全文获取类型
收费全文 | 292篇 |
免费 | 4篇 |
专业分类
化学 | 211篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 5篇 |
物理学 | 78篇 |
出版年
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 12篇 |
2012年 | 16篇 |
2011年 | 15篇 |
2010年 | 6篇 |
2009年 | 3篇 |
2008年 | 18篇 |
2007年 | 22篇 |
2006年 | 23篇 |
2005年 | 7篇 |
2004年 | 11篇 |
2003年 | 10篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1971年 | 3篇 |
1969年 | 1篇 |
1965年 | 1篇 |
1918年 | 1篇 |
排序方式: 共有296条查询结果,搜索用时 15 毫秒
91.
Joanne F. Kinneary Therese M. Roy Jeffrey S. Albert Heungsik Yoon Thomas R. Wagler Lucy Shen Cynthia J. Burrows 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(2):155-168
New nickel catalysts have been developed for the oxidation of alkenes to epoxides, alcohols, aldehydes and ketones. Mechanistic studies indicate that the oxidation reactions are very sensitive to the nature of the catalyst; only certain ligands including salen and the macrocycles cyclam and dioxocyclam render Ni(II) effective as a catalyst. A Ni(III) or Ni(IV)-oxo species has been postulated as the catalytically active oxidant which leads to oxygen atom transfer to alkenes in a stepwise process. Both iodosylbenzene and hypochlorite have been used as terminal oxidants; both systems give high yields of epoxidation of alkenes and varying amounts of C=C bond cleavage products. In order to reach an ultimate goal of hydrocarbon oxidation within a molecular recognition system, new molecular receptors for organic substrates have been investigated. The receptors are constructed from two subunits of cholic acid and display amphophilic character — a hydrophobic exterior and a hydrophilic interior. Conformational properties in the presence of polar guests in CDCl3 are described. 相似文献
92.
Torsten W. Bünnagel Benjamin S. Nehls Frank Galbrecht Kristina Schottler Christof J. Kudla Markus Volk João Pina João S. Seixas de Melo Hugh D. Burrows Ullrich SCherf 《Journal of polymer science. Part A, Polymer chemistry》2008,46(22):7342-7353
A series of step‐ladder copolymers based on thiophene–phenylene–thiophene SL1 ‐ SL3 and thiophene–naphthylene–thiophene SL4 repeat units with varying lengths of the oligothiophene segment has been designed and synthesized via a microwave‐assisted Stille‐type cross‐coupling reaction followed by a polymer‐analogous cyclization reaction. The optical properties of the step‐ladder copolymers have been investigated in detail, in particular at low temperature and in the solid‐state. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7342–7353, 2008 相似文献
93.
M. Concei o D. A. Mateus Abí lio M. Silva Hugh D. Burrows 《Journal of photochemistry and photobiology. A, Chemistry》1994,80(1-3):409-416
The photophysics and photochemistry of the pesticide fenarimol were studied. From the absorption and fluorescence spectra, quantum yields and lifetimes, it is suggested that the lowest excited singlet state has predominatly n,π* character, and is localized on the pyrimidine ring. Phosphorescence measurements suggest a small singlet—triplet splitting. Halide ions are found to quench fenarimol flourescence. Photodecomposition of fenarimol in a variety of solvents was studied by gas chromatography—mass spectrometry. Although the products have not yet been characterized, degradation of this compound appears to involve cleavage of bonds to the quaternary carbon without significant dechlorination. Preliminary studies of the kinetics and relative quantum yields of photodegration show that the reaction proceeds via a first-order process, which is independent of pH, but which involves a photoactive intermediate. Chloride and bromide ions inhibit the photolysis,whereas the triplet quencher sorbic acid has no effect. 相似文献
94.
95.
Hugh D. Burrows Maria da Gra a Miguel Rui P.C. Pereira Nuno M.B. Proen a S nia M.C. Cardoso Carlos F.G.C. Geraldes M. Helena Gil Wyn Brown 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):459-465
The solution behaviour has been studied of a series of even chain length lead(II) carboxylates (octanoate to octadecanoate) and the odd chain length lead(II) heptadecanoate in a variety of non-complexing organic solvents and in alcohols. In agreement with previous studies, solubility increases dramatically above a certain temperature, which depends on solute concentration, chain length and solvent. This solution temperature is also affected by traces of water. These results are complemented by studies using vapour pressure osmometry, dynamic light scattering, 1H and 13NMR spectroscopy. The results in water-free systems are consistent with the formation of rather ill-defined, polydisperse aggregates, which increase in size with concentration and decrease with temperature. These show similar local structure to lamellar mesophases in the pure lead(II) carboxylates, and are suggested to be formed by solvent induced swelling and break-up of these mesophases. In the presence of water, a more ordered structure is formed, in which a few water molecules are suggested to be bound to the lead(II) carboxylate headgroup. 相似文献
96.
Orphal J Perrin A Flaud J Smirnov M Himmelmann S Voigt S Burrows JP 《Journal of Molecular Spectroscopy》2000,204(1):72-79
New high-resolution Fourier transform absorption spectra of an (15)N(16)O(2) isotopic sample of nitrogen dioxide were recorded at the University of Bremen in the 6.3-μm region. Starting from the results of a previous study [Y. Hamada, J. Mol. Struct. 242, 367-377 (1991)], a new and more extended analysis of the nu(3) band located at 1582.1039 cm(-1) has been performed. The spin-rotation energy levels were satisfactorily reproduced using a theoretical model which takes into account both the Coriolis interactions between the spin-rotation energy levels of the (001) vibrational state with those of the (020) and (100) states and the spin-rotation resonances within each of the NO(2) vibrational states. Precise vibrational energies and rotational, spin-rotation, and coupling constants were obtained in this way for the first triad of (15)N(16)O(2) interacting states {(020), (100), (001)}. Finally, a comprehensive list of line positions and line intensities of the {nu(1), 2nu(2), nu(3)} interacting bands of (15)N(16)O(2) was generated, using for the line intensities the transition moment operators which were obtained previously for the main isotopic species. Copyright 2000 Academic Press. 相似文献
97.
98.
Electrophysiological evidence for the critical band phenomenon in humans using event-related potentials has been sought for many years with conflicting results. Components Na and Pa of the middle-latency response (MLR) and wave V of the auditory brain-stem response (ABR) were simultaneously recorded in response to a two-tone complex varying in bandwidth from 76 Hz to 1012 Hz, centered at 2 kHz, and presented at an overall level of 85 dB SPL, in ten normal female subjects. Only the amplitude of Na showed an abrupt increase as bandwidth changed from 268 to 330 Hz, yielding an estimate of critical bandwidth in good agreement with previous behavioral estimates. 相似文献
99.
100.
The molecular modulation spectroscopic technique was employed to study the kinetics of NO3 radicals produced in the 253.7 nm photolysis of flowing gas mixtures of HNO3/CH4/O2 at room temperature. By computer fitting of the NO3 temporal behavior, a rate coefficient of (2.3 ± 0.7) × 10?12 cm3 molecule?1 s?1 was obtained for the reaction between NO3 and CH3O2 at 298 K. 相似文献