全文获取类型
收费全文 | 1328篇 |
免费 | 63篇 |
国内免费 | 6篇 |
专业分类
化学 | 1112篇 |
晶体学 | 5篇 |
力学 | 6篇 |
数学 | 112篇 |
物理学 | 162篇 |
出版年
2023年 | 20篇 |
2022年 | 22篇 |
2021年 | 35篇 |
2020年 | 43篇 |
2019年 | 27篇 |
2018年 | 31篇 |
2017年 | 17篇 |
2016年 | 73篇 |
2015年 | 35篇 |
2014年 | 49篇 |
2013年 | 75篇 |
2012年 | 109篇 |
2011年 | 139篇 |
2010年 | 46篇 |
2009年 | 46篇 |
2008年 | 105篇 |
2007年 | 75篇 |
2006年 | 69篇 |
2005年 | 80篇 |
2004年 | 62篇 |
2003年 | 50篇 |
2002年 | 43篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 17篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1968年 | 4篇 |
1960年 | 2篇 |
1957年 | 2篇 |
1935年 | 2篇 |
排序方式: 共有1397条查询结果,搜索用时 0 毫秒
81.
Fadi HatoumJana Engler Christina ZelmerJohannes Wißen Cherie Ann MottiJohann Lex Michael Oelgemöller 《Tetrahedron letters》2012,53(42):5573-5577
A series of 3-(alkyl and aryl)methyleneisoindolin-1-one derivatives were synthesized in a simple two-step procedure using a recently established photodecarboxylative addition of carboxylates to phthalimides as the key-step. Subsequent acid-catalyzed dehydration and deprotection furnished the desired target compounds with high E-selectivity. The reaction sequence was applied to the synthesis of the known bioactive phenylethylene derivative, AKS-186. Different analogues, including heteroatom-containing isosteres were also synthesized using this approach. 相似文献
82.
83.
Fatty alcohol ethoxylates can be analyzed using a combination of liquid chromatography under critical conditions as the first dimension and liquid exclusion-adsorption chromatography as the second dimension. Transfer of fractions from the first to the second dimension is achieved using the full adsorption-desorption (FAD) technique. The peaks of interest in the first dimension are trapped on a short precolumn before injecting them into the second dimension. Full adsorption is achieved by increasing the water content in the mobile phase before the FAD column. When the fractions are desorbed by switching to the mobile phase of the second dimension, they are focused and reconcentrated. In this way, a full resolution of oligomers is achieved. As both dimensions are run in isocratic mode, density and refractive index detection can be applied, which allows an accurate quantitation. 相似文献
84.
85.
[reaction: see text] Beta-lactones are useful synthetic intermediates allowing access to a number of functional arrays. In this report, enantiomerically pure 4-trichloromethyl-2-oxetanone is shown to be a versatile amino acid synthon leading to a variety of gamma-substituted alpha-amino acid precursors. The utility of this methodology was demonstrated by the concise synthesis of a protected homoserine equivalent, alpha-azidobutyro lactone, and a naturally occurring alpha-amino acid from the seeds of Blighia unijugata. 相似文献
86.
87.
Brian Spencer Robert A Marr Edward Rockenstein Leslie Crews Anthony Adame Rewati Potkar Christina Patrick Fred H Gage Inder M Verma Eliezer Masliah 《BMC neuroscience》2008,9(1):109
Background
Proteolytic degradation has emerged as a key pathway involved in controlling levels of the Alzheimer's disease (AD)-associated amyloid-β (Aβ) peptide in the brain. The endopeptidase, neprilysin, has been implicated as a major Aβ degrading enzyme in mice and humans. Previous short and intermediate term studies have shown the potential therapeutic application of neprilysin by delivering this enzyme into the brain of APP transgenic mice using gene transfer with viral vectors. However the effects of long-term neprilysin gene transfer on other aspects of Aβ associated pathology have not been explored yet in APP transgenic mice. 相似文献88.
89.
Randy?L.?Vander WalEmail author Aaron?J.?Tomasek Michael?I.?Pamphlet Christina?D.?Taylor William?K.?Thompson 《Journal of nanoparticle research》2004,6(6):555-568
Image processing algorithms have been developed to extract fringe length, tortuosity and separation from high resolution transmission electron microscopy images. To validate the separation algorithm, a comparison is made between the image-based fringe separation and that obtained by analysis of X-ray diffraction data for a progressively heat-treated carbon black. Agreement is favorable. To illustrate the utility of the analysis parameters for a range of carbon nanostructures, analysis is applied to a series of pyrolytically prepared carbon soots – qualitatively described as containing amorphous, graphitic or fullerenic nanostructure. For all processing, the intermediate image, in the form of a skeletonized binary image of the original high resolution transmission electron micrograph, is shown and found to accurately reflect the nanostructural organization within the carbon as visually observed. Statistical results for each analysis parameter, extracted from the binary images, are presented in the form of histograms and quantitatively distinguish the different carbon nanostructures. 相似文献
90.
The present study investigated the relative contributions of water content and non-equilibrium cooling and warming rates to the survival of cryopreserved axes of recalcitrant P. trifoliata seeds. Reducing water contents from 1.7 and 0.26 g water per g dry mass is believed to increase cytoplasmic viscosity. Cooling to -196 degree C was done at rates averaging between 0.17 and 1300 degree C per second, and warming at 600 or 1.35 degree C per second. Survival was assessed after 4 weeks in vitro. Rapid warming resulted in higher survival and normal development of axes at all water contents. The effects of cooling rate were dependent on the water content of axes. Cooling rates resulting in >70 percent normal development ranged between 0.17 and about 1300 degree C per second for axes at a water content of 0.26 g water per g dry mass narrowing with increasing hydration to an apparent optimum at about 686 degree C per second in axes at 0.8 g water per g dry mass At 1.7 g water per g dry mass, axes cooled at 0.17 degree C per second yielded nearly 40 percent normal development, whereas faster cooling was deleterious. Results are interpreted in the context of the effect of water content on cytoplasmic viscosity and the rate of intracellular ice formation. At low water contents, the high intracellular viscosity slows ice crystallization making survival independent of cooling rate. At higher water contents, the reduced viscosity requires faster cooling to prevent ice crystal damage. The ability to cool rapidly with increasing hydration is balanced with an increasing limitation to dissipate heat fast enough to prevent severe damage. 相似文献