全文获取类型
收费全文 | 1777篇 |
免费 | 115篇 |
国内免费 | 166篇 |
专业分类
化学 | 329篇 |
晶体学 | 8篇 |
力学 | 504篇 |
综合类 | 32篇 |
数学 | 709篇 |
物理学 | 476篇 |
出版年
2024年 | 3篇 |
2023年 | 26篇 |
2022年 | 40篇 |
2021年 | 32篇 |
2020年 | 40篇 |
2019年 | 38篇 |
2018年 | 35篇 |
2017年 | 40篇 |
2016年 | 50篇 |
2015年 | 65篇 |
2014年 | 76篇 |
2013年 | 108篇 |
2012年 | 73篇 |
2011年 | 94篇 |
2010年 | 69篇 |
2009年 | 84篇 |
2008年 | 116篇 |
2007年 | 123篇 |
2006年 | 124篇 |
2005年 | 100篇 |
2004年 | 88篇 |
2003年 | 77篇 |
2002年 | 77篇 |
2001年 | 56篇 |
2000年 | 73篇 |
1999年 | 72篇 |
1998年 | 54篇 |
1997年 | 42篇 |
1996年 | 26篇 |
1995年 | 23篇 |
1994年 | 13篇 |
1993年 | 17篇 |
1992年 | 18篇 |
1991年 | 22篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 6篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有2058条查询结果,搜索用时 15 毫秒
61.
In this paper we investigate the nearly small twist mappings with intersection property. With a certain non-degenerate condition, we proved that the most of invariant tori of the original small twist mappings will survive afer small perturtations. The persisted invariant tori are close to the unperturbed ones when the perturbation are small. The orbits reduced by those mappings are quasi-periodic in the invariant tori with the frequences closing to the original ones. 相似文献
62.
We study the perturbation property of best approximation to a set defined by an abstract nonlinear constraint system. We show that, at a normal point, the perturbation property of best approximation is equivalent to an equality expressed in terms of normal cones. This equality is related to the strong conical hull intersection property. Our results generalize many known results in the literature on perturbation property of best approximation established for a set defined by a finite system of linear/nonlinear inequalities. The connection to minimization problem is considered.The authors thank the referees for valuable suggestions.K.F. Ng - This author was partially supported by Grant A0324638 from the National Natural Science Foundation of China and Grants (2001) 01GY051-66 and SZD0406 from Sichuan Province.
Y.R. He -This author was supported by a Direct Grant (CUHK) and an Earmarked Grant from the Research Grant Council of Hong Kong. 相似文献
63.
The effect of ZnO on phase emergence and microstructure properties of glass and glass-ceramics with composition 25SiO2-50CaO-15P2O5-(10 − x)Fe2O3-xZnO (where x = 0, 2, 5, 7 mol%) has been studied. They have been characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Surface modifications of these glass-ceramics in simulated body fluid have been studied using Fourier transform infrared reflection spectroscopy (FTIR), XPS and SEM. Results have shown a decrease in the fraction of non-bridging oxygen with increase in zinc oxide content. Emergence of crystalline phases in glass-ceramics at different heat treatment temperatures was studied using XRD. When glass is heat treated at 800 °C calcium phosphate, hematite and magnetite are developed as major phases in the glass-ceramics samples with ZnO up to 5 mol%. In addition to these, calcium silicate (Ca3Si2O7) phase is also observed when glass is heat treated at 1000 °C. The microstructure of the glass-ceramics heat treated at 800 °C exhibits the formation of nano-size (40-50 nm) grains. On heat treatment at 1000 °C crystallites grow to above 50 nm size and more than one phase are observed in the microstructure. The formation of thin flake-like structure with coarse particles is observed at high zinc oxide concentration (x = 7 mol%). In vitro studies have shown the surface modifications and formation of Ca-P-rich layer on the glass-ceramics when immersed in simulated body fluids (SBF) for different durations. The bioactive response was found to depend on ZnO content. 相似文献
64.
David A. Jorgensen 《代数通讯》2013,41(12):4461-4471
65.
66.
在文献[1]关于电子 离子束缚态的基本概念的基础上, 对电子-离子束缚态三体系统给出严格的薛定谔方程, 给出能量的近似解:(1)对pep束缚态, 释放单能Ep≈12.5keV的X射线; (2)对D+eD+束缚态, 释放单能ED≈25keV的X射线, 同时引发少量的核聚变, 放出γ、质子、中子、氚、3He和4He。这是两个独立发生的过程。以Ni-H和氘气辉光放 电实验为例,用束缚态模型给出定量的解释。进而提出太阳耀斑发生过程中也包含电子-离子束缚态放射12.5keV和25keV两种X射线并引发少量核聚变的过程, 给出了观测结果验证。 相似文献
67.
吴力荣 《应用数学与计算数学学报》2012,26(2):185-192
Sobolev不等式是联系分析和几何的基础不等式之一,而优化Sobolev体是优化Sobolev范数的临界几何核.首先,证明优化Sobolev体的一些仿射性质.然后,运用Barthe的优化迁移方法研究了凸体的特征函数和多胞形仿射函数的优化Sobolev体. 相似文献
68.
Jila Niknejad 《Topology and its Applications》2012,159(1):229-232
We show that every compact space of large enough size has a realcompact subspace of size κ, for κ?c. We also show that an uncountable realcompact space whose pseudocharacter is at most ω1, has a realcompact subspaces of size ω1, thus, by continuum hypothesis, every uncountable realcompact space has realcompact subspace of size ω1. 相似文献
69.
70.
The effect of pre or post-administration of vitamin A in ameliorating the radiation-induced alteration in intestinal and spleen Na+/K+-ATPase activity of rats was determined. Rats subjected to multifractionated γ-radiation (20 × 0.5 Gy) over the whole-body showed a significant reduction in Na+/K+-ATPase activity being more obvious in spleen than in intestine. Administration of vitamin A at a daily i. p. dose of 15,000 IU/kg bd. wt. for 7 days prior to fractionated γ-irradiation and thereafter twice weekly throughout the exposure period (as pretreatment regimen) or following the end of irradiation for 7 days (as posttreament regimen) afforded a significant protection from radiation-induced inhibition of spleen and intestinal Na+/K+-ATPase activity. Even though, pretreatment regimen is more efficient against radiation injury to this enzyme than posttreatment, so that its activity was nearly normalized in the first regimen. The regeneration of normal enzyme activity in the tissues of the vitamin A-pretreated group suggests that the intestinal and spleen epithelia in presence of vitamin A are rendered relatively radioresistant. 相似文献