全文获取类型
收费全文 | 287篇 |
免费 | 11篇 |
国内免费 | 4篇 |
专业分类
化学 | 248篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 22篇 |
物理学 | 25篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 15篇 |
2012年 | 14篇 |
2011年 | 15篇 |
2010年 | 8篇 |
2009年 | 9篇 |
2008年 | 14篇 |
2007年 | 13篇 |
2006年 | 24篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 9篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1978年 | 1篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1958年 | 15篇 |
1957年 | 23篇 |
1956年 | 7篇 |
1941年 | 2篇 |
排序方式: 共有302条查询结果,搜索用时 15 毫秒
71.
Dispersion of silica nanoparticles bearing perfluorohexyl units into fluorinated copolymers 下载免费PDF全文
Nelly Durand Jean‐Pierre Habas Bernard Boutevin Bruno Améduri 《Journal of polymer science. Part A, Polymer chemistry》2015,53(12):1512-1522
This study aims at determining the compatibility behavior of nanoparticles surface with fluorinated matrices to obtain a homogenous dispersion and better composites properties. First, modified silica nanoparticles by C6F13I and C6F13‐C2H4‐SH led to various fluorinated silica of different massic concentrations and grafting rates. The dispersion of these nanoparticles (in 5 wt %) into molten poly(VDF‐co‐HFP) and poly(TFE‐co‐HFP) matrices were studied as well as the hydrophobic, mechanical, and thermal properties of both fluorinated copolymers and resulting composites. In both series, the storage modulus of nanocomposites increased while the melting (Tm) and decomposition (T10%) temperatures varied with the polymer matrix. They increased for poly(VDF‐co‐HFP) composites (Tm= 134 to 144 °C and T10%= 441 to 464 °C) but decreased for poly(TFE‐co‐HFP) nanocomposites (Tm= 276 to 268 °C and T10%= 488 to 477 °C). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1512–1522 相似文献
72.
Frank Plastria José Gordillo Emilio Carrizosa 《Discrete Applied Mathematics》2013,161(16-17):2604-2623
A facility is to be located in the Euclidean plane to serve certain sites by covering them closely. Simultaneously, a set of polygonal areas must be protected from the negative effects from that facility. The problem is formulated as a margin maximization model. Necessary optimality conditions are studied and a finite dominating set of solutions is obtained, leading to a polynomial algorithm. The method is illustrated on some examples. 相似文献
73.
Atmospheric pressure chemical vapor deposition (APCVD) of TiO2 thin films has been achieved onto glass and onto ITO-coated glass substrates, from the reaction of TiCl4 with ethyl acetate (EtOAc). The effect of the synthesis temperature on the optical, structural and electrochemical properties was studied through spectral transmittance, X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) measurements. It was established that the TiO2 films deposited onto glass substrate, at temperatures greater than 400 °C grown with rutile type tetragonal structure, whereas the TiO2 films deposited onto ITO-coated glass substrate grown with anatase type structure. EIS was applied as suitable method to determine the charge transfer resistance in the electrolyte/TiO2 interface, typically found in dye-sensitized solar cells. 相似文献
74.
Grant E. Johnson Nelly M. Reilly A.W. Castleman Jr. 《International journal of mass spectrometry》2009,280(1-3):93
The collision induced fragmentation and reactivity of cationic and anionic nickel oxide clusters with carbon monoxide were studied experimentally using guided-ion-beam mass spectrometry. Anionic clusters with a stoichiometry containing one more oxygen atom than nickel atom (NiO2−, Ni2O3−, Ni3O4− and Ni4O5−) were found to exhibit dominant products resulting from the transfer of a single oxygen atom to CO, suggesting the formation of CO2. Of these four species, Ni2O3− and Ni4O5− were observed to be the most reactive having oxygen transfer products accounting for approximately 5% and 10% of the total ion intensity at a maximum pressure of 15 mTorr of CO. Our findings, therefore, indicate that anionic nickel oxide clusters containing an even number of nickel atoms and an odd number of oxygen atoms are more reactive than those with an odd number of nickel atoms and an even number of oxygen atoms. The majority of cationic nickel oxides, in contrast to anionic species, reacted preferentially through the adsorption of CO onto the cluster accompanied by the loss of either molecular O2 or nickel oxide units. The adsorption of CO onto positively charged nickel oxides, therefore, is exothermic enough to break apart the gas-phase clusters. Collision induced dissociation experiments, employing inert xenon gas, were also conducted to gain insight into the structural properties of nickel oxide clusters. The fragmentation products were found to vary considerably with size and stoichiometry as well as ionic charge state. In general, cationic clusters favored the collisional loss of molecular O2 while anionic clusters fragmented through the loss of both atomic oxygen and nickel oxide units. Our results provide insight into the effect of ionic charge state on the structure of nickel oxide clusters. Furthermore, we establish how the size and stoichiometry of nickel oxide clusters influences their ability to oxidize CO, an important reaction for environmental pollution abatement. 相似文献
75.
Le Fur N Mojovic L Plé N Turck A Reboul V Metzner P 《The Journal of organic chemistry》2006,71(7):2609-2616
Enantiopure aromatic (phenyl, naphthyl) and heteroaromatic (pyridyl, quinolyl, diazinyl) sulfoxides have been synthesized by reaction of (S)-tert-butyl tert-butanethiosulfinate with aryl- or heteroaryllithium derivatives. The ortho-directed metalation of the sulfoxides was performed with lithium bases. Subsequent addition of the lithiated intermediates to N-tosylimines afforded tosylaminoalkyl tert-butylsulfinyl arenes. In most cases a complete asymmetric induction was highlighted in favor of (S,S) isomers. Heating the aminosulfoxides provided an original cyclization to form novel cyclic sulfenamides. A novel enantiopure synthesis of a benzylamine was described. An application of an enantiopure aminosulfoxide as N,S ligand for the asymmetric catalysis of allylic nucleophilic substitution has been successfully tested. 相似文献
76.
