全文获取类型
收费全文 | 576篇 |
免费 | 8篇 |
国内免费 | 2篇 |
专业分类
化学 | 299篇 |
晶体学 | 10篇 |
力学 | 59篇 |
数学 | 60篇 |
物理学 | 158篇 |
出版年
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 55篇 |
2012年 | 23篇 |
2011年 | 24篇 |
2010年 | 15篇 |
2009年 | 8篇 |
2008年 | 18篇 |
2007年 | 27篇 |
2006年 | 31篇 |
2005年 | 22篇 |
2004年 | 14篇 |
2003年 | 9篇 |
2002年 | 18篇 |
2001年 | 9篇 |
2000年 | 22篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 5篇 |
1996年 | 21篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 9篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1968年 | 3篇 |
1961年 | 3篇 |
1886年 | 3篇 |
排序方式: 共有586条查询结果,搜索用时 15 毫秒
1.
Nicolaou KC Baran PS Zhong YL Barluenga S Hunt KW Kranich R Vega JA 《Journal of the American Chemical Society》2002,124(10):2233-2244
The discovery and development of the o-iodoxybenzoic acid (IBX) reaction with certain unsaturated N-aryl amides (anilides) to form heterocycles are described. The application of the method to the synthesis of delta-lactams, cyclic urethanes, hydroxy amines, and amino sugars among other important building blocks and intermediates is detailed. In addition to the generality and scope of this cyclization reaction, this article describes a number of mechanistic investigations suggesting a single electron transfer from the anilide functionality to IBX and implicating a radical-based mechanism for the reaction. 相似文献
2.
3.
Amino acids were derivatised with 4-fluoro-7-nitrobenzo-2,1,3-oxadiazol (NBD-F), separated by micellar electrokinetic chromatography (MEKC), and detected by argon-ion (488 nm) laser-induced fluorescence. The optimised MEKC background electrolyte conditions were: 40 mM sodium cholate, 5 mM beta-cyclodextrin in 20 mM aqueous borate buffer, pH 9.1, with 7% v/v acetonitrile. Using these conditions, 19 amino acids were separated within 17 min. The limits of detection were in the range of 7.6-42.2 pmol/mL and limits of quantitation from 0.05-0.14 nmol/mL. The method was systematically validated for injection volume error, migration time variation, calibration linearity, accuracy, precision, and recovery. Nanolitre volume samples of phloem sap of individual sieve element cells from the plant Arabidopsis thaliana and honeydew from the aphid Myzus persicae were directly analysed with this method. Quantitative amino acid concentrations in these two biological matrices were profiled for the first time. This method is particularly important because it allows the complete profile of the amino acids obtained from individual phloem elements, allowing cell to cell and plant to plant variation to be quantified, which to date has not been possible with Arabidopsis thaliana. 相似文献
4.
[reaction: see text] Glycosyl phosphates can be readily accessed on a solid support via a three-step procedure from support-bound glycals. These resin-bound glycosyl phosphates were successfully used as glycosylating agents for coupling with a series of nucleophiles. The stereochemical outcome of disaccharide formation was dependent on the nature of the linker connecting the saccharide to the polymer. Interestingly, other glycosyl donors such as thioglycosides and trichloroacetimidates did not exhibit such a dependence, indicating a different reaction mechanism for glycosylation. 相似文献
5.
Abstract— β-Carotene, at concentrations 0.1 m M , inhibits the formation of hydroperoxides and other oxidation products in a refined petroleum oil exposed to Pyrex-filtered UV. The effect appears to be due to 1 O2 quenching. A mechanism incorporating 1 O2 and radical processes is proposed as a model for environmental photooxidation of petroleum. 相似文献
6.
Measurements are reported of the dielectric properties of three laterally substituted dicyano compounds with large molecular dipole moments perpendicular to the long molecular axis. Results are given for the materials in solution, in the isotropic liquid state, and for one compound in the nematic state. There is evidence of a high degree of local ferroelectric order in all phases, and dipole correlation factors in excess of 3 were obtained. The significance of these observations for macroscopic ferroelectrically ordered and biaxial liquid-crystalline phases is considered. 相似文献
7.
Although models of branching in arterial and bronchial trees often predict a dependence of bifurcation parameters on the scale of the bifurcating vessels, direct verification of this dependence by comparison with data is uncommon. We compare measurements of bifurcation parameters of airways and arterial trees of different mammals as a function of scale to general features predicted by theoretical models based on minimization of pumping power and network volume. We find that the size dependence is more complex than existing theories based solely on energy and volume minimization explain, and suggest additional factors that may govern the branching at different scales. 相似文献
8.
The retrieval of phase information from only the magnitude of the Fourier transform of a signal remains an important problem for many applications. We present an algorithm for phase retrieval when there exist two related sets of Fourier-transform magnitude data. The data are assumed to come from a single object observed in two different polarizations through a distorting medium, so the phase component of the Fourier transform of the object is corrupted. Phase retrieval is accomplished by minimization of a suitable criterion function, which can take three different forms. 相似文献
9.
10.
Jian Tong Duncan L. MacFarlane Issa Panahi L. Roberts Hunt Govind Kannan Gary A. Evans 《Fiber and Integrated Optics》2013,32(4):201-215
Abstract An integrated photonic architecture is introduced and used to realize an optical filter with direct form I realization. The architecture offers gain from semiconductor optical amplifiers, and this gain results in an active optical filter whose filter response depends on the individual gains. The presence of gain provides advantages in filter performance, and tunable and adaptive functionality. The optical filter is modeled as a discrete time system and the z-transform is used in its analysis and design. A low-pass filter design example is presented and the filter coefficients are derived in terms of gains and coupler splitting ratios. The region of stable operations is derived by applying the Schur-Cohn stability test. 相似文献