全文获取类型
收费全文 | 617篇 |
免费 | 14篇 |
专业分类
化学 | 350篇 |
晶体学 | 8篇 |
力学 | 19篇 |
数学 | 34篇 |
物理学 | 220篇 |
出版年
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 16篇 |
2015年 | 8篇 |
2014年 | 10篇 |
2013年 | 29篇 |
2012年 | 22篇 |
2011年 | 37篇 |
2010年 | 20篇 |
2009年 | 34篇 |
2008年 | 40篇 |
2007年 | 34篇 |
2006年 | 29篇 |
2005年 | 34篇 |
2004年 | 31篇 |
2003年 | 23篇 |
2002年 | 18篇 |
2001年 | 17篇 |
2000年 | 8篇 |
1999年 | 14篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1970年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有631条查询结果,搜索用时 0 毫秒
511.
Fausta Loffredo Annamaria Pranzo Gaetano Guerra Vincenzo Venditto Pasquale Longo 《Macromolecular Symposia》2001,166(1):165-172
Clathrates with tetrahydrofuran of styrene‐p‐methyl styrene co‐syndiotactic copolymers have been characterized by wide‐angle X‐ray scattering and differential scanning calorimetry. Stable clathrate structures with THF molecules have been observed in whole range of composition. In particular, syndiotactic polystyrene like and syndiotactic poly‐p‐methylstyrene like clathrate phases are obtained for p‐methylstyrene contents lower and higher than 35% by mol, respectively. 相似文献
512.
The stability and presence of micron-scale bubbles (microbubbles) is of considerable interest in environmental, biomedical, and food sciences. Here we show that microbubbles can be formed and stabilized in a solution of low cost food-grade emulsifier (a mixture of saturated long-chain monoglycerides, diglycerides and sodium stearoyl-2-lactylate) in combination with polyethylene glycol (PEG)-40 stearate. Langmuir trough methods and fluorescence microscopy were combined to investigate the surface tension, interfacial elastic modulus, phase behavior and microstructure of monolayer shells coating these microbubbles. Our results strongly suggest that although the PEG40S is necessary to form microbubbles this component, as well as sodium stearoyl-2-lactylate, are "squeezed out" in the form of collapse aggregates. This process leaves a microbubble shell, composed of a condensed-phase low surface tension mono- and diglycerides mixture with some of the PEG40S and SSL2 remaining trapped between the condensed-phase domains. We find that other commercially available emulsifiers, containing unsaturated or bulky components unable to form condensed phases, do not to form or stabilize a microbubble layer, although they may form a foam, a finding that we relate to differences in surface tension. 相似文献
513.
514.
Pasquale Longo Ermelinda Siani Stefania Pragliola Guglielmo Monaco 《Journal of polymer science. Part A, Polymer chemistry》2002,40(19):3249-3255
Ethene–propene copolymerizations were performed in the presence of Cs symmetric group 4 metallocenes. The reactivity ratios were strongly influenced by both the transition metal and the ancillary ligands. Substantially alternate, almost random, and blocky copolymers were obtained with titanocene, zirconocene, and hafnocene, respectively, with the bis(dimethylsilyl)‐1,1′‐2,2′‐diyl‐(3′,5′‐diisopropyl)(4‐isopropyl)‐(cyclopentadienyl) ligand, and a blocky copolymer was obtained with (diphenyl methylidene)(cyclopentadienyl)(9‐fluorenyl)TiCl2. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3249–3255, 2002 相似文献
515.
In the present work, we report a polarized Raman study versus temperature of the complex O–H stretching vibrational band (3800–3000 cm−1) performed in a glass forming liquid, namely propylene-glycol (PG), with chemical formula given by H[OCH(CH3)CH2]OH. The spectra were collected in bulk and confined state within a sol–gel controlled porous glass having highly interconnected 25 Å diameter pores and characterized by a huge number of silanol groups (Si–OH), able to interact with PG molecules via hydrogen bond. The goal was to investigate how the hydrophilic nature of the surface influenced the molecular mobility of this hydrogen-bonded system, by monitoring intra- and inter-molecular host–host and host–guest interactions. The analysed O–H spectral region was decomposed into Gaussian symmetrical profiles, each of them associated to a well-defined aggregate, triggered by the presence of H-bond. Passing from the bulk state to the confined one, a clear change of the dynamical properties has been revealed and related to the interactions with the surface. The observed results were discussed on the basis of current models for associated liquids. 相似文献
516.
