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91.
Michelin SE Oliveira HL Kroin T Soares LS Veiteinheimer E Luz CA Lima MF Fujimoto MM Lee MT 《The Journal of chemical physics》2005,122(9):094309
In this work, we present a theoretical study on elastic electron collisions from three isoelectronic free radicals (CNN, NCN, and CCO) in the low incident energy range. More specifically, calculated differential, integral, and momentum transfer cross sections are reported in the 1-30 eV energy range. Calculations are performed in the static-exchange and static-exchange-polarization levels. The iterative Schwinger variational method is used to solve the scattering equations. Our study reveals that the calculated cross sections for the three targets are significantly different at incident energies below 10 eV. Above that energy, a remarkable similarity among the calculated results is seen. 相似文献
92.
Guillermo Restrepo Eugenio J. Llanos Héber Mesa 《Journal of mathematical chemistry》2006,39(2):401-416
We carried out a mathematical study of 72 chemical elements taking advantage of the chemotopological method. We selected 128
properties to define the elements (physico-chemical, geochemical and chemical properties). Then, we looked for correlated
properties and we reduced the number of them to 90. In this way we defined each element as a 90-tuple. Afterwards, we applied
principal component analysis and cluster analysis (4 similarity functions and 5 grouping methodologies). Then, we calculated
a consensus tree for the 20 dendrograms generated by the CA. Afterwards, we extracted the similarity relationships from the
consensus tree and built up a basis for a topology on the set of chemical elements. Finally, we calculated some topological
properties (closures, derived sets, boundaries, interiors and exteriors) of several subsets of chemical elements. We found
that alkali metals, alkaline earth metals and noble gases appear not related to the rest of the elements. Also, we found that
the boundary of non-metals are the semimetals with a stair-shape on the periodic table 相似文献
93.
Romualdo Caputo Marina Della Greca Luigi Longobardo Gabriella Pinto 《Tetrahedron letters》2007,48(8):1425-1427
The general synthesis of a new class of non-natural diamino acids, 2-amino-3-[(2′-aminoalkyl)seleno]propanoic acids, or Se-(aminoalkyl)selenocysteines, is reported. Under the conditions devised, enantiopure N-Boc-protected β-l-iodoamines, which are readily generated from proteinogenic α-amino acids, were treated with the selenolate anion obtained from NaBH4 splitting of the Se-Se bond in commercial l-selenocystine. The Se-alkylation products were enantiomerically pure and the reaction is high yielding (92-98%), without any detectable traces of accompanying by-products. 相似文献
94.
Novak P Tepes P Cindrić M Ilijas M Dragojević S Mihaljević K 《Journal of chromatography. A》2004,1033(2):299-303
Directly coupled LC-MS and LC-NMR were applied to identify and structurally characterize an acarbose degradation product A in acidic media. A comparative analysis of the stop-flow LC-NMR (1H and TOCSY) and LC-MS data provided evidence that A is structurally related to acarbose, differing from the parent compound in a number of subunits present in the molecule. Spectral analysis revealed that A was the alpha-glucosidase inhibitor amylostatin XG. Complementary information obtained from the two methods led to the structural elucidation of A which was later corroborated by high-resolution NMR spectroscopy of the isolated molecule. 相似文献
95.
Gómez-Carrasco S González-Snchez L Aguado A Roncero O Alvariño JM Hernández ML Paniagua M 《The Journal of chemical physics》2004,121(10):4605-4618
A theoretical study of the F(2P) + OH(2Pi) --> HF(1Sigma+) + O(3P) reactive collisions is carried out on a new global potential energy surface (PES) of the ground 3A" adiabatic electronic state. The ab initio calculations are based on multireference configuration interaction calculations, using the aug-cc-pVTZ extended basis sets of Dunning et al. A functional representation of the PES shows no nominal barrier to reaction, contrary to previous results by others. Wave packet and quasiclassical trajectory calculations have been performed for this PES to study the F + OH(v = 0,j) reactive collision. The comparison was performed at fixed and constant values of the total angular momentum from 0 to 110 and relative translational energy up to 0.8 eV. The reaction presents a dynamical barrier, essentially due to the zero-point energy for the bending vibration near the saddle point. This determines two different reaction mechanisms. At energies higher than approximately 0.125 eV the reaction is direct, while below that value it is indirect and mediated by heavy-light-heavy resonances. Such resonances, also found in the simulations of the photodetachment spectrum of the triatomic anion, manifest themselves in the quasiclassical simulations, too, where they are associated to periodic orbits. 相似文献
96.
