全文获取类型
收费全文 | 14955篇 |
免费 | 1251篇 |
国内免费 | 4432篇 |
专业分类
化学 | 14177篇 |
晶体学 | 412篇 |
力学 | 652篇 |
综合类 | 172篇 |
数学 | 2694篇 |
物理学 | 2531篇 |
出版年
2024年 | 24篇 |
2023年 | 131篇 |
2022年 | 322篇 |
2021年 | 352篇 |
2020年 | 393篇 |
2019年 | 335篇 |
2018年 | 360篇 |
2017年 | 435篇 |
2016年 | 506篇 |
2015年 | 417篇 |
2014年 | 696篇 |
2013年 | 1156篇 |
2012年 | 1462篇 |
2011年 | 817篇 |
2010年 | 677篇 |
2009年 | 908篇 |
2008年 | 1061篇 |
2007年 | 1134篇 |
2006年 | 1054篇 |
2005年 | 1040篇 |
2004年 | 923篇 |
2003年 | 780篇 |
2002年 | 679篇 |
2001年 | 542篇 |
2000年 | 533篇 |
1999年 | 500篇 |
1998年 | 441篇 |
1997年 | 388篇 |
1996年 | 385篇 |
1995年 | 351篇 |
1994年 | 315篇 |
1993年 | 230篇 |
1992年 | 293篇 |
1991年 | 216篇 |
1990年 | 173篇 |
1989年 | 128篇 |
1988年 | 96篇 |
1987年 | 74篇 |
1986年 | 78篇 |
1985年 | 60篇 |
1984年 | 44篇 |
1983年 | 26篇 |
1982年 | 29篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1974年 | 4篇 |
1972年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Jakob Jonsson 《Journal of Algebraic Combinatorics》2009,29(1):81-90
J.L. Andersen proved that there is 5-torsion in the bottom nonvanishing homology group of the simplicial complex of graphs
of degree at most two on seven vertices. We use this result to demonstrate that there is 5-torsion also in the bottom nonvanishing
homology group of the matching complex
on 14 vertices. Combining our observation with results due to Bouc and to Shareshian and Wachs, we conclude that the case
n=14 is exceptional; for all other n, the torsion subgroup of the bottom nonvanishing homology group has exponent three or is zero. The possibility remains that
there is other torsion than 3-torsion in higher-degree homology groups of
when n≥13 and n≠14.
Research of J. Jonsson was supported by European Graduate Program “Combinatorics, Geometry, and Computation”, DFG-GRK 588/2. 相似文献
993.
Jean-Daniel Boissonnat Leonidas J. Guibas Steve Y. Oudot 《Discrete and Computational Geometry》2009,42(1):37-70
It is a well-established fact that the witness complex is closely related to the restricted Delaunay triangulation in low
dimensions. Specifically, it has been proved that the witness complex coincides with the restricted Delaunay triangulation
on curves, and is still a subset of it on surfaces, under mild sampling conditions. In this paper, we prove that these results
do not extend to higher-dimensional manifolds, even under strong sampling conditions such as uniform point density. On the
positive side, we show how the sets of witnesses and landmarks can be enriched, so that the nice relations that exist between
restricted Delaunay triangulation and witness complex hold on higher-dimensional manifolds as well. We derive from our structural
results an algorithm that reconstructs manifolds of any arbitrary dimension or co-dimension at different scales. The algorithm
combines a farthest-point refinement scheme with a vertex pumping strategy. It is very simple conceptually, and it does not
require the input point sample to be sparse. Its running time is bounded by c(d)n
2, where n is the size of the input point cloud, and c(d) is a constant depending solely (yet exponentially) on the dimension d of the ambient space. Although this running time makes our reconstruction algorithm rather theoretical, recent work has shown
that a variant of our approach can be made tractable in arbitrary dimensions, by building upon the results of this paper.
This work was done while S.Y. Oudot was a post-doctoral fellow at Stanford University. His email there is no longer valid. 相似文献
994.
