全文获取类型
收费全文 | 85439篇 |
免费 | 1580篇 |
国内免费 | 1608篇 |
专业分类
化学 | 29849篇 |
晶体学 | 877篇 |
力学 | 7205篇 |
综合类 | 104篇 |
数学 | 32842篇 |
物理学 | 17750篇 |
出版年
2023年 | 161篇 |
2022年 | 328篇 |
2021年 | 325篇 |
2020年 | 352篇 |
2019年 | 342篇 |
2018年 | 10666篇 |
2017年 | 10457篇 |
2016年 | 6408篇 |
2015年 | 1195篇 |
2014年 | 747篇 |
2013年 | 908篇 |
2012年 | 4450篇 |
2011年 | 11186篇 |
2010年 | 6084篇 |
2009年 | 6498篇 |
2008年 | 7133篇 |
2007年 | 9191篇 |
2006年 | 618篇 |
2005年 | 1662篇 |
2004年 | 1794篇 |
2003年 | 2195篇 |
2002年 | 1229篇 |
2001年 | 440篇 |
2000年 | 446篇 |
1999年 | 309篇 |
1998年 | 324篇 |
1997年 | 271篇 |
1996年 | 326篇 |
1995年 | 235篇 |
1994年 | 179篇 |
1993年 | 174篇 |
1992年 | 131篇 |
1991年 | 127篇 |
1990年 | 99篇 |
1989年 | 94篇 |
1988年 | 87篇 |
1987年 | 87篇 |
1986年 | 72篇 |
1985年 | 68篇 |
1984年 | 50篇 |
1983年 | 43篇 |
1982年 | 44篇 |
1981年 | 44篇 |
1980年 | 48篇 |
1979年 | 44篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
Dominique Hulin 《Geometriae Dedicata》2007,130(1):109-136
La condition pour qu’il existe des n-gones de Poncelet, inscrits dans un cercle, et circonscrits à un autre cercle, est polynomiale en les paramètres définissant ces deux cercles. Nous décomposons ces polynômes “de Poncelet” en facteurs irréductibles que nous interprétons géométriquement. 相似文献
232.
A noncooperative game governed by a distributed-parameter predator-prey system is considered, assuming that two players control
initial conditions for predator and prey, respectively. Existence of a Nash equilibrium is shown under the condition that
the desired population profiles and the environmental carrying capacity for the prey are sufficiently small. A conceptual
approximation algorithm is proposed and analyzed. Finally, numerical simulations are performed, too. 相似文献
233.
Chris Quigg 《EPJ direct》2002,4(1):1-15
We study the branching ratio, CP-violating asymmetry, forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the exclusive decay B → Kτ+τ− in the two Higgs doublet model with tree level flavor changing neutral currents (model III). We analyse the dependencies of these quantities on the neutral Higgs boson contributions and the CP parameter sinθ in the model III. We observe that to determine the neutral Higgs boson effects, the measurements of the forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the decay B → Kτ+τ− are promising. 相似文献
234.
We introduce new classes of 2-weight cyclic codes which are direct sums of 1-weight irreducible cyclic codes
相似文献
235.
A scheme for vehicle density and velocity estimation in a stretch of highway based on a modified cell transmission model [C.
F. Daganzo, Transportation Research, Part B, 28B(4),269–287, 1994. Elsevier is presented. The scheme is intended for use with on-ramp metering control algorithms, providing
local knowledge of densities and velocities that is helpful to improve on-ramp metering control performance. Estimation of
density is obtained by nonlinear estimators, while velocity estimation is obtained by gradient algorithms. There is one density–velocity
estimator for free traffic flow and other for congested traffic flow. Both estimator schemes work in parallel. The final estimation
of density and velocity results from a convex combination of the predictions of the two estimators. This combination depends
on occupancy or density measurements at the boundaries of the stretch and is produced by a fuzzy inference system. Stability
and convergence of the density and velocity estimation scheme is proved by Lyapunov based techniques. Simulation results comparing
measured and estimated traffic data are presented. They confirm good performance of the estimators.
Research sponsored by grants UNAM PAPIIT IN110403 and CONACYT 47583. 相似文献
236.
237.
238.
Anindya Datta 《Pramana》2003,60(2):363-368
We propose a novel method for the search of supersymmetry, especially for the electroweak gauginos at the large hadron collider
(LHC). Gauge boson fusion technique was shown to be useful for heavy and intermediate mass Higgs bosons. In this article,
we have shown that this method can also be applied to find the signals of EW gauginos in supersymmetric theories where the
canonical search strategies for these particles fail. 相似文献
239.
Arman Melkumyan 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(2):330-349
The problem of electric and acoustic waves diffraction by a half-plane crack in a transversal isotropic piezoelectric medium
is investigated. The crack is assumed to be electric permeable and free of tractions. The so-called “quasi-hyperbolic approximation”
[15] is adopted. Applying Laplace transformations and Wiener–Hopf technique a closed form solution is obtained. By the means
of Cagniard–de Hoop method a detailed dynamic full electroacoustic wavefield’s investigation is conducted. Mode conversion
between electric and acoustic waves, effect of electroacoustic head wave, Bleustein–Gulyaev surface wave and the wavefield
structure depending on the type of the incident wave (acoustic or electric) and its angle of incidence are analyzed in details.
The dynamic field intensity factors at the crack tip depending on the angle of incidence and on time are derived explicitly.
Numerical analysis is presented. 相似文献
240.
Optimal explicit Runge–Kutta methods consider more stages in order to include a particular spectrum in their stability domain
and thus reduce time-step restrictions. This idea, so far used mostly for real-line spectra, is generalized to more general
spectra in the form of a thin region. In thin regions the eigenvalues may extend away from the real axis into the imaginary
plane. We give a direct characterization of optimal stability polynomials containing a maximal thin region and calculate these
polynomials for various cases. Semi-discretizations of hyperbolic–parabolic equations are a relevant application which exhibit
a thin region spectrum. As a model, linear, scalar advection–diffusion is investigated. The second-order-stabilized explicit
Runge–Kutta methods derived from the stability polynomials are applied to advection–diffusion and compressible, viscous fluid
dynamics in numerical experiments. Due to the stabilization the time step can be controlled solely from the hyperbolic CFL
condition even in the presence of viscous fluxes. 相似文献