3 content in the films, is found to be dependent on both the effective thermal resistance and the ion beam bombardment rate. In the model, the ‘window’ width in the ion energy scale for the formation of ta-C material increases with decreasing deposition rate and with a reduction in the effective thermal resistance, until limited by lower and upper boundary thresholds. Experimental data are reproduced by the model. The plasmon energy, which correlates with sp3 fraction, is found experimentally of be higher for lower deposition rate and smaller effective thermal resistance. Data points for high sp3 content ta-C films deposited on silicon substrates at room temperature occupy a region in the ion energy-deposition rate (E-r) diagram similar to that predicated from the theory. 相似文献
106.
107.
交联剂在碳/碳复合材料沥青基体中的作用 总被引:8,自引:1,他引:7
本文从C/C复合合材料的基体入手,分析了交联剂在沥青中的交联机理,并以此为基础对中温煤沥青在催化剂作用下进行交联反应。结果表明,交联剂在C/C复合材料基体中的交联作用非常明显,不仅基体本身的残碳率及耐热程度有很大提高,而且,以它制成的C/C复合材料的抗压强度也有显著增加。 相似文献
108.
F. Cœuret E. Oliveira Vilar E. Bezerra Cavalcanti 《Journal of Applied Electrochemistry》2002,32(10):1175-1182
The paper deals with carbon fibre cloth electrodes, employed in the fabrication of composite materials. The electrical conductivity of single bundles, groups of bundles and cloth is studied. Ohm's law applies to the electrical conduction in the direction of the fibre length, but bundle conductivity decreases with the number of fibres in the bundle. Electrochemical mass transfer between a flowing electrolyte and a cloth arranged as a flow-through or a flow-by porous electrode indicates the existence of double porosity in the material. Due to double porosity, only the external surface of the cloth works as an electrode. This finding shows that the material is not suitable for such an application. 相似文献
109.
It is demonstrated that glassy carbon powder can be thermochemically activated. During activation, a film with open pores is created on the glassy carbon particles. This film has a large internal surface area, which is accessible to liquids and gases. A simple model for the evolution of the internal surface area in glassy carbon powder during thermochemical gas-phase oxidation is also presented and compared with experimental data. Experimental results are in qualitative agreement with the model. We found that a sharp particle size distribution is desirable with regard to potential technical applications. 相似文献
110.
In recent years, three‐dimensionally (3D) braided composites have attracted a great deal of attention because of their high‐impact damage tolerance and fatigue life, superior fracture toughness, and so forth, and have been used in aeronautics, military, and transportation. These advantages make them strong candidates for osteosynthesis devices. In this study, 3D braided carbon fiber–epoxy (C3D/EP) composites were produced via a simple vacuum impregnation technique. The load‐deflection curve, mechanical properties, and influence of fiber volume fraction, braiding angle, and axial reinforcing fibers were examined to determine their suitability for internal fixation devices. It is found that the C3D/EP composites have excellent toughness and do not show brittleness when fractured because of their relatively high void content. The flexural, shear, and impact strengths of the C3D/EP composites are excellent. It was shown that a C3D/EP composite with a stiffness similar to load‐bearing bones can be made while maintaining enough strength. It is concluded that a relatively higher void content and braiding angle is more suitable for the C3D/EP composites from the viewpoint of requirements of fracture fixation materials. The moisture absorption behavior and changes in mechanical properties caused by moisture uptake were evaluated. Results show that absorbed moisture slightly decreases mechanical properties of the C3D/EP composites. Contrary to the unreinforced epoxy, the moisture absorption behavior of the C3D/EP composites cannot be described with Fick's law of diffusion, probably because of the presence of voids and/or 3D fiber structure. The exact mechanisms should be proposed in further investigations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1031–1039, 2002 相似文献