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51.
Salt efflorescences consisting of gypsum sampled mainly in the Schirmacher Oasis have been analyzed for the isotopic composition of the water of crystallization and of the sulphate-sulphur. For comparison, a few samples from other Antarctic locations (Guettard Range, Prince Charles Mts., Insel Mts.) were included in the study. The isotopic variations of the water of crystallization of secondary gypsum and the calculated isotopic composition of the mother solution reflect the local climatic conditions during the precipitation of the efflorescences. It is therefore possible to obtain qualitative information about the climatic conditions prevailing in the studied region. 相似文献
52.
The paper gives data on isotope composition of interstitial and near-bottom waters sampled in a region of gas-hydrate formation in the Sea of Okhotsk. The studies shows that heavy isotope of oxygen and hydrogen is used in gas-hydrate formation, with the result that isotope composition of its constitution water constitutes δ18O = +1.99‰, δD = +23‰ relatively to SMOW. Formation of autogenic carbonates leads to isotope exchange with interstitial water wich, in turn, changes its primary isotope composition in the direction of increasing of O-18 content. The near-bottom waters are isotope-light relatively to the SMOW standard and to the mean isotope composition of interstitial water in the studied region of gas-hydrate spreading. 相似文献
53.
Anne Seebach Christoph von Rohden Johann Ilmberger Stephan M. Weise Kay Knöller 《Isotopes in environmental and health studies》2013,49(3):291-298
This study presents selected results, applying environmental tracers to investigate lake water–groundwater interactions at two study sites located in Lusatia, Germany. The focus of the investigations were two meromictic pit lakes and their adjacent aquifers. In order to follow hydrodynamic processes between lake and groundwater, mixing patterns within the lakes as well as ages of lake and groundwater, water samples of ground- and lake water were collected at three occasions, representing summer and winter conditions in the aquatic systems. The water samples were analysed for stable isotopes (deuterium, oxygen-18) and tritium and sulphurhexafluoride (SF6 concentration). Lake water profiles of conductivity and 18O could validate the permanent stratification pattern of both the lakes. Groundwater data sets showed a heterogeneous local distribution in stable isotope values between rain and lake water. A two-component mixing model had been adopted only from 18O data to determine lake water proportions in the surrounding groundwater wells in order to correct measured tritium and SF6 concentrations in groundwater samples. This procedure had been hampered by upstream-located wells indicating strong 18O enrichment in groundwater samples. However, rough groundwater ages were estimated. For both study sites, Piston flow ages between 12.9 and 27.7 years were calculated. The investigations showed the good agreement between two different environmental dating tools, considering the marginal data sets. 相似文献
54.
The general thermodynamics in high pressure sorption processes and the isotopic shifts of the gases H2, N2, CH4 und CO2 were investigated by adsorption and desorption experiments on charcoal at pressures up to 25 MPa. The calculations of thermodynamic relations in the mentioned systems were carried out on the basis of a new three parameter equation for high pressure adsorption isotherms as well as a modified RAYLEIGH equation, in particular for the isotopic experiments. 相似文献
55.
P. Kränke H. Matschiner R. Trutschel M. Wahren 《Isotopes in environmental and health studies》2013,49(1-2):187-191
Abstract The electrochemical reduction of model carboxylic acid at lead cathodes in deuterated media was studied for potential use in the synthesis of special deuterated compounds. Oxalic acid-d2 in D2O gives good yields of glyoxylic acid-d2. An unexpected large isotope effect of 5.3 ± 1.7 was found in this reaction, leading to significant depletion of deuterium content in the aldehyde group. Benzoic acid-d in CD3OD/diluted D2SO4 yields benzyl alcohol-d, 7,7-d2. The isotope effect of 2.4 ± 1.0 is within the expected range. No deuterium is incorporated into the aromatic nucleus. Essentially unlabelled benzyl alcohol is obtained in CD3OH/dil. H2SO4. 相似文献
56.
