全文获取类型
收费全文 | 50556篇 |
免费 | 3089篇 |
国内免费 | 5019篇 |
专业分类
化学 | 33084篇 |
晶体学 | 569篇 |
力学 | 677篇 |
综合类 | 253篇 |
数学 | 16480篇 |
物理学 | 7601篇 |
出版年
2024年 | 68篇 |
2023年 | 634篇 |
2022年 | 900篇 |
2021年 | 798篇 |
2020年 | 1090篇 |
2019年 | 1605篇 |
2018年 | 1300篇 |
2017年 | 1350篇 |
2016年 | 1450篇 |
2015年 | 1503篇 |
2014年 | 2033篇 |
2013年 | 3655篇 |
2012年 | 2496篇 |
2011年 | 3366篇 |
2010年 | 2603篇 |
2009年 | 3146篇 |
2008年 | 3570篇 |
2007年 | 3272篇 |
2006年 | 2797篇 |
2005年 | 2310篇 |
2004年 | 2256篇 |
2003年 | 1908篇 |
2002年 | 2084篇 |
2001年 | 1305篇 |
2000年 | 1250篇 |
1999年 | 1168篇 |
1998年 | 997篇 |
1997年 | 841篇 |
1996年 | 871篇 |
1995年 | 892篇 |
1994年 | 768篇 |
1993年 | 622篇 |
1992年 | 586篇 |
1991年 | 402篇 |
1990年 | 331篇 |
1989年 | 325篇 |
1988年 | 249篇 |
1987年 | 200篇 |
1986年 | 187篇 |
1985年 | 217篇 |
1984年 | 195篇 |
1983年 | 91篇 |
1982年 | 168篇 |
1981年 | 171篇 |
1980年 | 111篇 |
1979年 | 107篇 |
1978年 | 88篇 |
1977年 | 74篇 |
1976年 | 80篇 |
1974年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
O. N. Karpenkov 《Monatshefte für Mathematik》2007,152(3):217-249
In this paper we develop an integer-affine classification of three-dimensional multistory, completely empty convex marked
pyramids. We apply it to obtain the complete lists of compact two-dimensional faces of multidimensional continued fractions
lying in planes at integer distances 2, 3, 4, … to the origin. The faces are considered up to the action of the group of
integer-linear transformations. 相似文献
102.
《Magnetic resonance in chemistry : MRC》2003,41(9):660-670
Reduced forms of iso‐α‐acids (isohumulones), used in modern beer brewing were separated and characterized by 1H and 13C NMR spectroscopy. Components from mixtures of rho‐iso‐α‐acids, tetrahydro‐iso‐α‐acids, and hexahydro‐iso‐α‐acids were isolated using high‐performance liquid chromatography (HPLC) and analyzed by use of one‐ and two‐dimensional NMR experiments. The data presented assign the identities of the main peaks in the HPLC traces for the reduced iso‐α‐acids. Previous tentative assignments regarding the cis and trans configurations and the structures of the acyl residues of the reduced iso‐α‐acids were confirmed and extensive NMR assignments were made. Furthermore, the previously unknown stereochemistry in the C‐4 side‐chain of the rho‐ and hexahydro‐iso‐α‐acids was assigned. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
103.
Yanghyun Byun 《Topology》2007,46(5):507-525
We construct a sphere fibration over a finite aspherical Poincaré complex X, which we call the tangential end fibration, under the condition that the universal cover of X is forward tame and simply connected at infinity. We show that it is tangent to X if the formal dimension of X is even or, when the formal dimension is odd, if the diagonal X→X×X admits a Poincaré embedding structure. 相似文献
104.
P. Rowlinson 《Linear algebra and its applications》2007,421(1):157-162
Suppose that the positive integer μ is the eigenvalue of largest multiplicity in an extremal strongly regular graph G. By interlacing, the independence number of G is at most 4μ2 + 4μ − 2. Star complements are used to show that if this bound is attained then either (a) μ = 1 and G is the Schläfli graph or (b) μ = 2 and G is the McLaughlin graph. 相似文献
105.
In this paper we first give a lower bound on multiplicities for Buchsbaum homogeneous k-algebras A in terms of the dimension d, the codimension c, the initial degree q, and the length of the local cohomology modules of A. Next, we introduce the notion of Buchsbaum k-algebras with minimal multiplicity of degree q, and give several characterizations for those rings. In particular, we will show that those algebras have linear free resolutions. Further, we will give many examples of those algebras. 相似文献
106.
Zero-schemes on smooth complex projective varieties, forcing all elements of ample and free linear systems to be reducible, are studied. Relationships among the minimal length of such zero-schemes, the positivity of the line bundle associated with the linear system, and the dimension of the variety are established. Bad linear spaces are also investigated. 相似文献
107.
Various types of LU-factorizations for nonsingular matrices, where L is a lower triangular matrix and U is an upper triangular matrix, are defined and characterized. These types of LU-factorizations are extended to the general m × n case. The more general conditions are considered in the light of the structures of [C.R. Johnson, D.D. Olesky, P. Van den Driessche, Inherited matrix entries: LU factorizations, SIAM J. Matrix Anal. Appl. 10 (1989) 99-104]. Applications to graphs and adjacency matrices are investigated. Conditions for the product of a lower and an upper triangular matrix to be the zero matrix are also obtained. 相似文献
108.
ZHANGZHAOJI 《高校应用数学学报(英文版)》1995,10(3):357-359
This paper solves an open problem of Vaserstein. The main result is: the equation x^m y^m=z^m has a solution in SL2z if and only if m is not divisible by 4 or 6 and m is not congruent to 3 modulo 6. 相似文献
109.
The detailed characterization of multifunctional hybrid organosilazane/organosilylamine telechelic oligomers by IR and 1H, 13C and 29Si NMR spectroscopy in one and two dimenions has been undertaken. The specific multifunctional oligomers, comprising NH/NH2 or SiCl functionalities depending on the monomer feed-ratio, were prepared from mono- and di-functionally reacted dichlorodimethylsilane (DDS) and mono-, di-, tri- and tetra-functionally reacted ethylenediamine (EDA). Varying the feed-ratio afforded control of the microstructures of the oligomers and the preparation of oligomers with, in some cases, conterminously located silicon–chlorine (SiCl) groups. The combination of the NMR methods with the IR technique has enabled the detailed microstructural characterization of the oligomers and the identification of the functionalities therein. This approach and the knowledge gained from the DDS/EDA system has been applied to the microstructural characterization of other hybrid organosilazane/silylamine preceramic telechelic oligomers. 相似文献
110.