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911.
N. B. Morozova A. E. Turgambaeva I. A. Baidina V. V. Krysyuk I. K. Igumenov 《Journal of Structural Chemistry》2005,46(6):1047-1051
The structure of titanyl dipivalylmethanate TiO(dpm)2 has been studied by X-ray diffraction analysis. The compound has a molecular structure formed by isolated centrosymmetrical dimers [TiO(dpm)2]2; the unit cell contains two structurally related, crystallographically unique binuclear molecules. The Ti...Ti distance in the dimer is 2.73 Å. Crystal data for Ti2C36H76O10: a = 32.477(6) Å, b = 14.409(3) Å, c = 25.630(5) Å; β = 107.82(3)°, space group C2/c, Z = 8, d calc = 1.002 g/cm3. 相似文献
912.
C. FRESNEAU B. ARRIO B. LECUYER A. DUPAIX N. LESCURE P. VOLFIN 《Photochemistry and photobiology》1984,39(2):255-261
Abstract— The fluorescence of scaleworms has been attributed by Harvey (1952) to a product of the bioluminescent reaction confined in the scales of these worms. We have purified this fluorescent molecule by gel filtration. This compound has an apparent low molecular weight as shown by polyacrylamide gel clectrophoresis in the presence of SDS. The yield of the fluorescent product, after gel filtration, varies with the stimulation of the bioluminescence, triggered either chemically or enzymatically. The fluorescence spectrum of the purified product is similar to the one observed in vivo , with a maximum centered at 520 nm. Consequently, the fluorescent compound isolated is likely the reaction product of the bioluminescent reaction. 相似文献
913.
T. Paryjczak J. M. Farbotko K. W. Jówiak 《Reaction Kinetics and Catalysis Letters》1982,20(1-2):227-231
Temperature-programmed reduction and oxidation of bimetallic catalysts Pd–Ni/Al2O3 seem to indicate phase segregation of palladium and nickel oxides and alloying of palladium and nickel in the process of reduction of oxidized catalysts.
- Pd–Ni/Al2O3 , .相似文献
914.
Summary Chiral compounds may be separated by gas chromatography by direct enantiomer separation on optically active stationary phases. More generally the separation can be achieved on conventional stationary phases after formation of diastereoisomeric derivatives. In this work we report on new results in enantiomer separation, indicating that hydrogen bond association is not the only kind of molecular interaction responsible for enantiomer separation. For the separation of a wide variety of chiral compounds with amino or hydroxy groups diastereo-isomeric derivatives may be formed by reaction with L--chlorisovaleryl chloride. The derivatives of amino acids, aliphatic and aromatic amines, amino alcohols and of some alcohols are separated in glass capillaries. Gas chromatography as a separation technique of high selectivity is specifically useful for the separation of mixtures of chemically related components with comparable molecular interactions with the molecules of the stationary phase of a gas chromatographic column. The separation of optically active compounds, particularly, requires highly efficient columns. Glass capillary chromatography is a tool that meets this standard and was applied exclusively in this work. 相似文献
915.
α,ω-Difluoropolydimethylsiloxanes F[(CH3)2SiO]n(CH3)2SiF have been prepared by reaction of (CH3)2SiF2 with cyclic dimethylsiloxanes [(CH3)2SiO]n (n = 3 or 4). An equilibrium is reached in the redistribution of fluorine vs. oxygen atoms after ca. 24 h at 200°C or 15 days at 150°C when catalysed by AlCl3. 16 equilibrated samples of varied (R = F/Si) overall compositions have been analysed by 1H and 19F NMR and by VPC. The presence of rings has been established for the lower values of R. The molecular constitution of the equilibrated samples is described by a set of constants. The abundance of the end units is slightly larger than expected from random distribution. The good resolution of the spectra permits the distinguishing of the 9th order of environment of the end units and the 5th order for the middle units and the verification that there is no preferential association among the building units, and thus the proportion of chains of various lengths obeys Flory's random distribution mode. The equilibrium molecular constitution of these α,ω-difluorosiloxanes is close to that of their dichloro analogs; the substitution of chlorine by fluorine atoms at the end of the chains thus appears to cause little perturbation. On the other hand, the kinetic evolution of the reaction appears to be different, since the first species which forms is always the pyro moleculeinstead of long chains and large rings as in the case of the chloro analogs. 相似文献
916.
