全文获取类型
收费全文 | 1652篇 |
免费 | 98篇 |
国内免费 | 12篇 |
专业分类
化学 | 1152篇 |
晶体学 | 1篇 |
力学 | 55篇 |
数学 | 224篇 |
物理学 | 330篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 18篇 |
2021年 | 57篇 |
2020年 | 66篇 |
2019年 | 60篇 |
2018年 | 40篇 |
2017年 | 33篇 |
2016年 | 85篇 |
2015年 | 68篇 |
2014年 | 71篇 |
2013年 | 102篇 |
2012年 | 111篇 |
2011年 | 142篇 |
2010年 | 67篇 |
2009年 | 92篇 |
2008年 | 117篇 |
2007年 | 112篇 |
2006年 | 102篇 |
2005年 | 92篇 |
2004年 | 63篇 |
2003年 | 41篇 |
2002年 | 53篇 |
2001年 | 12篇 |
2000年 | 22篇 |
1999年 | 14篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1944年 | 1篇 |
排序方式: 共有1762条查询结果,搜索用时 46 毫秒
971.
In this paper, we carry a detailed study of mechanical systems with configuration space Q?Q/G for which the base Q/G variables are being controlled. The overall system’s motion is considered to be induced from the base one due to the presence of general non-holonomic constraints. It is shown that the solution can be factorized into dynamical and geometrical parts. Moreover, under favorable kinematical circumstances, the dynamical part admits a further factorization since it can be reconstructed from an intermediate (body) momentum solution, yielding a reconstruction phase formula. Finally, we apply this results to the study of concrete mechanical systems. 相似文献
972.
Olivier Chalus Alexey Sukhinin Alejandro Aceves Jean-Claude Diels 《Optics Communications》2008,281(12):3356-3360
Ultraviolet pulses of 200 ps duration are focused in vacuum, and launched into the atmosphere through an aerodynamic window. Instead of diffracting, above a threshold of 100 mJ, the beam propagates in a self-induced waveguide in air. The peak electric field and beam profile are consistent with the eigenfunction of a modified nonlinear Schrödinger equation. The evolution of the beam waist with distance is calculated by a combination of the nonlinear Schrödinger equation and an equation for the nonlinear losses. 相似文献
973.
We propose a novel approach based on the generalized S-transform to retrieve optical phase distributions in temporal speckle pattern interferometry. The performance of the proposed approach is compared with those given by well-known techniques based on the continuous wavelet, the Hilbert transforms, and a smoothed time-frequency distribution by analyzing interferometric data degraded by noise, nonmodulating pixels, and modulation loss. The advantages and limitations of the proposed phase retrieval approach are discussed. 相似文献
974.
A novel stochastic fluid model is proposed with a nonideal structure factor consistent with compressibility, and adjustable transport coefficients. This stochastic hard-sphere dynamics (SHSD) algorithm is a modification of the direct simulation Monte Carlo algorithm and has several computational advantages over event-driven hard-sphere molecular dynamics. Surprisingly, SHSD results in an equation of state and a pair correlation function identical to that of a deterministic Hamiltonian system of penetrable spheres interacting with linear core pair potentials. The fluctuating hydrodynamic behavior of the SHSD fluid is verified for the Brownian motion of a nanoparticle suspended in a compressible solvent. 相似文献
975.
Alejandro Cordero-Vargas Béatrice Quiclet-Sire Samir Z. Zard 《Tetrahedron letters》2004,45(39):7335-7338
A new strategy has been developed for the synthesis of C-aryl glycosides based on a xanthate-mediated free radical addition-cyclization sequence of an acetophenone xanthate to a vinylic carbohydrate followed by aromatization. 相似文献
976.
A survey is reported on the use of additives in organic elemental analysis of compounds containing functional groups that
may compromise the combustion process. 28 substances containing the following functional groups were selected: organic fluorine,
hexafluorophosphate, tetrafluoroborate, tetraphenylborate, sulfonate, phosphine, nitrile, carbide, organometallic. Six additives
(powdered silver, silver tungstate with magnesium oxide, silica oxide, tungsten (VI) oxide with magnesium oxide, powdered
tin, cerium (IV) oxide) in various sample:additive ratios were assayed. Silver tungstate with magnesium oxide (mixture 1:1,
w/w) turned out to be most efficient for the analysis of nitrogen, carbon, hydrogen and sulfur for almost all the compounds
assayed.
Author for correspondence.
Received August 2, 2002; accepted December 12, 2002
Published online May 19, 2003 相似文献
977.
We study a continuous time growth process on (d?1) associated to the following interacting particle system: initially there is only one simple symmetric continuous time random walk of total jump rate one located at the origin; then, whenever a random walk visits a site still unvisited by any other random walk, it creates a new independent random walk starting from that site. Let us call Pd the law of such a process and S0d(t) the set of sites, visited by all walks by time t. We prove that there exists a bounded, non-empty, convex set , such that for every ε>0, Pd-a.s. eventually in t, the set Sd0(t) is within an ε neighborhood of the set [Cdt], where for we define . Moreover, for d large enough, the set Cd is not a ball under the Euclidean norm. We also show that the empirical density of particles within Sd0(t) converges weakly to a product Poisson measure of parameter one. To cite this article: A.F. Ram??rez, V. Sidoravicius, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 821–826. 相似文献
978.
979.
Alejandro Illanes 《Proceedings of the American Mathematical Society》2002,130(7):2179-2182
A topological space is said to be -contractible provided that there exists a continuous onto function such that is homotopic to a constant function. Answering a question by Sam B. Nadler, Jr., in this paper we construct a metric continuum such that its hyperspace of subcontinua is not -contractible.
980.
We report on the "molecular wiring" efficiency of glucose oxidase in organized self-assembled nanostructures comprised of enzyme layers alternating with layers of an osmium-derivatized poly(allylamine) cationic polyelectrolyte, acting as redox relays. Varying the relative position of the active enzyme layer in nanostructures alternating active enzyme and inactive apoenzyme we have demonstrated that the specific rate of bimolecular FADH(2) oxidation ("wiring efficiency") is limited by the diffusion-like electron hopping mechanism in the multilayers. 相似文献