全文获取类型
收费全文 | 31456篇 |
免费 | 1158篇 |
国内免费 | 1277篇 |
专业分类
化学 | 9488篇 |
晶体学 | 200篇 |
力学 | 497篇 |
综合类 | 63篇 |
数学 | 19593篇 |
物理学 | 4050篇 |
出版年
2023年 | 366篇 |
2022年 | 247篇 |
2021年 | 293篇 |
2020年 | 452篇 |
2019年 | 729篇 |
2018年 | 695篇 |
2017年 | 475篇 |
2016年 | 532篇 |
2015年 | 625篇 |
2014年 | 981篇 |
2013年 | 1881篇 |
2012年 | 1155篇 |
2011年 | 2167篇 |
2010年 | 1683篇 |
2009年 | 2188篇 |
2008年 | 2415篇 |
2007年 | 2223篇 |
2006年 | 1673篇 |
2005年 | 1272篇 |
2004年 | 1119篇 |
2003年 | 1013篇 |
2002年 | 1207篇 |
2001年 | 670篇 |
2000年 | 651篇 |
1999年 | 743篇 |
1998年 | 616篇 |
1997年 | 487篇 |
1996年 | 571篇 |
1995年 | 578篇 |
1994年 | 532篇 |
1993年 | 439篇 |
1992年 | 378篇 |
1991年 | 296篇 |
1990年 | 245篇 |
1989年 | 262篇 |
1988年 | 169篇 |
1987年 | 184篇 |
1986年 | 154篇 |
1985年 | 234篇 |
1984年 | 205篇 |
1983年 | 122篇 |
1982年 | 185篇 |
1981年 | 180篇 |
1980年 | 113篇 |
1979年 | 90篇 |
1978年 | 106篇 |
1977年 | 92篇 |
1976年 | 61篇 |
1974年 | 23篇 |
1971年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Said Hadd 《Journal of Evolution Equations》2005,5(4):545-555
This paper studies the concept of controllability for infinite-dimensional linear control systems in Banach spaces. First,
we prove that the set of admissible control operators for the semigroup generator is unchanged if we perturb the generator
by the Desch–Schappacher perturbations. Second we show that exact controllability is not changed by such perturbations. 相似文献
82.
报导了Yb :FAP和Yb :C3S2 _FAP晶体在不同温度下的吸收光谱和荧光光谱实验结果 ,研究发现由于电子_声子近共振耦合作用 ,Yb :FAP和Yb :C3S2 _FAP晶体均存在有明显的振动谱 ,Yb :FAP晶体的零声子线在低温下还劈裂为相差 10cm- 1 的两条线 .采用激光选择激发技术研究了Yb3 离子在FAP和C3S2 _FAP晶体中的格位特征 ,结果表明Yb3 离子在这两种基质中都只占据Ca(Ⅱ )格位 ,但由于CaF2 的挥发 ,导致了Ca(Ⅱ )格位的局部畸变 . 相似文献
83.
Fabio A. C. C. Chalub Peter A. Markowich Benoît Perthame Christian Schmeiser 《Monatshefte für Mathematik》2004,142(1-2):123-141
Kinetic models for chemotaxis, nonlinearly coupled to a Poisson equation for the chemo-attractant density, are considered. Under suitable assumptions on the turning kernel (including models introduced by Othmer, Dunbar and Alt), convergence in the macroscopic limit to a drift-diffusion model is proven. The drift-diffusion models derived in this way include the classical Keller-Segel model. Furthermore, sufficient conditions for kinetic models are given such that finite-time-blow-up does not occur. Examples are given satisfying these conditions, whereas the macroscopic limit problem is known to exhibit finite-time-blow-up. The main analytical tools are entropy techniques for the macroscopic limit as well as results from potential theory for the control of the chemo-attractant density.Present address: Centro de Matemática e Aplicações Fundamentais, Universidade de Lisboa, Av. Prof. Gama Pinto 2, 1649-003, Lisboa, Portugal 相似文献
84.
On a Definitizable Analog of the Trigonometric Moment Problem Generating an Indefinite Toeplitz Form
We prove the existence of an integro-polynomial representation for a sequence of numbers such that there exists a difference operator mapping this sequence to a sequence that generates the solvable trigonometric moment problem. A similar result related to the power moment problem was given in [12]. 相似文献
85.
Walter Benz 《Monatshefte für Mathematik》2004,141(1):1-10
The lines of euclidean and hyperbolic geometries are characterized as metric lines in the sense of Blumenthal–Menger, and the lines of spherical and elliptic geometry as periodic ones. In euclidean geometries there do not exist periodic lines. 相似文献
86.
We will prove a result concerning the inclusion of non-trivial invariant ideals inside non-trivial ideals of a twisted crossed
product. We will also give results concerning the primeness and simplicity of crossed products of twisted actions of locally
compact groups on -algebras.
Received: 25 January 2002; in final form: 22 May 2002/Published online: 2 December 2002
This work is partially supported by Hong Kong RGC Direct Grant. 相似文献
87.
Ramesh Sharma 《Journal of Geometry》2003,78(1-2):156-167
Contact hypersurfaces of a Kaehler manifold have been
characterized and classified, assuming the second fundamental form to be
Codazzi (in particular, parallel). We have also discussed the special
cases when the ambient space is a (i) Calabi-Yau manifold and (ii) a
complex space-form. 相似文献
88.
89.
The function lattice, or generalized Boolean algebra, is the set of ℓ-tuples with the ith coordinate an integer between 0 and a bound ni. Two ℓ-tuples t-intersect if they have at least t common nonzero coordinates. We prove a Hilton–Milner type theorem for systems of t-intersecting ℓ-tuples.Received September 29, 2004 相似文献
90.