全文获取类型
收费全文 | 3484篇 |
免费 | 123篇 |
国内免费 | 22篇 |
专业分类
化学 | 2063篇 |
晶体学 | 11篇 |
力学 | 145篇 |
数学 | 495篇 |
物理学 | 685篇 |
无线电 | 230篇 |
出版年
2024年 | 5篇 |
2023年 | 44篇 |
2022年 | 81篇 |
2021年 | 122篇 |
2020年 | 107篇 |
2019年 | 96篇 |
2018年 | 65篇 |
2017年 | 52篇 |
2016年 | 142篇 |
2015年 | 98篇 |
2014年 | 145篇 |
2013年 | 178篇 |
2012年 | 239篇 |
2011年 | 270篇 |
2010年 | 152篇 |
2009年 | 133篇 |
2008年 | 216篇 |
2007年 | 207篇 |
2006年 | 215篇 |
2005年 | 195篇 |
2004年 | 152篇 |
2003年 | 133篇 |
2002年 | 130篇 |
2001年 | 54篇 |
2000年 | 26篇 |
1999年 | 30篇 |
1998年 | 33篇 |
1997年 | 41篇 |
1996年 | 37篇 |
1995年 | 21篇 |
1994年 | 22篇 |
1993年 | 18篇 |
1992年 | 7篇 |
1991年 | 16篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 15篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 9篇 |
排序方式: 共有3629条查询结果,搜索用时 11 毫秒
221.
222.
223.
The Ugi four-component condensation between anilines, aromatic aldehydes, isocyanides, and α-oxoacids afforded the expected adducts which were cleaved in mild conditions to give 2,N-diarylglycines in high yields. 相似文献
224.
225.
A very important issue in optical burst switching (OBS) networks is the excessive burst drop when no suitable network resources
are found during path reservation. In this study, a network scenario is evaluated in which AWG-based optical nodes are used
as burst router nodes within the optical network. The two classical solutions to solve the burst contentions on the channels
outgoing from the node are considered, that is, either based on buffering within the node, or by exploiting deflection routing.
A performance evaluation is carried out to evaluate and compare these solutions for different network topologies with different
node and traffic parameters. Our main contribution is to set numerical tradeoffs between burst deflection through the network
and buffering in the node, so that a guidance in optical network design is provided where node buffering is inherently technologically
limited. 相似文献
226.
227.
Sabrina Brait Stefano Deabate Selby A. R. Knox Enrico Sappa 《Journal of Cluster Science》2001,12(1):139-173
A survey of the synthetic pathways and of the reactivity and catalytic activity of transition metal carbonyl clusters substituted with benzyne (and, for comparison, benzene and diene) ligands is given. Cluster-surface analogies are helpful in gaining an understanding of the homogeneous and heterogeneous catalytic behaviour of the clusters. 相似文献
228.
229.
Most methods of measuring the interfacial tension between two immiscible polymers are based on the analysis of the shape
that a drop of one polymer immersed in the other one exhibits under the action of flow or gravity. In such a situation, the
small, yet nonzero mutual solubility between the two polymers acts toward mass transfer between the drop and the surrounding
fluid. In this work, diffusion effects on the interfacial tension of the pair polyisobutylene/polydimethylsiloxane have been
investigated by drop deformation under shear flow. When the drop was made of polyisobutylene, drop size decreased with time
due to diffusion. Drop shrinkage was associated with a significant increase in interfacial tension, until an apparent plateau
value was reached. The effect was attributed to a selective migration of molecular weights, which would act to enrich the
drop with higher molar mass material. To support such an interpretation, drop viscosity was evaluated by drop shape analysis
and it was actually found to increase with time. In some cases, the ratio between drop and continuous phase viscosity became
higher than the critical value for drop breakup in shear flow. Upon inverting the phases (i.e., when the drop was made of
polydimethylsiloxane), no significant transient effects were observed. In the light of these results, the problem of what
are the correct values of interfacial tension and viscosity ratio for a polymer blend of a certain composition will also be
discussed.
Received: 25 January 1999 Accepted: 24 May 1999 相似文献
230.