Tania R. Giraldi Cezar C. Arruda Geraldo M. da Costa Elson Longo Caue Ribeiro 《Journal of Sol-Gel Science and Technology》2009,52(2):299-303
Nanoparticles composed of iron oxides and iron salts were obtained from polymeric resins produced by polymerizing Fe2+-citrate and Fe3+-citrate complexes with ethylene glycol. The citric acid:Fe molar ratio was varied to obtain different synthesis conditions. The materials were treated at 450 °C for 2 h to obtain nanoparticles, which were characterized by XRD, Mössbauer spectroscopy, FEG, CHNS, atomic absorption and surface area through N2 physisorption. Rhodamine B photo degradation in the presence of these nanoparticles and hydrogen peroxide was carried out to analyze the possible behavior of nanoparticles as heterogeneous Fenton reactants. UV–visible spectroscopy revealed that the catalytic activity in the presence of nanoparticles obtained with a citric acid:Fe molar ratio of 12:1 was the condition that provided the best results in this work. 相似文献
517.
Giuseppe Basini Fulvio Bongiorno Salvatore Capozziello Giuseppe Longo 《Rendiconti del Circolo Matematico di Palermo》2004,53(2):272-282
We construct a 5D space in which conservation laws are always and absolutely valid. This general result holds also scaling
in 4D space even inducing, when necessary, changes of topology. The inequality of representations of physical laws in 4D and
in 5D generalized spaces is founded not on phenomenological but on mathematical results. Essentially, the mechanism is based
on the fact that we take into account also transformations where the Jacobian of the change of variables can assume null values.
We derive that stress-energy and metric tensors, due to Bianchi identities, are always conserved through the mechanism presented
in the following based on the fact that we introduce transformations with null Jacobian in the space definition. Moreover,
in the case of metric tensor, conservation is a necessary feature in order to have physically defined theories. 相似文献
518.
An Understanding of the Photocatalytic Properties and Pollutant Degradation Mechanism of SrTiO3 Nanoparticles 下载免费PDF全文
Luís F. da Silva Osmando F. Lopes Vagner R. de Mendonça Kele T. G. Carvalho Elson Longo Caue Ribeiro Valmor R. Mastelaro 《Photochemistry and photobiology》2016,92(3):371-378
Strontium titanate nanoparticles have attracted much attention due to their physical and chemical properties, especially as photocatalysts under ultraviolet irradiation. In this paper, we analyze the effect of heating rate during the crystallization process of SrTiO3 nanoparticles in the degradation of organic pollutants. The relationship between structural, morphological and photocatalytic properties of the SrTiO3 nanoparticles was investigated using different techniques. Transmission electron microscopy and N2 adsorption results show that particle size and surface properties are tuned by the heating rate of the SrTiO3 crystallization process. The SrTiO3 nanoparticles showed good photoactivity for the degradation of methylene blue, rhodamine B and methyl orange dyes, driven by a nonselective process. The SrTiO3 sample with the largest particle size exhibited higher photoactivity per unit area, independent of the molecule to be degraded. The results pointed out that the photodegradation of methylene blue dye catalyzed by SrTiO3 is caused by the action of valence band holes (direct pathway), and the indirect mechanism has a negligible effect, i.e. degradation by O2?? and ?OH radicals attack. 相似文献
519.
Mariagrazia Napoli Rosanna De Vita Ivano Immediata Pasquale Longo Gaetano Guerra 《先进技术聚合物》2011,22(4):458-462
The syntheses of low‐molecular‐weight polyethylene (PE), in the presence of catalysts based on five different metallocene frameworks, have been compared. High yields and low molecular masses, typical of industrially relevant PE waxes, can be easily achieved by using overpressure of hydrogen. Particularly suitable for the production of PE waxes are catalytic systems based on the C2 symmetric rac‐dimethyl‐silyl‐bis‐(2‐methyl‐4‐phenyl‐1‐indenyl)‐zirconium dichloride ( 1 ) and the C2v symmetric bis‐cyclopentadienyl‐zirconium dichloride ( 5 ). The wax yields can be substantially increased by increasing the MAO/Zr molar ratio. The control of the PE molecular weight allows an easy control of physical properties. In fact, as Mn increases in the range 103–104 g/mol, the degree of crystallinity decreases from nearly 85 to 60% while the melting temperature increases from 125°C up to 135°C. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
520.
The present review describes several examples of the use of soluble and immobilized complexes of rhodium with pyridine ligands as catalysts. Examples include the water-gas shift reaction, the carbonylation of methanol, the reduction of nitroarenes, the hydrocarboxylation and oligomerization of CO/ethylene, the hydrocarbonylation of 1-hexene, the hydroesterification and hydroformylation–acetalization of 1-hexene, the hydrodechlorination of dichloroethane, the carbonylation of naphtha and the hydrogenation and hydroformylation of alkenes. 相似文献