全文获取类型
收费全文 | 25694篇 |
免费 | 758篇 |
国内免费 | 816篇 |
专业分类
化学 | 4743篇 |
晶体学 | 875篇 |
力学 | 498篇 |
综合类 | 76篇 |
数学 | 18014篇 |
物理学 | 3062篇 |
出版年
2023年 | 91篇 |
2022年 | 170篇 |
2021年 | 199篇 |
2020年 | 219篇 |
2019年 | 633篇 |
2018年 | 645篇 |
2017年 | 439篇 |
2016年 | 435篇 |
2015年 | 400篇 |
2014年 | 766篇 |
2013年 | 1455篇 |
2012年 | 779篇 |
2011年 | 1620篇 |
2010年 | 1648篇 |
2009年 | 1866篇 |
2008年 | 2012篇 |
2007年 | 1930篇 |
2006年 | 1542篇 |
2005年 | 1130篇 |
2004年 | 1080篇 |
2003年 | 894篇 |
2002年 | 725篇 |
2001年 | 551篇 |
2000年 | 489篇 |
1999年 | 522篇 |
1998年 | 471篇 |
1997年 | 388篇 |
1996年 | 533篇 |
1995年 | 471篇 |
1994年 | 466篇 |
1993年 | 397篇 |
1992年 | 312篇 |
1991年 | 197篇 |
1990年 | 184篇 |
1989年 | 186篇 |
1988年 | 125篇 |
1987年 | 126篇 |
1986年 | 133篇 |
1985年 | 189篇 |
1984年 | 123篇 |
1983年 | 93篇 |
1982年 | 114篇 |
1981年 | 106篇 |
1980年 | 89篇 |
1979年 | 57篇 |
1978年 | 72篇 |
1977年 | 70篇 |
1976年 | 62篇 |
1975年 | 17篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
131.
132.
In [7] point-reflection geometries were studied which can be derived from commutative kinematic
spaces without involutory elements. But the class of point-reflection geometries is larger. For example, elliptic
planes with their reflections cannot be derived from commutative kinematic spaces. Here we investigate a larger
class of reflection geometries.This paper was sponsored by Vigoni Program 1999. 相似文献
133.
In 1934, Romanoff proved that there are a positive proportion natural numbers which can be expressed as the sum of a prime and a power of 2. In this paper, a quantitative version of this theorem is given. We show that the proportion is larger than 0.0868 and for a positive proportion of odd integers the number of such representations is between 1 and 16. 相似文献
134.
Hirofumi Tsumura 《Journal of Number Theory》2004,106(1):155-168
In this paper, we define the multiple Euler numbers and consider some multiple harmonic series of Mordell-Tornheim's type, which is a partial sum of the Mordell-Tornheim zeta series defined by Matsumoto. Indeed, we prove a certain reducibility of these series as well as the multiple zeta values. 相似文献
135.
Precise measurement of magnetic moment of short-lived β-emitting nuclei12B ( I π=1+, T 1/2=20.18 ms)
Zhou Dongmei Zheng Yongnan Du Enpeng Xu Yongjun Zhu Jiazheng Yuan Daqing Wang Zhiqiang Luo Hailong Zuo Yi Ma Ruigang Duan Xiao M. Mihara M. Fukuda K. Matsuta T. Minamisono Zhu Shengyun 《中国科学G辑(英文版)》2004,47(5):531-539
The spin polarized β-emitting nuclei12B (I
π=1+,T
1/2=20.18 ms) were produced by the nuclear reaction11B(d, p)12B and by the selection technique of the incident deuteron energy and the12B recoil angle following the nuclear reaction. The nuclear magnetic moment of the short-lived nuclei12B was measured by β-NMR with the β-NMR and β-NQR setup established for the first time in China. The nuclear magnetic moment
of12B was determined to be μ=0.99993±0.00048 nm org=0.99993±0.00048 after the precise correction of the Knight shift. 相似文献
136.
