全文获取类型
收费全文 | 241篇 |
免费 | 7篇 |
专业分类
化学 | 149篇 |
晶体学 | 5篇 |
力学 | 17篇 |
数学 | 41篇 |
物理学 | 36篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 12篇 |
2015年 | 10篇 |
2014年 | 3篇 |
2013年 | 14篇 |
2012年 | 12篇 |
2011年 | 11篇 |
2010年 | 13篇 |
2008年 | 11篇 |
2007年 | 12篇 |
2006年 | 9篇 |
2005年 | 12篇 |
2004年 | 15篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1989年 | 3篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 5篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1960年 | 2篇 |
1958年 | 2篇 |
1957年 | 1篇 |
1956年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有248条查询结果,搜索用时 31 毫秒
71.
In the presence of sulfur dioxide and an acid promoter, (-)-(1E,3Z)-2-methyl-1-((1S)-1-phenylethoxy)penta-1,3-dien-3-yl isobutyrate reacts with (Z)-3-(trimethylsilyloxy)pent-2-ene giving a silyl sulfinate intermediate that undergoes, in the presence of palladium catalyst, a desilylation and retro-ene elimination of SO(2) with formation of (-)-(1Z,2S,3R,4S)-1-ethylidene-2,4-dimethyl-5-oxo-3-((1S)-1-phenylethoxy)-heptyl isobutyrate as major product. This ethyl ketone undergoes cross-aldol reaction with (2S)-2-methyl-3-[(tert-butyldimethylsilyl)oxy]propanal giving an aldol that is reduced into a stereoheptad corresponding to the C(19)-C(27)-segment of Rifamycins with high diastereoselectivity and enantiomeric excess. 相似文献
72.
Liquid chromatographic-mass spectrometric analysis of supercritical-fluid extracts of rosemary plants 总被引:2,自引:0,他引:2
Señoráns FJ Ibañez E Cavero S Tabera J Reglero G 《Journal of chromatography. A》2000,870(1-2):491-499
A two-step supercritical fluid extraction process of rosemary leaves, on a pilot plant scale, is proposed to divide the oleoresin into two fractions with different antioxidant activities and essential oil composition. Rosemary leaves were extracted by using different conditions of pressure and temperature as well as different conditions for fractionation of the extracts. Conditions can be tuned to selectively extract one antioxidant fraction with almost no residual aroma. In the present investigation, the antioxidant fraction was exhaustively studied in terms of antioxidant activity measurements as well as of chemical composition. An LC–MS method was adapted to perform the analysis and identification of the compounds responsible for the antioxidant activity of the extracts. Different extraction and fractionation conditions were studied in order to correlate the process conditions with the antioxidant activities obtained. 相似文献
73.
Bagineni Prasad Mara Doimo Mns Andrasson Valentin LHte Erik Chorell Sjoerd Wanrooij 《Chemical science》2022,13(8):2347
G-quadruplex (G4) DNA structures are implicated in central biological processes and are considered promising therapeutic targets because of their links to human diseases such as cancer. However, functional details of how, when, and why G4 DNA structures form in vivo are largely missing leaving a knowledge gap that requires tailored chemical biology studies in relevant live-cell model systems. Towards this end, we developed a synthetic platform to generate complementary chemical probes centered around one of the most effective and selective G4 stabilizing compounds, Phen-DC3. We used a structure-based design and substantial synthetic devlopments to equip Phen-DC3 with an amine in a position that does not interfere with G4 interactions. We next used this reactive handle to conjugate a BODIPY fluorophore to Phen-DC3. This generated a fluorescent derivative with retained G4 selectivity, G4 stabilization, and cellular effect that revealed the localization and function of Phen-DC3 in human cells. To increase cellular uptake, a second chemical probe with a conjugated cell-penetrating peptide was prepared using the same amine-substituted Phen-DC3 derivative. The cell-penetrating peptide conjugation, while retaining G4 selectivity and stabilization, increased nuclear localization and cellular effects, showcasing the potential of this method to modulate and direct cellular uptake e.g. as delivery vehicles. The applied approach to generate multiple tailored biochemical tools based on the same core structure can thus be used to advance the studies of G4 biology to uncover molecular details and therapeutic approaches.The development of an approach to generate multiple tailored biochemical tools based on the same core structure, Phen-DC3, to advance studies of G4 biology to uncover molecular details and therapeutic approaches. 相似文献
74.
