全文获取类型
收费全文 | 188篇 |
免费 | 2篇 |
专业分类
化学 | 112篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 38篇 |
物理学 | 38篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2013年 | 15篇 |
2012年 | 8篇 |
2011年 | 9篇 |
2010年 | 9篇 |
2009年 | 7篇 |
2008年 | 6篇 |
2007年 | 15篇 |
2006年 | 9篇 |
2005年 | 12篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有190条查询结果,搜索用时 31 毫秒
41.
Yang SM Shie JJ Fang JM Nandy SK Chang HY Lu SH Wang G 《The Journal of organic chemistry》2002,67(15):5208-5215
By the promotion of samarium diiodide, thiophene-2-carboxylate reacted with 2 equiv of ketones at the C-4 and C-5 positions to give diols such as 2 and 9. Because the intermediary organosamarium species were oxophilic but not too basic, the double hydroxyalkylations with various ketone substrates, including alkyl aryl ketones, acetylthiophenes, cyclohexanone, alpha-tetralone, and alpha-phenylacetophenones, were realized without complication of side reactions. The diol products underwent an acid-catalyzed dehydration to give dienes such as 3 and 10, which were treated with DDQ to give either polysubstituted thiophenes (e.g., 4 and 11) or benzothiophenes (e.g., 5, 13, and 14) depending on the reaction conditions. Oxidative annulations of 4,5-diarylthiophenes 11 and 4,5,6,7-tetraphenylbenzothiophenes 14 were carried out by photochemical or chemical methods to give the sulfur-containing polycyclic aromatic compounds, such as phenanthro[9,10-b]thiophene-2-carboxylate, piceno[13,14-b]thiophene-2-carboxylate, and tribenzo[fg,ij,rst]pentapheno[15,16-b]thiophene-2-carboxylates. This method is applicable to the preparation of polysubstituted thiophenes, benzothiophenes, and the related compounds possessing liquid crystalline, photochromic, and other functional properties. 相似文献
42.
Salvador A Jaime MA Becerra G Guardia Mde L 《Analytical and bioanalytical chemistry》1996,356(2):109-122
The applications of supercritical fluid chromatography to the analysis of drugs have been carefully revised from the literature compiled in the Analytical Abstracts until March 1994. Easy-to-read tables provide useful information about the state-of-the-art and possibilities offered by SFC in pharmaceutical analysis. The tables comprise extensive data about samples analyzed, pharmaceutical principles determined, solvents used and sample quantity injected, supercritical fluids and modifiers employed, injection system, instrumentation, experimental conditions for chromatographic separations (density, pressure, flow, temperature), characteristics of columns employed (type, support, length, diameter, particle film thickness, stationary phase), detectors, type of restrictors, and also some analytical features of the methods developed (such as retention time, resolution, sensitivity, limit of detection and relative standard deviation). 相似文献
43.
Amparo Salvador M. Angeles Jaime Gladys Becerra M. De La Guardia 《Fresenius' Journal of Analytical Chemistry》1996,356(2):109-122
The applications of supercritical fluid chromatography to the analysis of drugs have been carefully revised from the literature
compiled in the Analytical Abstracts until March 1994. Easy-to-read tables provide useful information about the state-of-the-art
and possibilities offered by SFC in pharmaceutical analysis. The tables comprise extensive data about samples analyzed, pharmaceutical
principles determined, solvents used and sample quantity injected, supercritical fluids and modifiers employed, injection
system, instrumentation, experimental conditions for chromatographic separations (density, pressure, flow, temperature), characteristics
of columns employed (type, support, length, diameter, particle film thickness, stationary phase), detectors, type of restrictors,
and also some analytical features of the methods developed (such as retention time, resolution, sensitivity, limit of detection
and relative standard deviation). 相似文献
44.
45.
