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951.
Pamela M. St. John Rainer D. Beck Robert L. Whetten 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(1):226-228
We review the processes which have been observed from collisions between alkali-halide clusters and solid surfaces. Soft impact of nanocrystalline NanF n?1 + clusters against solid surfaces causes them to cleave along the lowest energy (100) plane. At higher collision energies (Ei>1 eV/atom), an evaporative cascade occurs which is characteristic of a transformation of the nanocrystal to a molten state. Efficient F? transfer from the cluster to the surface can occur for the larger clusters (>60 atoms) scattering from Si(111), in direct competition with the cleaving channel at low energies. In this regime, strong bonds can form between the F? and silicon surface. The reaction probability increases with cluster size indicating that an impact-initiated shock wave is needed to enhance the reactive process. 相似文献
952.
John Mullay 《Journal of computational chemistry》1988,9(4):399-405
A simple electronegativity method is used to calculate atomic charges for molecules of interest to biochemistry. These include purines, pyrimidines, and amino acids. Results are compared to those obtained from other theoretical methods (ab initio and semiempirical) as well as to nuclear magnetic resonance (NMR) data. Correlation is fair with CNDO results but very good for ab initio, DelRe, and other electronegativity methods. Good correlation was also achieved with NMR data. It is shown that a correction factor may be required in some cases and that important resonance effects need to be taken into account. Because of the small amount of calculational effort involved, these results suggest that this method could be quite useful in this field. 相似文献
953.
Athinoula L. Petrou Maria V. Koromantzou John M. Tsangaris 《Transition Metal Chemistry》1991,16(1):48-52
Summary The preparation of complexes of 3,4-dihydroxyphenylpropoionic acid (hydrocaffeic acid): K2[Cu2(hydcafH)2-Cl2]·2KCl·2MeOH, K2[Co(hydcafH)2]·2KCl, K2[Ni2(hydcafH)2Cl2]·2KCl·2MeOH and Fe2 (hydcafH)2Cl2·2KCl·2H2O was achieved. Spectroscopic and magnetic studies are commensurate with tetrahedral structures for the prepared complexes in which the catechol-like coordination is present. 相似文献
954.
Phillip T. Mead John C. Traeger John R. Christie Peter. J. Derrick 《Journal of mass spectrometry : JMS》1978,13(7):386-388
The internal energies of [C3H7]+ ions contributing to the metastable peak [C3H7]+ → [C3H5]+ + H2 are higher (by perhaps > 100 kJ mol?1) than those of the ion contributing to the threshold current in appearance energy measurements on [C3H5]+. The measured appearance energy may lead to an underestimation of the activation energy, i.e. negative ‘kinetic shift’, due to quantum, mechanical tunnelling. The distribution of energy released in the decomposition can be explained on the basis that much of the reverse activation energy and a statistical proportion of the excess energy is released as translation. 相似文献
955.
The stability constants and the partial molal volume and isentropic partial molal compressibility changes of complex formation between cations and crown ethers in water at 25°C are presented. The cations involved are Na+, K+, Rb+, Cs+, Ca2+, and Ba2+, and the crown ethers are 12-crown-4, 15-crown-5, and 18-crown-6. Values of V of complex formation have been discussed in terms of two simple models, one based on the scaled particle theory, and the others on the Drude-Nernst continuum model. The results indicate that the charge of the potassium cation in 18-crown-6 is especially well screened from the water. On this basis hydration numbers of complexed cations have been calculated. This shows that the size of the cation compared to the crown ether hole is important for the contacts between complexed cations and water. 相似文献
956.
John C. Schug 《Theoretical chemistry accounts》1979,53(2):197-201
Ab initio projected-unrestricted Hartree-Fock calculations have been carried out on a number of excited and ionic states of the water molecule. Results have been compared with large-scale CI calculations, with IVO calculations, and with those of Mrozek and Golebiewski obtained by the 2 × 2 rotation method applied to orbitals. It is concluded that the PUHF method may provide the most useful alternative to large-scale CI for calculating properties of open-shell systems. But it will not be generally useful for calculating spectral transition energies. 相似文献
957.
