全文获取类型
收费全文 | 1231篇 |
免费 | 27篇 |
国内免费 | 2篇 |
专业分类
化学 | 1015篇 |
晶体学 | 4篇 |
力学 | 22篇 |
数学 | 68篇 |
物理学 | 151篇 |
出版年
2023年 | 18篇 |
2022年 | 35篇 |
2021年 | 43篇 |
2020年 | 39篇 |
2019年 | 51篇 |
2018年 | 47篇 |
2017年 | 29篇 |
2016年 | 52篇 |
2015年 | 30篇 |
2014年 | 32篇 |
2013年 | 107篇 |
2012年 | 73篇 |
2011年 | 87篇 |
2010年 | 58篇 |
2009年 | 47篇 |
2008年 | 60篇 |
2007年 | 43篇 |
2006年 | 57篇 |
2005年 | 48篇 |
2004年 | 43篇 |
2003年 | 22篇 |
2002年 | 26篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1974年 | 4篇 |
1973年 | 8篇 |
1972年 | 8篇 |
1971年 | 9篇 |
1969年 | 8篇 |
1968年 | 4篇 |
排序方式: 共有1260条查询结果,搜索用时 31 毫秒
1.
2.
O. V. Andreeva V. G. Bespalov A. L. Pyait V. N. Sizov A. S. Cherkasov 《Optics and Spectroscopy》2004,96(2):149-156
The results of a complex investigation of the recording of dynamic holograms by pulsed radiation with a duration of 20 ns and 300 ps in fullerene-containing media based on porous glasses and polymethyl methacrylate matrices are reported. Spectral analysis of these media in the range 300–700 nm was performed. The efficiency of hologram recording was found to relate with the occurrence of a band at 330 nm in the absorption spectrum of a medium. It is shown that dynamic holograms can be recorded in the fullerene-containing media by nanosecond and picosecond pulses. In the latter case, holograms arise mainly due to a change in the electronic polarizability of fullerene molecules, which is almost inertialess. The results obtained can be used in the development of ultrafast switching devices based on dynamic holograms. 相似文献
3.
A. I. Artem’ev D. N. Klochkov K. Oganesyan Yu. V. Rostovtsev M. V. Fedorov 《Laser Physics》2007,17(10):1213-1216
The spatial amplification of a wave in a magnetostatic undulator with noncollinear electron and laser beams is studied in the framework of the dispersion relation for single-frequency and collective regimes. The dependence of the gain on the electron beam width is estimated with regard to the spatial boundedness of the beams. The laser power threshold at which the selection with respect to the transverse velocity is possible is obtained for a free-electron laser without inversion. 相似文献
4.
Alexei Yu. Lukin Sergei V. Shevyakov Alexei V. Laptev Olga I. Davydova Vitali I. Shvets Olga V. Demina Yury P. Strokach Valery A. Barachevsky Michail V. Alfimov Sergei P. Gromov Artem I. Vedernikov Johan Lugtenburg Andrey A. Khodonov 《Journal of inclusion phenomena and macrocyclic chemistry》2004,49(1-2):153-161
An effective synthetic approach to the preparation of a new crown-ether vinylogs involving the Horner–Emmons olefination of carbonyl precursors with the use of C2- and C5-phosphonates was proposed. The effects of the conjugation chain length and the nature of the terminal polar functions in the phosphonate reagent on the yield and process stereoselectivity were discussed. 相似文献
5.
6.
A. A. Sobanov A. V. Zolotukhin I. V. Galkina V. I. Galkin R. A. Cherkasov 《Russian Journal of General Chemistry》2006,76(3):421-429
A complex spectral (UV, IR, and 31P NMR), preparative, and kinetic investigation of the mechanism of the noncatalytic variant of the Pudovik reaction in the series of imines was carried out. The reaction proceeds through a four-center cyclic transition state. The transition state is highly labile, which determines its high sensitivity to the structure of the reagents, the nature of the solvent and catalyst, and some other factors. The necessary condition for the hydrophosphorylation of imines to occur is the participation of proton-donor reagents and acidic admixtures, specifically hydrolysis products of dialkyl hydrogen phosphites, such as monoalkyl dihydrogen phosphates and phosphorous acid, which act as acid catalysts. When the starting reagents are thoroughly purified and no such catalysts are present, the Pudovik reaction fails to occur in the imine series. 相似文献
7.
L. P. Prikazchikova B. M. Khutova V. M. Cherkasov 《Chemistry of Heterocyclic Compounds》1974,10(8):998-999
Reaction of 4,6-dimethylpyrimidine with the acyl chlorides of aromatic carboxylic acids gave N-acyl-4-phenacyl-6-acylmethylidynepyrimidines, which undergo alcoholysis to give the corresponding diketones — 4,6-diphenacylpyrimidines. 相似文献
8.
9.
10.
In contrast to the classical method where a single molecule is designed to extract metal cations under specific conditions, dynamic covalent chemistry provides an approach based on the implementation of an adaptive dynamic covalent library for inducing the generation of the extractant species. This approach has been applied to the liquid–liquid extraction of copper(ii) nitrate based on a dynamic library of acylhydrazones constituents that self-build and distribute through the interface of a biphasic system. The addition of copper(ii) cations to this library triggers a modification of its composition and the up-regulation of the ligand molecules driven by coordination to the metal cations. Among these, one species has proven to be sufficiently lipophilic to play the role of carrier agent and its formation by component exchange enables the partial extraction of the copper(ii). The study of different pathways to generate the dynamic covalent library demonstrates the complete reversibility and the adaptability of the system. The detailed analytical investigation of the system provides a means to assess the mechanism of the dynamic extraction process.Phase transfer of Cu(ii) cations is achieved by component exchange in a dynamic covalent library of acylhydrazone ligands. B1/B2 component exchange leads to the generation of a lipophilic carrier agent that extracts Cu(ii) into chloroform. 相似文献