全文获取类型
收费全文 | 2607篇 |
免费 | 353篇 |
国内免费 | 161篇 |
专业分类
化学 | 193篇 |
晶体学 | 2篇 |
力学 | 1437篇 |
综合类 | 61篇 |
数学 | 765篇 |
物理学 | 663篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 52篇 |
2021年 | 65篇 |
2020年 | 74篇 |
2019年 | 67篇 |
2018年 | 66篇 |
2017年 | 92篇 |
2016年 | 139篇 |
2015年 | 86篇 |
2014年 | 145篇 |
2013年 | 182篇 |
2012年 | 171篇 |
2011年 | 176篇 |
2010年 | 147篇 |
2009年 | 150篇 |
2008年 | 154篇 |
2007年 | 155篇 |
2006年 | 140篇 |
2005年 | 129篇 |
2004年 | 126篇 |
2003年 | 126篇 |
2002年 | 86篇 |
2001年 | 81篇 |
2000年 | 69篇 |
1999年 | 57篇 |
1998年 | 44篇 |
1997年 | 54篇 |
1996年 | 32篇 |
1995年 | 39篇 |
1994年 | 20篇 |
1993年 | 25篇 |
1992年 | 27篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 20篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有3121条查询结果,搜索用时 15 毫秒
81.
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
82.
R. Nieva G. S. Christensen M. E. El-Hawary 《Journal of Optimization Theory and Applications》1981,35(2):261-275
This paper considers the problem of short-term optimal operation of nuclear-hydro-thermal electric power systems. The solution is obtained by use of a functional analytic optimization technique that employs the minimum norm formulation.A power system with an arbitrary number of generating stations is considered. The limited flexibility exhibited by the thermal nuclear reactors, when operating in a load-following mode, is accounted for by means of a model of the xenon concentration in their cores. The nonlinear effects induced by trapezoidal water reservoirs and the time delay of the water flow between upstream and downstream hydroplants is taken into consideration as well.A two-level iterative scheme of the feasible type is proposed for implementing the optimal solution.This work was supported in part by the National Research Council of Canada, Grant No. A-4146. 相似文献
83.
The stability of a curved rail under a constant moving load has been investigated using a linear theory; critical speeds of the moving load, and the dynamic rail deflections and rotation were calculated. The effect of the foundation was included through distributed linear springs. It was assumed that the moving load remains in constant contact with the rail and travels along a fixed path on the rail head. 相似文献
84.
This paper considers the problem of the robust H
filtering for a class of nonlinear discrete-time Markovian jump systems with real time-varying norm-bounded parameter uncertainty. For each mode, the nonlinearity is assumed to satisfy the global Lipschitz conditions and appears in both the state and measured output equations. The problem that we address is the design of a nonlinear filter which ensures robust stochastic stability and a prescribed H
performance level of the filtering error system for all admissible uncertainties. A sufficient condition for the solvability of this problem is obtained in terms of a set of linear matrix inequalities; an explicit expression of a desired nonlinear H
filter is also given. Finally, an example is provided to demonstrate the effectiveness of the proposed approach. 相似文献
85.
The paper studies the dynamic behavior of perfect rigid-plastic plates in the form of a sector with hinged or clamped sides under short-term intensive loads. Two dynamic deformation mechanisms are demonstrated. The dynamic equation is derived for each of the mechanisms. The realization conditions for the mechanisms are analyzed. Analytical expressions are derived for the ultimate (high) loads and the maximum residual deflection. Numerical examples are given 相似文献
86.
We derive asymptotic expansions for tails of infinite weighted convolutions of some heavy-tailed distributions. Applications
are given to tail expansion of the marginal distribution of ARMA processes, randomly stopped sums, as well as limiting waiting
time distribution.
AMS 2000 Subject Classifications. Primary—62E99, Secondary—41A60, 44A35, 60G50, 60K25 相似文献
87.
G. Doucas M. F. Kimmitt Th. Kormann G. Korschinek C. Wallner 《International Journal of Infrared and Millimeter Waves》2003,24(6):829-845
Spontaneous Smith-Purcell radiation at wavelengths of 100 and 220m has been observed. The angles of observation were 17° and 28° and the electron beam energies 1.9 and 1.56MeV, respectively. The radiated power was about 320nW at 17° and 92nW at 28°. These values are in reasonable agreement with what is theoretically expected if the emission process is due to the acceleration of image charges induced on the grating surface by the electrons of the beam. 相似文献
88.
A monotone dependence of the critical buckling load of a simplysupported TimoshenkoMindlin beam both on the shear correctionfactor and on the stiffness of foundation is proved. Then theworst-scenario method is employed to find the most dangerousinput data. 相似文献
89.
90.