We have compared the experimental results of study of the preferential solvation of polyvinylpyrrolidone in halogenated solvent/proton-donor solvent mixtures, obtained by light scattering and i.r. spectroscopy and described in the two preceding papers. The preferential adsorption of the proton-donor solvent is explained by the formation of a hydrogen-bond complex of polymer with proton-donor solvent, on which other proton-donor molecules are bound by induced autoassociation. This complexing occurs even in mixtures where the “inert” solvent (1,2-dichloroethane) is preferentially adsorbed; this is experimental proof of a differing solvation of the chains in their close neighbourhood and within short range of them. 相似文献
917.
W.C. Herndon 《Tetrahedron》1973,29(1):3-12
Simple MO techniques are described that can be used to count resonance structures for unsaturated hydrocarbons, ions, and radicals. Alternant or non-alternant unsaturated species can be treated accurately and rapidly. The relationship of the structure count to the calculated values of highest filled and lowest vacant HMO energy levels is discussed. A qualitative relationship of the structure count with reactivity and stability if exemplified with several cases. A known correspondence of resonance theory and perturbational MO theory, previously limited to benzenoid and acyclic systems, is expanded to include all pi molecular systems. 相似文献
918.
T. M. Gorrie S. Kalyana Raman H. K. Rouette Heinrich Zollinger 《Helvetica chimica acta》1973,56(1):175-195
An NMR. investigation of the state of formaldehyde in acidic solutions has been carried out. Solutions of DCl/D2O/CD3COOD containing two sources of formaldehyde, i.e. paraformaldehyde (I) and trioxane (II), were used for this purpose. In systems I and II the effect of various D2O/CD3COOD ratios, at a constant DCl concentration, was studied, while for II the effect of changing DCl concentration was also investigated. The results show that in aqueous solution, formaldehyde exists primarily as the monomeric and linear oligomeric forms of methylene glycol. Reducing the amount of D2O (at constant DCl concentration), while increasing the CD3COOD content, results in an increase in the polymeric species and in trioxane. In addition, substitution of water by acetic acid results in systems that are catalytically more active than aqueous solutions of the same hydrochloric acid concentration. Along with the usual polymer-monomer equilibria which exist in such solutions, side reactions of methylene glycol with the hydrochloric acid present also occur to a small extent, e.g. acetylation, substitution of OH by Cl and the Cannizzaro reaction. It is suggested that these findings will result in a better understanding of the formaldehyde crosslinking reactions in cotton cellulose. 相似文献
919.
Boron was analysed in ore and glass samples by prompt proton spectrometry, using deuterons of 2.7 MeV to coincide with a region
where the excitation function of the10B(d, p)11B reaction did not vary appreciably with energy.
Targets of approximately 300 μg/cm2 thick of powdered samples were prepared by centrifugation. Concentrations down to 0.2% were determined. Possible interference
by other elements, particularly nitrogen, magnesium and titanium, was investigated. 相似文献
920.
It has been noticed that the major part of the loss of ?H from the molecular ion of most of the o-methoxythioamides results from an ortho effect of the methoxy group. Comparison of the MIKE spectra of the [M? SH]+ of 1-(2-methoxyphenylthioxomethyl)piperidine and 1-(2-methoxyphenylthioxomethyl)pyrrolidine with the MIKE spectra of [M? SH]+ of the corresponding unsubstituted compounds, reported earlier, indicated two parallel pathways for the formation of [M? SH]+ in the o-methoxy compounds. In the first pathway, as has been noticed in thioamides in general, the loss of ?H involves the migration of either the α-hydrogen in the amine moiety or the hydrogen attached to nitrogen. In the second pathway, the migration of a hydrogen from the o-methoxy group to the sulphur atom followed by ejection of SH from the molecular ion leads to a stable cyclized ion. Interesting secondary fragmentations as a consequence of this ortho effect have also been noticed. 相似文献