An almost disjoint family is constructed which is isomorphic to any almost disjoint family which can be constructed from it by taking subsets and finite unions. This is applied to the construction of a Boolean algebra with related properties.Presented by R. McKenzie.Partially supported by Israel-US Binational Research Fund.Partially supported by NSERC. 相似文献
75.
For a Polish group let be the minimal number of translates of a fixed closed nowhere dense subset of required to cover . For many locally compact this cardinal is known to be consistently larger than which is the smallest cardinality of a covering of the real line by meagre sets. It is shown that for several non-locally compact groups . For example the equality holds for the group of permutations of the integers, the additive group of a separable Banach space with an unconditional basis and the group of homeomorphisms of various compact spaces. 相似文献
76.
Alberto Della Martina Lszl Garamszegi Jns G. Hilborn 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):2036-2046
This article describes the pore size modification and in situ surface functionalization of macroporous crosslinked poly(dicyclopentadiene), produced by chemically induced phase separation, with norbornene‐functionalized poly(ethylene glycol) telechelic oligomers. The microstructure of the open porosity materials produced with this technique consisted of agglomerated particles. The incorporation of these telechelic oligomers allowed a substantial decrease in the pore size and a related increase in the internal surface area. These functionalized oligomers acted as stabilizers around the primary particles produced by phase separation and blocked their growth so that the materials resulting from the agglomeration of these smaller particles showed finer microstructures. The resulting porous materials were characterized by scanning electron microscopy, density measurements, nitrogen adsorption, and mercury porosimetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2036–2046, 2003 相似文献
77.
We consider the (2,0) supersymmetric theory of tensor multiplets and self-dual strings in six space-time dimensions. Space-time diffeomorphisms that leave the string world-sheet invariant appear as gauge transformations on the normal bundle of the world-sheet. The naive invariance of the model under such transformations is however explicitly broken by anomalies: The electromagnetic coupling of the string to the two-form gauge field of the tensor multiplet suffers from a classical anomaly, and there is also a one-loop quantum anomaly from the chiral fermions on the string world-sheet. Both of these contributions are proportional to the Euler class of the normal bundle of the string world-sheet, and consistency of the model requires that they cancel. This imposes strong constraints on possible models, which are found to obey an ADE-classification. We then consider the decoupled world-sheet theory that describes low-energy fluctuations (compared to the scale set by the string tension) around a configuration with a static, straight string. The anomaly structure determines this to be a supersymmetric version of the level one Wess-Zumino-Witten model based on the group 相似文献
78.
The dynamics of the strong-anisotropic Ising model in a transverse field is used with the purpose to explain the dielectric critical slowing down observed experimentally in the quasi-one-dimensional hydrogen-bonded ferroelectric crystal CsH2PO4. A good agreement with the experimental data of the temperature dependence of the dielectric constant and the relaxation time is obtained. 相似文献
79.
Juris Steprāns 《Topology and its Applications》1981,12(2):181-185
Trees of height ω1 are characterized in terms of continuous mappings to the real line. In particular Souslin trees are characterized as those uncountable trees with no uncountable continuous image in the real line. Trees which can not be continuously embeded in the real line are also characterized. 相似文献
80.
J.V. Kunzler T.A. Grandi W.H. Schreiner P. Pureur D.E. Brandāo 《Journal of Physics and Chemistry of Solids》1980,41(10):1023-1026
Electrical resistivity measurements have been performed on the Cu2Mn(Al1?xSnx) Heusler alloys, where x = 0; 0.05; 0.10; 0.15, in the temperature range of 4–800 K. The experimental curves clearly show the importance of the ferromagnetic character on the resistivities of the alloys. The results obtained are in agreement with an interpretation in terms of a spin-disorder model. 相似文献