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51.
M. E. Niyazymbetov B. Kostizella I. Keitel K. H. Schwartz 《Russian Chemical Bulletin》1991,40(1):182-186
The cathodic electrolysis of aliphatic alcohols and alkylphosphonates in acetonitrile with 0.5 N Et4NClO4 as the base electrolyte leads to mono- and ditransesterified phosphonates. The yield and ratio of these products is a function of the nature of the starting reagents and amount of current passed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 200–204, January, 1991. 相似文献
52.
Summary A method is proposed for calculating surface selfdiffusion coefficients in sparingly soluble monolayers at fluid interfaces based on radiotracer measurements and allowing for counter geometry. On this basis an analysis of experimental results is possible without having to allow for processes competing with surface self-diffusion. Monolayers of various long-chainn-alcohols andn-alkane-carboxylic acids were studied in the area range between 0.23 nm2/molecule and 2.0 nm2/molecule. Surface self-diffusion coefficientsD
s
were determinded only up to areas of 0.75 nm2/molecule since, in case of greater areas, the analysis of surface concentration becomes inexact due to the increasing influence of density convection. For the systems studied,D
s
values lie in the order of 10–5 cm2/s. In all compounds studied, the values ofD
s
increase with area per molecule. In addition, dependence on the type of hydrophilic group and alkyl-chain length of monolayer molecules was proved. The results are discussed by means of various model concepts.
With 8 figures and 1 table 相似文献
Zusammenfassung Ein Verfahren zur Berechnung der Oberflächenselbstdiffusionskoeffizienten in schwerlöslichere Monoschichten an fluiden Phasengrenzen auf der Grundlage von Radiotracermessungen und unter Berücksichtigung der Zählrohrgeometrie wird vorgeschlagen. Auf dieser Basis ist eine Auswertung der Experimentalergebnisse möglich, ohne daß zur Oberflächenselbstdiffusion in Konkurrenz stehende Transportvorgänge berücksichtigt werden müssen. Untersucht wurden Monoschichten verschiedener längerkettigern-Alkanole undn-Alkancarbonsäuren im Flächenbereich zwischen 0,23 nm2/Molekül und 2 nm2/Molekül. OberflächenselbstdiffusionskoeffizientenD s wurden nur bis zu Flächenwerten von 0,75 nm2/Molekül bestimmt, weil bei höheren Flächen die Auswertung der Oberflächenkonzentrationsänderungen wegen des zunehmenden Einflusses von Dichtekonvektion ungenau wird. DieD s -Werte liegen für die untersuchten Systeme in der Größenordnung 10–5 cm2/s. Bei allen untersuchten Verbindungen nehmen die Werte von Ds mit steigender Fläche pro Molekül zu. Außerdem wurde die Abhängigkeit von der Art der hydrophilen Gruppe und der Alkylkettenlänge der Monoschichtmoleküle nachgewiesen. Die Ergebnisse wurden anhand verschiedener Modellvorstellungen diskutiert.
With 8 figures and 1 table 相似文献
53.
Bradley D. Fahlman Andrew D. Daniels Gustavo E. Scuseria Andrew R. Barron 《Journal of Cluster Science》2002,13(4):587-599
Thermodynamic and mechanistic features of the chalcogen exchange reaction between [RGa(
3-Te)]4 and elemental sulfur or selenium have been studied employing density functional theory (DFT) calculations using the BL3YP basis set and Stuttgart pseudopotentials. For [MeGa(
3-E)]4 (E=S, Se, Te) the correlation between the calculated parameters and diffraction data for their isolable analogs is greater than 98%. Each step of the conversion of [MeGa(
3-Te)]4 to [MeGa(
3-E)]4 via [Me4Ga4(
3-Te)4–x
(
3-E)
x
] (E=S, Se) is predicted to occur as a series of isolated reactions. The entropy change for each chalcogen exchange is small in magnitude and corresponds to the degree of cage distortion within the cubane molecules. Calculations performed on [MeGa(
3-Te)]4...S8 and [MeGa(
3-Te)]4-S suggest that an increase in electrophilicity of the gallium next to a surface bound tellurium may result in nucleophilic cage opening for which intermediate structures are calculated. 相似文献
54.
Dušan J. Radanović Zoran D. Matović Gustavo Ponticelli Paola Scano Inessa A. Efimenko 《Transition Metal Chemistry》1994,19(6):646-650
Summary The synthesis and characterization of AuIII complexes with several heterocyclic ligands are reported. The compounds have general formula [AuX3(L)], where L =N-methylimidazole (N-MeIz),N-ethylimidazole (N-EtIz),N-propylimidazole (N-PrIz), benzoxazole (BO), 2-methylbenzoxazole (2-MeBO), 2,5-dimethylbenzoxazole (2,5-diMeBO), 2-amino-pyrimidine (2-APm), 4(6) -hydroxy-pyrimidine [4(6)-hydrPm] or hypoxanthine (Hypox) and X = Cl or Br. Elemental analysis, conductivity measurements and spectral studies were used for the characterization of the complexes. A square-planar geometry withN-bonded heterocyclic ligands is suggested. 相似文献
55.
