全文获取类型
收费全文 | 538篇 |
免费 | 69篇 |
国内免费 | 28篇 |
专业分类
化学 | 39篇 |
晶体学 | 4篇 |
力学 | 141篇 |
综合类 | 5篇 |
数学 | 258篇 |
物理学 | 188篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 10篇 |
2020年 | 16篇 |
2019年 | 21篇 |
2018年 | 13篇 |
2017年 | 20篇 |
2016年 | 31篇 |
2015年 | 10篇 |
2014年 | 48篇 |
2013年 | 65篇 |
2012年 | 21篇 |
2011年 | 38篇 |
2010年 | 37篇 |
2009年 | 35篇 |
2008年 | 42篇 |
2007年 | 32篇 |
2006年 | 31篇 |
2005年 | 22篇 |
2004年 | 19篇 |
2003年 | 25篇 |
2002年 | 13篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有635条查询结果,搜索用时 625 毫秒
581.
582.
583.
本文用数值方法和场致发射的福勒—诺德海姆公式计算了薄膜场致发射阴极(TFFEC)的伏安特性和其应用于平板显示系统的空间扩展特性以及格雷型场效应管的时间响应特性 通过计算得到了TFFEC在不同失端和表面形状情况下的伏安特性曲线,并分析了阴极结构的一致对其发射的均匀性和稳定性的影响。应用TFFEC的新型平板显示系统,其空间分辨能力与阳栅距、栅极电压有很大关系。格雷型场效应管具有皮秒级的响应时间。 相似文献
584.
We present an alternate definition of the mod Z component of the AtiyahPatodi-Singer η invariant associated to (not necessary unitary) fiat vector bundles, which identifies explicitly its real and imaginary parts. This is done by combining a deformation of flat connections introduced in a previous paper with the analytic continuation procedure appearing in the original article of Atiyah, Parodi and Singer. 相似文献
585.
Harvesting in a pelagic fishery: The case of Northern Chile 总被引:1,自引:0,他引:1
This paper analyses the pelagic fishery of Northern Chile, estimating harvesting functions that contribute to understand why rather poor incentives to exit may predominate in pelagic fisheries, despite scarcer fish stocks. Our results show that pervessel catch's stock sensitivity (the catchtobiomass elasticity value) varies negatively with stock levels. Stock levels preceding a marked fall into biological overfishing would have been associated to biomass elasticities lower than the unitary value. This suggests that during catch bonanza periods, catchperunitofeffort would fail to detect a rapidly declining stock trend, increasing the risk of fishing collapse. Moreover, external economies in search efforts would have reduced the incentives to exit, particularly for the smaller vessels in our sample. Finally, we find evidence of either constant or increasing marginal returns in the use of pervessel fishing effort, which suggests that inefficiency in production has resulted from direct restrictions upon fishing effort. Overall, our findings provide consistent evidence that enhances the necessity of more efficient regulations upon harvesting in pelagic fisheries. 相似文献
586.
587.
Mohamed Boucetta 《代数通讯》2013,41(10):4185-4195
A flat Lorentzian Lie algebra is a left symmetric algebra endowed with a symmetric bilinear form of signature (?, +,…, +) such that left multiplications are skew-symmetric. In geometrical terms, a flat Lorentzian Lie algebra is the Lie algebra of a Lie group with a left-invariant Lorentzian metric with vanishing curvature. In this article, we show that any flat nonunimodular Lorentzian Lie algebras can be obtained as a double extension of flat Riemannian Lie algebras. As an application, we give all flat nonunimodular Lorentzian Lie algebras up to dimension 4. 相似文献
588.
《代数通讯》2013,41(2):819-830
We define a function between the lattice of left exact preradicals in R-mod and the complete boolean lattice R-nat of natural classes in R-mod in such a way that the image of this function results to be a complete sublattice of R-nat. The image of this function is R-nat if and only if R is left semiartinian. We prove that every flat ring epimorphism from R to S induces a function between the lattice of left exact preradicals in R-mod and the lattice of left exact preradicals in S-mod. In this context, we obtain a lattice decomposition of S-nat for each left exact preradical. 相似文献
589.
590.
One may represent polynomials not only by their coefficients but also by arithmetic circuits which evaluate them. This idea allowed in the past fifteen years considerable complexity progress in effective polynomial equation solving. We present a circuit based computation model which captures all known symbolic elimination algorithms in effective Algebraic Geometry and exhibit a class of simple elimination problems which require exponential size circuits to be solved in this model. This implies that the known, circuit based elimination algorithms are already optimal. 相似文献