全文获取类型
收费全文 | 12056篇 |
免费 | 252篇 |
国内免费 | 300篇 |
专业分类
电工技术 | 263篇 |
技术理论 | 1篇 |
综合类 | 352篇 |
化学工业 | 1736篇 |
金属工艺 | 1392篇 |
机械仪表 | 1016篇 |
建筑科学 | 810篇 |
矿业工程 | 550篇 |
能源动力 | 1209篇 |
轻工业 | 349篇 |
水利工程 | 141篇 |
石油天然气 | 343篇 |
武器工业 | 44篇 |
无线电 | 587篇 |
一般工业技术 | 1502篇 |
冶金工业 | 620篇 |
原子能技术 | 430篇 |
自动化技术 | 1263篇 |
出版年
2024年 | 11篇 |
2023年 | 111篇 |
2022年 | 246篇 |
2021年 | 300篇 |
2020年 | 294篇 |
2019年 | 229篇 |
2018年 | 217篇 |
2017年 | 256篇 |
2016年 | 230篇 |
2015年 | 249篇 |
2014年 | 618篇 |
2013年 | 728篇 |
2012年 | 626篇 |
2011年 | 1007篇 |
2010年 | 697篇 |
2009年 | 819篇 |
2008年 | 703篇 |
2007年 | 729篇 |
2006年 | 679篇 |
2005年 | 574篇 |
2004年 | 475篇 |
2003年 | 505篇 |
2002年 | 369篇 |
2001年 | 283篇 |
2000年 | 262篇 |
1999年 | 259篇 |
1998年 | 227篇 |
1997年 | 170篇 |
1996年 | 181篇 |
1995年 | 147篇 |
1994年 | 99篇 |
1993年 | 78篇 |
1992年 | 51篇 |
1991年 | 36篇 |
1990年 | 27篇 |
1989年 | 38篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 18篇 |
1985年 | 12篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1944年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
41.
42.
43.
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
44.
45.
Hydroprocessing of heavy petroleum feeds: Tutorial 总被引:1,自引:0,他引:1
46.
用多种快重离子辐照高定向石墨(HOPG),借助扫描隧道显微镜(STM)系统地研究了表面及体内缺陷,结果表明,离子在表面及解理面上都形成了小丘状的缺陷,且在表面较容易形成,可以用非连续损伤径迹结构来对其进行解释。 相似文献
48.
The effect of particle distribution on damage formation in particulate reinforced metal matrix composites deformed in compression 总被引:1,自引:0,他引:1
P.B. Prangnell S.J. Barnes S.M. Roberts P.J. Withers 《Materials Science and Engineering: A》1996,220(1-2):41-56
Image analysis results are reported on the generation of damage in particulate reinforced metal matrix composites during compressive deformation. The technique allows the automated collection of data on the incidence of particle fracture and void formation in the matrix as a function of important microstructural parameters such as local particle volume fraction and particle size. There is a strong relationship between damage and the local volume fraction of the reinforcement proving that damage formation is accentuated in regions of particle clustering. With the SiC reinforced materials examined, there was observed to be a change in dominance of damage mechanism from particle fracture at low local volume fractions to void formation in the matrix within strongly clustered regions. The results are compared with finite element (FE) modelling of the compressive deformation of clustered particles using a simple cluster of equi-spaced particles. The FE results suggest that plastic flow is generally inhibited in clustered regions. In certain highly clustered configurations shielding is such that flow does not occur in the heart of the cluster even at high levels of average plastic strain. The modelling suggests that the change in dominance of damage mechanism is related to the dramatic increase in tensile hydrostatic stresses in the matrix with higher levels of particle clustering. 相似文献
49.
Yoshiyuki Uno Akira Okada Kensuke Uemura Purwadi Raharjo Toshihiko Furukawa Kosaku Karato 《Precision Engineering》2005,29(4):171-455
A new finishing process for metal molds by large-area electron beam (EB) irradiation is proposed in this study. In the large-area EB irradiation equipment used here, an EB with high-energy density is irradiated without focusing the beam, and so the EB with a maximum diameter of 60 mm can be used for melting or evaporating metal surface instantly. Experimental results show that the surface roughness decreases from 6 μmRz to less than 1 μmRz in just a few minutes under proper machining conditions. The corrosion resistance of metal mold surface also could be greatly improved by large-area EB irradiation. Furthermore, the surface roughness of tilting surface close to 90° could be well improved. Therefore, large-area EB irradiation method has a possibility to become a high-efficiency finishing process for metal molds. 相似文献
50.
新产品——钢带增强聚乙烯螺旋波纹管 总被引:1,自引:0,他引:1
钢带增强聚乙烯螺旋波纹管是一种创新的埋地排水管,把钢材的高刚度、高强度和聚乙烯的柔韧、耐腐结合在一起,突出的优点是环刚度高和节约原材料. 相似文献