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131.
Lanthanum-europium-copper oxides of composition La2?x Eu x CuO4 with structures related to those of the high temperature superconducting oxides have been prepared by solid state reactions between the component oxides in air. The X-ray powder diffraction data demonstrate that an orthorhombic to tetragonal structural transformation occurs at compositions betweenx=0.5 andx=0.8. The151Eu Mössbauer spectra show that europium is present in all phases as Eu3+. Thermal analysis studies in hydrogen show that a two-step reduction process occurs in the lanthanum-europium-copper oxides with the orthorhombic type structure.151Eu Mössbauer spectroscopy shows that the process does not involve the reduction of the lanthanide ion. 相似文献
132.
L.J. GillieA.J. Wright J. HadermannG. Van Tendeloo C. Greaves 《Journal of solid state chemistry》2002,167(1):145-151
The nuclear and magnetic structures of polycrystalline Sr2MnO3.5 have been determined by the Rietveld analysis of neutron powder diffraction data and electron diffraction techniques. The pure Mn3+ single-layered phase crystallizes in the primitive monoclinic space-group P21/c with lattice constants a=6.8524(3) Å b=10.8131(4) Å c=10.8068(4) Å β=113.247(4)°. The oxygen defects form an ordered superstructure within the perovskite block layers consisting of interconnected MnO5 square pyramids, slightly different from those observed for the defect perovskites SrMnO2.5 and Ca2MnO3.5. Magnetic susceptibility studies show a broad transition at ∼280 K, which is attributed to an overall antiferromagnetic ordering of spins, which leads to doubling of the unit cell along [100]. The magnetic unit cell comprises ferromagnetic clusters of four corner-sharing MnO5 pyramids, which are antiferromagnetically aligned to other similar clusters within the perovskite block layers. 相似文献
133.
Song W Chen W Cooper WJ Greaves J Miller GE 《The journal of physical chemistry. A》2008,112(32):7411-7417
Many pharmaceutical compounds and metabolites are being found in surface and ground waters, indicating their ineffective removal by conventional wastewater treatment technologies. Advanced oxidation/reduction processes (AO/RPs), which utilize free-radical reactions to directly degrade chemical contaminants, are alternatives to traditional water treatment. This study reports the absolute rate constants for reaction of three beta-lactam antibiotics (penicillin G, penicillin V, amoxicillin) and a model compound (+)-6-aminopenicillanic acid with the two major AO/RP reactive species: hydroxyl radical ((*)OH) and hydrated electron (e(-)aq). The bimolecular reaction rate constants (M(-1) s(-1)) for penicillin G, penicillin V, amoxicillin, and (+)-6-aminopenicillanic acid for (*)OH were (7.97 +/- 0.11) x 10(9), (8.76 +/- 0.28) x 10(9), (6.94 +/- 0.44) x 10(9), and (2.40 +/- 0.05) x 10(9) and for e(-)aq were (3.92 +/- 0.10) x 10(9), (5.76 +/- 0.24) x 10(9), (3.47 +/- 0.07) x 10(9), and (3.35 +/- 0.06) x 10(9), respectively. To provide a better understanding of the decomposition of the intermediate radicals produced by hydroxyl radical reactions, transient absorption spectra were observed from 1 to 100 micros. In addition, preliminary degradation mechanisms and major products were elucidated using (137)Cs gamma irradiation and LC-MS. These data are required for both evaluating the potential use of AO/RPs for the destruction of these compounds and studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime. 相似文献
134.
Retail B Rose RA Pearce JK Greaves SJ Orr-Ewing AJ 《Physical chemistry chemical physics : PCCP》2008,10(12):1675-1680
Rotational state distributions and state-selected CM-frame angular distributions were measured for HCl (v' = 0, j') products from the reaction of Cl-atoms with tetramethylsilane (TMS) under single collision conditions at a collision energy, E(coll), of 8.2 +/- 2.0 kcal mol(-1). The internal excitation of these products was very low with only 2% of the total energy available partitioned into HCl rotation. A transition state with a quasi-linear C-H-Cl moiety structure was computed and used to explain this finding. A backward peaking differential cross section was also reported together with a product translational energy (T') distribution with a maximum at T' approximately E(coll). This scattering behaviour is accounted for by reactions proceeding through a tight transition state on a highly skewed potential energy surface, which favours collisions at low impact parameters with a strong kinematic constraint on the internal excitation of the products. The large Arrhenius pre-exponential factor previously reported for this reaction is reconciled with the tight differential scattering observed in our study by considering the large size of the TMS molecule. 相似文献
135.