Let G be a finite group. A complete Sylow product of G is a product of Sylow subgroups of G, one for each prime divisor of |G|. We shall call G a Sylow factorizable group if it is equal to at least one of its complete Sylow products. We prove that if G is a Sylow factorizable group then the
intersection of all complete Sylow products of G is equal to the solvable radical of G. We generalize the concepts and the result to Sylow products which involve an arbitrary subset of the prime divisors of |G|.
Received: 26 January 2005 相似文献
137.
Anissa Gömann Karsten Gömann Volker Kempter Wolfgang Maus-Friedrichs 《Applied Surface Science》2005,252(1):196-199
Perovskites of ABO3 type like strontium titanate (SrTiO3) are of great practical concern as materials for oxygen sensors operating at high temperatures. It is well known that the surface layer shows different properties compared to the bulk. Numerous studies exist for the SrTiO3(1 0 0) and (1 1 0) surfaces which have investigated the changes in the electronic structure and topography as a function of the preparation conditions. They have indicated a rather complex behaviour of the surface and the near surface region of SrTiO3 at elevated temperatures. Up to now, the behaviour of the SrTiO3(1 1 1) surfaces under thermal treatment is not sufficiently known. This contribution is intended to work out the relation between alteration of the surface topography with respect to the preparation conditions and the simultaneous changes of the electronic structure. We applied scanning tunneling microscopy (STM) to investigate the surface topography and, additionally, metastable impact electron spectroscopy (MIES) to study the surface electronic structure of reconstructed SrTiO3(1 1 1) surfaces. The crystals were heated up to 1000 °C under reducing and oxidizing conditions. Both preparation conditions cause strong changes of the surface topography and electronic structure. A microfaceting of the topmost layers is found. 相似文献
138.
Luc Miller 《Bulletin des Sciences Mathématiques》2005,129(2):175-185
We make two remarks about the null-controllability of the heat equation with Dirichlet condition in unbounded domains. Firstly, we give a geometric necessary condition (for interior null-controllability in the Euclidean setting) which implies that one cannot go infinitely far away from the control region without tending to the boundary (if any), but also applies when the distance to the control region is bounded. The proof builds on heat kernel estimates. Secondly, we describe a class of null-controllable heat equations on unbounded product domains. Elementary examples include an infinite strip in the plane controlled from one boundary and an infinite rod controlled from an internal infinite rod. The proof combines earlier results on compact manifolds with a new lemma saying that the null-controllability of an abstract control system and its null-controllability cost are not changed by taking its tensor product with a system generated by a non-positive self-adjoint operator. 相似文献
139.
Annalisa Baldi Bruno Franchi 《Calculus of Variations and Partial Differential Equations》2003,16(3):283-298
Abstract. In this paper we study the notion of perimeter associated with doubling metric measures or strongly weights. We prove that the metric perimeter in the sense of L. Ambrosio and M. Miranda jr. coincides with the metric Minkowski
content and can be obtained also as a -limit of Modica-Mortola type degenerate integral functionals.
Received: 27 August 2001 / Accepted: 29 November 2001 / Published online: 10 June 2002
Investigation supported by University of Bologna, funds for selected research topics and by GNAMPA of INdAM, Italy. The authors
are very grateful to Luigi Ambrosio and Francesco Serra Cassano for making their preprints available to them, for listening
with patience and for many unvaluable suggestions. 相似文献
140.
Moira Chas 《Topology》2004,43(3):543-568
Goldman (Invent. Math. 85(2) (1986) 263) and Turaev (Ann. Sci. Ecole Norm. Sup. (4) 24 (6) (1991) 635) found a Lie bialgebra structure on the vector space generated by non-trivial free homotopy classes of curves on a surface. When the surface has non-empty boundary, this vector space has a basis of cyclic reduced words in the generators of the fundamental group and their inverses. We give a combinatorial algorithm to compute this Lie bialgebra on this vector space of cyclic words. Using this presentation, we prove a variant of Goldman's result relating the bracket to disjointness of curve representatives when one of the classes is simple. We exhibit some examples we found by programming the algorithm which answer negatively Turaev's question about the characterization of simple curves in terms of the cobracket. Further computations suggest an alternative characterization of simple curves in terms of the bracket of a curve and its inverse. Turaev's question is still open in genus zero. 相似文献