New quaternary intermetallic phases REMGa(3)Ge (1) (RE = Y, Sm, Tb, Gd, Er, Tm; M = Ni, Co) and RE(3)Ni(3)Ga(8)Ge(3) (2) (RE = Sm, Gd) were obtained from exploratory reactions involving rare-earth elements (RE), transition metal (M), Ge, and excess liquid Ga the reactive solvent. The crystal structures were solved with single-crystal X-ray and electron diffraction. The crystals of 1 and 2 are tetragonal. Single-crystal X-ray data: YNiGa(3)Ge, a = 4.1748(10) A, c = 23.710(8) A, V = 413.24(2) A(3), I4/mmm, Z = 4; Gd(3)Ni(3)Ga(8)Ge(3), a = 4.1809(18) A, c = 17.035(11) A, V = 297.8(3) A(3), P4/mmm, Z = 1. Both compounds feature square nets of Ga atoms. The distribution of Ga and Ge atoms in the REMGa(3)Ge was determined with neutron diffraction. The neutron experiments revealed that in 1 the Ge atoms are specifically located at the 4e crystallographic site, while Ga atoms are at 4d and 8g. The crystal structures of these compounds are related and could be derived from the consecutive stacking of disordered [MGa](2) puckered layers, monatomic RE-Ge planes and [MGa(4)Ge(2)] slabs. Complex superstructures with modulations occurring in the ab-plane and believed to be associated with the square nets of Ga atoms were found by electron diffraction. The magnetic measurements show antiferromagnetic ordering of the moments located on the RE atoms at low temperature, and Curie-Weiss behavior at higher temperatures with the values of mu(eff) close to those expected for RE(3+) free ions. 相似文献
97.
Elena G. Zhizhina Marina V. Simonova Viktor F. Odyakov Klavdiy I. Matveev 《Reaction Kinetics and Catalysis Letters》2006,89(1):157-166
Summary Oxidation of propene to acetone in water solutions in the presence of homogeneous catalysts (Pd2+ + HPA-x, where HPA-x = H3+xPVxMo12-xO40, x = 1-4) is studied. This reaction is shown to be of the 1st order with respect to C3H6 and of the 0.5th order with respect to Pd. The reaction rate does not depend on the concentration of HPA-x and acidity of
the catalyst solution. The apparent activation energy of the reaction is 21 kJ/mol. A reaction mechanism is proposed. 相似文献
98.
Summary. Two main types of binary systems with distinctive solubility behavior under sub- and supercritical conditions were used to
subdivide ternary water-salt systems into three classes. Characteristic features of solubility behavior and phase equilibria
in ternary water-salt systems of each class at temperatures above 200°C are discussed on the basis of available experimental
data and some conclusions obtained as a result of theoretical derivation of fluid and complete phase diagrams.
Corresponding author. E-mail: Valyashko@IGIC.RAS.RU
Received September 25, 2002; accepted (revised) November 28, 2002
Published online April 24, 2003
RID="a"
ID="a" Dedicated to Prof. Dr. H. Gamsjaeger on the occasion of his 70th birthday anniversary 相似文献
99.
Mercedes Cano JosV. Heras M.Luz Gallego Josefina Perles Caridad Ruiz‐Valero Elena Pinilla M.Rosario Torres 《Helvetica chimica acta》2003,86(9):3194-3203
Two new (η3‐allyl)palladium complexes containing the ligand 3,5‐dimethyl‐4‐nitro‐1H‐pyrazole (Hdmnpz) were synthesized and characterized as [Pd(η3‐C3H5)(Hdmnpz)2]BF4 ( 1 ) and [Pd(η3‐C3H5)(Hdmnpz)2]NO3 ( 2 ). The structures of these compounds were determined by single‐crystal X‐ray diffraction to evaluate the intermolecular assembly. Each complex exhibits similar coordination behavior consistent with cationic entities comprised of two pyrazole ligands coordinated with the [Pd(η3‐C3H5)]+ fragment in an almost square‐planar coordination geometry. In 1 , the cationic entities are propagated through strong intermolecular H‐bonds formed between the pyrazole NH groups and BF ions in one‐dimensional polymer chains along the a axis. These chains are extended into two‐dimensional sheet networks via bifurcated H‐bonds. New intermolecular interactions established between NO2 and Me substituents at the pyrazole ligand of neighboring sheets give rise to a three‐dimensional network. By contrast, compound 2 presents molecular cyclic dimers formed through N? H???O H‐bonds between two NO counterions and the pyrazole NH groups of two cationic entities. The dimers are also connected to each other through C? H???O H‐bonds between the remaining O‐atom of each NO ion and the allyl CH2 H‐atom. Those interactions expand in a layer which lies parallel to the face (101). 相似文献
100.
Natalia V. Kuratieva Marina I. Naumova Dmitry Yu. Naumov 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):i129-i131
The title compounds, hexaaquacobalt(II) bis(hypophosphite), [Co(H2O)6](H2PO2)2, and hexaaquacobalt(II)/nickel(II) bis(hypophosphite), [Co0.5Ni0.5(H2O)6](H2PO2)2, are shown to adopt the same structure as hexaaquamagnesium(II) bis(hypophosphite). The packing of the Co(Ni) and P atoms is the same as in the structure of CaF2. The CoII(NiII) atoms have a pseudo‐face‐centred cubic cell, with a = b~ 10.3 Å, and the P atoms occupy the tetrahedral cavities. The central metal cation has a slightly distorted octahedral coordination sphere. The geometry of the hypophosphite anion in the structure is very close to ideal, with point symmetry mm2. Each O atom of the hypophosphite anion is hydrogen bonded to three water molecules from different cation complexes, and each H atom of the hypophosphite anion is surrounded by three water molecules from further different cation complexes. 相似文献