Jelena Šamonina-Kosicka 《Isotopes in environmental and health studies》2013,49(3):357-364
Diamine oxidase (DAO), the enzyme that is responsible for amine biodegradation in animals, plants and humans, catalyses the biotransformation of amines such as histamine (HA), putrescine, 1-phenylethylamine, tyrosine, tryptamine, serotonine and spermine. The kinetic and solvent isotope effects (SIEs) were applied to study the mechanism of the biotransformation using HA and its methylderivatives. The SIE for the biotransformation of HA, Nτ-methylhistamine and Nπ-methylhistamine was found to be 3.58, 2.22 and 5.70 on Vmax, and 1.58, 1.06 and 1.14 on Vmax/KM, respectively. On the other hand, the kinetic isotope effect for oxidation of stereospecifically deuterium-labelled [(α R)-2H]-Nτ-methylhistamine and [(α R)-2H]-Nπ-methylhistamine was 0.69 and 0.62 on Vmax, and 15.06 and 7.50 on Vmax/KM, respectively. These results demonstrate that DAO catalyses amine biotransformation by stereospecifically cleaving the αC\bond H bond in the pro-S position. Moreover, the oxidation of amine to aldehyde involves several transition states, including hybridisation change from sp3 (Schiff base) to sp2 (imine), then back again to sp3 to give a final product with hybridisation sp2 (aldehyde). 相似文献
57.
Geoff Koehler Leonard I. Wassenaar Jim Hendry 《Isotopes in environmental and health studies》2013,49(3):378-386
The requirement to measure the stable isotopic compositions of saline pore fluids by optical methods has prompted a re-evaluation of the isotopic salt effect for common salts. Hydrogen and oxygen isotopic salt effects were measured at room temperature (21°C) by optical methods. For hydrogen isotopes, our results agree well with those of previous studies and better define these effects at low temperatures. In contrast, measured oxygen isotope salt effects disagree within error for NaCl and CaCl2 solutions from those reported previously. Subtle differences between measurement methods may account for the discrepancy. In studies that involve highly saline fluids, the isotopic salt effect must be taken into account because modern methods that measure stable isotopic compositions as activities or concentrations may be not directly comparable to historical data sets. 相似文献
58.
M. P. Marsan I. Muller A. Milon W. Warnock Y. Nakatani G. Ourisson J. Jaud 《Journal of chemical crystallography》1995,25(11):783-786
Synthesis of sterols with varying side chains, including deuterium labeled stigmasterol and sitosterol may be performed via the Wittig-Horner coupling of a 22 aldehyde derived from stigmasterol and a suitable sulfoxide derivative of the side chain. The X-ray structure determination of this synthon have been performed since it is a crucial step in order to know the absolute configuration of the chiral carbon atoms. Crystallographic data were as follows:a=7.437(2),b=10.103(4),c=10.274(3)Å, =100.32(6)o,
=759.4 Å3, space group P21 (No.4),Z=2,D
c=1.239 g cm–3. 相似文献
59.
Stimulated by a suggestion of the late Professor Jack D. Dunitz, that perdeuterated Janus face cycloalkanes may be more polar than their unlabelled forms, the deuterated isotopologue of all cis-1,2,3,4,5,6-hexafluorocyclohexane ([2H6]- 1a ) and all cis-1,2,3,4-tetrafluorocyclopentane ([2H6]- 3a ) were prepared. Computation at the B3LYP−D3 level indicated that [2H6]- 1a is not more polar than its protio form 1, however perdeuterated cyclopentane [2H6]- 3a may indeed be more polar than 3 , although the magnitude is predicted to be small. None-the-less retention time analysis on a reverse phase GC/MS column of an add-mix of 3 and [2H6]- 3a gave some indication that the per-deuterated isotopologue 3a was detected marginally before the unlabelled compound consistent with increased polarity associated with perdeuteration. 相似文献
60.
The concerted mechanism of free radical SH2′ reaction of 2‐substituted allyl chloride was suggested again by inverse secondary α‐deuterium isotope effect. The transition state of free radical SH2′ reaction of allyl chlorides seems to be symmetrical and is not as early as that of a free radical addition reaction. 相似文献