全文获取类型
收费全文 | 4823篇 |
免费 | 952篇 |
国内免费 | 334篇 |
专业分类
化学 | 2006篇 |
晶体学 | 89篇 |
力学 | 515篇 |
综合类 | 39篇 |
数学 | 461篇 |
物理学 | 2999篇 |
出版年
2024年 | 8篇 |
2023年 | 36篇 |
2022年 | 129篇 |
2021年 | 164篇 |
2020年 | 195篇 |
2019年 | 149篇 |
2018年 | 137篇 |
2017年 | 144篇 |
2016年 | 233篇 |
2015年 | 178篇 |
2014年 | 225篇 |
2013年 | 379篇 |
2012年 | 274篇 |
2011年 | 321篇 |
2010年 | 235篇 |
2009年 | 294篇 |
2008年 | 316篇 |
2007年 | 340篇 |
2006年 | 316篇 |
2005年 | 256篇 |
2004年 | 216篇 |
2003年 | 224篇 |
2002年 | 183篇 |
2001年 | 134篇 |
2000年 | 132篇 |
1999年 | 105篇 |
1998年 | 110篇 |
1997年 | 76篇 |
1996年 | 93篇 |
1995年 | 61篇 |
1994年 | 70篇 |
1993年 | 58篇 |
1992年 | 46篇 |
1991年 | 32篇 |
1990年 | 38篇 |
1989年 | 30篇 |
1988年 | 27篇 |
1987年 | 24篇 |
1986年 | 20篇 |
1985年 | 18篇 |
1984年 | 9篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1974年 | 4篇 |
1973年 | 8篇 |
1971年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有6109条查询结果,搜索用时 15 毫秒
31.
32.
在LP(1 P<∞)空间研究了板模型中一类带广义边界条件具各向异性、连续能量、均匀介质迁移算子的谱,证明了该迁移算子生成C0半群的D yson—Ph illips展开式的二阶余项在LP(1
相似文献
33.
A fully coupled formulation combining reactive transport and an existing thermo-hydro-mechanical (THM) code is presented.
Special attention has been given to phenomena likely to be encountered in clay barriers used as part of containment systems
of nuclear waste. The types of processes considered include hydrolysis, complex formation, oxidation/reduction reactions,
acid/base reactions, precipitation/dissolution of minerals and cation exchange. Both kinetically-controlled and equilibrium-controlled
reactions have been incorporated. The total analytical concentrations (including precipitated minerals) are adopted as basic
transport variables and chemical equilibrium is achieved by minimizing Gibbs Free Energy. The formulation has been incorporated
in a general purpose computer code capable of performing numerical analysis of engineering problems. A validation exercise
concerning a laboratory experiment involving the heating and hydration of an expansive compacted clay is described. 相似文献
34.
Stability of tokamak plasmas with internal transport barriers against high n ideal magnetohydrodynamic ballooning mode 下载免费PDF全文
A ballooning mode equation for tokamak plasma, with the toroidicity and the Shafranov shift effects included, is derived for a shift circular flux tokamak configuration. Using this equation, the stability of the plasma configuration with an internal transport barrier (ITB) against the high n (the toroidal mode number) ideal magnetohydrodynamic (MHD) ballooning mode is analysed. It is shown that both the toroidicity and the Shaftanov shift effects are stabilizing. In the ITB region, these effects give rise to a low shear stable channel between the first and the second stability regions. Out of the ITB region towards the plasma edge, the stabilizing effect of the Shaftanov shift causes the unstable zone to be significantly narrowed. 相似文献
35.
36.
采用模匹配方法,研究了非均匀磁场下开放的四端量子波导中的电子输运性质. 结果表明,从一端入射的电子可以透射到两个与之垂直的输出端和一个与之平行的输出端. 在没有外加磁场的情况下,两个垂直输出端的输运概率是相同的,但垂直端与水平端的输运概率不同;在外加磁场下,由于磁边缘态效应,两个垂直输出端的输运概率也有着相当大的差别. 通过施加不同的磁场,我们能获得丰富的电子输运结构,如台阶,宽谷,尖峰等;通过调节磁场的大小和比例以及结构参数可控制该量子结构在各输出端的输运概率.
关键词:
电子输运
介观体系
磁效应 相似文献
37.
38.
The transport of scalar quantities passively advected by velocity fields with a component at small scale ℓ can be modeled at scales larger than ℓ by means of an effective drift and an effective diffusivity, which can be determined by means of multiple-scale techniques. We show that the presence of a weak flow at large scales Lℓ induces interesting effects on the scalar transport at the meso-scales (i.e. at scales intermediate between ℓ and L). In particular, it gives rise to non-isotropic and non-homogeneous corrections to the meso-scale drift and diffusivity. We discuss an approximation that allows us to retain the second-order effects caused by the large-scale flow. This provides a rather accurate meso-scale modeling for both asymptotic and pre-asymptotic scalar transport properties. Numerical simulations in model flows are used to illustrate the importance of such large-scale effects. 相似文献
39.
We start with a stochastic flow of diffeomorphisms of the space. Particles enter the space at random times and places. Each particle is carried by the flow for some random amount of time. We examine the point process formed by the particles at a fixed time, on the evolution of that point process as time varies, and on the equilibrium law of the point process. 相似文献
40.
Ryuhei Wakita Masanori Miyakoshi Yohji Nakatsuji Mitsuo Okahara 《Journal of inclusion phenomena and macrocyclic chemistry》1991,10(1):127-139
A series of noncyclic neutral ionophores has been synthesized by the reaction of oligoethylene glycol dihalides with 8-quinolinol. Complexation properties for alkali metal picrates were evaluated from solvent extraction and bulk liquid membrane transport experiments. Complexation profiles of the newly synthesized ionophores with a hexyl chain were similar to those of their homologues without the hexyl chain in the extraction experiments. Among them, the pentaethylene glycol derivatives showed the highest extraction efficiency and selectivity towards potassium ion. From the1H NMR spectra (400 MHz), the change in chemical shifts of the aromatic protons upon the addition of alkali metal thiocyanates suggested the existence of a stabilization effect which is caused by intramolecular stacking conformations between the quinoline rings during complexation. Aryl stacking interactions depend on the size of the cations and on the chain length of the oligoethylene glycol. The relationship between transport ability towards alkali metal cations and lipophilicity of these ionophores is also discussed. 相似文献