全文获取类型
收费全文 | 564篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
化学 | 388篇 |
晶体学 | 3篇 |
力学 | 16篇 |
数学 | 66篇 |
物理学 | 118篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 22篇 |
2015年 | 14篇 |
2014年 | 15篇 |
2013年 | 29篇 |
2012年 | 32篇 |
2011年 | 41篇 |
2010年 | 24篇 |
2009年 | 21篇 |
2008年 | 36篇 |
2007年 | 45篇 |
2006年 | 28篇 |
2005年 | 23篇 |
2004年 | 39篇 |
2003年 | 14篇 |
2002年 | 19篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有591条查询结果,搜索用时 78 毫秒
141.
Angela Luis Matos Tej B. Limbu Ivan Castillo Muhammad Shehzad Sultan Balram Tripathi Ram S. Katiyar Brad R. Weiner Gerardo Morell 《Macromolecular Symposia》2024,413(1):2300040
Large area single and bilayer graphene are grown on Pt/Ti/SiO2 substrates by hot filament chemical vapor deposition (HFCVD) with and without the assistance of Cu foil. The quality and number of graphene layers deposited on the substrate are assessed by Raman Spectroscopy. Atomic Force Microscopy (AFM) is used for assessing the surface topography of the graphene films grown on the Pt/Ti/SiO2 substrates. The microstructure and elemental analyses are performed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results show that bilayer graphene growth is facilitated by a copper foil placed nearby Pt/Ti/SiO2 substrate and by a high filament temperature in the HFCVD reactor. Monolayer graphene grows only when no copper foil is placed near the Pt/Ti/SiO2 substrate at a low filament temperature. The approach paves a novel pathway towards the layer-controlled growth of graphene on Pt/Ti/SiO2 substrates by HFCVD for frontier applications. 相似文献
142.
Maricla Marrone Francesca Tarantino Alessandra Stellacci Stefania Lonero Baldassarra Gerardo Cazzato Francesco Vinci Alessandro DellErba 《Molecules (Basel, Switzerland)》2022,27(1)
A mass disaster is a situation that involves criticality between the number of victims and resources, in terms of both men and means, present on the site of an event that is mostly unexpected and sudden. In the multidisciplinary teams that intervene, the role of forensic pathologists, who are responsible for the direction and coordination of post-mortem operations, is central, and must remain so. The authors report the case of an explosion of a pyrotechnic artifice factory, as a result of which numerous victims and injuries are recorded. So, the team completed the autopsies and created a protocol to obtain biological samples (bones, blood, teeth, muscles), while the forensic pathologists contacted the families of the alleged victims and each provided a blood sample that was collected for the DNA. The geneticist, using the method of gene extraction and amplification, obtained the DNA from each bone, tooth, and muscle of blood taken from the victims and then compared it with that extracted from the blood samples of the relatives; the electropherograms showed at least one allele for each genetic marker of the “Combined DNA Index System” in common between the victims and the families, thus allowing to establish the identity of all the subjects involved in the event. Having established the identity of all workers, it was possible to determine their whereabouts in the environment at the time of the location of fires and explosions. The results of the various forensic analyzes (autopsies, genetic investigations and even traumatological investigations) have allowed us to validate a scientific method useful in all mass disasters even when any type of anthropological or forensic dental research is difficult. 相似文献
143.
The reaction of 1-substituted-3-methylpyrazol-5-ones 1 with alkyl chloroformates and calcium hydroxide in dioxane have been studied. With 1-phenyl-3-methylpyrazol-5-one, the isolated product was alkyl 3-methyl-5-oxo-1-phenylpyrazole-4-carboxylate 2 but with 1-alkyl-3-methylpyrazol-5-one formation of 1-alkyl-5-alkoxycarbonyloxy-3-methylpyrazole 3 was observed. Replacement of alkyl chloroformate by bis(alkoxythiocarbonyl) sulfide results in the formation of 4-alkoxythiocarbonyl derivatives 4 in low yield with both 1-substituted-3-methylpyrazol-5-ones. 相似文献
144.
Howard Barnum Gerardo Ortiz Rolando Somma Lorenza Viola 《International Journal of Theoretical Physics》2005,44(12):2127-2145
We define what it means for a state in a convex cone of states on a space of observables to be generalized-entangled relative to a subspace of the observables, in a general ordered linear spaces framework for operational theories. This extends
the notion of ordinary entanglement in quantum information theory to a much more general framework. Some important special
cases are described, in which the distinguished observables are subspaces of the observables of a quantum system, leading
to results like the identification of generalized unentangled states with Lie-group-theoretic coherent states when the special
observables form an irreducibly represented Lie algebra. Some open problems, including that of generalizing the semigroup
of local operations with classical communication to the convex cones case, are discussed.
