全文获取类型
收费全文 | 3521篇 |
免费 | 101篇 |
国内免费 | 15篇 |
专业分类
化学 | 2182篇 |
晶体学 | 15篇 |
力学 | 195篇 |
数学 | 744篇 |
物理学 | 501篇 |
出版年
2023年 | 19篇 |
2022年 | 51篇 |
2021年 | 98篇 |
2020年 | 73篇 |
2019年 | 51篇 |
2018年 | 65篇 |
2017年 | 57篇 |
2016年 | 111篇 |
2015年 | 104篇 |
2014年 | 80篇 |
2013年 | 186篇 |
2012年 | 207篇 |
2011年 | 247篇 |
2010年 | 145篇 |
2009年 | 121篇 |
2008年 | 202篇 |
2007年 | 220篇 |
2006年 | 162篇 |
2005年 | 154篇 |
2004年 | 145篇 |
2003年 | 117篇 |
2002年 | 99篇 |
2001年 | 43篇 |
2000年 | 26篇 |
1999年 | 37篇 |
1998年 | 34篇 |
1997年 | 34篇 |
1996年 | 36篇 |
1995年 | 26篇 |
1994年 | 30篇 |
1993年 | 47篇 |
1992年 | 18篇 |
1991年 | 27篇 |
1990年 | 29篇 |
1989年 | 17篇 |
1988年 | 26篇 |
1987年 | 22篇 |
1986年 | 23篇 |
1985年 | 46篇 |
1984年 | 41篇 |
1983年 | 23篇 |
1982年 | 25篇 |
1981年 | 29篇 |
1980年 | 26篇 |
1979年 | 22篇 |
1978年 | 26篇 |
1977年 | 23篇 |
1976年 | 22篇 |
1975年 | 13篇 |
1974年 | 21篇 |
排序方式: 共有3637条查询结果,搜索用时 0 毫秒
961.
D'Acquarica I Gasparrini F Pierini M Villani C Zappia G 《Journal of separation science》2006,29(10):1508-1516
Dynamic HPLC on enantioselective stationary phases has become a well-established technique to investigate chiral molecules with internal motions that result in stereoinversion and occur on the time scale of the separation process. Kinetic parameters for the on-column interconversion phenomena can be extracted from experimental peak profiles by computer simulation or by direct calculation methods. The technique has been used in a wide range of temperatures and is complementary in scope to dynamic NMR spectroscopy. 相似文献
962.
We report the statistical analysis of the movement of a submicron particle confined in a harmonic potential in the presence of a torque. The absolute value of the torque can be found from the auto- and cross-correlation functions of the particle's coordinates. We experimentally prove this analysis by detecting the torque produced onto an optically trapped particle by an optical beam with orbital angular momentum. 相似文献
963.
Gibbs free-energy calculations based on density functional theory have been used to determine the possible source of failure of boron carbide just above the Hugoniot elastic limit (HEL). A range of B4C polytypes is found to be stable at room pressure. The energetic barrier for shock amorphization of boron carbide is by far the lowest for the B12(CCC) polytype, requiring only 6 GPa approximately = P(HEL) for collapse under hydrostatic conditions. The results clearly demonstrate that the collapse of the B12(CCC) phase leads to segregation of B12 and amorphous carbon in the form of 2-3 nm bands along the (113) lattice direction, in excellent agreement with recent transmission electron microscopy results. 相似文献
964.
Surface plasmon radiation forces 总被引:1,自引:0,他引:1
We report the first experimental observation of momentum transfer from a surface plasmon to a single dielectric sphere. Using a photonic force microscope, we measure the plasmon radiation forces on different polystyrene beads as a function of their distance from the metal surface. We show that the force magnitude at resonance is strongly enhanced compared to a nonresonant illumination. Measurements performed as a function of the probe particle size indicate that optical manipulation by plasmon fields has a strong potential for optical sorting. 相似文献
965.
We present a method for finding exact solutions of Max-Cut, the problem of finding a cut of maximum weight in a weighted graph.
