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991.
An emission spectrographic method is described for determination of 20 elements present as impurities in telluric acid. Samples are excited in a 12-A. d.c. arc with the use of NaCl-KCl as a spectrographic buffer and germanium as internal standard. The limit of determination lies between 10(-5) and 10(-2)%. The precision of the method calculated as relative standard deviation is 10-25%. 相似文献
992.
Atomic fluorescence in flames is measured by an adaptation of a commercially available flame spectrophotometer. A study is reported of the effect of background radiation and source scattering on 3 flames, air-propane, air-hydrogen and air-acetylene, and of the effects of variation of fuel gas pressure, zone of measurement in the flame, analysing monochromator slit-width and wavelength of measurement. The air-propane flame appears to offer several advantages. The atomic fluorescence of 10 metals is described; those of Co, Fe and Mn have not been previously reported. Excitation of spectra is achieved by means of an a.c. xenon arc lamp or individual discharge lamps. 相似文献
993.
Hydrofluoro ethers (HFES) are considered to be an ideal cleaning solvent in applications like vapor degreasing and wet cleaning. It is also a good solvent replacement for CFCs (chlorofluorocarbons), HCFCs (hydrochlorofluorocarbons), HFCs (hydrofluorocarbons) and chlorinated solvents because they have a short atmospheric lifetime and low global warming potential. Based upon their properties, hydrofluoro ethers are ideally suited for the demands of the electronics industry. However, the electronics industry requires these solvents to have high purity, especially in the area of residual anions. This paper will present information on an extraction methodology for the transfer of anions from the hydrofluoro ether to water. Then, an analytical method utilizing ion chromatography that is capable of detection of 10 anions (fluoride, acetate, formate, chloride, nitrite, bromide, nitrate, sulfate, oxalate, and phosphate) in the part per billion level will be demonstrated. 相似文献
994.
R. A. Lukaszew H. Bellavigna R. Cretella M. Denari C. Noutary 《Journal of Radioanalytical and Nuclear Chemistry》1989,136(3):211-217
A photoplate calibration procedure is suggested for spark source mass spectrometry /SSMS/ with photoplate detection. The technique uses the Churchill two-line method applied to the two stable isotopes of copper. The calibration curve thus obtained is split into fragments and each fragment is approximated by a polynomial. The method was applied for the quantitative determination of Hf as impurity in zirconium sponge obtained from a pilot plant dedicated to the depletion of the hafnium content in zirconium by fractional crystallization. 相似文献
995.
Abstract— Flavin mononucleotide radicals, FMNH', generated by laser flash photolysis of FMN in the presence of the electron donors, histidine, guanosine monophosphate or EDTA, were found to reduce cytochrome c with an apparent rate constant of 6 ± 107 M −1 s−1 . These flash photolysis results were, however, complicated by the electron donor radicals formed simultaneously which, particularly with EDTA, also lead to reduction of cytochrome c. Pulse radiolysis of a nitrous oxide saturated aqueous solution of FMN containing a high concentration of HCOONa, leads to the exclusive formation of FMNH'. By adding small concentrations of cytochrome c to this solution, a rate constant of 4.0 ± 10−1 M −1 s−1 was obtained for the reduction of cytochrome c by FMNH'. Replacement of the HCOONa by EDTA in such solutions leads to further routes for reduction of cytochrome c on radiolysis. as in the photolytic situation. The relevance of these results to flavin-photosensitised reduction of cytochrome c and other components of the mitochondrial electron transport chain is discussed. 相似文献
996.
Second order MCSCF theory is presented in a unitary group formulation for any multiplicity without spin projection. Its reduction to lower order theory is discussed, as well as its extension through the use of effective Hamiltonians. 相似文献
997.
Within the limits of a comparative study of solid-state transformations induced by different constraints (thermodynamics, mechanics, electromagnetics, etc.), the authors present the phase-modifications brought about by the grinding of someoxalates (K2C2O4. H2O; CaC2O4. H2O; BaC2O4 ·n H2O withn=0, 1/2, 1 and 2). The water vapour pressure and temperature during the mechanical treatment were selected and fixed. The specificity of the mechanical constraint is discussed. This study mainly shows that (a) the grinding may or may not bring about dehydration, but it may also bring about rehydration; (b) the evolution of a hydrate during treatment, following a well-defined process, shows all the phases known from the most hydrated to the anhydrous form; (c) the mechanical dehydration may be stopped by a change in the grinding temperature and vapour pressure conditions. 相似文献
998.
Long-lived metastable negative ions of CO2 have been observed in the gas phase as direct products of electron and cesium collisions with organic molecules which contain “bent” CO2 as a basic unit. The long autodetachment life-times are attributed to two related factors - first, the potential energy curve of CO−2(2A1) lies below that of CO2(1A1) at 134°, and, second, an unfavorable Franck-Condon overlap exists between the bent ion (134°) and the linear neutral parent. 相似文献
999.
J.C. Phillips 《Journal of solid state chemistry》1976,19(3):309-311
The relationship between crystal structures and metallic conductivities of linear organic materials such as TTF-TCNQ is explained in terms of strong lateral elastic interactions between chains. A microdomain model is presented in which at high temperatures there are, in general, two coexisting phases on each stacked molecular chain. 相似文献
1000.
The rotational spectrum of 1,1-difluorobenzocyclopropene, measured in the X- and R-bands, has been analysed to give the rotational constants in the ground and first four vibrational states. These constants are in agreement with a structure based on those of crystallographically determined related molecules. Indirect evidence is adduced that the carbon skeleton is indeed planar. The dipole moment in the ground (3.572 ± 0.02 D) and first excited state (3.54 ± 0.03 D) has been determined through an analysis of the second-order Stark effect. This high value implies considerable polarisation of the π-electron framework. 相似文献