全文获取类型
收费全文 | 5069篇 |
免费 | 198篇 |
国内免费 | 16篇 |
专业分类
化学 | 3705篇 |
晶体学 | 11篇 |
力学 | 164篇 |
数学 | 676篇 |
物理学 | 727篇 |
出版年
2023年 | 43篇 |
2022年 | 70篇 |
2021年 | 86篇 |
2020年 | 96篇 |
2019年 | 95篇 |
2018年 | 79篇 |
2017年 | 69篇 |
2016年 | 142篇 |
2015年 | 121篇 |
2014年 | 162篇 |
2013年 | 237篇 |
2012年 | 346篇 |
2011年 | 374篇 |
2010年 | 183篇 |
2009年 | 171篇 |
2008年 | 336篇 |
2007年 | 300篇 |
2006年 | 284篇 |
2005年 | 282篇 |
2004年 | 250篇 |
2003年 | 160篇 |
2002年 | 166篇 |
2001年 | 52篇 |
2000年 | 42篇 |
1999年 | 45篇 |
1998年 | 30篇 |
1997年 | 48篇 |
1996年 | 45篇 |
1995年 | 31篇 |
1994年 | 35篇 |
1993年 | 34篇 |
1992年 | 41篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1985年 | 48篇 |
1984年 | 44篇 |
1983年 | 30篇 |
1982年 | 39篇 |
1981年 | 47篇 |
1980年 | 33篇 |
1979年 | 41篇 |
1978年 | 48篇 |
1977年 | 34篇 |
1976年 | 38篇 |
1975年 | 42篇 |
1974年 | 41篇 |
1973年 | 31篇 |
1970年 | 16篇 |
排序方式: 共有5283条查询结果,搜索用时 0 毫秒
1.
We give a Gray code and constant average time generating algorithm for derangements, i.e., permutations with no fixed points. In our Gray code, each derangement is transformed into its successor either via one or two transpositions or a rotation of three elements. We generalize these results to permutations with number of fixed points bounded between two constants. 相似文献
2.
3.
Vincent Maurice 《Surface science》2005,581(1):88-104
STM, STS, LEED and XPS data for crystalline θ-Al2O3 and non-crystalline Al2O3 ultra-thin films grown on NiAl(0 0 1) at 1025 K and exposed to water vapour at low pressure (1 × 10−7-1 × 10−5 mbar) and room temperature are reported. Water dissociation is observed at low pressure. This reactivity is assigned to the presence of a high density of coordinatively unsaturated cationic sites at the surface of the oxide film. The hydroxyl/hydroxide groups cannot be directly identify by their XPS binding energy, which is interpreted as resulting from the high BE positions of the oxide anions (O1s signal at 532.5-532.8 eV). However the XPS intensities give evidence of an uptake of oxygen accompanied by an increase of the surface coverage by Al3+ cations, and a decrease of the concentration in metallic Al at the alloy interface. A value of ∼2 for the oxygen to aluminium ions surface concentration ratio indicates the formation of an oxy-hydroxide (AlOxOHy with x + y ∼ 2) hydroxylation product. STM and LEED show the amorphisation and roughening of the oxide film. At P(H2O) = 1 × 10−7 mbar, only the surface of the oxide film is modified, with formation of nodules of ∼2 nm lateral size covering homogeneously the surface. STS shows that essentially the valence band is modified with an increase of the density of states at the band edge. With increasing pressure, hydroxylation is amplified, leading to an increased coverage of the alloy by oxy-hydroxide products and to the formation of larger nodules (∼7 nm) of amorphous oxy-hydroxide. Roughening and loss of the nanostructure indicate a propagation of the reaction that modifies the bulk structure of the oxide film. Amorphisation can be reverted to crystallization by annealing under UHV at 1025 K when the surface of the oxide film has been modified, but not when the bulk structure has been modified. 相似文献
4.
We propose a new scheme for the long time approximation of a diffusion when the drift vector field is not globally Lipschitz. Under this assumption, a regular explicit Euler scheme–with constant or decreasing step–may explode and implicit Euler schemes are CPU-time expensive. The algorithm we introduce is explicit and we prove that any weak limit of the weighted empirical measures of this scheme is a stationary distribution of the stochastic differential equation. Several examples are presented including gradient dissipative systems and Hamiltonian dissipative systems. 相似文献
5.
We investigate the combinatorics of a topological space that is generated by the set of edge-weighted finite trees. This space arises by multiplying the weights of edges on paths in trees and is closely connected to tree reconstruction problems involving finite state Markov processes. We show that this space is a contractible finite CW-complex whose face poset can be described via a partial order on semilabelled forests. We then describe some combinatorial properties of this poset, showing that, for example, it is pure, thin and contractible. 相似文献
6.
7.
8.
Vincent Bailliez 《Tetrahedron》2004,60(5):1079-1085
Polynitrogenated analogues of glucopyranoses were synthesised from levoglucosan. These compounds are useful intermediates for the synthesis of new aminoglycoside mimetics. 相似文献
9.
10.
Roucoules V Fail CA Schofield WC Teare DO Badyal JP 《Langmuir : the ACS journal of surfaces and colloids》2005,21(4):1412-1415
A substrate-independent method has been devised for ring formation at solid surfaces. This entails the aminolysis reaction of allylamine with maleic anhydride pulsed plasma polymer films to yield terminal alkene groups at the surface. Subsequent exposure to 1,3-cyclohexadiene leads to a Diels-Alder type (4 + 2) cycloaddition reaction to give a mixture of endo- and exo-bicyclo[2.2.2]oct-2-ene rings. 相似文献