全文获取类型
收费全文 | 243495篇 |
免费 | 2425篇 |
国内免费 | 872篇 |
专业分类
化学 | 130617篇 |
晶体学 | 3711篇 |
力学 | 9919篇 |
综合类 | 2篇 |
数学 | 27133篇 |
物理学 | 75410篇 |
出版年
2020年 | 1773篇 |
2019年 | 2042篇 |
2018年 | 2478篇 |
2017年 | 2414篇 |
2016年 | 3836篇 |
2015年 | 2598篇 |
2014年 | 3906篇 |
2013年 | 11187篇 |
2012年 | 8098篇 |
2011年 | 10035篇 |
2010年 | 6587篇 |
2009年 | 6488篇 |
2008年 | 9023篇 |
2007年 | 9161篇 |
2006年 | 8411篇 |
2005年 | 7857篇 |
2004年 | 7001篇 |
2003年 | 6220篇 |
2002年 | 6150篇 |
2001年 | 7210篇 |
2000年 | 5378篇 |
1999年 | 4224篇 |
1998年 | 3556篇 |
1997年 | 3587篇 |
1996年 | 3298篇 |
1995年 | 3147篇 |
1994年 | 2964篇 |
1993年 | 3025篇 |
1992年 | 3312篇 |
1991年 | 3329篇 |
1990年 | 3149篇 |
1989年 | 3106篇 |
1988年 | 3168篇 |
1987年 | 3038篇 |
1986年 | 2926篇 |
1985年 | 3993篇 |
1984年 | 4157篇 |
1983年 | 3407篇 |
1982年 | 3756篇 |
1981年 | 3654篇 |
1980年 | 3529篇 |
1979年 | 3561篇 |
1978年 | 3784篇 |
1977年 | 3611篇 |
1976年 | 3821篇 |
1975年 | 3390篇 |
1974年 | 3522篇 |
1973年 | 3822篇 |
1972年 | 2327篇 |
1971年 | 1787篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
Recently, Chawla et al. described a second order finite difference method for the class of singular two-point boundary value problems:
相似文献
982.
After recalling the basic properties of para-coKählerian manifolds \(\tilde M\) with concircular structure vector field ξ, the infinitesimal auto morphismsX of the structure 1-form \(\tilde \eta \) are considered. One of the results is that the Lie derivative of all powers of the structure 2-form \(\tilde \Omega ,\) i.e. \(\mathcal{L}x\tilde \Omega ^p ;p = 1,...,m,\) is exterior recurrent. Further two types of horizontal distributionsD n which are normal to ξ. IfD t (resp.D n ) is involutive, the corresponding leafM t (resp.M n ) is a minimal submanifold of \(\tilde M\) . FurtherM n is a symplectic submanifold and ξ is an umbilical normal section ofM n . Finally proper immersion \(M \to \tilde M\) are discussed, whereM is aCR-sub-manifold whose horizontal distribution isD t . It is shown that the vertical distribution is involutive, and the restriction of ξ toM is an symptotic direction. Some interesting special cases are treated. 相似文献
983.
K. R. Muraleedharan Nair N. Unnikrishnan Nair 《Annals of the Institute of Statistical Mathematics》1988,40(2):267-271
In this note, a characterization of the Gumbel's bivariate exponential distribution based on the properities of the conditional moments is discussed. The result forms a sort of bivariate analogue of the characterization of the univariate exponential distribution given by Sahobov and Geshev (1974) (cited in Lau and Rao ((1982), Sankhy Ser. A, 44, 87)). A discrete version of the property provides a similar conclusion relating to a bivariate geometric distribution. 相似文献
984.
R. M. Megrabian 《Analysis Mathematica》1988,14(1):37-47
В статье рассматрива ются множестваM N , 1≦N<∞ всех систем функций Φ={?(x)} j =1/N , заданных на [0,1] с где (ε i, j ) i, j =1/N — матрица с э лементами ± 1. Изучаетс я поведение наМ N функц ии $$\alpha _N (\Phi ) = \mathop {\sup }\limits_\sigma \mathop {\sup }\limits_{\sum a_j^2 = 1} (\int\limits_0^1 {\mathop {\sup }\limits_{1 \leqq k \leqq N} (\sum\limits_{j = 1}^k {a_j \varphi _{\sigma (j)} (x)} } )^2 dx)^{1/2} $$ гдеσ: {1, ...,N}?{1, ...,N}. Дока зьгаается, что сущест вуют абсолютные постоянн ыеc 3,c 4>0,y 0>1, такие, что для любог оN=1,2, ... иy>y 0 $$\mu _N (\{ \Phi \in {\rm M}_{\rm N} :\alpha _N (\Phi )/\left\| \Phi \right\| > y\} ) \leqq c_3 \exp [ - \exp (c_4 y)N]$$ гдеμ N — мера наM N с µ N ({Ф}) = 2?N2 дл я любой системыΦ∈M 相似文献
985.
We present a modification of the Cyclic Subgradient Projection (CSP) method by Censor and Lent, which solves the convex feasibility problem in a finite number of steps when a Slater type condition holds, while preserving its row-action properties. A linear rate of convergence for the CSP method is established assuming the same hypothesis.Research partially supported by CNPq, under Grant No. 301699/81. 相似文献
986.
This paper is concerned with a study of bounded perturbations of resonant linear problems. It follows from our results that for certain types of bounded domains Ω ? Rn, n ≥ 2, the Dirichlet problem $\matrix{\Delta u+\lambda_{1}u+g(u)=h(x),\ \ \ x\in\Omega\cr \quad\quad\quad\quad\quad\quad u=0,\ \ \ x\in\partial\Omega,}$ has infinitely many positive solutions, in case λ1 is the principal eigenvalue of ?Δ subject to trivial Dirichlet boundary conditions, g is a nontrivial periodic nonlinearity of zero mean and ∫03A9h(x)?(x)dx = 0, where ? is an eigenfunction corresponding to λ1. 相似文献
987.
We study sequences (X
0, X
1, ...) of random variables, taking values in the positive integers, which grow faster than branching processes in the sense that
, for m, n0, where the X
n
(m, i) are distributed as X
n
and have certain properties of independence. We prove that, under appropriate conditions, X
n
1/n
almost surely and in L
1, where =sup E(X
n
)1/n
. Our principal application of this result is to study the Lebesgue measure and (Hausdorff) dimension of certain projections of sets in a class of random Cantor sets, being those obtained by repeated random subdivisions of the M-adic subcubes of [0, 1]
d
. We establish a necessary and sufficient condition for the Lebesgue measure of a projection of such a random set to be non-zero, and determine the box dimension of this projection.Work done partly whilst visiting Cornell University with the aid of a Fulbright travel grant 相似文献
988.
989.
R. W. R. Darling 《Probability Theory and Related Fields》1988,77(2):211-229
Let Z
1, Z
2,... be a sequence of i.i.d. random transformations (possibly discontinuous) of a compact metric space M, and let E denote the space of normalized mass distributions on M. Given in E, let
n
denote the random measure °(Z
n
°...°Z
1)–1 (when well-defined). We construct the transition probability P of the E-valued Markov chain (
n
), and give a necessary and sufficient condition for P to have a unique invariant measure concentrated on the degenerate mass distributions. Convergence to statistical equilibrium of the associated discrete-time stochastic flow is investigated.Research supported by NSF grants INT-8420360 and DMS-8502802. This work was done while the author was visiting the Universities of Warwick and Minnesota 相似文献
990.
|