全文获取类型
收费全文 | 12461篇 |
免费 | 552篇 |
国内免费 | 94篇 |
专业分类
化学 | 8511篇 |
晶体学 | 95篇 |
力学 | 321篇 |
综合类 | 1篇 |
数学 | 2159篇 |
物理学 | 2020篇 |
出版年
2023年 | 125篇 |
2022年 | 129篇 |
2021年 | 255篇 |
2020年 | 309篇 |
2019年 | 330篇 |
2018年 | 185篇 |
2017年 | 210篇 |
2016年 | 482篇 |
2015年 | 364篇 |
2014年 | 402篇 |
2013年 | 696篇 |
2012年 | 740篇 |
2011年 | 800篇 |
2010年 | 527篇 |
2009年 | 456篇 |
2008年 | 706篇 |
2007年 | 720篇 |
2006年 | 586篇 |
2005年 | 626篇 |
2004年 | 498篇 |
2003年 | 401篇 |
2002年 | 393篇 |
2001年 | 183篇 |
2000年 | 163篇 |
1999年 | 107篇 |
1998年 | 119篇 |
1997年 | 118篇 |
1996年 | 123篇 |
1995年 | 106篇 |
1994年 | 92篇 |
1993年 | 109篇 |
1992年 | 89篇 |
1991年 | 87篇 |
1990年 | 80篇 |
1989年 | 73篇 |
1988年 | 55篇 |
1987年 | 62篇 |
1986年 | 78篇 |
1985年 | 116篇 |
1984年 | 110篇 |
1983年 | 88篇 |
1982年 | 80篇 |
1981年 | 85篇 |
1980年 | 78篇 |
1979年 | 75篇 |
1978年 | 75篇 |
1977年 | 54篇 |
1976年 | 50篇 |
1975年 | 59篇 |
1974年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
Let be a bounded, connected linearly convex set in with boundary. We show that the maximal ideal (both in ) and ) consisting of all functions vanishing at is generated by the coordinate functions .
Received: 2 July 2001; in final form: 26 September 2001 / Published online: 28 February 2002 相似文献
84.
Jan J. Slawianowski 《General Relativity and Gravitation》2003,35(5):965-966
85.
Jan Andres Karel Pastor Pavla Šnyrychová 《Journal of Fixed Point Theory and Applications》2007,2(1):153-170
A multivalued version of Sharkovskiĭ’s theorem is formulated for M-maps on linear continua and, more generally, for triangular M-maps on a Cartesian product of linear continua. This improves the main result of [AP1] in the sense that our multivalued
analogue holds with at most two exceptions. A further specification requires some additional restrictions. For instance, 3-
orbits of m-maps imply the existence of k-orbits for all
k ? \mathbbNk \in {\mathbb{N}}
, except possibly for
k ?k \in
{4, 6}. It is also shown that, on every connected linearly ordered topological space, an M-map with orbits of all periods can always be constructed. This demonstrates that Baldwin’s classification of linear continua
in terms of admissible periods [Ba] is useless for multivalued maps. 相似文献
86.
We present a construction which shows that some special continua do not have the nonwandering-eventually-periodic property. The construction applies e.g. to the topologist's sin curve and to the harmonic fan. 相似文献
87.
We investigate traces of functions, belonging to a class of functions with dominating mixed smoothness in ℝ3, with respect to planes in oblique position. In comparison with the classical theory for isotropic spaces a few new phenomenona
occur. We shall present two different approaches. One is based on the use of the Fourier transform and restricted to p = 2. The other one is applicable in the general case of Besov-Lizorkin-Triebel spaces and based on atomic decompositions. 相似文献
88.
Hynd Remita Prem Felix Siril Israel-Martyr Mbomekalle Bineta Keita Louis Nadjo 《Journal of Solid State Electrochemistry》2006,10(7):506-511
Three Pt-based catalysts prepared in different radiolytic conditions and supported on graphite powder were packed into a carbon paste electrode configuration. They were compared to each other, to the commercial (Pt) deposited on activated carbon powder (Johnson Matthey) and to pure Vulcan XC-72 for their respective abilities toward the hydrogen evolution reaction (HER). The Tafel parameters were determined for all these electrodes. From the I–V curves and their quantitative treatment, the following order of activity emerged unambiguously and reads: (PtCO)2 (fcc structure) > (PtCO)1 (Chini cluster) > (Pt)neat > (Pt)JM (Johnson Matthey) ≫ (Vulcan XC-72). As expected, all the Pt-loaded electrodes were more efficient than Vulcan XC-72. The classification appears to be linked with the mean nanoparticle size, and for comparable sizes, with the surface morphology of the materials. The results and the stability of the electrodes suggest that the small particle sizes and the good dispersity on the carbon support were maintained during the HER. 相似文献
89.
The stoichiometric reactions of trimethylaluminum with 2,6‐(MeOCH2)2C6H3OH (LH) revealed compounds L3Al ( 1 ) and L2AlMe ( 2 ). On the other hand reaction of 1 equiv. of LH with trimethylaluminum did not lead to the formation of complex LAlMe2 ( 3 ), rather 2 together with Me3Al were observed as a result of a disproportionation of 3 . Compounds 1 and 2 were characterized by elemental analysis, 1H and 13C NMR spectroscopy and in the case of 1 by X‐ray diffraction. Derivative 2 underwent transmetalation with Ph3SnOH, giving LSnPh3 ( 4 ) as the result of a migration of ligand L from the aluminum to the tin atom. The identity of 4 was established by elemental analysis, 1H, 13C and 119Sn NMR spectroscopy and 1H, 119Sn HMBC experiments. The system 2 and B(C6F5)3 in a 1:1 molar ratio was shown to be active in the polymerization of propylene oxide and ε‐caprolactone. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
90.
Daniel Král’ Jan Kratochvíl Andrzej Proskurowski Heinz-Jürgen Voss 《Discrete Applied Mathematics》2006,154(4):660-672
A mixed hypergraph is a triple (V,C,D) where V is its vertex set and C and D are families of subsets of V, called C-edges and D-edges, respectively. For a proper coloring, we require that each C-edge contains two vertices with the same color and each D-edge contains two vertices with different colors. The feasible set of a mixed hypergraph is the set of all k's for which there exists a proper coloring using exactly k colors. A hypergraph is a hypertree if there exists a tree such that the edges of the hypergraph induce connected subgraphs of the tree.We prove that feasible sets of mixed hypertrees are gap-free, i.e., intervals of integers, and we show that this is not true for precolored mixed hypertrees. The problem to decide whether a mixed hypertree can be colored by k colors is NP-complete in general; we investigate complexity of various restrictions of this problem and we characterize their complexity in most of the cases. 相似文献