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941.
The synthesis of a polypseudorotaxane, polyrotaxane, and polycatenane containing the electron-deficient cyclophane cyclobis(paraquat-p-phenylene) (CBPQT4+) subunit in the side chain is described. These interlocked supramolecular polymers have been prepared from an azide-functionalized polystyrene derivative and an acetylene-functionalized [2]rotaxane, [2]catenane and their parent tetracationic cyclophane via Cu(I)-catalyzed 1,3 dipolar cycloadditions (‘click chemistry’). The synthesis and characterization of the polymers and intermediates has been described using IR, 1H NMR, UV spectroscopies, and voltammetry. We have shown that the CBPQT4+ unit of the side chain polystyrene derivative has the ability to reversibly undergo complexation with a complementary dialkoxynaphthalene derivative. 相似文献
942.
Amor Ben Ali Jean-Marc Grenche Marc Leblanc Vincent Maisonneuve 《Solid State Sciences》2009,11(9):1631-1638
The hydrothermal synthesis, using tris-(2-ethylamino)amine (tren) as a template, and the crystal structures of three new hybrid iron fluorides, (H3O)2·[H3tren]2·(FeF6)2·(FeF5(H2O))·2H2O (I), [H3tren]2·(FeF6)2·(FeF2(H2O)4)·8H2O (II) and [H3tren]2·(FeF6)·(F)3·H2O (III), are reported. I, II, and III are triclinic (P-1), monoclinic (P21/c) and orthorhombic (I222), respectively. The structure of I is built up from isolated FeF6 and FeF5(H2O) distorted octahedra separated by triprotonated [H3tren]3+ cations, disordered H3O+ cations and H2O molecules. In II, FeIIIF6 and neutral [FeIIF2(H2O)4] octahedra form, together with [H3tren]3+ cations, infinite (100) layers separated by extra water molecules. The structure of III consists of isolated and disordered FeF6 octahedra, fluoride anions F− connected to [H3tren]3+ cations and extra fluoride anions F− disordered with H2O molecules. All [H3tren]3+ cations have a “spider” type conformation. 57Fe Mössbauer characterization shows that +III valence state can only be considered for iron cations in I and III and preliminary Mössbauer results are consistent with the presence of both +II and +III valences for iron cations in II, in agreement with the crystallographic results. 相似文献
943.
944.
Prediction of bulk metallic glass (BMG) forming compositions has always been a challenge due to thermodynamic and kinetic constraints. In the present investigation, a parameter based on the enthalpy of chemical mixing (?Hchem) and the mismatch entropy (?Sσ/kB) has been used to correlate with glass forming ability in some Zr based BMGs. The new thermodynamic parameter, PHS = ?Hchem × ?Sσ/kB, is found to have strong correlation with glass forming ability in the configurational entropy (?Sconfig/R) range of 0.9–1.0. PHS has been calculated for compositions in Zr–Cu–Ag, Zr–Cu–Al, Zr–Cu–Ti and Zr–Cu–Ga ternary systems. It is observed that in all the systems studied, the best BMG composition (highest critical diameter (Zc) of glass formation) is the one that corresponds to the highest negative PHS value. Present approach using PHS could be road map to design new BMG forming compositions. 相似文献
945.
We investigate iterative algorithms for solving complex symmetric constrained singular systems arising in magnetized multicomponent transport. The matrices of the corresponding linear systems are symmetric with a positive semi-definite real part and an imaginary part with a compatible nullspace. We discuss well posedness, the symmetry of generalized inverses and Cholesky methods. We investigate projected stationary iterative methods as well as projected orthogonal residuals algorithms generalizing previous results on real systems. As an application, we consider the linear systems arising from the kinetic theory of gases and providing transport coefficients of partially ionized gas mixtures subjected to a magnetic field. 相似文献
946.
