全文获取类型
收费全文 | 16284篇 |
免费 | 302篇 |
国内免费 | 124篇 |
专业分类
化学 | 10031篇 |
晶体学 | 202篇 |
力学 | 438篇 |
数学 | 2725篇 |
物理学 | 3314篇 |
出版年
2020年 | 144篇 |
2019年 | 143篇 |
2018年 | 124篇 |
2017年 | 97篇 |
2016年 | 229篇 |
2015年 | 200篇 |
2014年 | 250篇 |
2013年 | 804篇 |
2012年 | 630篇 |
2011年 | 735篇 |
2010年 | 431篇 |
2009年 | 417篇 |
2008年 | 703篇 |
2007年 | 717篇 |
2006年 | 787篇 |
2005年 | 730篇 |
2004年 | 641篇 |
2003年 | 563篇 |
2002年 | 564篇 |
2001年 | 282篇 |
2000年 | 285篇 |
1999年 | 191篇 |
1998年 | 201篇 |
1997年 | 204篇 |
1996年 | 283篇 |
1995年 | 204篇 |
1994年 | 249篇 |
1993年 | 255篇 |
1992年 | 253篇 |
1991年 | 198篇 |
1990年 | 186篇 |
1989年 | 192篇 |
1988年 | 154篇 |
1987年 | 190篇 |
1986年 | 170篇 |
1985年 | 287篇 |
1984年 | 272篇 |
1983年 | 187篇 |
1982年 | 218篇 |
1981年 | 237篇 |
1980年 | 264篇 |
1979年 | 229篇 |
1978年 | 235篇 |
1977年 | 192篇 |
1976年 | 219篇 |
1975年 | 214篇 |
1974年 | 224篇 |
1973年 | 219篇 |
1972年 | 104篇 |
1971年 | 106篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
81.
A central problem that arises in evolutionary biology is that of displaying partitions of subsets of a finite set X on a tree whose vertices are partially labelled with the elements of X. Such a tree is called an X-tree and, for a collection of partitions of subsets of X, characterisations for the existence and uniqueness of an X-tree that displays have been previously given in terms of chordal graphs. In this paper, we obtain two closely related characterisations also in terms of chordal graphs. The first describes when identifies an X-tree, and the second describes when a compatible subset of is of maximum size. 相似文献
82.
Let G be a compact Hausdorff group and n a positive integer. It is proved that all subnormal subgroups of G of index dividing n are open if and only if there are only finitely many such subgroups, and that all subgroups of finite index in G are open if and only if there are only countably many such subgroups. 相似文献
83.
Mark P. WattersonAlison A. Edwards John A. LeachMartin D. Smith Osamu IchiharaGeorge W.J. Fleet 《Tetrahedron letters》2003,44(31):5853-5857
Efficient syntheses of all diastereomers of methyl 2,5-anhydro-3-deoxy-hexonate from mannono- or gulono-lactones provide precursors for C-nucleosides of 2-deoxyribose and for THF-templated γ- and δ-amino acids. 相似文献
84.
In previous work, a probabilistic approach to controlling difficulties of density in hyperbolic space led to a workable notion of optimal density for packings of bodies. In this paper we extend an ergodic theorem of Nevo to provide an appropriate definition of those packings to be considered optimally dense. Examples are given to illustrate various aspects of the density problem, in particular the shift in emphasis from the analysis of individual packings to spaces of packings. 相似文献
85.
Logic Regression is an adaptive regression methodology mainly developed to explore high-order interactions in genomic data. Logic Regression is intended for situations where most of the covariates in the data to be analyzed are binary. The goal of Logic Regression is to find predictors that are Boolean (logical) combinations of the original predictors. In this article, we give an overview of the methodology and discuss some applications. We also describe the software for Logic Regression, which is available as an R and S-Plus package. 相似文献
86.
Y.Charles Li 《Journal of Mathematical Analysis and Applications》2004,292(1):311-315
Isospectral problem of both 2D and 3D Euler equations of inviscid fluids, is investigated. Connections with the Clay problem are described. Spectral theorem of the Lax pair is studied. 相似文献
87.
Martin R. Bridson Charles F. Miller III 《Proceedings of the American Mathematical Society》2004,132(1):59-65
We give examples of direct products of three hyperbolic groups in which there cannot exist an algorithm to decide which finitely presented subgroups are isomorphic.
88.
The rotational spectra of nine isotopomers of dimethyl diselenide, CH3SeSeCH3, have been measured with a molecular-beam Fourier transform microwave spectrometer. The spectra were complex due to the presence of many isotopomers in natural abundance and the splitting caused by the interactions with two methyl internal rotors. The spectra were assigned and fit to experimental precision to an effective rotational Hamiltonian for molecules with two periodic internal motions. The spectra of the symmetric isotopomers are consistent with a C2 equilibrium structure. The rotational constants were used to determine the rs structure of the C-Se-Se-C frame with the results r(SeSe)=2.306(3) Å, r(SeC)=1.954(6) Å, ?(CSeSe)=99.8(2)°, ?(CSeSeC)=85.2(1)°. A barrier to internal rotation of the methyl groups of 395 ± 2 cm−1 was derived from the internal rotation splittings. 相似文献
89.
90.
Laurent Charles 《Communications in Mathematical Physics》2003,239(1-2):1-28
This article is devoted to the Toeplitz Operators [4] in the context of the geometric quantization [11, 15]. We propose an ansatz for their Schwartz kernel. From this, we deduce the main known properties of the principal symbol of these operators and obtain new results : we define their covariant and contravariant symbols, which are full symbols, and compute the product of these symbols in terms of the Kähler metric. This gives canonical star products on the Kählerian manifolds. This ansatz is also useful to introduce the notion of microsupport. 相似文献