Greaves TL Weerawardena A Fong C Drummond CJ 《Langmuir : the ACS journal of surfaces and colloids》2007,23(2):402-404
A large number of protic ionic liquids (PILs) have been found to mediate solvent-hydrocarbon interactions and promote amphiphile self-assembly. Hexagonal, cubic, and lamellar lyotropic liquid crystalline phases were observed in PIL-hexadecyltrimethylammonium bromide systems. The driving force for the formation of the self-assembled aggregate structures has been attributed to an entropic contribution to the free energy of association, analogous to the hydrophobic effect in water. The specific aggregate structures formed depend upon the cationic and anionic components of the PIL and their interactions with the amphiphiles. 相似文献
136.
A mathematical model is proposed for the process of vacuum superplasticforming. The model exploits the fact that in most industrialapplications the sheet aspect ratio (thickness/sheet width)is small. After an initial consideration of some of the moregeneral properties and the literature of superplastic materials,the elastic/plastic deformation of an internally-inflated thin-walledcylinder is examined. Plates of arbitrary geometry are thenconsidered. A quasisteady model in which the sheet moves througha sequence of steady states is developed. Some simplified closed-formsolutions are examined, but for general cases a system of nonlinearpartial differential equations must be solved numerically. Anefficient and accurate semi-explicit numerical scheme is proposedand a simplified stability analysis is presented; the methodis then used to compute properties of superplastic vacuum mouldedsheets in a number of practically motivated cases. 相似文献
137.
R. Padilla Alvarez E. Chinea Cano J. R. Estévez Alvarez E. D. Greaves 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(2):517-522
“Cut-off” reflectors, which allow obtaining a reflected beam with almost no high energy radiation, as well as different monochromator
devices that reflect a beam of monoenergetic and polarized radiation are the most widely employed artifacts to perform the
excitation radiation improvement in analytical “non-expensive” TR spectrometers. The aim of this work consisted in testing
several monochromator devices: a multilayer structured mirror for soft X-rays (0.7–12.5 nm), as well as different bent and
flat crystals of wavelength dispersive spectrometers. The achieved instrumental detection limits for the selected monochromator
device are compared with the values obtained using a Suprasil Cut-off reflector and a C-W multilayer (d∼5 nm). Several human corporal fluid samples were analyzed to compare the spectral characteristics when using the Cut-Off
Reflector and the RAP flat crystal, respectively. 相似文献
138.
Alasdair K. Cooper Megan E. Greaves William Donohoe Paul M. Burton Thomas O. Ronson Alan R. Kennedy David J. Nelson 《Chemical science》2021,12(42):14074
A nickel/dppf catalyst system was found to successfully achieve the Suzuki–Miyaura cross-coupling reactions of 3- and 4-chloropyridine and of 6-chloroquinoline but not of 2-chloropyridine or of other α-halo-N-heterocycles. Further investigations revealed that chloropyridines undergo rapid oxidative addition to [Ni(COD)(dppf)] but that α-halo-N-heterocycles lead to the formation of stable dimeric nickel species that are catalytically inactive in Suzuki–Miyaura cross-coupling reactions. However, the corresponding Kumada–Tamao–Corriu reactions all proceed readily, which is attributed to more rapid transmetalation of Grignard reagents.Nickel complexes with a dppf ligand can form inactive dinickel(ii) complexes during Suzuki–Miyaura cross-coupling reactions. However, these complexes can react with Grignard reagents in Kumada–Tamao–Corriu cross-coupling reactions. 相似文献
139.
L. Saj-Bohus J. Plfalvi F. Urbani D. Castro E. D. Greaves J. A. Liendo 《Radiation measurements》1999,31(1-6):283-286
Environmental gamma exposure and radon concentration levels measured in Venezuelan regions are presented. A new generation image analyser was used for particle track counting in CR-39 detectors. Mineral water wells from where water is supplied for massive consumption have an alpha activity around 0.450 Bq L−1 and few of them have concentrations above 50 Bq L−1. Coastal potable water activity is on the average around 5.3 ± 12% Bq L−1. Indoor radon national average is 36 ± 5% Bq m−3; in two of the 36 monitored sites, the measured average is above 400 ± 5% Bq m−3. In air gamma dose values are between 100 and 144 nGy h−1. In soil, 137Cs concentration is around 0.5 and 10 Bq kg−1 at the depth of down to 20 cm. Building materials were included in this study. 7Be and 137Cs were measured in low concentration in tropical plants on Tepuy-s (sacred mountains in the Amazonas State). Geological active faults were identified by radon concentration measurements using LR-115. 相似文献
140.
We show that the existence of ‐matrices having largest possible determinant is equivalent to the existence of certain tournament matrices. In particular, we prove a recent conjecture of Armario. We also show that large submatrices of conference matrices are determined by their spectrum. 相似文献