全文获取类型
收费全文 | 4889篇 |
免费 | 341篇 |
国内免费 | 169篇 |
专业分类
电工技术 | 194篇 |
综合类 | 252篇 |
化学工业 | 754篇 |
金属工艺 | 223篇 |
机械仪表 | 212篇 |
建筑科学 | 335篇 |
矿业工程 | 128篇 |
能源动力 | 113篇 |
轻工业 | 249篇 |
水利工程 | 86篇 |
石油天然气 | 149篇 |
武器工业 | 46篇 |
无线电 | 685篇 |
一般工业技术 | 705篇 |
冶金工业 | 615篇 |
原子能技术 | 51篇 |
自动化技术 | 602篇 |
出版年
2024年 | 20篇 |
2023年 | 73篇 |
2022年 | 146篇 |
2021年 | 199篇 |
2020年 | 111篇 |
2019年 | 123篇 |
2018年 | 143篇 |
2017年 | 148篇 |
2016年 | 117篇 |
2015年 | 180篇 |
2014年 | 183篇 |
2013年 | 228篇 |
2012年 | 242篇 |
2011年 | 294篇 |
2010年 | 258篇 |
2009年 | 246篇 |
2008年 | 289篇 |
2007年 | 220篇 |
2006年 | 199篇 |
2005年 | 155篇 |
2004年 | 105篇 |
2003年 | 105篇 |
2002年 | 99篇 |
2001年 | 111篇 |
2000年 | 123篇 |
1999年 | 136篇 |
1998年 | 234篇 |
1997年 | 157篇 |
1996年 | 111篇 |
1995年 | 72篇 |
1994年 | 68篇 |
1993年 | 65篇 |
1992年 | 34篇 |
1991年 | 29篇 |
1990年 | 23篇 |
1989年 | 28篇 |
1988年 | 27篇 |
1987年 | 22篇 |
1986年 | 28篇 |
1985年 | 14篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 34篇 |
1956年 | 8篇 |
排序方式: 共有5399条查询结果,搜索用时 15 毫秒
71.
针对图像拼接算法中计算量大的问题,提出了一种基于边缘扩展相位相关的图像拼接算法。该算法采用迭代阈值分割法对图像进行边缘检测,并对检测出的边缘进行扩展相位相关计算,得出图像间的平移、旋转和尺度变化。利用这些参数拼接图像,用渐进渐出的方法实现拼接图像的融合。实验证明,该算法能够简化计算,并有效地实现图像的拼接。 相似文献
72.
74.
75.
76.
In order to solve the problems of appearance change, scale and rotation change in the visual tracking, a two-level searching tracking algorithm based on Fast Fourier Transform(FFT)is proposed. It achieves two-level searching by establishing the object's kernel ridge regression model in the Cartesian coordinates and log-polar coordinates, respectively, and the efficiency can be improved by transforming the operation into the frequency domain based on FFT. First, the kernel ridge regression model is constructed in the Cartesian coordinate and the object's center position is obtained by the exhaustive search method based on the circular structure matrix. Then, it transforms the object area to the log-polar coordinates and searches the shift using the kernel ridge regression model in the log-polar coordinates. Finally, the object's state is calculated according to the searching results and the object's model is updated. Experimental results indicate that the proposed algorithm not only can obtain a distinct improvement in coping with the appearance change, scale and rotation change, but also have a high tracking efficiency. 相似文献
77.
为研究H形柱传统弱轴连接节点的抗震性能,对已有缩尺试验进行了有限元模拟和8个足尺模型的有限元模拟分析.通过与缩尺试验模型相同尺寸的有限元模型对试验进行了模拟,两者吻合较好.并且对8个足尺有限元模型结果的分析和对比,得出了该种连接的抗震延性、塑性转动能力等相关结论.并给出了对该种连接不足之处的一些改进建议. 相似文献
78.
Xiaonan Lu Joelle T. Reiser Benjamin Parruzot Lu Deng Igor M. Gussev Jörg C. Neuefeind Trent R. Graham Hongshen Liu Joseph V. Ryan Seong H. Kim Nancy Washton Maik Lang Jincheng Du John D. Vienna 《Journal of the American Ceramic Society》2021,104(1):183-207
High-alumina containing high-level waste (HLW) will be vitrified at the Waste Treatment Plant at the Hanford Site. The resulting glasses, high in alumina, will have distinct composition-structure-property (C-S-P) relationships compared to previously studied HLW glasses. These C-S-P relationships determine the processability and product durability of glasses and therefore must be understood. The main purpose of this study is to understand the detailed structural changes caused by Al:Si and (Al + Na):Si substitutions in a simplified nuclear waste model glass (ISG, international simple glass) by combining experimental structural characterizations and molecular dynamics (MD) simulations. The structures of these two series of glasses were characterized by neutron total scattering and 27Al, 23Na, 29Si, and 11B solid-state nuclear magnetic resonance (NMR) spectroscopy. Additionally, MD simulations were used to generate atomistic structural models of the borosilicate glasses and simulation results were validated by the experimental structural data. Short-range (eg, bond distance, coordination number, etc) and medium-range (eg, oxygen speciation, network connectivity, polyhedral linkages) structural features of the borosilicate glasses were systematically investigated as a function of the degree of substitution. The results show that bond distance and coordination number of the cation-oxygen pairs are relatively insensitive to Al:Si and (Al + Na):Si substitutions with the exception of the B-O pair. Additionally, the Al:Si substitution results in an increase in tri-bridging oxygen species, whereas (Al + Na):Si substitution creates nonbridging oxygen species. Charge compensator preferences were found for Si-[NBO] (Na+), [3]B-[NBO] (Na+), [4]B (mostly Ca2+), [4]Al (nearly equally split Na+ and Ca2+), and [6]Zr (mostly Ca2+). The network former-BO-network former linkages preferences were also tabulated; Si-O-Al and Al-O-Al were preferred at the expense of lower Si-O-[3]B and [3]B-O-[3]B linkages. These results provide insights on the structural origins of property changes such as glass-transition temperature caused by the substitutions, providing a basis for future improvements of theoretical and computer simulation models. 相似文献
79.
Owing to its high degree of crystallinity and orientation, the surface of aramid fiber is smooth, causing its low bonding strength with polymer matrix. This has restricted the application of aramid fiber in reinforced polymer materials. Effective methods are by introducing functional groups through surface modification and by increasing its surface roughness thereby greatly improving its bonding strength with the polymer. In this work, molecular dynamics (MD) simulation study fiber functionalized with hydroxyl (OH), carboxyl (COOH), and the silane coupling agent as nanofillers for polymer nanocomposites. The interfacial characteristics and the mechanical behavior of polymer nanocomposites are investigated. The results show that the functionalization can enhance the interfacial shear stress and tensile strength. The functional group not only provides a stronger interface, but also provides additional mechanical interlocking effect, which effectively improves load-bearing transmission capacity. The analysis of the micro-mechanism from the energy level also provides new insights for the functionalized design of nanocomposites. 相似文献
80.