全文获取类型
收费全文 | 10511篇 |
免费 | 297篇 |
国内免费 | 98篇 |
专业分类
化学 | 434篇 |
晶体学 | 11篇 |
力学 | 66篇 |
综合类 | 6篇 |
数学 | 9439篇 |
物理学 | 632篇 |
无线电 | 318篇 |
出版年
2023年 | 21篇 |
2022年 | 25篇 |
2021年 | 30篇 |
2020年 | 54篇 |
2019年 | 280篇 |
2018年 | 286篇 |
2017年 | 172篇 |
2016年 | 141篇 |
2015年 | 129篇 |
2014年 | 274篇 |
2013年 | 624篇 |
2012年 | 298篇 |
2011年 | 627篇 |
2010年 | 526篇 |
2009年 | 705篇 |
2008年 | 824篇 |
2007年 | 836篇 |
2006年 | 636篇 |
2005年 | 394篇 |
2004年 | 401篇 |
2003年 | 339篇 |
2002年 | 278篇 |
2001年 | 203篇 |
2000年 | 198篇 |
1999年 | 248篇 |
1998年 | 227篇 |
1997年 | 166篇 |
1996年 | 243篇 |
1995年 | 214篇 |
1994年 | 205篇 |
1993年 | 172篇 |
1992年 | 121篇 |
1991年 | 89篇 |
1990年 | 87篇 |
1989年 | 88篇 |
1988年 | 60篇 |
1987年 | 60篇 |
1986年 | 65篇 |
1985年 | 88篇 |
1984年 | 61篇 |
1983年 | 51篇 |
1982年 | 63篇 |
1981年 | 60篇 |
1980年 | 54篇 |
1979年 | 39篇 |
1978年 | 44篇 |
1977年 | 35篇 |
1976年 | 38篇 |
1975年 | 10篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Sander C. Hille 《Integral Equations and Operator Theory》2005,53(4):597-601
A linear semigroup in a Banach space induces a linear semigroup on a Banach space that can be continuously embedded in the
former such that its image is invariant. This restriction need not be strongly continuous, although the original semigroup
is strongly continuous. We show that norm or weak compactness of partial orbits is a necessary and sufficient condition for
strong continuity of the restriction of a C0-semigroup. We then show that if the embedded Banach space is reflexive and the norms of the restricted semigroup operators
are bounded near the initial time, then the restricted semigroup is strongly continuous. 相似文献
172.
We introduce triplet spaces for symmetric relations with defect index (1, 1) in a Pontryagin space. Representations of Pontryagin spaces by spaces of vector-valued analytic functions are investigated. These concepts are used to study 2×2-matrix valued analytic functions which satisfy a certain kernel condition. 相似文献
173.
Helge Glöckner 《manuscripta mathematica》1998,97(2):205-215
Let G be a p-adic Lie group. Then G is a locally compact, totally disconnected group, to which Willis [14] associates its scale function G : G→ℕ. We show that s can be computed on the Lie algebra level. The image of s consists of powers of p. If G is a linear algebraic group over ℚ
p
, s(x)=s(h) is determined by the semisimple part h of x∈G. For every finite extension K of ℚ
p
, the scale functions of G and H:=G(K) are related by s
H
∣
G
=s
G
[
K
:ℚ
p
]. More generally, we clarify the relations between the scale function of
a p-adic Lie group and the scale functions of its closed subgroups and Hausdorff quotients.
Received: 20 February 1997; Revised version: 18 May 1998 相似文献
174.
Elói Medina Galego 《Monatshefte für Mathematik》2002,136(2):87-97
We study the relation of to the subspaces and quotients of Banach spaces of continuous vector-valued functions , where K is an arbitrary dispersed compact set. More precisely, we prove that every infinite dimensional closed subspace of totally incomparable to X contains a copy of complemented in . This is a natural continuation of results of Cembranos-Freniche and Lotz-Peck-Porta. We also improve our result when K is homeomorphic to an interval of ordinals. Next we show that complemented subspaces (resp., quotients) of which contain no copy of are isomorphic to complemented subspaces (resp., quotients) of some finite sum of X. As a consequence, we prove that every infinite dimensional quotient of which is quotient incomparable to X, contains a complemented copy of . Finally we present some more geometric properties of spaces.
Received 8 November 2000; in revised form 7 December 2001 相似文献
175.
Smooth Solutions to Optimal Investment Models with Stochastic Volatilities and Portfolio Constraints
Pham 《Applied Mathematics and Optimization》2002,46(1):55-78
Abstract. This paper deals with an extension of Merton's optimal investment problem to a multidimensional model with stochastic volatility
and portfolio constraints. The classical dynamic programming approach leads to a characterization of the value function as
a viscosity solution of the highly nonlinear associated Bellman equation. A logarithmic transformation expresses the value
function in terms of the solution to a semilinear parabolic equation with quadratic growth on the derivative term. Using a
stochastic control representation and some approximations, we prove the existence of a smooth solution to this semilinear
equation. An optimal portfolio is shown to exist, and is expressed in terms of the classical solution to this semilinear equation.
This reduction is useful for studying numerical schemes for both the value function and the optimal portfolio. We illustrate
our results with several examples of stochastic volatility models popular in the financial literature. 相似文献
176.
All the symmetries and conservation laws of Navier-Stokes equations are calculated. 相似文献
177.
178.
A stage-structured predator–prey system with delays for prey and predator, respectively, is proposed and analyzed. Mathematical analysis of the model equations with regard to boundedness of solutions, permanence and stability are analyzed. Some sufficient conditions which guarantee the permanence of the system and the global asymptotic stability of the boundary and positive equilibrium, respectively, are obtained. 相似文献
179.
180.
Moessbauer studies on the effect of substitution with 3% Al, Co, Mn atoms in the intermetallic compound of Hf0.8Ta0.2Fe2 are reported. The Al substitution leads to increase of the FM-AFM transition temperature and to decrease of the AFM-PM transition temperature. The Co substitution leads to disappearance of the FM state, only showing some FM impurity component, while Mn substituted compound indicates coexistence of FM and AFM states at low temperature. The phenomena imply complex itinerant electron properties in these magnetic systems. 相似文献