全文获取类型
收费全文 | 2686篇 |
免费 | 81篇 |
国内免费 | 17篇 |
专业分类
化学 | 1772篇 |
晶体学 | 9篇 |
力学 | 52篇 |
数学 | 498篇 |
物理学 | 453篇 |
出版年
2023年 | 22篇 |
2022年 | 61篇 |
2021年 | 73篇 |
2020年 | 80篇 |
2019年 | 58篇 |
2018年 | 52篇 |
2017年 | 56篇 |
2016年 | 104篇 |
2015年 | 83篇 |
2014年 | 96篇 |
2013年 | 212篇 |
2012年 | 217篇 |
2011年 | 222篇 |
2010年 | 130篇 |
2009年 | 105篇 |
2008年 | 161篇 |
2007年 | 178篇 |
2006年 | 153篇 |
2005年 | 115篇 |
2004年 | 101篇 |
2003年 | 83篇 |
2002年 | 76篇 |
2001年 | 29篇 |
2000年 | 26篇 |
1999年 | 31篇 |
1998年 | 19篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 22篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有2784条查询结果,搜索用时 15 毫秒
31.
32.
We investigate the deformation of D-brane world-volumes in curved backgrounds. We calculate the leading corrections to the boundary conformal field theory involving
the background fields, and in particular we study the correlation functions of the resulting system. This allows us to obtain
the world-volume deformation, identifying the open string metric and the noncommutative deformation parameter. The picture
that unfolds is the following: when the gauge invariant combination ω=B+F is constant one obtains the standard Moyal deformation of the brane world-volume. Similarly, when dω= 0 one obtains the noncommutative Kontsevich deformation, physically corresponding to a curved brane in a flat background.
When the background is curved, H=dω≠ 0, we find that the relevant algebraic structure is still based on the Kontsevich expansion, which now defines a nonassociative
star product with an A
∞ homotopy associative algebraic structure. We then recover, within this formalism, some known results of Matrix theory in
curved backgrounds. In particular, we show how the effective action obtained in this framework describes, as expected, the
dielectric effect of D-branes. The polarized branes are interpreted as a soliton, associated to the condensation of the brane gauge field.
Received: 22 March 2001 / Accepted: 13 July 2001 相似文献
33.
Ilda Abe Rafael E. de Ges Jos L. Fabris Hypolito J. Kalinowski Mrcia Müller Meire C. Fugihara Rosane Falate Barbara W. Diesel Ricardo C. Kamikawachi Carmen L. Barbosa 《Optics and Lasers in Engineering》2003,39(5-6):537-548
In this work, we report production and modelling of both Bragg gratings and rocking filters in high birefringence fibre optics. Bragg gratings are produced by UV (257.0 nm) external interferometric exposition of a frequency-doubled Ar+ ion laser, whereas for rocking filters formation the visible Ar+ ion laser lines in 488.0 and 514.5 nm are used in an internal method. The spectral characteristics due to the birefringence properties are studied through numerical methods and experimental techniques. The spectral responsivity of the structures under temperature changes and stress application is presented. 相似文献
34.
Interactive music uses wearable sensors (i.e., gestural interfaces—GIs) and biometric datasets to reinvent traditional human–computer interaction and enhance music composition. In recent years, machine learning (ML) has been important for the artform. This is because ML helps process complex biometric datasets from GIs when predicting musical actions (termed performance gestures). ML allows musicians to create novel interactions with digital media. Wekinator is a popular ML software amongst artists, allowing users to train models through demonstration. It is built on the Waikato Environment for Knowledge Analysis (WEKA) framework, which is used to build supervised predictive models. Previous research has used biometric data from GIs to train specific ML models. However, previous research does not inform optimum ML model choice, within music, or compare model performance. Wekinator offers several ML models. Thus, we used Wekinator and the Myo armband GI and study three performance gestures for piano practice to solve this problem. Using these, we trained all models in Wekinator and investigated their accuracy, how gesture representation affects model accuracy and if optimisation can arise. Results show that neural networks are the strongest continuous classifiers, mapping behaviour differs amongst continuous models, optimisation can occur and gesture representation disparately affects model mapping behaviour; impacting music practice. 相似文献
35.
