全文获取类型
收费全文 | 23451篇 |
免费 | 697篇 |
国内免费 | 730篇 |
专业分类
化学 | 4119篇 |
晶体学 | 860篇 |
力学 | 524篇 |
综合类 | 69篇 |
数学 | 16566篇 |
物理学 | 2740篇 |
出版年
2023年 | 79篇 |
2022年 | 103篇 |
2021年 | 168篇 |
2020年 | 171篇 |
2019年 | 538篇 |
2018年 | 598篇 |
2017年 | 397篇 |
2016年 | 374篇 |
2015年 | 359篇 |
2014年 | 742篇 |
2013年 | 1245篇 |
2012年 | 781篇 |
2011年 | 1536篇 |
2010年 | 1528篇 |
2009年 | 1756篇 |
2008年 | 1801篇 |
2007年 | 1791篇 |
2006年 | 1390篇 |
2005年 | 1055篇 |
2004年 | 949篇 |
2003年 | 752篇 |
2002年 | 644篇 |
2001年 | 537篇 |
2000年 | 464篇 |
1999年 | 483篇 |
1998年 | 424篇 |
1997年 | 358篇 |
1996年 | 462篇 |
1995年 | 395篇 |
1994年 | 423篇 |
1993年 | 371篇 |
1992年 | 299篇 |
1991年 | 194篇 |
1990年 | 192篇 |
1989年 | 185篇 |
1988年 | 121篇 |
1987年 | 133篇 |
1986年 | 135篇 |
1985年 | 174篇 |
1984年 | 119篇 |
1983年 | 71篇 |
1982年 | 122篇 |
1981年 | 99篇 |
1980年 | 81篇 |
1979年 | 42篇 |
1978年 | 64篇 |
1977年 | 71篇 |
1976年 | 51篇 |
1975年 | 15篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
We propose a new scheme for the long time approximation of a diffusion when the drift vector field is not globally Lipschitz. Under this assumption, a regular explicit Euler scheme–with constant or decreasing step–may explode and implicit Euler schemes are CPU-time expensive. The algorithm we introduce is explicit and we prove that any weak limit of the weighted empirical measures of this scheme is a stationary distribution of the stochastic differential equation. Several examples are presented including gradient dissipative systems and Hamiltonian dissipative systems. 相似文献
92.
Q. Gong R. N tzel P.J. van Veldhoven T.J. Eijkemans J.H. Wolter 《Journal of Crystal Growth》2005,280(3-4):413-418
We report on the shape transition from InAs quantum dashes to quantum dots (QDs) on lattice-matched GaInAsP on InP(3 1 1)A substrates. InAs quantum dashes develop during chemical-beam epitaxy of 3.2 monolayers InAs, which transform into round InAs QDs by introducing a growth interruption without arsenic flux after InAs deposition. The shape transition is solely attributed to surface properties, i.e., increase of the surface energy and symmetry under arsenic deficient conditions. The round QD shape is maintained during subsequent GaInAsP overgrowth because the reversed shape transition from dot to dash is kinetically hindered by the decreased ad-atom diffusion under arsenic flux. 相似文献
93.
In this paper, we present a numerical scheme for solving the coupled system of compressible miscible displacement problem in porous media. The flow equation is solved by the mixed finite element method, and the transport equation is approximated by a discontinuous Galerkin method. The scheme is continuous in time and a priori hp error estimates is presented. 相似文献
94.
95.
Marilyn Breen 《Journal of Geometry》1989,36(1-2):8-16
LetS be a compact, simply connected set inR
2. If every boundary point ofS is clearly visible viaS from at least one of the three pointsa, b, c, thenS is a union of three starshaped sets whose kernels containa, b, c, respectively. The result fails when the number three is replaced by four.As a partial converse, ifS is a union of three starshaped sets whose kernels containa, b, c, respectively, then the set of points in the boundary ofS clearly visible from at least one ofa, b, orc is dense in the boundary ofS.Supported in part by NSF grant DMS-8705336. 相似文献
96.
Valery Agoshkov Paola Gervasio Alfio Quarteroni 《Mediterranean Journal of Mathematics》2006,3(2):147-176
New domain decomposition methods (DDM) based on optimal control approach are introduced for the coupling of first and second
order equations on overlapping subdomains. Several cost functionals and control functions are proposed. Uniqueness and existence
results are proved for the coupled problem, and the convergence of iterative processes is analyzed.
The work was supported by the Russian Foundation for Basic Research (04-01-00615) and it was partly carried out while the
first author was visiting the IACS at EPFL. 相似文献
97.
The authors give a consistent affirmative response to a question of Juhász, Soukup and Szentmiklóssy: If GCH fails, there are (many) extraresolvable, not maximally resolvable Tychonoff spaces. They show also in ZFC that for ω<λ?κ, no maximal λ-independent family of λ-partitions of κ is ω-resolvable. In topological language, that theorem translates to this: A dense, ω-resolvable subset of a space of the form (DI(λ)) is λ-resolvable. 相似文献
98.
We give a new and comparably short proof of Gittins’ index theorem for dynamic allocation problems of the multi-armed bandit type in continuous time under minimal assumptions. This proof gives a complete characterization of optimal allocation strategies as those policies which follow the current leader among the Gittins indices while ensuring that a Gittins index is at an all-time low whenever the associated project is not worked on exclusively. The main tool is a representation property of Gittins index processes which allows us to show that these processes can be chosen to be pathwise lower semi-continuous from the right and quasi-lower semi-continuous from the left. Both regularity properties turn out to be crucial for our characterization and the construction of optimal allocation policies. 相似文献
99.
Christos Kravvaritis Marilena Mitrouli Jennifer Seberry 《Linear and Multilinear Algebra》2007,55(5):471-490
In the present article we concentrate our study on the growth problem for the weighing matrix W(12,11) and show that the unique W(12,11) has three pivot structures. An improved algorithm for extending a k × k (0,+,-) matrix to a W(n,n-1), if possible, has been developed to simplify the proof. For the implementation of the algorithm special emphasis is given to the notions of data structures and parallel processing. 相似文献
100.
Martin Loebl 《Advances in Mathematics》2007,211(2):546-565
We define a q-chromatic function and q-dichromate on graphs and compare it with existing graph functions. Then we study in more detail the class of general chordal graphs. This is partly motivated by the graph isomorphism problem. Finally we relate the q-chromatic function to the colored Jones function of knots. This leads to a curious expression of the colored Jones function of a knot diagram K as a chromatic operator applied to a power series whose coefficients are linear combinations of long chord diagrams. Chromatic operators are directly related to weight systems by the work of Chmutov, Duzhin, Lando and Noble, Welsh. 相似文献