全文获取类型
收费全文 | 22317篇 |
免费 | 1519篇 |
国内免费 | 1092篇 |
专业分类
化学 | 9697篇 |
晶体学 | 119篇 |
力学 | 282篇 |
综合类 | 149篇 |
数学 | 13195篇 |
物理学 | 1486篇 |
出版年
2023年 | 146篇 |
2022年 | 271篇 |
2021年 | 294篇 |
2020年 | 435篇 |
2019年 | 586篇 |
2018年 | 539篇 |
2017年 | 403篇 |
2016年 | 548篇 |
2015年 | 535篇 |
2014年 | 816篇 |
2013年 | 1471篇 |
2012年 | 961篇 |
2011年 | 1340篇 |
2010年 | 1212篇 |
2009年 | 1601篇 |
2008年 | 1664篇 |
2007年 | 1663篇 |
2006年 | 1337篇 |
2005年 | 1027篇 |
2004年 | 984篇 |
2003年 | 860篇 |
2002年 | 547篇 |
2001年 | 453篇 |
2000年 | 485篇 |
1999年 | 495篇 |
1998年 | 464篇 |
1997年 | 392篇 |
1996年 | 411篇 |
1995年 | 400篇 |
1994年 | 341篇 |
1993年 | 254篇 |
1992年 | 220篇 |
1991年 | 169篇 |
1990年 | 168篇 |
1989年 | 162篇 |
1988年 | 118篇 |
1987年 | 110篇 |
1986年 | 114篇 |
1985年 | 149篇 |
1984年 | 127篇 |
1983年 | 65篇 |
1982年 | 107篇 |
1981年 | 83篇 |
1980年 | 93篇 |
1979年 | 62篇 |
1978年 | 67篇 |
1977年 | 43篇 |
1976年 | 40篇 |
1975年 | 28篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
In this paper one specifies the ergodic behavior of the 2D-stochastic Navier–Stokes equation by giving a Large Deviation Principle for the occupation measure for large time. It describes the exact rate of exponential convergence. The considered random force is non-degenerate and compatible with the strong Feller property. 相似文献
132.
We continue the studies on the so–called genuine Bernstein–Durrmeyer operators U
n
by establishing a recurrence formula for the moments and by investigating the semigroup T(t) approximated by U
n
. Moreover, for sufficiently smooth functions the degree of this convergence is estimated. We also determine the eigenstructure
of U
n
, compute the moments of T(t) and establish asymptotic formulas.
Received: January 26, 2007. 相似文献
133.
134.
D.P. Baturov 《Topology and its Applications》2007,154(2):374-383
Let M be a separable metric space consisting of more than one point. We construct perfectly normal dense subspaces Z⊂Mc2 and (under additional set-theoretic assumption) Y⊂Mc which are not collectionwise Hausdorff. 相似文献
135.
In 1997 Lampert and Slater introduced parallel knock-out schemes, an iterative process on graphs that goes through several rounds. In each round of this process, every vertex eliminates exactly one of its neighbors. The parallel knock-out number of a graph is the minimum number of rounds after which all vertices have been eliminated (if possible). The parallel knock-out number is related to well-known concepts like perfect matchings, hamiltonian cycles, and 2-factors.We derive a number of combinatorial and algorithmic results on parallel knock-out numbers: for families of sparse graphs (like planar graphs or graphs of bounded tree-width), the parallel knock-out number grows at most logarithmically with the number n of vertices; this bound is basically tight for trees. Furthermore, there is a family of bipartite graphs for which the parallel knock-out number grows proportionally to the square root of n. We characterize trees with parallel knock-out number at most 2, and we show that the parallel knock-out number for trees can be computed in polynomial time via a dynamic programming approach (whereas in general graphs this problem is known to be NP-hard). Finally, we prove that the parallel knock-out number of a claw-free graph is either infinite or less than or equal to 2. 相似文献
136.
If g and G are the pdf and the cdf of a distribution symmetric around 0 then the pdf 2g(u)G(λ
u) is said to define a skew distribution. In this paper, we provide a mathematical treatment of the skew distributions when
g and G are taken to come from one of Pearson type II, Pearson type VII or the generalized t distribution.
相似文献
137.
We study the asymptotic behaviour of non-negative solutions of Yamabe type equations on a complete Riemannian manifold. Then we provide a comparison result, based on a form of the weak maximum principle at infinity, which together with the “a priori” estimates previously obtained, yields uniqueness under very general Ricci assumptions. The paper ends with an existence result and an application to the non-compact Yamabe problem. 相似文献
138.
Hubert de Fraysseix 《Discrete Applied Mathematics》2007,155(9):1079-1095
Using a general resolution of barycentric systems we give a generalization of Tutte's theorem on convex drawing of planar graphs. We deduce a characterization of the edge coverings into pairwise non-crossing paths which are stretchable: such a system is stretchable if and only if each subsystem of at least two paths has at least three free vertices (vertices of the outer face of the induced subgraph which are internal to none of the paths of the subsystem). We also deduce that a contact system of pseudo-segments is stretchable if and only if it is extendible. 相似文献
139.
Adriana Tudose 《Tetrahedron letters》2006,47(48):8529-8533
Simple catalysts formed in situ from palladium acetate and a variety of imidazolium and imidazolinium carboxylates and dithiocarboxylates have been screened in the coupling of aryl halides with trans-2-phenylvinylboronic acid. Imidazol(in)ium carboxylates show an excellent activity, which compares to that displayed by the parent imidazol(in)ium chlorides, whereas imidazol(in)ium dithiocarboxylates are poorly efficient. Interestingly, the base employed exerts a profound influence on the trans/cis stereochemistry of the coupling product. 相似文献
140.
文章合成了N,N'-二正丁基苝四羧酸二酰亚胺,并纯化、调晶,进行了IR、元素分析、X射线等测定.分析该化合物在DMF中的紫外光谱(最大吸收波长524.80 nm)、荧光光谱(最大发射波长539.0 nm)、Stokes位移(数值15 nm)等光谱性质.在400~700 nm范围内,α晶型薄膜紫外-可见吸收出现很强的吸收峰,且由β型变为α型,最大吸收波长有明显的红移(545 nm变为580 nm).X射线粉末衍射也反映出α晶型的2θ在26.0°处衍射峰CPS为2 508,β型在25.2°为1 891.α,β晶型作为电荷产生材料制得的功能分离型有机光导体,在光源滤波波长λ=532 nm曝光下,测得含α,β感光体达到饱和电位的时间分别为46,93.98 s,光衰电位(5.3千伏电压负充电电晕,1~2 s后的表面电位)分别为727和525 V,半衰曝光量分别为4.32,4.34μJ·cm-2,残余电位分别为30和45 V等光导性能数值. 相似文献