全文获取类型
收费全文 | 154110篇 |
免费 | 29871篇 |
国内免费 | 15628篇 |
专业分类
化学 | 120049篇 |
晶体学 | 1770篇 |
力学 | 8357篇 |
综合类 | 939篇 |
数学 | 16781篇 |
物理学 | 51713篇 |
出版年
2024年 | 277篇 |
2023年 | 2482篇 |
2022年 | 3049篇 |
2021年 | 4293篇 |
2020年 | 5911篇 |
2019年 | 6702篇 |
2018年 | 4946篇 |
2017年 | 4535篇 |
2016年 | 8713篇 |
2015年 | 8733篇 |
2014年 | 9994篇 |
2013年 | 12696篇 |
2012年 | 13813篇 |
2011年 | 13672篇 |
2010年 | 10503篇 |
2009年 | 10407篇 |
2008年 | 10655篇 |
2007年 | 9049篇 |
2006年 | 8293篇 |
2005年 | 7076篇 |
2004年 | 5694篇 |
2003年 | 4722篇 |
2002年 | 5222篇 |
2001年 | 4070篇 |
2000年 | 3652篇 |
1999年 | 2870篇 |
1998年 | 2129篇 |
1997年 | 2056篇 |
1996年 | 2031篇 |
1995年 | 1701篇 |
1994年 | 1543篇 |
1993年 | 1306篇 |
1992年 | 1129篇 |
1991年 | 996篇 |
1990年 | 861篇 |
1989年 | 654篇 |
1988年 | 535篇 |
1987年 | 417篇 |
1986年 | 451篇 |
1985年 | 394篇 |
1984年 | 239篇 |
1983年 | 210篇 |
1982年 | 161篇 |
1981年 | 114篇 |
1980年 | 97篇 |
1979年 | 63篇 |
1977年 | 47篇 |
1976年 | 43篇 |
1974年 | 54篇 |
1973年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
961.
二元域上n数组空间上的非线性置换在分组码,杂凑函数与流密码等密码学领域中有重要应用.域GF(2n)上的幂函数提供了二元域上n数组空间上的一类非线性置换.本文着重研究幂函数的强完全性、完全性与非线性度等密码学性质.作为结果,本文证明了幂函数具有完全性;证明了具有强完全性的函数必有较高的拓扑非线性度;木文找到一类具有强完全性的幂函数;周时也定出了幂函数的代数非线性度. 相似文献
962.
用三维样边界元法分析水闸闸室结构。底板,闸墩和载水墙等为其子结构,交通桥,工作桥和胸墙等处理为内部支撑。地基和边载可以是任意的,只要能给定地表位移面力关系。在各种工况下,不论是设置平板门还是弧形门,是平底板是反拱底板,即使在稀疏剖分下也能给出高精度的位移场,应力场和地基反力场。 相似文献
963.
964.
965.
Xiangdong Xu Hockleong Kweh Zhengcao Zhang Zhihong Liu Wei Zhou Wei Zhang Peixin Qian 《Applied Surface Science》2006,252(20):7594-7598
Large-scale preparation of thin strain-relaxed SiGe is achieved by combining ion implantation and ultrahigh vacuum chemical vapor deposition. The resulting materials were analyzed by double crystal X-ray diffraction, micro-Raman spectroscopy, and tapping mode atomic force microscope. Results revealed that 100-nm-thick Si0.7Ge0.3 layers with the diameter of 125 mm and full strain relaxation are successfully prepared by pre-modifying the Si substrates using 50 keV Ar+ ions. The strain relaxation is also disclosed to change with both ion species and energy. However, post-modification of SiGe by ion implantation will cause serious damage to the crystal structures, and result in the formation of poly-crystal SiGe. 相似文献
966.
Films of polytetrafluoroethylene (PTFE) were exposed to sodium naphthalenide (Na/naphtha) etchant so as to defluorinate the surface for obtaining hydroxyl functionality. Surface-initiators were immobilized on the PTFE films by esterification of 4,4′-azobis(4-cyanopentanoic acid) (ACP) and the hydroxyl groups covalently linked to the surface. Grafting of polymer brushes on the PTFE films was carried out by the surface-initiated free radical polymerization. Homopolymers brushes of methyl methacrylate (MMA) were prepared by free radical polymerization from the azo-functionalized PTFE surface. The chemical composition and topography of the graft-functionalized PTFE surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IR spectroscopy and atomic force microscopy (AFM). Water contact angles on PTFE films were reduced by surface grafting of MMA. 相似文献
967.
F.T. Yuan S.K. Chen W.M. Liao C.W. Hsu S.N. Hsiao W.C. Chang 《Journal of magnetism and magnetic materials》2006
The Au/FePt samples were prepared by depositing a gold cap layer at room temperature onto a fully ordered FePt layer, followed by an annealing at 800 °C for the purpose of interlayer diffusion. After the deposition of the gold layer and the high-temperature annealing, the gold atoms do not dissolve into the FePt Ll0 lattice. Compared with the continuous FePt film, the TEM photos of the bilayer Au(60 nm)/FePt(60 nm) show a granular structure with FePt particles embedded in Au matrix. The coercivity of Au(60 nm)/FePt(60 nm) sample is 23.5 kOe, which is 85% larger than that of the FePt film without Au top layer. The enhancement in coercivity can be attributed to the formation of isolated structure of FePt ordered phase. 相似文献
968.
B. Zhang S. D. Yao K. Wang D. B. Ding Beijing P.R. China Beijing P.R. China Beijing P.R 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(1):9-13
Summary Department of Technical Physics, School of Physics, Peking Unive 相似文献
969.
The theory of asymptotic speeds of spread and monotone traveling waves is established for a class of monotone discrete and continuous‐time semiflows and is applied to a functional differential equation with diffusion, a time‐delayed lattice population model and a reaction‐diffusion equation in an infinite cylinder. © 2005 Wiley Periodicals, Inc. 相似文献
970.
The surface energies for 24 surfaces of all bcc transition metals Fe, Cr, Mo, W, V, Nb and Ta have been calculated by using the second nearest-neighbor modified embedded atom method. The results show that, for all bcc transition metals, the order among three low-index surface energies E(1 1 0) < E(1 0 0) < E(1 1 1) is in agreement with experimental results and E(1 1 0) is also the lowest surface energy for various surfaces. So that from surface energy minimization, the (1 1 0) texture should be favorable in the bcc films. This is also consistent with experimental results. The surface energy for the other surfaces increases linearly with increasing angle between the surfaces (h k l) and (1 1 0). Therefore, a deviation of a surface orientation from (1 1 0) can be used to estimate the relative values of the surface energy. 相似文献