We use a Branch-and-Bound setting that applies a dynamic version of the bundle method as bounding procedure. This approach
uses Lagrangian duality to obtain a “nearly optimal” solution of the basic semidefinite Max-Cut relaxation, strengthened by
triangle inequalities. The expensive part of our bounding procedure is solving the basic semidefinite relaxation of the Max-Cut
problem, which has to be done several times during the bounding process. We review other solution approaches and compare the
numerical results with our method. We also extend our experiments to instances of unconstrained quadratic 0–1 optimization
and to instances of the graph equipartition problem. The experiments show that our method nearly always outperforms all other
approaches. In particular, for dense graphs, where linear programming-based methods fail, our method performs very well. Exact
solutions are obtained in a reasonable time for any instance of size up to n = 100, independent of the density. For some problems of special structure we can solve even larger problem classes. We could
prove optimality for several problems of the literature where, to the best of our knowledge, no other method is able to do
so.
Supported in part by the EU project Algorithmic Discrete Optimization (ADONET), MRTN-CT-2003-504438. 相似文献
966.
Marco Bramanti Giovanni Cupini Ermanno Lanconelli Enrico Priola 《Mathematische Zeitschrift》2010,266(4):789-816
We consider a class of degenerate Ornstein–Uhlenbeck operators in ${\mathbb{R}^{N}}We consider a class of degenerate Ornstein–Uhlenbeck operators in
\mathbbRN{\mathbb{R}^{N}} , of the kind
A o ?i, j=1p0aij?xixj2 + ?i, j=1Nbijxi?xj\mathcal{A}\equiv\sum_{i, j=1}^{p_{0}}a_{ij}\partial_{x_{i}x_{j}}^{2} + \sum_{i, j=1}^{N}b_{ij}x_{i}\partial_{x_{j}} 相似文献
967.
Gabriele Stabile Giovanni Luca Torrisi 《Methodology and Computing in Applied Probability》2010,12(3):415-429
We consider risk processes with non-stationary Hawkes claims arrivals, and we study the asymptotic behavior of infinite and
finite horizon ruin probabilities under light-tailed conditions on the claims. Moreover, we provide asymptotically efficient
simulation laws for ruin probabilities and we give numerical illustrations of the theoretical results. 相似文献
968.
Giovanni Colombo Khai T. Nguyen 《Calculus of Variations and Partial Differential Equations》2010,37(1-2):141-166
Quantitative versions (i.e., taking into account a suitable “distance” of a set from being a sphere) of the isoperimetric inequality are obtained, in the spirit of Fuglede (Trans Am Math Soc 314:619–638, 1989) and Fusco et al. (Ann Math 168:941–980, 2008) for a class of not necessarily convex sets called φ-convex sets. Our work is based on geometrical results on φ-convex sets, obtained using methods of both nonsmooth analysis and geometric measure theory. 相似文献
969.
Giacomo Luigi Petretto Sergio Stoccoro Maria Agostina Cinellu Giovanni Minghetti 《Journal of organometallic chemistry》2010,695(2):256-259
Taking advantage of palladium peculiar “rollover” C,N cyclometallation, it is possible to promote C(3) functionalization of 6-alkyl-substituted-2,2′-bipyridines. The carbonylation reaction of rollover species [Pd(Ln)Cl]2, (HL1 = 6-isopropyl-2,2′-bipy, 1; HL2 = 6-neopentyl-2,2′-bipy, 2; HL3 = 6-ethyl-2,2′-bipy, 3; HL4 = 6-methyl-2,2′-bipy, 4) allowed the synthesis of 2-(pyridin-2-yl)-6-alkyl-nicotinic acids or esters. These nicotinic derivatives are extremely rare and, as far as we know, quite unreported in the case of the 6-substituted molecules. 相似文献
970.
Carstensen O Sielk J Schönborn JB Granucci G Hartke B 《The Journal of chemical physics》2010,133(12):124305
In a large-scale simulation study of ultrafast photochemical dynamics for an azobenzene compound with an additional ethylenic bridge we have found unexpected features: while the dynamics starting from the Z isomer follow a barrierless path with steep gradients, the dynamics starting from the E isomer proceed through a different conical intersection surrounded by a rather flat potential energy landscape and then encounter a sizeable barrier in the electronic ground state that markedly influences the reaction behavior. Direct comparisons with experimental static UV spectra, quantum yields, and transient absorption spectra show good agreement and reveal signatures of this unusual behavior. 相似文献
|