36.
37.
We investigate the interface dynamics of the two-dimensional stochastic Ising model in an external field under helicoidal boundary conditions. At sufficiently low temperatures and fields, the dynamics of the interface is described by an exactly solvable high-spin asymmetric quantum Hamiltonian that is the infinitesimal generator of the zero range process. Generally, the critical dynamics of the interface fluctuations is in the Kardar–Parisi–Zhang universality class of critical behavior. We remark that a whole family of RSOS interface models similar to the Ising interface model investigated here can be described by exactly solvable restricted high-spin quantum XXZ-type Hamiltonians. 相似文献
38.
We obtain high-velocity estimates with error bounds for the scattering operator of the Schrödinger equation in three dimensions with electromagnetic potentials in the exterior of bounded obstacles that are handlebodies. A particular case is a finite number of tori. We prove our results with time-dependent methods. We consider high-velocity estimates where the direction of the velocity of the incoming electrons is kept fixed as its absolute value goes to infinity. In the case of one torus our results give a rigorous proof that quantum mechanics predicts the interference patterns observed in the fundamental experiments of Tonomura et al. that gave conclusive evidence of the existence of the Aharonov-Bohm effect using a toroidal magnet. We give a method for the reconstruction of the flux of the magnetic field over a cross-section of the torus modulo 2π. Equivalently, we determine modulo 2π the difference in phase for two electrons that travel to infinity, when one goes inside the hole and the other outside it. For this purpose we only need the high-velocity limit of the scattering operator for one direction of the velocity of the incoming electrons. When there are several tori-or more generally handlebodies-the information that we obtain in the fluxes, and on the difference of phases, depends on the relative position of the tori and on the direction of the velocities when we take the high-velocity limit of the incoming electrons. For some locations of the tori we can determine all the fluxes modulo 2π by taking the high-velocity limit in only one direction. We also give a method for the unique reconstruction of the electric potential and the magnetic field outside the handlebodies from the high-velocity limit of the scattering operator. 相似文献
39.
Barbara Nelli Ricardo Sa Earp Walcy Santos Eric Toubiana 《Annals of Global Analysis and Geometry》2008,33(4):307-321
We prove that a H-surface M in ${\mathbb{H}}^2 \times {\mathbb{R}} ,\vert H\vert \leq 1/2$ , inherits the symmetries of its boundary $\partial M,$ when $\partial M$ is either a horizontal curve with curvature greater than one or two parallel horizontal curves with curvature greater than one, whose distance is greater or equal to π. Furthermore we prove that the asymptotic boundary of a surface with mean curvature bounded away from zero consists of parts of straight lines, provided it is sufficiently regular. 相似文献
40.
E. V. Spinacé Ricardo R. Dias Michele Brandalise Marcelo Linardi Almir Oliveira Neto 《Ionics》2010,16(1):91-95
PtRh/C (90:10), PtRh/C (50:50), PtSn/C (50:50), and PtSnRh/C (50:40:10) electrocatalysts were prepared by an alcohol-reduction
process using ethylene glycol as solvent and reduction agent and Vulcan Carbon XC72 as supports. The electrocatalysts were
characterized by energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The electro-oxidation
of ethanol was studied by cyclic voltammetry chronoamperometry at room temperature and on a single cell of a direct ethanol
fuel cell at 100 °C. Cyclic voltammetry and chronoamperometry experiments showed that PtSnRh/C and PtSn/C electrocatalysts
have similar performance for ethanol oxidation at room temperature, while the activity of PtRh/C electrocatalysts was very
low. At 100 °C on a single cell, PtSnRh/C showed superior performance compared to PtSn/C and PtRh/C electrocatalysts. 相似文献