全文获取类型
收费全文 | 46948篇 |
免费 | 1642篇 |
国内免费 | 1533篇 |
专业分类
化学 | 30597篇 |
晶体学 | 342篇 |
力学 | 1222篇 |
综合类 | 19篇 |
数学 | 6503篇 |
物理学 | 11440篇 |
出版年
2023年 | 270篇 |
2022年 | 690篇 |
2021年 | 839篇 |
2020年 | 712篇 |
2019年 | 707篇 |
2018年 | 774篇 |
2017年 | 716篇 |
2016年 | 1426篇 |
2015年 | 1166篇 |
2014年 | 1308篇 |
2013年 | 2546篇 |
2012年 | 2911篇 |
2011年 | 3233篇 |
2010年 | 1798篇 |
2009年 | 1958篇 |
2008年 | 2561篇 |
2007年 | 2503篇 |
2006年 | 2172篇 |
2005年 | 2649篇 |
2004年 | 2882篇 |
2003年 | 2093篇 |
2002年 | 1654篇 |
2001年 | 1101篇 |
2000年 | 972篇 |
1999年 | 645篇 |
1998年 | 563篇 |
1997年 | 522篇 |
1996年 | 609篇 |
1995年 | 494篇 |
1994年 | 469篇 |
1993年 | 544篇 |
1992年 | 486篇 |
1991年 | 377篇 |
1990年 | 323篇 |
1989年 | 296篇 |
1988年 | 262篇 |
1987年 | 266篇 |
1986年 | 263篇 |
1985年 | 363篇 |
1984年 | 357篇 |
1983年 | 284篇 |
1982年 | 278篇 |
1981年 | 274篇 |
1980年 | 240篇 |
1979年 | 196篇 |
1978年 | 235篇 |
1977年 | 199篇 |
1976年 | 184篇 |
1975年 | 158篇 |
1974年 | 175篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
131.
Mathilde Kammerer-Colin de Verdière 《Comptes Rendus Mathematique》2004,339(9):625-629
For generic families of vector fields or transformations, normally hyperbolic invariant products of spheres appear near partially elliptic rest points. To cite this article: M. Kammerer-Colin de Verdière, C. R. Acad. Sci. Paris, Ser. I 339 (2004). 相似文献
132.
We show that the tensor product B-spline basis and the triangular Bernstein basis are in some sense best conditioned among all nonnegative bases for the spaces of tensor product splines and multivariate polynomials, respectively. We also introduce some new condition numbers which are analogs of component-wise condition numbers for linear systems introduced by Skeel. 相似文献
133.
This paper describes an application of statics to geometrical proofs in the classroom. The aim of the study was to find out whether the use of concepts and arguments from statics can help students understand and produce proofs of geometrical theorems. The two theorems studied were (1) that the medians in a triangle meet at a single point which is the centre of gravity of the triangle, and (2) the Varignon theorem, that the lines joining the midpoints of successive sides of a quadrilateral form a parallelogram. The classroom experiment showed that most students were successful in using arguments from statics in their proofs, and that they gained a better understanding of the theorems. These findings lend support to the claim that the introduction of statics helps students produce proofs and grasp their meaning. 相似文献
134.
135.
We perform three tests on our proposal to implement diffeomorphism invariance in the non-abelian D0-brane DBI action as a base-point independence constraint between matrix Riemann normal coordinate systems. First, we show that T-duality along an isometry correctly interchanges the potential and kinetic terms in the action. Second, we show that the method to impose base-point independence using an auxiliary dN2-dimensional nonlinear sigma model also works for metrics which are curved along the brane, provided a physical gauge choice is made at the end. Third, we show that without alteration this method is applicable to higher order in velocities. Testing specifically to order 4, we elucidate the range of validity of the symmetrized trace approximation to the non-abelian DBI action. 相似文献
136.
N. Segovia M. A. Armienta C. Valdes M. Mena J. L. Seidel M. Monnin P. Pea M. B. E. Lopez A. V. Reyes 《Radiation measurements》2003,36(1-6):379-383
Soil radon has been monitored at two fixed stations in the northern flank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate diffuse degassing through the flanks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000–2002). 相似文献
137.
L.G. Casado I. García T. Csendes V.G. Ruíz 《Journal of Optimization Theory and Applications》2003,118(1):27-43
Based on the investigation carried out in Ref. 1, this paper incorporates new studies about the properties of inclusion functions on subintervals while a branch-and-bound algorithm is solving global optimization problems. It is found that the relative place of the global minimum value within the inclusion function value of the objective function at the current interval indicates mostly whether the given interval is close to a minimizer point. This information is used in a heuristic interval rejection rule that can save a considerable amount of computation. Illustrative examples are discussed and an extended numerical study shows the advantages of the new approach. 相似文献
138.
139.
E.D. Aydin C.R.E. de Oliveira 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(3):247-260
In this paper, we solve the steady-state form of the Boltzmann transport equation in homogeneous and heterogeneous tissue-like media with a finite element-spherical harmonics (FE-PN) radiation transport method. We compare FE-transport and diffusion solutions in terms of the ratio of absorption to reduced scattering coefficient, (μa/μs′) and the anisotropy factor g. Two different scattering phase function formulas are employed to model anisotropic scattering in the slab media with high g-value. Influence of void-like heterogeneities, and of their boundaries with the surrounding medium on the transport of photons are also examined. 相似文献
140.
We show that reductions of KP hierarchies related to the loop algebra of SLn with homogeneous gradation give solutions of the Darboux-Egoroff system of PDE's. Using explicit dressing matrices of the Riemann-Hilbert problem generalized to include a set of commuting additional symmetries, we construct solutions of the Witten– Dijkgraaf–E. Verlinde–H. Verlinde equations. 相似文献