全文获取类型
收费全文 | 159447篇 |
免费 | 29749篇 |
国内免费 | 18058篇 |
专业分类
化学 | 125608篇 |
晶体学 | 1935篇 |
力学 | 8281篇 |
综合类 | 1119篇 |
数学 | 18296篇 |
物理学 | 52015篇 |
出版年
2024年 | 293篇 |
2023年 | 2441篇 |
2022年 | 3435篇 |
2021年 | 4584篇 |
2020年 | 6042篇 |
2019年 | 7009篇 |
2018年 | 5301篇 |
2017年 | 4843篇 |
2016年 | 8923篇 |
2015年 | 9078篇 |
2014年 | 10439篇 |
2013年 | 13284篇 |
2012年 | 14261篇 |
2011年 | 14160篇 |
2010年 | 11204篇 |
2009年 | 10984篇 |
2008年 | 10997篇 |
2007年 | 9505篇 |
2006年 | 8721篇 |
2005年 | 7547篇 |
2004年 | 6052篇 |
2003年 | 5039篇 |
2002年 | 5476篇 |
2001年 | 4293篇 |
2000年 | 3858篇 |
1999年 | 2968篇 |
1998年 | 2183篇 |
1997年 | 1953篇 |
1996年 | 1879篇 |
1995年 | 1645篇 |
1994年 | 1512篇 |
1993年 | 1238篇 |
1992年 | 1091篇 |
1991年 | 936篇 |
1990年 | 791篇 |
1989年 | 593篇 |
1988年 | 461篇 |
1987年 | 405篇 |
1986年 | 408篇 |
1985年 | 316篇 |
1984年 | 219篇 |
1983年 | 182篇 |
1982年 | 142篇 |
1981年 | 94篇 |
1980年 | 70篇 |
1979年 | 46篇 |
1978年 | 30篇 |
1977年 | 29篇 |
1975年 | 30篇 |
1957年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The Randi? index R(G) of a (chemical) graph G is also called connectivity index. Hansen and Mélot [Variable neighborhood search for extremal graphs 6: analyzing bounds for the connectivity index, J. Chem. Inf. Comput. Sci. 43 (2003) 1-14] in their paper, characterized the chemical trees of given order and number of pendent vertices which have the minimum and maximum Randi? index, respectively. In this note, we point out the mistakes in the proofs of their results Theorems 8 and 10, while we still believe that the two theorems are true, and then we give their corrected proofs. 相似文献
993.
In this article,two uniqueness theorems of meromorphic mappings on moving targets with truncated multiplicities are proved. 相似文献
994.
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
995.
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
996.
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
997.
We consider in this paper the Lagrangian dual method for solving general integer programming. New properties of Lagrangian
duality are derived by a means of perturbation analysis. In particular, a necessary and sufficient condition for a primal
optimal solution to be generated by the Lagrangian relaxation is obtained. The solution properties of Lagrangian relaxation
problem are studied systematically. To overcome the difficulties caused by duality gap between the primal problem and the
dual problem, we introduce an equivalent reformulation for the primal problem via applying a pth power to the constraints. We prove that this reformulation possesses an asymptotic strong duality property. Primal feasibility
and primal optimality of the Lagrangian relaxation problems can be achieved in this reformulation when the parameter p is larger than a threshold value, thus ensuring the existence of an optimal primal-dual pair. We further show that duality
gap for this partial pth power reformulation is a strictly decreasing function of p in the case of a single constraint.
Dedicated to Professor Alex Rubinov on the occasion of his 65th birthday. Research supported by the Research Grants Council
of Hong Kong under Grant CUHK 4214/01E, and the National Natural Science Foundation of China under Grants 79970107 and 10571116. 相似文献
998.
Compact Single-Stage Femtosecond Multipass Ti:Sapphire Amplifier at 1 kHz with High Beam Quality
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A compact femtosecond Ti:sapphire amplifier system is reported using single-stage multipass configuration with high beam quality. A high dispersion glass stretcher and a pair of double prisms for compression are introduced based on broadband femtosecond seed pulses. The non-grating-based pulse stretcher and compressor are advantageous to increase high beam quality and to reduce the high-order dispersion. A Gaussian filter is used to reduce the gain narrowing effect in amplification. The compact femtosecond Ti:sapphire nine-pass amplifier delivers pulses with a duration of 26 fs and an energy of 800μJ at 7mJ pumping pulses energy at I kHz. The 1-kHz femtosecond amplifier with high beam quality and high stability is very suitable for ultrafast physics research applications, such as attosecond science, ultra-precision micromachining, and THz wave generation. 相似文献
999.
The effect of γ-ray irradiation on the magnetic properties of NdFeB and Fe–Cr–Co permanent magnets has been investigated. The magnetic flux loss of two kinds of magnets before and after irradiation was measured. Results show that the effect of γ-ray irradiation on the magnetic properties of sintered NdFeB is not so obvious as that on Fe–Cr–Co magnet. Irradiation-induced damage from γ-ray for the Fe–Cr–Co magnets was characterized for the first time. The decline of permanent magnetic properties of Fe–Cr–Co magnet induced by γ-ray irradiation is reversible except for the maximum energy product (BH)max. The difference of coercivity mechanism between these two kinds of permanent magnets is responsible for the different dependence of magnetic properties loss induced by γ-ray irradiation. 相似文献
1000.