PACS: 03.65.Ud. 相似文献
145.
The use of lanthanides as radionuclides in nuclear medicine is well-known, because they can be used for detecting and treating cancerous tumors. Due to the fact that the doses are directly related to the number of unstable atoms involved, the possibility of obtaining controlled-size lanthanide nanoparticles opens a wide scope for their application in nuclear medicine. In this work, we report the synthesis of anew samarium nanoparticle by using the bioreduction method, where the pH conditions play an important role in the size control of the produced clusters. The nanoparticles were characterized by using an transmission electron microscope, in addition to the use of a quantum mechanical method to relate the atomic and electronic structures to the chemical selectivity, which allows us to predict a direct coordination between the DTPA-bis-biotin molecules with the samarium nanoparticles larger than 55 atoms. This work involves experimental and theoretical methods to propose a totally new application for nanotechnology in nuclear medicine. 相似文献
146.
M. Luisa Quijano Manuel Nogueras Aldolfo Snchez Gerardo Alvarez De Cienfuegos Miguel Melgarejo 《Journal of heterocyclic chemistry》1990,27(4):1079-1083
Reactions of 6-amino-3,4-dihydro-2-methoxy-4-oxopyrimidine 1a and its 3-methyl derivative 1b with chloroacetaldehyde and chloroacetyl chloride are discussed in this paper. Amongst others compounds, we have obtained, in low yield, the novel ring system oxazolo[3,2-c]pyrrolo[3,2-e]pyrimidine. The anticancer and antimicrobial activities of some of the obtained products are described. 相似文献
147.
Benito Alcaide Gerardo Escobar JoséL. González-Simó Carmen López-Mardomingo Rafael Pérez-Ossorio Joaquin Plumet 《Tetrahedron letters》1982,23(19):2033-2036
Total stereoselectivity is observed in the sodium borohydride reduction of α-aminodeoxybenzoins and their hydrochlorides in various hydroxylic solvents. RS - SR isomer (erythro) was the only aminoalcohol obtained. 相似文献
148.
Khuong TA Zepeda G Sanrame CN Dang H Bartberger MD Houk KN Garcia-Garibay MA 《Journal of the American Chemical Society》2004,126(45):14778-14786
Crankshaft motion has been proposed in the solid state for molecular fragments consisting of three or more rotors linked by single bonds, whereby the two terminal rotors are static and the internal rotors experience circular motion. Bis-[tri-(3,5-di-tert-butyl)phenylmethyl]-peroxide 2 was tested as a model in search of crankshaft motion at the molecular level. In the case of peroxide 2, the bulky trityl groups may be viewed as the external static rotors, while the two peroxide oxygens can undergo the sought after internal rotation. Evidence for this process in the case of peroxide 2 was obtained from conformational dynamics determined by variable-temperature (13)C and (1)H NMR between 190 and 375 K in toluene-d(8). Detailed spectral assignments for the interpretation of two coalescence processes were based on a correlation between NMR spectra obtained in solution at low temperature, in the solid state by (13)C CPMAS NMR, and by GIAO calculations based on a B3LYP/6-31G structure of 2 obtained from its X-ray coordinates as the input. Evidence supporting crankshaft rotation rather than slippage of the trityl groups was obtained from molecular mechanics calculations. 相似文献
149.
Gerardo Torres 《Tetrahedron》2004,60(45):10245-10251
The VO(acac)2 catalyzed epoxidation of hindered homoallylic alcohols was conducted under microwave irradiation in an open vessel using toluene as solvent. The reaction time for the epoxidation of a series of cis- and trans-2-methyl-3-alkenols was dramatically reduced from 6 to 10 days to less than 3 h when compared to conventional heating. The cis alkenols exhibited very high diastereoselectivity. The more elaborated polypropionate precursors 12, 14 and 16 were epoxidized in good yield and excellent diastereoselectivities using the microwave-assisted epoxidation technique described here, which is safe and suitable for multi-gram scales. 相似文献
150.
Huerta A Naumis GG Wasan DT Henderson D Trokhymchuk A 《The Journal of chemical physics》2004,120(3):1506-1510
Monte Carlo simulation techniques were employed to explore the effect of short-range attraction on the orientational ordering in a two-dimensional assembly of monodisperse spherical particles. We find that if the range of square-well attraction is approximately 15% of the particle diameter, the dense attractive fluid shows the same ordering behavior as the same density fluid composed of purely repulsive hard spheres. Fluids with an attraction range larger than 15% show an enhanced tendency to crystallization, while disorder occurs for fluids with an attractive range shorter than 15% of the particle diameter. A possible link with the existence of "repulsive" and "attractive" states in dense colloidal systems is discussed. 相似文献