The type-II photosensitization process is mediated by the formation of singlet oxygen (O2[1deltag]). The short lifetime of this species dictates that chemical reactions with biological substrates can only occur when O2(1deltag) is in very close proximity to the photosensitizer itself. In this study, deuteroporphyrin, a type-II, membrane-localized photosensitizer, was used to generate O2(1deltag) in human lymphoblast WTK-1 cells, and the range of influence was determined by a variety of biological assays. Surprisingly, the initial membrane-confined events were shown, by comet assay, to induce DNA damage in these cells. DNA damage was inhibited both by membrane-localized (alpha-tocopherol acetate) and by cytoplasmic (trolox) free radical scavengers. Comet formation also was inhibited by treatment at low temperature. DNA fragmentation was not influenced by treatment with the pan-caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone, showing that apoptosis was not responsible for fragmentation. Taken together, these results show that primary photosensitization reactions involving O2(1deltag), even when tightly confined in extranuclear locations, leads to the production of secondary reactive oxygen species, probably as a result of lipid peroxidation, that can act at greater distances from the photosensitizer itself. These experiments were carried out under conditions where cell survival was significant and raise questions regarding DNA damage and mutagenesis pathways, even when extranuclear O2(1deltag)-generating compounds are used. 相似文献
46.
Carlos G. Bruhin Jorge M. Piwonka Mauricio O. Jerardino Gladys M. Navarrete Paulina C. Maturana 《Analytica chimica acta》1987
An electrothermal atomic-absorption procedure with the L'vov platform and a simple five- or ten-fold sample dilution with a matrix-modifier solution containing diammonium hydrogenphosphate, Triton X-100 and nitric acid, is described for the direct determination of relatively low levels of lead in heparinized blood. The graphite-furnace parameters and matrix-modifier composition are optimized. Sensitivity, imprecision, accuracy and detection limit are reported. Results obtained by standard addition for ten human blood samples (30–400 μg l?1 lead) were confirmed by an extraction/flame atomic-absorption reference method. Differences in mean lead values ranged from 2 to 31 μg l?1 with 5.1% mean relative difference. The mean relative standard deviations for consecutive and between-day determinations were 4.6 and 9%, respectively. Accuracy was verified by analyzing six bovine-blood standards certified for lead in the range 70–1100 μg l?1; deviations of found concentrations from expected values ranged from 0 to 44 μg l?1 with 4.3% mean relative error. Recovery experiments done with human blood gave 104% (90–121%) of the added lead. The method offers several advantages for routine application in comparison with the extraction/flame atomic-absorption procedure. 相似文献
47.
E. Castro Luna A. M. Becerra M. I. Dimitrijewits 《Reaction Kinetics and Catalysis Letters》1999,67(2):247-252
The effect of Rh addition upon catalyst characteristics and performance in methane steam reforming was investigated using
Rh-promoted Ni/Al2O3 catalysts. The number of reduced metal atoms exposed on the surface increased for the Rh-promoted catalysts. Rh-promoted
catalysts showed an increase in CH4 reforming activity; however, constant turnover frequencies for promoted and unpromoted catalysts suggest that the increase
in the number of metal surface atoms caused the activity enhancement. Rh also facilitated reduction of Ni/Al2O3. 相似文献
48.
The Geometry of Convex Transitive Banach Spaces 总被引:1,自引:0,他引:1
Becerra Guerrero Julio; Rodriguez Palacios Angel 《Bulletin London Mathematical Society》1999,31(3):323-331
Throughout this paper, X will denote a Banach space, S=S(X)and B=B(X) will be the unit sphere and the closed unit ballof X, respectively, and G=G(X) will stand for the group of allsurjective linear isometries on X. Unless explicitly statedotherwise, all Banach spaces will be assumed to be real. Nevertheless,by passing to real structures, the results remain true for complexspaces. 1991 Mathematics Subject Classification 46B04, 46B10,46B22. 相似文献
49.
Fluorescence recovery after pattern photobleaching is used to measure the self-diffusion of surfactant molecules, along cylinders and perpendicular to their main axis in an oriented hexagonal lyotropic phase. Unexpectedly, while the motion along cylinders is diffusive, a superdiffusive behavior is observed in the direction perpendicular to the cylinder axis. Moreover, varying the lattice parameter, we found that the perpendicular diffusion time is governed only by the number of cylinders to cross, providing experimental evidence for superdiffusion with a bounded step length. 相似文献
50.
2,4-Benzodiazepines can be prepared by condensation of an activated 2-benzoylbenzoic acid with 2-(aminomelhyl)phthalimide. A synthesis of this reagent is described. 相似文献