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41.
A. Y. Meyer 《Journal of computational chemistry》1980,1(2):111-117
A molecular mechanical force field for fluorinated ethylenes and propylenes is described. The field computes geometries, dipole moments, and energy differences between isomers and rotamers. Component analysis indicates that “classical” strains alone (skeletal, nonbonded, electrostatic) cannot account for energy relationships. The discussion is supplemented by a semiempirical quantum chemical comparison of cis- and trans-FCH?CHF and of gauche- and anti-FCH2CH2F. 相似文献
42.
Excess enthalpies and excess volumes were determined at 298.15 K for: dimethoxymethane+heptane, diethoxymethane+heptane, 1,1-dimethoxyethane+heptane, 1,1-diethoxyethane+heptane, 2,2-dimethoxypropane+heptane and 1,1-diethoxypropane+heptane. 相似文献
43.
Breakstone A Crawley HB Dallavalle GM Doroba K Drijard D Fabbri F Firestone A Fischer HG Frehse F Geist W Giacomelli G Gokieli R Gorbics M Hanke P Heiden M Herr W Kluge EE Lamsa JW Lohse T Meyer WT Mornacchi G Nakada T Panter M Putzer A Rauschnabel K Rimondi F Siroli GP Sosnowski R Szczekowski M Ullaland O Wegener D 《Physical review letters》1985,55(20):2180-2183
44.
The alkali phosphides of 1.2-bis-phosphinobenzene, and 1-alkyl-derivatives react with (Me2N)2COEt+BF4? to give the title compounds with dicoordinated phosphorus. The structure is proved by their nmr spectra. 相似文献
45.
Abstract— Clover yellow mosaic virus, in common with other plant viruses with flexuous, rod-like particles, can be photoreactivated. At lower U.V. doses, photoreactivation is masked by an inhibitory effect on virus infection of visible light alone. 相似文献
46.
Ernst Meyer 《Angewandte Chemie (International ed. in English)》1970,9(8):583-589
The principles of the topological encoding of formulas and machine searching are briefly described. These methods have been developed to the point where it is now possible to carry out a computer search for a given structural fragment without the risk of false drops. It is also possible to carry out searches whose requirements, while well-defined and readily used by chemists, cannot be represented exclusively by element symbols and chemical bonds. 相似文献
47.
A. Bickermann H. Spitzer H. Stiller H. Meyer R. E. Lechner F. Volino 《Zeitschrift für Physik B Condensed Matter》1978,31(4):345-354
Incoherent neutron scattering experiments are reported at a number of scattering angles for solid H2 using the time-of-flight technique. The samples had an ortho concentration ofX0.91 and the temperatures were 4.2, 2.2 and 1.2 K. The recorded scattering functions exhibit the elastic line, the ortho-para conversion line, the phonon spectrum on the energy-gain side of the neutrons and finally the phonon spectrum on the energy-loss side. Analysis of the data shows multiple scattering to be very important especially at small scattering angles. Accordingly, the results of an extensive calculation are reported that include up to four-fold scattering. The phonon spectrum that brings calculation and experiment in agreement at all angles is presented. It is concluded from the comparison between the spectra at various temperatures that unexpectedly the samples have always remained in the hexagonal close-packed phase even below the usual transition temperature into the cubic phase. Comparison is made with the spectrum (also in thehcp phase) obtained from coherent neutron scattering. The high-energy phonon tail, to be expected for quantum crystals, is observed and is qualitatively consistent with that in a similar spectral density derived theoretically from ortho-para conversion data under pressure. No evidence of a libron spectrum atT=2.2 K for a sample withX=0.91 could be found, which is consistent with the absence of the cubic orientationally ordered phase in these experiments.Supported in this research by a grant from the National Science Foundation 相似文献
48.
Potential curves for proton transfer in [H5O2]+ and for the dissociation of one OH bond in [H3O]+ were calculated by both ab initio and semi-empirical LCAO MO SCF CI methods. The energy barrier of the symmetric double minimum potential in [H5O2]+ is very sensitive to electron correlation. At an OO distance of 2.74 Å it decreases from the HF value of 9.5 kcal/mole to about 7.0 kcal/mole. The results of the semi-empirical calculations agree well with the ab initio data as long as only relative effects are regarded. The partitioning of correlation energy into contributions of individual electron pairs is very similar for proton transfer in [H5O2]+ and for the dissociation of one OH bond in [H3O]+. In this example the proton transfer appears as a superposition of two “contracted ionic dissociation” processes. An interpretation of the behaviour of correlation during these processes is presented. 相似文献
49.
Hughes RP Meyer MA Tawa MD Ward AJ Williamson A Rheingold AL Zakharov LN 《Inorganic chemistry》2004,43(2):747-756
Reaction of Pd(TMEDA)(CH(3))(2) [TMEDA = tetramethylethylenediamine] with fluoroalkyl iodides R(F)I affords a series of square planar Pd(II) complexes Pd(TMEDA)(CH(3))(R(F)) [R(F) = CF(2)CF(3) (9), CFHCF(3) (10), CH(2)CF(3) (11)], presumably by oxidative addition followed by reductive elimination of CH(3)I. The solid-state structures of each compound have been determined by single crystal X-ray diffraction studies, allowing the effect of increasing alpha-fluorination on the structural trans-influence of alkyl ligands to be examined. In these compounds there is no significant difference observed in the trans-influence of the three fluorinated alkyl ligands toward the trans-N atom, although a significant cis-influence on the neighboring methyl ligand is apparent. Oxidative addition of the same series of fluoroalkyl ligands to the corresponding Pt(TMEDA)(CH(3))(2) affords octahedral Pt(IV) complexes trans-Pt(TMEDA)(CH(3))(2)(R(F))I [R(F) = CF(2)CF(3) (12), CFHCF(3) (13), CH(2)CF(3) (14)] as the kinetic products. In each case, subsequent isomerization to the corresponding all cis-isomers is observed; in the case of 13, the stereocenter at the alpha-carbon results in two diastereomeric cis-isomers, which are formed at different rates. The molecular structures of 13 and its more stable all cis-isomer 16b have been crystallographically determined. Kinetic studies of the trans-cis isomerization reactions show the mechanism to involve a polar transition state, presumably involving iodide dissociation, followed by rearrangement of the cation, and iodide recombination. High dielectric solvents increase the rate, but solvent coordinating ability has no effect. Dissolved salts (LiI, LiOTf) show normal accelerative salt effects, with no inhibition in the case of added iodide, consistent with the formation of an intimate ion pair intermediate. The kinetic parameters show that the trans-effects of fluoroalkyl ligands in these compounds follow the order expected from the relative sigma-donor properties of the ligands, with CF(2)CF(3) < CFHCF(3) < CH(2)CF(3). 相似文献
50.
J. Hladký S. NĚmeček M. Novák A. Prokeš J. Votruba K. -F. Albrecht A. Meyer M. Sachwitz B. N. Guskov V. G. Krivokhizhin M. F. Likhachev I. A. Savin G. Vesztergombi 《Czechoslovak Journal of Physics》1977,27(11):1210-1218
Results of the first elastic K
S
o
regeneration experiment on carbon, using magnetic spark chamber spectrometer, are presented in the beam momentum interval 10p50 GeV/c. The d ifferentia cross section d/dt is reconstructed in the range 0·0025–t0·02 (GeV/c)2 and its slopeB is found to be momentum independent with an average valueB=(65±11) (GeV/c)–2. The results are in agreement with the calculations using the coherent production model. 相似文献