全文获取类型
收费全文 | 619篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
化学 | 418篇 |
晶体学 | 4篇 |
力学 | 17篇 |
数学 | 121篇 |
物理学 | 83篇 |
出版年
2023年 | 3篇 |
2022年 | 14篇 |
2021年 | 18篇 |
2020年 | 13篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 26篇 |
2013年 | 27篇 |
2012年 | 41篇 |
2011年 | 47篇 |
2010年 | 32篇 |
2009年 | 22篇 |
2008年 | 31篇 |
2007年 | 43篇 |
2006年 | 46篇 |
2005年 | 31篇 |
2004年 | 27篇 |
2003年 | 24篇 |
2002年 | 19篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1946年 | 2篇 |
1939年 | 2篇 |
1937年 | 4篇 |
1913年 | 2篇 |
1911年 | 2篇 |
1910年 | 2篇 |
1908年 | 2篇 |
1891年 | 2篇 |
1889年 | 2篇 |
1870年 | 2篇 |
排序方式: 共有643条查询结果,搜索用时 15 毫秒
581.
Esteban-Martín A Taranenko VB García J de Valcárcel GJ Roldán E 《Physical review letters》2005,94(22):223903
We report the controlled observation of the nonequilibrium Ising-Bloch transition in a broad area nonlinear optical cavity (a quasi-1D single longitudinal-mode photorefractive oscillator in a degenerate four-wave mixing configuration). Our experimental technique allows for the controlled injection of the domain walls. We use cavity detuning as control parameter and find that both Ising and Bloch walls can exist for the same detuning values within a certain interval of detunings; i.e., the Ising-Bloch transition is hysteretic in our case. A complex Ginzburg-Landau model is used for supporting the observations. 相似文献
582.
583.
Interferometry is a technique for reconstructing the profiles of phase objects. We present a novel interferometric setup for generating interferograms with doubled phase profile and enhanced contrast compared with the standard interferogram. The proposed system consists of a two-beam interferometer in which the reference and test waves are circularly polarized orthogonally to each other. They are superposed upon a bacteriorhodopsin film, creating a polarization grating that is distorted by the phase of the test object. This polarization pattern is read by a polarized He-Ne beam. We show analytically and experimentally that, when the zero diffraction order is removed, an interferogram with doubled phase profile and enhanced contrast is obtained. 相似文献
584.
585.
Barison S Barreca D Battiston GA Daolio S Fabrizio M Gerbasi R Tondello E 《Rapid communications in mass spectrometry : RCM》2003,17(9):996-1001
Mixed CeO(2)-ZrO(2) systems have attracted widespread interest for their use in three-way catalyst (TWC) technology for automotive exhaust conversion to non-toxic products. In this work, CeO(2)-ZrO(2) thin films were deposited, via chemical vapor deposition, in order to obtain nanoscale materials with a high surface-to-volume ratio, with precise control of system properties. The addition of TiO(2) as buffer layer was also investigated. Cordierite was chosen as substrate, being the usual refractory material for catalytic mufflers. The multilayers were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). In particular, the combination of SIMS and XPS allowed us to investigate both surface and in-depth chemical composition, studying also film-intermixing phenomena induced by annealing processes. 相似文献
586.
Omar A. Guagnini Eugenio E. Vonesch Agustín M. Fassi Saul V. Guagnini 《Mikrochimica acta》1955,43(5-6):1061-1068
Resumen Se ha estudiado la investigación cualitativa de microcantidades de barbitúricos en materiales biológicos. Se propone una técnica basada en la extracción de estos compuestos con metanol, purificación del extracto por ascenso capilarimétrico en papel de filtro y reconocimiento mediante la reacción deParri yKoppanyi. Se consideran las interferencias y las condiciones particulares del trabajo sobre vísceras, sangre y orina. El límite de identificacíon de la técnica llega a 10g y representa un método económico en cuanto a tiempo y material.
