全文获取类型
收费全文 | 245篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 125篇 |
力学 | 11篇 |
数学 | 6篇 |
物理学 | 109篇 |
出版年
2020年 | 2篇 |
2019年 | 3篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 2篇 |
2013年 | 9篇 |
2012年 | 14篇 |
2011年 | 19篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 15篇 |
2007年 | 20篇 |
2006年 | 8篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 12篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 6篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1965年 | 2篇 |
1962年 | 1篇 |
1935年 | 1篇 |
1932年 | 1篇 |
1930年 | 1篇 |
1925年 | 2篇 |
1909年 | 1篇 |
排序方式: 共有251条查询结果,搜索用时 203 毫秒
1.
Sustainable Synthesis of Chiral Tetrahydrofurans through the Selective Dehydration of Pentoses 下载免费PDF全文
Robert W. Foster Dr. Christopher J. Tame Dr. Dejan‐Krešimir Bučar Prof. Helen C. Hailes Dr. Tom D. Sheppard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(45):15947-15950
L ‐Arabinose is an abundant resource available as a waste product of the sugar beet industry. Through use of a hydrazone‐based strategy, L ‐arabinose was selectively dehydrated to form a chiral tetrahydrofuran on a multi‐gram scale without the need for protecting groups. This approach was extended to other biomass‐derived reducing sugars and the mechanism of the key cyclization investigated. This methodology was applied to the synthesis of a range of functionalized chiral tetrahydrofurans, as well as a formal synthesis of 3R‐3‐hydroxymuscarine. 相似文献
2.
3.
4.
5.
6.
Rapid Assembly of Functionalised Spirocyclic Indolines by Palladium‐Catalysed Dearomatising Diallylation of Indoles with Allyl Acetate 下载免费PDF全文
Dr. Persis Dhankher Dr. Laure Benhamou Dr. Tom D. Sheppard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13375-13381
Herein, we report the application of allyl acetate to the palladium‐catalysed dearomatising diallylation of indoles. The reaction can be carried out by using a readily available palladium catalyst at room temperature, and can be applied to a wide range of substituted indoles to provide access to the corresponding 3,3‐diallylindolinines. These compounds are versatile synthetic intermediates that readily undergo Ugi reactions or proline‐catalysed asymmetric Mannich reactions. Alternatively, acylation of the 3,3‐diallylindolinines with an acid chloride or a chloroformate, followed by treatment with aluminium chloride, enables 2,3‐diallylindoles to be prepared. By using ring‐closing metathesis, functionalised spirocyclic indoline scaffolds can be accessed from the Ugi products, and a dihydrocarbazole can be prepared from the corresponding 2,3‐diallylindole. 相似文献
7.
J. Finlay S. Sheppard S. Tookey M. J. Hill P. J. Barham 《Journal of Polymer Science.Polymer Physics》2001,39(12):1404-1414
Young's moduli of a series of quenched isotactic polypropylene/high‐density polyethylene blends were measured. The moduli of many of the blends exceeded the upper bound, calculated from the parallel model with the moduli of the two quenched homopolymers as those of the two components. In fact, both components crystallized at higher temperatures in the blends than they did on their own. It is argued that the higher crystallization temperatures of the components lead to higher component moduli and that this can explain the observation that the measured moduli of the blends apparently exceeded the upper bound. The implications of this work are discussed in light of other studies concerning the measurement and calculation of blend moduli. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1404–1414, 2001 相似文献
8.
Xanthomonas campestris polysaccharide in the solid state is stable to 225°C in air and 250°C in inert atmosphere. In solution, even at moderate temperatures, the polymer undergoes hydrolytic degradation via the glycosidic linkages, and occurrence of main-chain scission results in lower solution viscosity. In solution, the polymer can exist in ordered and disordered conformations. In distilled water at temperatures ≤ 50°C, the polymer exists in the disordered conformation. In the presence of salt, acid, or base the polymer exists in the ordered conformation. In the ordered conformation the polymer exhibits a far greater hydrolytic stability. The higher stability of the ordered conformation is especially demonstrated when the polymer is aged in acid or base solutions. Contrary to the expected lower stability of the glycosidic linkages in acid or base than in water, Xanthomonas campestris polysaccharide shows higher stability in these media. 相似文献
9.
Several authors have demonstrated how reductions can be used to improve the efficiency with which the Steiner Problem in Graphs can be solved. Previous reduction algorithms have been largely ad hoc in nature. This paper uses a theory of confluence to show that, in many cases, all maximal reduction sequences are equivalent, gaining insights into the design of reduction algorithms that obtain a maximum degree of reduction. 相似文献
10.
The interpretation of ABC-type spectra is discussed in relation to several series of calculated spectra; some frequency and intensity sum rules are indicated. The hydrogen spectra of some vinyl derivatives, X. CH = CH2 (X = F, Cl, Br, O and C) have been analysed. It is shown that and that a modified correlation holds between the Jgem coupling constants of CH2 groups and the H-C-H angle in a range of molecules. All three coupling constants of the vinyl compounds decrease approximately linearly with the electronegativity of X; these effects are probably transmitted through the sigma bonds. By contrast the difference between the chemical shift of the = CH2 group and that of the XHC = group is approximately linearly dependent on Taft's resonance parameter, σR , suggesting that the pi-electron distribution is principally concerned in this case. 相似文献