为了刻画复杂随机系统的理性决策,提出了复杂随机系统的生存性及不变性的概念,给出并证明了复杂随机系统的生存性定理及不变性定理.并提出了均方相依锥,生存域与不变域的概念.得到了与文献中的一致的结论. 相似文献
995.
Sanvesh Srivastava Glen DePalma Chuanhai Liu 《Journal of computational and graphical statistics》2019,28(2):233-243
The family of expectation--maximization (EM) algorithms provides a general approach to fitting flexible models for large and complex data. The expectation (E) step of EM-type algorithms is time-consuming in massive data applications because it requires multiple passes through the full data. We address this problem by proposing an asynchronous and distributed generalization of the EM called the distributed EM (DEM). Using DEM, existing EM-type algorithms are easily extended to massive data settings by exploiting the divide-and-conquer technique and widely available computing power, such as grid computing. The DEM algorithm reserves two groups of computing processes called workers and managers for performing the E step and the maximization step (M step), respectively. The samples are randomly partitioned into a large number of disjoint subsets and are stored on the worker processes. The E step of DEM algorithm is performed in parallel on all the workers, and every worker communicates its results to the managers at the end of local E step. The managers perform the M step after they have received results from a γ-fraction of the workers, where γ is a fixed constant in (0, 1]. The sequence of parameter estimates generated by the DEM algorithm retains the attractive properties of EM: convergence of the sequence of parameter estimates to a local mode and linear global rate of convergence. Across diverse simulations focused on linear mixed-effects models, the DEM algorithm is significantly faster than competing EM-type algorithms while having a similar accuracy. The DEM algorithm maintains its superior empirical performance on a movie ratings database consisting of 10 million ratings. Supplementary material for this article is available online. 相似文献
996.
Sheree T. Sharpe 《Mathematical Thinking and Learning》2019,21(1):78-84
In this study, the author examined student attempts to translate a verbal problem into an algebraic statement relating two variables, after they had solved an arithmetic question from the same problem. A total of 645 students from New England (U.S.A.) answered the problem on a mathematics assessment administered at the beginning of the school year. Among students who could solve the arithmetic part of the problem, the use of variables in the correct conventional notation appeared from grade 7 and continuously increased through grade 9. These results suggest that there is a relationship between students’ arithmetic understanding and translating verbal problems into algebraic statements relating two variables. 相似文献
997.
998.
A systematic and intuitive approach for the separation of variables of the three-dimensional Dirac equation in spherical coordinates is presented. Using this approach, we consider coupling of the Dirac spinor to electromagnetic four-vector potential that satisfies the Lorentz gauge. The space components of the potential have angular (non-central) dependence such that the Dirac equation becomes separable in all coordinates. We obtain exact solutions for a class of three-parameter static electromagnetic potential whose time component is the Coulomb potential. The relativistic energy spectrum and corresponding spinor wave functions are obtained. The Aharonov–Bohm and magnetic monopole potentials are included in these solutions. 相似文献
999.
ABSTRACTWe consider a certain family of CIFSs of the generalized complex continued fractions with a complex parameter space. We show that for each CIFS of the family, the Hausdorff measure of the limit set of the CIFS with respect to the Hausdorff dimension is zero and the packing measure of the limit set of the CIFS with respect to the Hausdorff dimension is positive (main result). This is a new phenomenon of infinite CIFSs which cannot hold in finite CIFSs. We prove the main result by showing some estimates for the unique conformal measure of each CIFS of the family and by using some geometric observations. 相似文献
1000.
ABSTRACTThe paper deals with a mixed problem for nonstationary generalised Maxwell equations. The boundary conditions are of Riemann-Hilbert type. The problem is reduced to a mixed problem for a wave equation where the boundary conditions are of Dirichlet type as they were introduced by D. Spencer in the middle 1950?s. We use the Fourier method to construct an approximate solution to the problem in certain function spaces of Sobolev type. 相似文献