全文获取类型
收费全文 | 961篇 |
免费 | 26篇 |
国内免费 | 8篇 |
专业分类
化学 | 738篇 |
晶体学 | 4篇 |
力学 | 47篇 |
数学 | 65篇 |
物理学 | 141篇 |
出版年
2023年 | 11篇 |
2022年 | 12篇 |
2021年 | 20篇 |
2020年 | 22篇 |
2019年 | 25篇 |
2018年 | 17篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 33篇 |
2013年 | 26篇 |
2012年 | 50篇 |
2011年 | 71篇 |
2010年 | 42篇 |
2009年 | 34篇 |
2008年 | 63篇 |
2007年 | 56篇 |
2006年 | 56篇 |
2005年 | 49篇 |
2004年 | 60篇 |
2003年 | 50篇 |
2002年 | 39篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 12篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 11篇 |
1982年 | 5篇 |
1980年 | 7篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1975年 | 8篇 |
1972年 | 4篇 |
1970年 | 7篇 |
1969年 | 6篇 |
1968年 | 5篇 |
1967年 | 7篇 |
1927年 | 4篇 |
1921年 | 4篇 |
1920年 | 4篇 |
排序方式: 共有995条查询结果,搜索用时 31 毫秒
941.
A very short and efficient synthesis of (−)-centrolobine has been achieved by using two successive one-pot reactions. The first sequence involves a cross-metathesis reaction/hydrogenation/lactonization and the second sequence is a Grignard addition/reduction. 相似文献
942.
943.
944.
The nature of small ions in electrolytic (e.g., aqueous) solutions is discussed in terms of the configuration of the adjoining polarized medium, and the role of this configuration in electronic transitions involving one or a pair of ions is treated in a general way. Light absorption by a single ion is shown to depend critically on this configuration; a theory developed previously by the authors is reviewed, and future possibilities of exploring the nature of the configuration by investigation of such spectra are explained. Electronic transitions, such as an “electron transfer” process, during binary collisions of ions are treated, and a general method is developed, based uponDebye's “diffusion” theory for ion collision rates and a nonadiabatic type of potential curve. Rates of chemical processes are found to depend decisively on the interaction of two ions at separations where the simple coulomb law is not valid. 相似文献
945.
[reaction: see text] The double deprotonation of acetylenic oxiranes gives allenic ketones through the 1,2-H or 1,2-Ar shift on the transient oxiranyl dianion intermediates. The resulting dilithium ynenolates give allenic ketones upon hydrolysis or can be quenched with various electrophiles. 相似文献
946.
Respiratory adaptations of a deep-sea hydrothermal vent crab 总被引:1,自引:0,他引:1
947.
We consider free convection in a horizontal shallow cavity with different end temperatures, filled with a high Prandtl number fluid. From scaling analysis, we find two kinematic regimes resulting from the competition of heat transfer by conduction and by convection. Numerical simulations realized for a large range of Rayleigh number and aspect ratio confirm the phenomenological analysis and provide the threshold between the two regimes. The conductive and convective regimes occur at smaller and larger than 443 respectively, where Ra is the Rayleigh number and A is the aspect ratio. In the convective regime, the characteristic velocity is independent of depth of the cavity. To cite this article: J.-M. Flesselles, F. Pigeonneau, C. R. Mecanique 332 (2004). 相似文献
948.
Luigi A. Agrofoglio Franck Amblard Steve Charamon Thomas A. Zevaco 《Tetrahedron》2004,60(38):8397-8404
The enantiomeric synthesis of l-cyclopentenyl nucleosides is described. The key intermediate (+)-cyclopentenyl alcohol (8) was prepared from methyl-α-d-galactopyranoside 1 using a ring closing metathesis reaction. Transformation of the allylic alcohol 8 into the allylic acetate (9) or carbonate (10), allows their coupling with purine and pyrimidine bases under Pd(0)-catalyzed Tsuji-Trost allylic alkylation's to yield 12a-c. The Pd catalyzed reaction was found to require the use of AlEt3. 相似文献
949.
In a non-convex polyhedral domain, we describe the local trace (i.e. defined on a face) of the normal derivative of an function, with Laplacian. We then provide generalized integration by parts formulae for the Laplace, divergence and curl operators. Finally, these results allow us to split electromagnetic fields into regular and singular parts, which can be characterized. To cite this article: F. Assous et al., C. R. Acad. Sci. Paris, Ser. I 341 (2005). 相似文献
950.
Protochlorophyllide (Pchlide) reductases are key enzymes in the process of chlorophyll biosynthesis. In this review, current knowledge on the molecular organization, substrate specificity and assembly of the light-dependent reduced nicotinamide adenine dinucleotide phosphate:Pchlide oxidoreductases are discussed. Characteristics of light-independent enzymes are also described briefly, and the possible reasons for the selection of light-dependent enzymes during the course of evolution are discussed. 相似文献