全文获取类型
收费全文 | 29436篇 |
免费 | 4223篇 |
国内免费 | 3087篇 |
专业分类
化学 | 21149篇 |
晶体学 | 284篇 |
力学 | 1410篇 |
综合类 | 184篇 |
数学 | 4392篇 |
物理学 | 9327篇 |
出版年
2024年 | 99篇 |
2023年 | 532篇 |
2022年 | 882篇 |
2021年 | 947篇 |
2020年 | 1160篇 |
2019年 | 1068篇 |
2018年 | 949篇 |
2017年 | 903篇 |
2016年 | 1447篇 |
2015年 | 1370篇 |
2014年 | 1574篇 |
2013年 | 2152篇 |
2012年 | 2557篇 |
2011年 | 2711篇 |
2010年 | 1901篇 |
2009年 | 1673篇 |
2008年 | 1990篇 |
2007年 | 1823篇 |
2006年 | 1617篇 |
2005年 | 1409篇 |
2004年 | 1174篇 |
2003年 | 913篇 |
2002年 | 931篇 |
2001年 | 668篇 |
2000年 | 544篇 |
1999年 | 544篇 |
1998年 | 407篇 |
1997年 | 378篇 |
1996年 | 396篇 |
1995年 | 340篇 |
1994年 | 273篇 |
1993年 | 203篇 |
1992年 | 201篇 |
1991年 | 186篇 |
1990年 | 157篇 |
1989年 | 115篇 |
1988年 | 72篇 |
1987年 | 80篇 |
1986年 | 85篇 |
1985年 | 74篇 |
1984年 | 52篇 |
1983年 | 39篇 |
1982年 | 23篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1975年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Juan Gonzá lez-Meneses Luis Paris 《Transactions of the American Mathematical Society》2004,356(1):219-243
We show that Vassiliev invariants separate braids on a closed oriented surface, and we exhibit a universal Vassiliev invariant for these braids in terms of chord diagrams labeled by elements of the fundamental group of the surface.
102.
103.
Using Lagrange's multiplier rule, we find upper and lower bounds of the energy of a bipartite graph G, in terms of the number of vertices, edges and the spectral moment of fourth order. Moreover, the upper bound is attained in a graph G if and only if G is the graph of a symmetric balanced incomplete block design (BIBD). Also, we determine the graphs for which the lower bound is sharp. 相似文献
104.
Gabriela Jeronimo Teresa Krick Juan Sabia Martín Sombra 《Foundations of Computational Mathematics》2004,4(1):41-117
We present a bounded probability algorithm for the computation of the
Chowforms of the equidimensional components of an algebraic variety. In particular,
this gives an alternative procedure for the effective equidimensional decomposition
of the variety, since each equidimensional component is characterized by its Chow
form.
The expected complexity of the algorithm is polynomial in the size and the geometric
degree of the input equation system defining the variety. Hence it improves (or
meets in some special cases) the complexity of all previous algorithms for computing Chow forms. In addition to this, we clarify the probability and uniformity aspects,
which constitutes a further contribution of the paper.
The algorithm is based on elimination theory techniques, in line with the geometric
resolution algorithm due to M. Giusti, J. Heintz, L. M. Pardo, and their collaborators.
In fact, ours can be considered as an extension of their algorithm for zero-dimensional
systems to the case of positive-dimensional varieties. The key element for dealing
with positive-dimensional varieties is a new Poisson-type product formula. This
formula allows us to compute the Chow form of an equidimensional variety from a
suitable zero-dimensional fiber.
As an application, we obtain an algorithm to compute a subclass of sparse resultants,
whose complexity is polynomial in the dimension and the volume of the input
set of exponents. As another application, we derive an algorithm for the computation
of the (unique) solution of a generic overdetermined polynomial equation system. 相似文献
105.
Shu Fen Wang Wen Guo Zou Su Wen Liu Dong Xu Duo Rong Yuan Guang Jun Zhou 《Journal of Physics and Chemistry of Solids》2004,65(7):1243-1245
The photoluminescence properties of the Bi3+ in sol-gel derived ZnTiO3 nanocrystals have been investigated. An ultra-violet emission at 360 nm and a visible emission band at 506 nm have been observed, originating from two kinds of emission centers. The former is ascribed to the 3P1-1S0 transition of Bi3+ and the latter to the recombination of the electrons with the photo-generated holes trapped in the zinc vacancies. In all cases the latter contribution is predominant. 相似文献
106.
明确从地胆草中分离得到的两对牦牛儿内酯型的立体异构体即地胆草种内酯(scabertopin)、异地胆草种内酯(isoscabertopin)、异去氧地胆草内酯(isodeoxyelephantopin)和去氧地胆草内酯(deoxyelephantopin)的C-2相对构型;方法 NOESY技术,并结合这4个化合物的1H NMR,13C NMR,HMQC谱;结果 两对立体异构体的NOESY谱有明显差异;结论 通过分析NOESY谱,找寻H-1相关信息,若发现H-1与H-8,H-9β和14-CH3有NOE相关,可以判断化合物的C-2为α构型,若H-1与H-5,H-7,H-3α及H-9α之间有NOE相关,则化合物的C-2为β构型. 相似文献
107.
Piotr Winiarek Juan Carlos Q. Colmenares Elbieta Fedoryska 《Reaction Kinetics and Catalysis Letters》2004,81(2):333-339
Transformations of diphenylmethane were investigated in a flow system in the presence of alumina and silica-alumina modified
with boron trifluoride at atmospheric pressure and elevated temperatures. Hydrogen transfer reaction was observed on addition
of tetralin to the substrate stream.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
108.
LD泵浦固体激光器基模振荡光的场分布噪音 总被引:3,自引:3,他引:0
通过调整泵浦光直径,使得LD端面泵浦固体激光器的振荡光工作于基模.在排除高阶横模的条件下,测量了由于热透镜的不稳定引起的光场场分布的噪音.实验发现,基模振荡光的高斯半径、光束指向角都在波动,而且光斑存在畸变波动.对一个未采取抑制措施的2W连续LD端面泵浦Nd:YAG固体激光器进行了测量.结果表明,在总功率不变的情况下,激光束峰值点附近的光强波动达到6.3%;激光的高斯半径波动达到5.8%;激光的指向角波动达到0.3mrad. 相似文献
109.
110.
Spectral and Pseudospectral Approximations Using Hermite Functions: Application to the Dirac Equation 总被引:1,自引:0,他引:1
We consider in this paper spectral and pseudospectral approximations using Hermite functions for PDEs on the whole line. We first develop some basic approximation results associated with the projections and interpolations in the spaces spanned by Hermite functions. These results play important roles in the analysis of the related spectral and pseudospectral methods. We then consider, as an example of applications, spectral and pseudospectral approximations of the Dirac equation using Hermite functions. In particular, these schemes preserve the essential conservation property of the Dirac equation. We also present some numerical results which illustrate the effectiveness of these methods. 相似文献