An algebraic method that includes Gibbs minimization for performing phase equilibrium calculations for any number of components or phases 总被引:1,自引:0,他引:1
Gustavo A. Iglesias-Silva Adrin Bonilla-Petriciolet Philip T. Eubank James C. Holste Kenneth R. Hall 《Fluid Phase Equilibria》2003,210(2):229-245
The most widely used technique for performing phase equilibria calculations is the K-value method (equality of chemical potentials). This paper proposes a more efficient algorithm to achieve the results that includes Gibbs minimization when we know the number of phases. Using the orthogonal derivatives, the tangent plane equation and mass balances, it is possible to reduce the Gibbs minimization procedure to the task of finding the solution of a system of non-linear equations. Such an operation is easier and faster than finding tangents or areas, and appears to converge as fast as the K-value method. Examples illustrate application of the new technique to two and three phases in equilibrium for binary and ternary mixtures. 相似文献
56.
Pavel V. Avramov Konstantin N. Kudin Gustavo E. Scuseria 《Chemical physics letters》2003,370(5-6):597-601
We study the electronic structure of a variety of single wall carbon nanotubes and report density of states obtained with the Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation and hybrid PBE0 approximation of density functional theory using Gaussian orbitals and periodic boundary conditions. PBE gives very good results for metallic tubes but the addition of a portion of exact exchange in the hybrid PBE0 functional worsens the agreement between experiment and theory. On the other hand, the PBE0 hybrid significantly improves the theoretical predictions (compared to PBE) for semiconducting tubes. 相似文献
57.
Ricardo Schwartz Schor 《Communications in Mathematical Physics》1978,59(3):213-233
In this work we study thev-dimensional Ising model at low temperatures and establish the existence of an upper gap in the energy-momentum spectrum of the two-point function forv3. Forv=2, it is known that this gap is absent.Supported in part by Conselho Nacional de Pesquisas (CNPq-Brazil), Universidade Federal de Minas Gerais (Brazil) and the National Science Foundation under Grant PHY76-17191 相似文献
58.
György Schultz Tamás Nagy Gustavo Portalone Fabio Ramondo István Hargittai Aldo Domenicano 《Structural chemistry》1993,4(3):183-190
The molecular structure and benzene ring distortions of ethynylbenzene have been investigated by gas-phase electron diffraction and ab initio MO calculations at the HF/6-31G* and 6-3G** levels. Least-squares refinement of a model withC
2v, symmetry, with constraints from the MO calculations, yielded the following important bond distances and angles:r
g(C
i
-C
o
)=1.407±0.003 Å,r
g(C
o
-C
m
)=1.397±0.003 Å,r
g(C
m
-C
p
)=1.400±0.003 Å,r
g(Cr
i
-CCH)=1.436 ±0.004 Å,r
g(C=C)=1.205±0.005 Å, C
o
-C
i
-C
o
=119.8±0.4°. The deformation of the benzene ring of ethynylbenzene given by the MO calculations, including o-Ci-Co=119.4°, is insensitive to the basis set used and agrees with that obtained by low-temperature X-ray crystallography for the phenylethynyl fragment, C6H5-CC-, in two different crystal environments. The partial substitution structure of ethynylbenzene from microwave spectroscopy is shown to be inaccurate in the ipso region of the benzene ring. 相似文献
59.
Observation of the 35 GHz EPR spectrum of γ-irradiated 10 M NaOH/H2O and 10 M NaOD/D2O glassy ices at 77°K has revealed proton spin flip satellites associated with the trapped elctron EPR line. This suggests that forbidden satellite transitions contribute to the lineshape of the trapped electron line in the 9 GHz spectrum which has commonly been studied. 相似文献
60.
Carbon–hydrogen bond dissociation enthalpies (BDEs) were computed for all haloethenes, C2H4−nXn (n=0–3, X=F, Cl, Br, I), at the B3LYP/6-311+G(3df,2p) level using isodesmic reactions. It was found that C–H bond strengths in the monohaloethenes varied substantially, by as much as 18 kJ mol−1, dependent upon the bond's stereochemical position relative to the halogen. BDEs in the dihaloethanes varied in the order CX2CH–H>(E)-CHXCX–H>(Z)-CHXCX–H. Trends in the computed bond enthalpies were discussed and explained on the basis of relative steric repulsions and hyperconjugative delocalization interactions, as determined from Natural Bond Orbital analysis. 相似文献