全文获取类型
收费全文 | 7079篇 |
免费 | 161篇 |
国内免费 | 207篇 |
专业分类
电工技术 | 176篇 |
综合类 | 201篇 |
化学工业 | 657篇 |
金属工艺 | 932篇 |
机械仪表 | 1789篇 |
建筑科学 | 385篇 |
矿业工程 | 265篇 |
能源动力 | 180篇 |
轻工业 | 107篇 |
水利工程 | 99篇 |
石油天然气 | 86篇 |
武器工业 | 21篇 |
无线电 | 256篇 |
一般工业技术 | 738篇 |
冶金工业 | 343篇 |
原子能技术 | 168篇 |
自动化技术 | 1044篇 |
出版年
2024年 | 5篇 |
2023年 | 56篇 |
2022年 | 118篇 |
2021年 | 148篇 |
2020年 | 110篇 |
2019年 | 95篇 |
2018年 | 124篇 |
2017年 | 133篇 |
2016年 | 138篇 |
2015年 | 186篇 |
2014年 | 343篇 |
2013年 | 677篇 |
2012年 | 347篇 |
2011年 | 528篇 |
2010年 | 448篇 |
2009年 | 430篇 |
2008年 | 348篇 |
2007年 | 441篇 |
2006年 | 430篇 |
2005年 | 355篇 |
2004年 | 247篇 |
2003年 | 292篇 |
2002年 | 230篇 |
2001年 | 223篇 |
2000年 | 181篇 |
1999年 | 155篇 |
1998年 | 148篇 |
1997年 | 137篇 |
1996年 | 95篇 |
1995年 | 88篇 |
1994年 | 54篇 |
1993年 | 20篇 |
1992年 | 30篇 |
1991年 | 13篇 |
1990年 | 22篇 |
1989年 | 16篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有7447条查询结果,搜索用时 15 毫秒
21.
22.
A good understanding of environmental effects on structural modal properties is essential for reliable performance of vibration-based damage diagnosis methods. In this paper, a method of combining principal component analysis (PCA) and support vector regression (SVR) technique is proposed for modeling temperature-caused variability of modal frequencies for structures instrumented with long-term monitoring systems. PCA is first applied to extract principal components from the measured temperatures for dimensionality reduction. The predominant feature vectors in conjunction with the measured modal frequencies are then fed into a support vector algorithm to formulate regression models that may take into account thermal inertia effect. The research is focused on proper selection of the hyperparameters to obtain SVR models with good generalization performance. A grid search method with cross validation and a heuristic method are utilized for determining the optimal values of SVR hyperparameters. The proposed method is compared with the method directly using measurement data to train SVR models and the multivariate linear regression (MLR) method through the use of long-term measurement data from a cable-stayed bridge. It is shown that PCA-compressed features make the training and validation of SVR models more efficient in both model accuracy and computational costs, and the formulated SVR model performs much better than the MLR model in generalization performance. When continuously measured data is available, the SVR model formulated taking into account thermal inertia effect can achieve more accurate prediction than that without considering thermal inertia effect. 相似文献
23.
一种新型陶瓷材料及其耐磨性 总被引:5,自引:0,他引:5
对新型Al2O3-TiC-Co陶瓷的磨粒磨损,冲蚀磨损及其在单颗粒作用下的摩擦磨损行为进行了研究。与AT30(70wt%Al2O3-30wt%TiC)陶瓷相比,Al2O3-TiC-Co陶瓷具有更为良好的耐磨性,金属钴的存在提高了基体的韧性,细化了晶粒,其综合力学性能得到了显著提高,ATC陶瓷样品耐磨性与其强韧化水平和细致的组织结构有关。 相似文献
24.
R. Heinemann S. Hinduja G. Barrow 《The International Journal of Advanced Manufacturing Technology》2007,33(3-4):243-250
Detailed knowledge about the relation between wear progression of a cutting tool and the cutting forces generated is of paramount
importance for the development of a tool condition monitoring strategy. This paper discusses the changes in the different
process signals with progressing tool wear of small diameter twist drills (D=1.5 mm), when drilling boreholes having a depth
of 10 times the diameter in plain carbon steel using MQL. The effect of different wear patterns on the process signals is
presented. Furthermore, several features, which evolve over the life of the drills, are identified and extracted from the
process signals. Knowledge about the evolution of these features can support the user to determine the final tool life stage,
so that the drill can be replaced before the final fracture occurs. 相似文献
25.
The infiltration of compacted cubic BN (cBN) with molten aluminum has been investigated as a potential route for a cheap and easy method of manufacturing cBN/metal composites. CBN compacts have been infiltrated with molten Al at a temperature between 670 and 800 °C and pressure of 15 MPa in vacuum. At these temperatures no pronounced interactions between hexagonal and cubic BN with Al was observed, allowing the complete infiltration of cBN with 12 μm mean grain size. After infiltration at 800 °C, the temperature was increased without pressure to convert aluminum into borides and AlN. The hardness of the resulting materials depends on the content of hexagonal, cubic BN and the rate of conversion of Al into borides and AlN. The infiltration height of less than 1 mm obtained from infiltrating the 3 μm cBN powder green compacts gave a hardness of 22.0 ± 0.6 GPa after heat treatment. 相似文献
26.
In wintertime, the use of studded tyres is common in the Nordic countries, steeply in creasing road wear. Apart from reducing surface quality and durability, the airborne dust presents a potential health hazard. To reduce road wear and dust release, there is a tendency to use harder and more wear-resistant aggregate materials.On the roads in and around Trondheim, mid-Norway, three types of aggregate material are common: greenstone, jasper and ‘mylonite’, in fact a cataclasite. Extensive laboratory testing suggests that cataclasite aggregate has better wear resistance than greenstone, but less than jasper [Erichsen E, Schiellerup H, Gautneb, H, Ottesen RT, Broekmans M. Road dust in Trondheim — analysis of the mineral content of airborne dust. (In Norwegian.) Geological Survey of Norway, NGU-report 2004. 037; 2004. p. 73]. However , observations on fluorescence-impregnated plane and thin sections demonstrate that in practice, cataclasite wears faster than greenstone, which may be attributed to its oriented fabric, as opposed to the random fabric in greenstone and jasper. The original article by Rosiwal from 1896 [Rosiwal A. Neue Untersuchungser gebnisse über die Härte von Mineralien und Gesteine. Verhandlungen der kaiserlich-königlichen geologischen Reichsanstalt, vol. 17/18; 1896. p. 475–491] on abrasion hardness and anisotropy provides an elegant explanation for the field observations. 相似文献
27.
28.
机群监控系统可有效的提高大型机群的可管理性和可用性。本文提出了一种基于JAVA RMI技术的机群监控系统模型,并给出其实现方法。该系统具有开发快速、可跨平台、易于扩展等特性。 相似文献
29.
在陕西宝鸡峡引水枢纽浆砌石大坝改建过程中 ,Ⅱ坝段的全部以及Ⅵ坝段的部分须用爆破方法拆除。为了避免爆破震动对相邻的和保留的浆砌石坝体的不利影响 ,利用伸缩缝和预先开挖的沟槽隔震 ,采用了浅孔爆破分层拆除的方法 ,实施微差爆破 ,严格控制最大一段药量。爆破震动监测和声波测试的结果表明 ,保留的浆砌石坝体没有受到损伤 相似文献
30.
总结了动力能源调度监控技术在冶金企业的应用情况,介绍了这项技术的发展历程及企业在应用时需要注意的几个重要事项,分析了目前存在的问题,提出了相应对策。 相似文献