全文获取类型
收费全文 | 722篇 |
免费 | 26篇 |
国内免费 | 6篇 |
专业分类
化学 | 572篇 |
晶体学 | 4篇 |
力学 | 14篇 |
数学 | 87篇 |
物理学 | 77篇 |
出版年
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 11篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 17篇 |
2015年 | 24篇 |
2014年 | 19篇 |
2013年 | 33篇 |
2012年 | 45篇 |
2011年 | 71篇 |
2010年 | 30篇 |
2009年 | 23篇 |
2008年 | 46篇 |
2007年 | 56篇 |
2006年 | 46篇 |
2005年 | 39篇 |
2004年 | 45篇 |
2003年 | 40篇 |
2002年 | 35篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 1篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1974年 | 4篇 |
排序方式: 共有754条查询结果,搜索用时 62 毫秒
1.
2.
Alfredo Paio Sylvie GehanneElena Grandini Gianna ReginatoPierfausto Seneci 《Tetrahedron letters》2003,44(9):1867-1870
A rapid and quantitative method for monitoring the efficiency of coupling of amino compounds to polystyrene resin through a carbamate linker has been developed. para-Nitrophenyl carbonate activating group has been shown to release a valuable chromophore for quantitatively monitoring the progress and the yield of the reaction. 相似文献
3.
Sylvie Large-Radix 《Journal of fluorine chemistry》2003,124(2):147-149
In the presence of a stoichiometric amount of Bu4NF·3H2O, (trifluoromethyl)trimethylsilane reacts with aromatic thiones in both thiophilic and carbophilic ways to deliver, in medium yield, a mixture of (trifluoromethylthio)diarylmethane and 1,1-diaryl-2,2,2-trifluoroethanethiol, the former product being the major one. 相似文献
4.
The stereoregularity of polymethylthiiranes initiated by zinc and cadmium thiolates depends upon the nature of the metal, temperature, solvent and the monomer/initiator concentrations ratio. Complexation of the metal with monomer has been studied by (13C) and (1H) NMR on a model molecule, dimethylcadmium. Cryoscopic measurements made on a soluble cadmium thiolate have shown the presence of aggregates. The relationship between these observations and polymer stereoregularity is discussed. 相似文献
5.
6.
[reaction: see text] The first examples of the Pd(0)-catalyzed amination of aryl halides using Rink-resins as nitrogen source are described. Pd(2)dba(3)/BINAP/NaO-t-Bu was found to be the most efficient catalyst/base system, while a solvent mixture of dioxane and tert-butyl alcohol was shown to enhance the selectivity toward the desired monoarylation. Moderate to good yields and excellent purities of the amination products were found with electron-poor aryl halides, while electon-rich aryl halides failed to react under these conditions. 相似文献
7.
The kinetics of peptide release during in vitro digestion of 4 protein sources (casein, cod protein, soy protein, and gluten) were investigated. Samples were sequentially hydrolyzed with pepsin (30 min) and pancreatin (2, 4, or 6 h) in a dialysis cell with continuous removal of digestion products. Nondialyzed digests were fractionated by ion-exchange chromatography and ultrafiltration. Animal proteins were digested at a greater rate than plant proteins. Target amino acids of specific enzymes appeared more rapidly in the dialyzed fractions when compared to other amino acids. Throughout the hydrolysis, nondialyzed digests contained a higher proportion of peptide mixtures with basic-neutral properties. Except for gluten, peptide fractions with molecular weights that exceeded 10 kDa (basic-neutral, BN > 10) were rapidly hydrolyzed during the first 2 h of pancreatin digestion. The kinetics of release and the composition of peptide fractions were different when the protein sources were compared. The analysis of amino acids revealed that threonine and proline proportions were relatively high in BN > 10 and in peptide fractions with molecular weight between 10-1 kDa (BN 10-1), while tyrosine, phenylalanine, lysine, and arginine predominated in the low molecular weight (<1 kDa) fractions. More resistant peptides were generally rich in proline and glutamic acid. The role of in vitro digestion assays in dietary protein quality evaluation is discussed. 相似文献
8.
Rijssenbeek JT Saito T Malo S Azuma M Takano M Poeppelmeier KR 《Journal of the American Chemical Society》2005,127(2):675-681
The related parameters of cation size and valence that control the crystallization of Sr(3)CaRu(2)O(9) into a 1:2 B-site-ordered perovskite structure were explored by cationic substitution at the strontium and calcium sites and by the application of high pressure. At ambient pressures, Sr(3)MRu(2)O(9) stoichiometries yield multiphasic mixtures for M = Ni(2+), Mg(2+), and Y(3+), whereas pseudocubic perovskites result for M = Cu(2+) and Zn(2+). For A-site substitutions, an ordered perovskite structure results for Sr(3-x)Ca(x)CaRu(2)O(9), with 0 = x = 1.5. In contrast, Ba(2+) substitution for Sr(2+) is accompanied by a phase change to a hexagonal BaTiO(3) structure type. At high pressures and temperatures, a 1:2 B-site-ordered perovskite structure is stabilized for Sr(3-x)Ba(x)CaRu(2)O(9), with 0 = x = 3. The scarcity of B-site-ordered perovskite ruthenates at ambient pressure and the metastable nature of the high-pressure phases underscore the strict size and valence requirements that must be met by the constituent cations to achieve these uncommon ordered structures. 相似文献
9.
1-(2-Methoxyethoxy)-2-methylbenzene and 1-(2-dimethylaminoethoxy)-2-methylbenzene have been lithiated using sec-BuLi under a variety of conditions and the laterally lithiated species trapped with electrophiles. 相似文献
10.
Tertiary phosphine oxides have been prepared in excellent yield from primary alkyl halides or aromatic halides and activated sodium phosphinates obtained by reaction of dialkyl phosphine oxides with complex bases (NaNH2/tBuONa). This reaction has been successfully applied to soluble and cross-linked bromopolystyrenes and to macroporous polystyrenes with bromooctyl substituents giving polymers which contain pendant phosphine oxide groups. 相似文献