Presentado al III Congreso Panamericano de Farmacia y Bioquímica, Sao Paulo, Brasil, XII, 1954. 相似文献
Summary A study was made of the qualitative detection of micro amounts of barbiturates in biological materials. A procedure is suggested based on extraction of these compounds with methanol, followed by purification of the extract by ascending paper chromatography, and identification with the aid of theParri andKoppanyi reaction. The interferences and the special conditions of applying the test to viscera, blood, and urine were studied. The identification limits of the procedure is 10g. The method saves time and material.
Zusammenfassung Der qualitative Nachweis von Mikromengen von Barbituraten in biologischem Material wurde studiert. Zu diesem Zweck wird eine Arbeitstechnik vorgeschlagen, die auf der Extraktion dieser Verbindungen mit Methanol, der nachfolgenden Reinigung des Extraktes durch aufsteigende Papierchromatographie und Identifizierung mit Hilfe der Reaktion nachParri undKoppanyi beruht. Störende Einflüsse und die besonderen Bedingungen der Anwendung der Methode auf Eingeweide, Blut und Harn wurden untersucht. Die Erfassungsgrenze des beschriebenen Verfahrens erreicht 10 g. Es ermöglicht Zeit- und Materialersparnis.
Résumé Etude de l'identification qualitative de microquantités de barbituriques dans les milieux biologiques. A cette fin on recommande une technique opératoire qui comporte une extraction de ces composés dans le méthanol, une purification consécutive de l'extrait par chromatographie ascendante sur papier et une identification par la réaction deParri etKoppanyi. On a étudié les influences gênantes ainsi que les conditions particulières d'emploi de la méthode pour les viscères, le sang et l'urine. Sa limite de sensibilité est de 10g; elle permet d'épargner du temps et du matériel.
Presentado al III Congreso Panamericano de Farmacia y Bioquímica, Sao Paulo, Brasil, XII, 1954. 相似文献
587.
The oxidation of CFClCFCl and CF2CCl2 were studied at room temperature by chlorine- and oxygen-atom initiation. The chlorine-atom initiated oxidation of CFClCFCl yields CCl2FCF(O) as the exclusive product. Its quantum yield is ~420, which gives k3a/k3b=210 where reactions (3a) and (3b) are The O(3P)? CFClCFCl reaction gives CClFO with a quantum yield of 0.80, polymer, and small amounts of an unidentified product which is probably cyclo-(CFCl)3. Thereaction paths are with k9a/k9=0.80. The overall reaction of O(3P) with CFClCFCl proceed one fifth as fast as the O(3P)-C2F4 reaction. When O2 is also present, the same free-radical chain oxidation occurs by O(3P)initiation as by chlorine-atom initiation. The chlorine-atom initiated oxidation of CF2CCl2 gives CF2ClCCl(O) as the major product, with quantum yields ranging from 42 to 85. Smaller amounts of CF2O and CCl2O are produced in equal amounts with quantum yields of ~3.5. The reactions responsible for the products are The O(3P)-CF2CCl2interaction yields CF2O and with quantum yields of 1.0 and ~0.85, respectively. In thepresence of O2 the radical chain products are observed, but the mechanism is different than that for other chloroolefins. 相似文献
588.
589.
590.
Alessandro D'Aprano Ines Dorina Donato Eugenio Caponetti Valeria Agrigento 《Journal of solution chemistry》1979,8(11):793-800
Viscosity measurements have been made at 25°C on solutions of water inn-propanol, and at 15, 25, 35, and 45°C on solutions of water inn-butanol,n-pentanol, andn-hexanol over the respective solubility ranges. For most of the systems, water decreases the viscosity of the dry alcohols, while for the lower members of the series literature data report an increase in viscosity on addition of water. These results are rationalized in terms of two kinds of interaction between water molecules and alcohols: participation of water molecules in chain formation for the lower alcohols and formation of water-centered complexes for butanol and higher alcohols. 相似文献