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71.
Studies of the preparation of 1,8-dihydroazocines and transannular cyclization of hydroazocines to produce functionalized pyrrolizidines are described. Results are presented which demonstrate that unsymmetrically substituted acetylenes bearing at least one electron withdrawing groups undergo efficient cycloaddition to 1 - β - styryl - 1,2 - dihydropyridine producing in a regio-selective fashion 3,4 - disubstituted - 1,8 - dihydroazocines. The dihydroazocines generated in this manner can be converted to 1 - formyl - Δ4,5 - epoxyazocines which undergo interesting rearrangement reactions to form pyrrolizidines when subjected to methoxide deformylation followed by acid treatment. In addition, 1,6,7,8 - tetrahydroazocines can be converted to pyrrolizidines under bromination conditions. The intriguing chemical process which occur under the conditions outlined above are described. 相似文献
72.
The number of products and the H2/CH4 ratio obtained from the flow pyrolyses of (CH3)3GeH and (CH3)3SiH were very different. The (CH3)3GeH decomposition is consistent with the following mechanism:
The pyrolysis of (CH3)3SiH was found to be much more complex, presumably due to the formation of silicon-carbon double bonded intermediates and the (CH3)2Si(H)CH2 radical. We also present data which supports the presence of a H atom chain sequence during this pyrolysis. 相似文献
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73.
Flow visualization of chemical flocs in a simple extensional flow field reveals two distinct mechanisms for their breakage: splitting into a relatively small number of daughter fragments whose sizes are comparable to the parent flocs, along with continual disintegration by erosion to produce extremely fine particles from the extremities of the parent floc along the axis of extension. In turbulent flow, these two mechanisms still occur, although the kinematics of flow are more complex. This work presents a formulation of the population balance equation that governs the floc size distribution in turbulent flow, incorporating both the splitting and erosion mechanisms discussed above. Experiments were conducted in which floc size distributions of dilute suspensions are measured by a combination of techniques, including computerized optical scanning of photographs and pulse height analysis of signals from a light blockage transducer. The experimentally determined size distributions are then fit to those computed from the population balance equation, using constrained nonlinear least squares. This yields best values of certain coefficients that appear in the governing equation, providing a strategy to obtain a data base to promote deeper theoretical analysis. The method is demonstrated by analyzing data for kaolin-Fe(OH)3 flocs in aqueous suspensions. 相似文献
74.
In our former investigations, the phenomenon high temperature corrosion (HTC) was described exemplarily on selected materialcoating combinations for blades of stationary gas turbines, mainly in the temperature region of up to 750° C. To answer the question, in which manner higher gas inlet and/or higher material surface temperature would influence the HTC behaviour, a special analytical technique—the integral layer profile analysis—was introduced to ameliorate concentration profile methods. By examining IN 738 LC specimens with CoCrAlY plasma spray coating, stressed by hot gas at 900° C, the limits of this system are shown by explaining the corrosion mechanism; the method is also used for other systems, e.g. U 520 with NiCrAlY coating at 750° C. 相似文献
75.
James F. Rusling Barry J. Scheer Azita Owlia Thomas T.-t. Chou James M. Bobbitt 《Journal of Electroanalytical Chemistry》1984,178(1):129-142
1-Carbomethoxy-1,2,3,4-tetrahydrocarbazole (1) and its 7-methoxy derivative (2) were oxidized at carbon felt anodes in acetonitrile containing 0.2 M LiClO4 and 2-17 M water at potentials on the rising portion of the primary oxidation peak to yield products formed by formal substitution of the C-1 H atom with hydroxide. The resulting 1-hydroxy-l-carbomethoxy-1,2,3,4-tetrahydrocarbazole and its 7-methoxy derivative were isolated in 44 and 22% yields, respectively, when sodium bicarbonate was used to control acidity of the medium. Structures were elucidated by NMR, IR, elemental analysis, and mass spectrometry. Voltammetry at carbon-paste and glassy carbon electrodes showed that the oxidations proceed by an ECE or DISPI pathway. The rate-determining step is the reaction of water with a cation radical electrochemically generated from 1 or 2, involving either proton abstraction or nucleophilic addition. 相似文献
76.