We propose a new formalism for quantum field theory (QFT) which is neither based on functional integrals, nor on Feynman graphs,
but on marked trees. This formalism is constructive, i.e., it computes correlation functions through convergent rather than
divergent expansions. It applies both to Fermionic and Bosonic theories. It is compatible with the renormalization group,
and it allows to define non-perturbatively differential renormalization group equations. It accommodates any general stable polynomial Lagrangian. It can equally well treat noncommutative
models or matrix models such as the Grosse–Wulkenhaar model. Perhaps most importantly it removes the space-time background
from its central place in QFT, paving the way for a non-perturbative definition of field theory in non-integer dimension. 相似文献
947.
Vincent Siess 《Comptes Rendus Mathematique》2009,347(21-22):1317-1320
This Note is devoted to the presentation of a linear diffusion scheme that respects the maximum principle on very distorted meshes. The main idea is to use a classical Finite Volumes scheme and to perform a first integration on the Voronoï mesh based on the centers of the cells. A second integration on the primary mesh is then performed. By construction the scheme preserves the maximum principle. A numerical example is also given. To cite this article: V. Siess, C. R. Acad. Sci. Paris, Ser. I 347 (2009). 相似文献
948.
The initial state of liquid atomization by a fast gas stream is considered by viscous linear spatial stability analysis for parallel two-fluid flow. The unbounded basic velocity profile is characterized by different asymptotic velocities and a velocity deficit near the interface. We examine the influence of the velocity deficit on the spatial growth rates of two competing modes originating from the Kelvin-Helmholtz and viscosity contrast mechanisms. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
949.
Göttker-Schnetmann I Heinekey DM Brookhart M 《Journal of the American Chemical Society》2006,128(51):17114-17119
Mixtures of deuterium labeled complexes (p-XPOCOP)IrH2-xDx (1-6-d0-2) {POCOP = [C6H2-1,3-[OP(tBu)2]2] X = MeO (1), Me (2), H (3), F (4), C6F5 (5), and ArF = 3,5-(CF3)2-C6H3 (6)} have been generated by reaction of (p-XPOCOP)IrH2 complexes with HD gas in benzene followed by removal of the solvent under high vacuum. Spectroscopic analysis employing 1H and 2D NMR reveals significant temperature and solvent dependent isotopic shifts and HD coupling constants. Complexes 1-6-d1 in toluene and pentane between 296 and 213 K exhibit coupling constants JHD of 3.8-9.0 Hz, suggesting the presence of an elongated H2 ligand, which is confirmed by T1(min) measurements of complexes 1, 3, and 6 in toluene-d8. In contrast, complex 6-d1 exhibits JHD = 0 Hz in CH2Cl2 or CDCl2F whereas isotopic shifts up to -4.05 ppm have been observed by lowering the temperature from 233 to 133 K in CDCl2F. The large and temperature-dependent isotope effects are attributed to nonstatistical occupation of two different hydride environments. The experimental observations are interpreted in terms of a two component model involving rapid equilibration of solvated Ir(III) dihydride and Ir(I) dihydrogen structures. 相似文献
950.
Reczek JJ Villazor KR Lynch V Swager TM Iverson BL 《Journal of the American Chemical Society》2006,128(24):7995-8002
Derivatives of relatively electron rich 1,5-dialkoxynaphthalene (Dan) donors and relatively electron deficient 1,4,5,8-naphthalenetetracarboxylic diimide (Ndi) acceptors have been exploited in the folding and self-assembly of a variety of complex molecular systems in solution. Here, we report the use of Dan and Ndi derivatives to direct assembly of extended columns with alternating face-centered stacked structure in the solid state. A variety of 1:1 Dan:Ndi mixtures produced mesophases that were found to be stable over temperature ranges extending up to 110 degrees C. Analysis of these mesophases indicates mixtures with soft/plastic crystal phases and a few mixtures with the thermodynamic properties of true liquid crystals, all composed of alternating donor-acceptor columns within. Importantly, a correspondence was found between the clearing and crystallization points of the mesophase mixtures and the melting/clearing points of the component Ndi and Dan units, respectively. This correspondence enables the predictable tuning of mesophase phase transition temperatures. The study of sterically hindered derivatives led to a set of mixtures in which a dramatic and sudden color change (deep red to yellow) was observed upon crystallization of the mesophase due to a phase separation of the component donor and acceptor units. 相似文献