Metastable ion peak shapes, dimensions and relative abundances have been measured for the three fragmentations [C3H6]+· → [C3H4]+· + H2, [C3H6]+· → [C3H5]+ + H· and [C3H6]+· → [C3H3]+ + H2 + H·. [C3H6]+· ions were derived from propene, cyclopropane, tetrahydrofuran, cyclohexanone, 2-methyl but-1-ene and cis-pent-2-ene. Activation energies for these fragmentations have been evaluated. Three daughter ion dissociations ([C3H5]+ → [C3H3]+ + H2, [C3H5]+ → [C3H4]+· + H· and [C3H4]+· → [C3H3]+ + H·) have been similarly examined. Ion structures have been determined and the metastable energy releases have been correlated with the thermochemical data. It is concluded that the molecular ions of propene and cyclopropane become structurally indistinguishable prior to fragmentation and that differences in their metastable ion characteristics can be ascribed wholly to internal energy differences; the latter can be correlated with the photoelectron spectra of the isomers. The pathway for the consecutive fragmentation which generates the metastable ion peak (m/e 42 → m/e.39) has been shown to be It is likewise concluded that fragmentating [C3H6]+· ions generated from the various precursor molecules are also structurally indistinguishable and cannot be classified with either molecular ion of the isomeric C3H6 hydrocarbons. 相似文献
958.
Kadish KM Phan TD Giribabu L Shao J Wang LL Thuriere A Van Caemelbecke E Bear JL 《Inorganic chemistry》2004,43(3):1012-1020
Eleven different Ru(2)(4+) and Ru(2)(3+) derivatives are characterized by thin-layer FTIR and UV-visible spectroelectrochemistry under a CO atmosphere. These compounds, which were in-situ electrogenerated from substituted anilinopyridine complexes with a Ru(2)(5+) core, are represented as Ru(2)(L)(4)Cl where L = 2-CH(3)ap, ap, 2-Fap, 2,3-F(2)ap, 2,4-F(2)ap, 2,5-F(2)ap, 3,4-F(2)ap, 3,5-F(2)ap, 2,4,6-F(3)ap, or F(5)ap. The Ru(2)(5+) complexes do not axially bind CO while mono- and bis-CO axial adducts are formed for the Ru(2)(4+) and Ru(2)(3+) derivatives, respectively. Six of the eleven investigated compounds exist in a (4,0) isomeric form while five adopt a (3,1) geometric conformation. These two series of compounds thus provide a large enough number of derivatives to examine trends and differences in the spectroscopic data of the two types of isomers in their lower Ru(2)(4+) and Ru(2)(3+) oxidation states. UV-visible spectra of the Ru(2)(4+) derivatives and IR spectra of the Ru(2)(3+) complexes under CO are both isomer dependent, thus suggesting that these data can be used to reliably predict the isomeric form, i.e., (3,1) or (4,0), of diruthenium complexes containing four unsymmetrical substituted anilinopyridinate bridging ligands; this was confirmed by X-ray crystallographic data for seven compounds whose structures were available. 相似文献
959.
1-Ethyl-6-fluoro-1,4-dihydro-7-methyl-4-oxo-1,8-naphthyridine-3-carboxylic acid ( 8 ) has been prepared in large quantities by a highly efficient process. It has in turn been degraded to give 7-chloro-1-ethyl-6-fluoro-1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxylic acid ( 11 ). This intermediate has been reacted with piperazine to give the known antibacterial agent, enoxacin ( 12 ). 相似文献
960.
West Douglas X. Scovill John P. Silverton J. V. Bavoso Alfonso 《Transition Metal Chemistry》1986,11(4):123-131
Summary The ligand 3-azabicyclo[3.2.2]nonane-3-thiocarboxylic acid 2-[1-(2-pyridinyl)ethylidene]hydrazide (HL), which is observed in an unusual tautomeric form in the solid state, and its selenium analogue (HLSe) have been used to prepare a series of nickel(II) complexes. Compounds of the general formula [NiLX] (X=Cl, Br, NCS, N3, NO2 or NCSe) as well as [Ni(LSe)Cl] have been found to be diamagnetic, planar complexes. A single crystal study of [NiL(NCS)] shows the deprotonated ligand bound in a tridentate mannervia its pyridyl nitrogen, imine nitrogen and the thione sulphur atom with the nitrogen atom of the thiocyanato-ligand occupying the fourth coordination position. The solids prepared from the nickel(II) salts having tetrafluoroborate, nitrate and iodide ions approximate to octahedral symmetry and have neutral HL ligands coordinated in a bidentate fashionvia the pyridine and imine nitrogens with the remaining coordination sites being occupied by the anions or water molecules. The [NiL2] solid is also octahedral with the two deprotonated ligands bonding as tridentate groupsvia the same atoms as in the [NiLX] complexes. 相似文献