The pyrolyses of silyl esters of pyruvic acid and phenylglyoxylic acid gave rise to acylsilanes in high yield. An intramolecular rearrangement involving an intermediate siloxycarbene is proposed to account for the reaction. 相似文献
77.
Four compounds in the system (Li, Na)VO3 were synthesized and their structures refined in the space group . Site population analysis showed that their compositions are (Na0.5Li0.5)VO3, (Na0.62Li0.38)VO3, (Na0.71Li0.29)VO3 and (Na0.84Li0.16)VO3. All have the structure of LiVO3 and α-NaVO3 which are related to the silicate pyroxenes. Structural data of eight compounds in the system (K, Na, Li)VO3 were compiled, and correlations were established by multiple regression analyses between the effective ionic radii rM1 and rM2 of the alkali metal ions and various structural parameters. The size of the M2 site and the relative displacement of the (VO3)∞ chains are found to depend primarily on rM2 only. The size of the M1 site and the amount of chain rotation are affected by both rM1 and rM2. Changes in lattice parameters are related to the chain movements. The anomalous chain configuration of LiVO3 is also discussed. 相似文献
78.
Unimolecular rate constants, ket (s?1), and transfer coefficients, αcet, for the outer-sphere electroreduction of several Co(III) ammine and ethylenediamine complexes have been evaluated by electrostatically adsorbing the reactants at silver electrodes coated with chloride or bromide monolayers. Sufficiently strong diffuse-layer adsorption is thereby produced so to enable kcet and αcet to be determined by means of linear sweep voltammetry, employing sufficiently fast sweep rates (10–100 V s?1) and dilute reactant concentrations (≤ 50 μM) so that the bulk solution reactant contributes negligibly to the observed faradaic transients. Comparison with corresponding rate constants and transfer coefficients for the solution reactants enables the influence of precursor-state stability upon the latter rate parameters to be assessed. 相似文献
79.
The degradation of acenaphthylene, acenaphthene, 2-methylnaphthalene, 2-methylindene, 3-methylindene and indene in water solutions was studied. These compounds at the 25-150 mug/l. level were almost totally degraded at ambient temperature within three days. The microbial population responsible for the degradation occurs naturally in ground-water taken from an aquifer in Ames, Iowa, which is contaminated with coal-tar products. These unidentified micro-organisms adapt readily to other waters when used as an inoculant for the degradation of aromatic compounds. The preservation of water to prevent such degradation was also investigated. Filtration through a 0.45-mum filter was found the most effective procedure for preserving the hydrocarbons in these waters. 相似文献
80.
The 1-methylquinolinium cations derived from 8-aminoquinoline and 8-amino-6-methoxyquinoline were prepared by methylation of the corresponding nitroquinolines and reduction of the nitro-compounds. The dissociation constants of the protonated species of these compounds are almost identical to those of doubly-protonated 8-aminoquinoline and 8-amino-6-methoxyquinoline, respectively, suggesting that the parent quinolines are exclusively first protonated at the ring nitrogen atom. However, the molar absorptivities of the 1-methyl derivatives at their longest-wavelength absorption maxima are substantially greater than the corresponding absorptivities of the unmethylated aminoquinolines, a result which suggests tautomerism of the singly-protonated parent quinolines, with a proportion of the population protonated at the amino group. Fluorescence spectroscopy reveals a single emission from the 8-amino-6-methoxy-1-methylquinolinium ion and two excitation-wavelength-dependent fluorescences from the 8-amino-6-methoxyquinolinium ion, confirming the occurrence of tautomerism and supporting choice of the absorptiometric approach rather than the titrimetric approach as the preferred method for the detection of tautomerism and the calculation of tautomeric equilibrium constants. 相似文献