全文获取类型
收费全文 | 1291篇 |
免费 | 78篇 |
国内免费 | 6篇 |
专业分类
化学 | 1102篇 |
晶体学 | 5篇 |
力学 | 6篇 |
数学 | 112篇 |
物理学 | 150篇 |
出版年
2023年 | 20篇 |
2022年 | 14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 | 137篇 |
2010年 | 46篇 |
2009年 | 46篇 |
2008年 | 104篇 |
2007年 | 75篇 |
2006年 | 69篇 |
2005年 | 79篇 |
2004年 | 61篇 |
2003年 | 50篇 |
2002年 | 43篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 6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1375条查询结果,搜索用时 343 毫秒
71.
72.
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
73.
74.
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
75.
76.
[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
77.
78.
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79.
80.
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