全文获取类型
收费全文 | 23428篇 |
免费 | 2091篇 |
国内免费 | 1362篇 |
专业分类
化学 | 1857篇 |
晶体学 | 34篇 |
力学 | 2707篇 |
综合类 | 218篇 |
数学 | 17885篇 |
物理学 | 4180篇 |
出版年
2024年 | 44篇 |
2023年 | 236篇 |
2022年 | 221篇 |
2021年 | 355篇 |
2020年 | 615篇 |
2019年 | 643篇 |
2018年 | 616篇 |
2017年 | 633篇 |
2016年 | 670篇 |
2015年 | 559篇 |
2014年 | 1009篇 |
2013年 | 2360篇 |
2012年 | 1003篇 |
2011年 | 1296篇 |
2010年 | 1098篇 |
2009年 | 1513篇 |
2008年 | 1440篇 |
2007年 | 1474篇 |
2006年 | 1323篇 |
2005年 | 1060篇 |
2004年 | 981篇 |
2003年 | 938篇 |
2002年 | 927篇 |
2001年 | 734篇 |
2000年 | 760篇 |
1999年 | 693篇 |
1998年 | 571篇 |
1997年 | 540篇 |
1996年 | 390篇 |
1995年 | 270篇 |
1994年 | 252篇 |
1993年 | 180篇 |
1992年 | 176篇 |
1991年 | 127篇 |
1990年 | 116篇 |
1989年 | 86篇 |
1988年 | 72篇 |
1987年 | 59篇 |
1986年 | 59篇 |
1985年 | 88篇 |
1984年 | 120篇 |
1983年 | 57篇 |
1982年 | 86篇 |
1981年 | 87篇 |
1980年 | 80篇 |
1979年 | 69篇 |
1978年 | 64篇 |
1977年 | 42篇 |
1976年 | 38篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Zhang J. Z. Deng N. Y. Chen L. H. 《Journal of Optimization Theory and Applications》1999,102(1):147-167
In unconstrained optimization, the usual quasi-Newton equation is B
k+1
s
k=y
k, where y
k is the difference of the gradients at the last two iterates. In this paper, we propose a new quasi-Newton equation,
, in which
is based on both the function values and gradients at the last two iterates. The new equation is superior to the old equation in the sense that
better approximates 2
f(x
k+1)s
k than y
k. Modified quasi-Newton methods based on the new quasi-Newton equation are locally and superlinearly convergent. Extensive numerical experiments have been conducted which show that the new quasi-Newton methods are encouraging. 相似文献
992.
Mochi M. Pacelli G. Recchioni M. C. Zirilli F. 《Journal of Optimization Theory and Applications》1999,100(1):29-57
In this paper, we consider an inverse problem for a class of two-dimensional diffusion equations with piecewise constant coefficients. This problem is studied using an explicit formula for the relevant spectral measures and an asymptotic expansion of the solution of the diffusion equations. A numerical method that reduces the inverse problem to a sequence of nonlinear least-square problems is proposed and tested on synthetic data. 相似文献
993.
1.引言考虑非线性代数方程组这里, 为连续的对角映射,二者的导函数均存在,但并不一定连续.这类非线性代数方程组具有丰富的实际背景.譬如,Stefan问题和许多弱非线性椭圆型偏微分方程,就可归结为(1.1)的数值求解问题.根据方程组(1.1)的特殊结构,并利用矩阵多重分裂思想,文tZ]讨论了一类并行非线性Gauss-Seidel型迭代算法.这类算法具有很好的数值性质和较高的并行效率·在此基础上,运用松弛加速技术,文[8]进一步研究了一类并行多分… 相似文献
994.
一阶时滞微分方程解的零点分布 总被引:3,自引:0,他引:3
Abstract. The paper gives two estimates of the distance between adjacent zeros of solutions 相似文献
995.
Sufficient conditions are established for the oscillation of proper solutions of the system
where f
i
:+ × 2m (i=1,2) satisfy the local Carathéodory conditions and
i
,
i
:+ +(i=1,...,m) are continuous functions such that
i
(t) t for
. 相似文献
996.
We show that if a bounded analytic semigroup on satisfies a Gaussian estimate of order and is the generator of its consistent semigroup on , then generates a -regularized group on where . We obtain the estimate of () and the -independence of , and give applications to Schrödinger operators and elliptic operators of higher order.
997.
Milan Kučera 《Czechoslovak Mathematical Journal》1999,49(3):449-474
Variational inequalities
are studied, where K is a closed convex cone in
, 3, B
is a × matrix, G is a small perturbation, a real parameter. The assumptions guaranteeing a Hopf bifurcation at some 0 for the corresponding equation are considered and it is proved that then, in some situations, also a bifurcation of periodic solutions to our inequality occurs at some I 0. Bifurcating solutions are obtained by the limiting process along branches of solutions to penalty problems starting at 0 constructed on the basis of the Alexander-Yorke theorem as global bifurcation branches of a certain enlarged system. 相似文献
998.
J M Landsberg 《Compositio Mathematica》1999,118(2):189-201
Let XP be a variety (respectively an open subset of an analytic submanifold) and let xX be a point where all integer valued differential invariants are locally constant. We show that if the projective second fundamental form of X at x is isomorphic to the second fundamental form of a point of a Segre P× P, n,m2, a Grassmaniann G(2,n+2), n4, or the Cayley plane OP2, then X is the corresponding homogeneous variety (resp. an open subset of the corresponding homogeneous variety). The case of the Segre P2×P2 had been conjectured by Griffiths and Harris in [GH]. If the projective second fundamental form of X at x is isomorphic to the second fundamental form of a point of a Veronese v2(P) and the Fubini cubic form of X at x is zero, then X=v2 (P) (resp. an open subset of v2(P)). All these results are valid in the real or complex analytic categories and locally in the C category if one assumes the hypotheses hold in a neighborhood of any point x. As a byproduct, we show that the systems of quadrics I2(P P) S2C, I2(P1× P) S2C and I2(S5) S2C16 are stable in the sense that if A S* is an analytic family such that for t0,AA, then A0A. We also make some observations related to the Fulton–:Hansen connectedness theorem. 相似文献
999.
Oleg Palumbíny 《Czechoslovak Mathematical Journal》1999,49(4):779-790
The paper deals with the oscillation of a differential equation L
4
y + P(t)L
2
y + Q(t)y 0 as well as with the structure of its fundamental system of solutions. 相似文献
1000.
Orbits of the ODE y=0 in corresponding jet bundles are investigated. Explicit relations for the right-hand side of an arbitrary 3-order ODE necessary and sufficient for the existence of a contact transformation reducing this equation locally to the form y=0 are obtained. 相似文献