Javier Hernández Francisco M. Goycoolea Josué Juárez-Onofre Jaime Lizardi Bárbara Gordillo Oscar García-Barradas Zaira Domínguez 《Tetrahedron》2006,62(11):2520-2528
Six tris(aryloxy)phosphorothionates substituted in the para position of the aromatic rings were synthesized and studied by 31P NMR, X-ray diffraction techniques and ab initio calculations at a RHF/6-31G** level of theory, in order to find the main structural factors associated with the δ31P in these compounds. As the electron-withdrawing (EW) ability of the substituents was increased, an ‘abnormal’ shielding effect on δ31P of the arylphosphorothionates was observed. The analyses of the geometrical properties obtained through both experimental and theoretical methods showed that a propeller-type conformation is preferred for the arylphosphorothionates, except in the case of the tris(O-4-methylphenyl)phosphorothionate, since one of the aromatic rings is not rotated in the same direction as the other two in the solid state. The main features associated with the δ31P NMR of compounds 1-6 were a decrease of the averaged O-P-O angle and mainly the shortening of the PS bond length, which is consistent with an increase of the thiophosphoryl bond order as δ31P values go upfield. On the other hand, comparison of the experimental and calculated bond lengths and bond angles involving α bonded atoms to phosphorus of the six compounds suggested that stereoelectronic interactions of the type nπO-σ*PS, nπO-σ*P-OAr and nπS-σ*P-OAr could be present in the arylphosphorothionates 1-6. 相似文献
77.
[reaction: see text] The complexes [PdCl2L2], where L is a crown-ether-containing triarylphosphane, catalyze the formation of biaryls from arylsiloxanes and aryl bromides with high yields in water as solvent and under air. The water-insoluble catalysts [PdCl2(PhCN)2] and [PdCl2(PPh3)2] are also efficient, although they decompose more quickly to form black Pd0. 相似文献
78.
Recent developments in whole-cell spectroscopic methods allow rapid characterization of microorganisms of interest to human health, but have yet to be widely applied to marine microbiological studies. In this study of bacteria associated with the kelp Laminaria digitata, we have isolated 18 epiphytic bacterial strains from several thalli, sequenced their 16S rDNA, built corresponding phylogenetic trees, and characterized them using spectroscopic methods. Molecular taxonomy revealed Gram+Actinobacteria and Gram−Alphaproteobacteria, Gammaproteobacteria and Bacteroidetes. Twelve marine reference strains (Gram+Firmicutes, and Gram−Alphaproteobacteria, Gammaproteobacteria and Bacteroidetes) were treated accordingly. Whole-cell MALDI-TOF MS spectral profiles of 29 of the 30 strains were built into a database against which 16 replicate spectra of each strain were compared and categorized into groups. The proton HR-MAS NMR stack plots allowed visual delineation into taxonomic groups according to their most common peaks, in agreement with identifiable compounds from corresponding D2O solution spectra. With both methods, these groups corresponded to taxa identified by 16S rDNA sequences, MALDI-TOF MS being more discriminative than HR-MAS NMR. Culture age did not influence the spectral signatures in both approaches. Most cells grown under minimal conditions (VNSS medium) afforded HR-MAS NMR profiles markedly different to those grown in enriched conditions (ZoBell medium), indicating different adaptive metabolic responses between the two media. Spectral signatures obtained under strictly controlled conditions can be used as rapid and reliable tools for taxonomic purposes and as markers of physiological status. 相似文献
79.
Molecular dynamics simulation of liquid water confined inside graphite channels: dielectric and dynamical properties 总被引:1,自引:0,他引:1
Electric and dielectric properties and microscopic dynamics of liquid water confined between graphite slabs are analyzed by means of molecular dynamics simulations for several graphite-graphite separations at ambient conditions. The electric potential across the interface shows oscillations due to water layering, and the overall potential drop is about -0.28 V. The total dielectric constant is larger than the corresponding value for the bulklike internal region of the system. This is mainly due to the preferential orientations of water nearest the graphite walls. Estimation of the capacitance of the system is reported, indicating large variations for the different adsorption layers. The main trend observed concerning water diffusion is 2-fold: on one hand, the overall diffusion of water is markedly smaller for the closest graphite-graphite separations, and on the other hand, water molecules diffuse in interfaces slightly slower than those in the bulklike internal areas. Molecular reorientational times are generally larger than those corresponding to those of unconstrained bulk water. The analysis of spectral densities revealed significant spectral shifts, compared to the bands in unconstrained water, in different frequency regions, and associated to confinement effects. These findings are important because of the scarce information available from experimental, theoretical, and computer simulation research into the dielectric and dynamical properties of confined water. 相似文献
80.
Alain Turck Nelly Pl Pamla Pollet Guy Quguiner 《Journal of heterocyclic chemistry》1998,35(2):429-436
In the pyridazine series, the use of tert-butylsulfinyl and tert-butylsulfonyl as ortho directing groups for metalation has been tested. Various functionalized products were obtained in good yields. In the case of 3-tert-butylsulfinyl-6-methoxypyridazine, the metalation was regioselective in ortho to the sulfinyl group. The metalation of 2-tert-butylsulfinyl and 2-tert-butylsulfonylpyrazine gave low to moderate yields. Synthesis of diazinesulfonamides were improved and the metalation of N-tert-butylsulfonamidopyrazine was achieved. 相似文献