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991.
Multianalytical Study of Patina Formed on Archaeological Metal Objects from Bliesbruck-Reinheim 总被引:1,自引:0,他引:1
Michael Wadsak Ina Constantinides Guido Vittiglio Annemie Adriaens Koen Janssens Manfred Schreiner Freddy C. Adams Philippe Brunella Michel Wuttmann 《Mikrochimica acta》2000,133(1-4):159-164
Patinas naturally formed on archaeological bronze alloys were characterized using light microscopy (LM), micro energy dispersive
X-ray fluorescence analysis (μ-EDXRF), time of flight secondary ion mass spectrometry (TOF-SIMS) and scanning electron microscopy
in combination with energy dispersive X-ray microanalysis (SEM/EDX). The examinations carried out on cross-sections of samples
have shown that in all samples the copper content in the corrosion layer is lower than in the bulk, while an increase of tin
and lead could be observed. Two different types of corrosion were found: first type, a corrosion formation leading to a three
layer structure was observed on lead bronze. The outer layer consists mainly of Cu(II) compounds and soil material, followed
by a fragmented layer of cuprous oxide and the surface layer of the alloy, where a depletion of copper and an enrichment of
tin and high amounts of Cl could be detected. The second type of corrosion is characterized by a two layer structure on the
tin bronze sample consisting of an outer layer with copper containing corrosion products and a layer with cracks, which reveals
a depletion of copper whereas tin and lead are enriched. Also high amounts of Si were detected in this surface layer. 相似文献
992.
Nelson Maculan Philippe Michelon Adilson E. Xavier 《Annals of Operations Research》2000,96(1-4):209-220
A nonconvex mixed-integer programming formulation for the Euclidean Steiner Tree Problem (ESTP) in Rn is presented. After obtaining separability between integer and continuous variables in the objective function, a Lagrange
dual program is proposed. To solve this dual problem (and obtaining a lower bound for ESTP) we use subgradient techniques.
In order to evaluate a subgradient at each iteration we have to solve three optimization problems, two in polynomial time,
and one is a special convex nondifferentiable programming problem.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
993.
Fast algorithm for solving the Hankel/Toeplitz Structured Total Least Squares problem 总被引:4,自引:0,他引:4
The Structured Total Least Squares (STLS) problem is a natural extension of the Total Least Squares (TLS) problem when constraints
on the matrix structure need to be imposed. Similar to the ordinary TLS approach, the STLS approach can be used to determine
the parameter vector of a linear model, given some noisy measurements. In many signal processing applications, the imposition
of this matrix structure constraint is necessary for obtaining Maximum Likelihood (ML) estimates of the parameter vector.
In this paper we consider the Toeplitz (Hankel) STLS problem (i.e., an STLS problem in which the Toeplitz (Hankel) structure
needs to be preserved). A fast implementation of an algorithm for solving this frequently occurring STLS problem is proposed.
The increased efficiency is obtained by exploiting the low displacement rank of the involved matrices and the sparsity of
the associated generators.
The fast implementation is compared to two other implementations of algorithms for solving the Toeplitz (Hankel) STLS problem.
The comparison is carried out on a recently proposed speech compression scheme. The numerical results confirm the high efficiency
of the newly proposed fast implementation: the straightforward implementations have a complexity of O((m+n)3) and O(m3) whereas the proposed implementation has a complexity of O(mn+n2).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
994.
Several threshold methods have been proposed for the purpose of estimating a bivariate extreme value distribution from a sample of data whose distribution is only in its domain of attraction. An integrated view of these methods is presented which leads to the introduction of a new asymptotically consistent estimator of the dependence function characterizing the extreme dependence structure. Through Monte Carlo simulations, the new estimator is also shown to do as well as its competitors and to outperform them in cases of weak dependence. To the authors' knowledge, this is the first time that the small-sample behavior of nonparametric bivariate threshold methods has ever been investigated. 相似文献
995.
In the inviscid limit the generalized complex Ginzburg–Landau equation reduces to the nonlinear Schr?dinger equation. This
limit is proved rigorously with H
1 data in the whole space for the Cauchy problem and in the torus with periodic boundary conditions. The results are valid
for nonlinearities with an arbitrary growth exponent in the defocusing case and with a subcritical or critical growth exponent
at the level of L
2 in the focusing case, in any spatial dimension. Furthermore, optimal convergence rates are proved. The proofs are based on
estimates of the Schr?dinger energy functional and on Gagliardo–Nirenberg inequalities.
Received: 2 April 1999 / Accepted: 29 March 2000 相似文献
996.
Dilyana Paneva Laetitia Mespouille Nevena Manolova Philippe Degée Iliya Rashkov Philippe Dubois 《Macromolecular rapid communications》2006,27(17):1489-1494
Summary: Well‐defined poly[(ethylene oxide)‐block‐(sodium 2‐acrylamido‐2‐methyl‐1‐propane sulfonate)] diblock copolymers [P(EOm‐b‐AMPSn)], have been obtained by water‐based ATRP using α‐methoxy‐ω‐(2‐methylbromoisobutyrate) poly(ethylene oxide)s (MeO‐P[EO]m‐BriB with m ranging from 12 to 113) and CuBr · 2Bpy (Bpy for 2,2′‐bipyridyl) as macroinitiator and catalytic complex, respectively. Compared to direct polymerization in water, it has been demonstrated that the water/methanol (3:1, v/v) mixture is better suited for predicting the final number‐average molar mass from the initial monomer‐to‐macroinitiator molar ratio and achieving a quite narrow polydispersity, even at high monomer conversion ( ≈ 1.4 at 80% conversion). The effect of temperature, solvent mixture composition and addition of NaCl salt on the polymerization rate and extent of control over the copolymer molecular parameters have been highlighted as well.
997.
Sophie Peeterbroeck Fouad Laoutid Benjamin Swoboda Jos‐Marie Lopez‐Cuesta Nicolas Moreau Janos B. Nagy Michaël Alexandre Philippe Dubois 《Macromolecular rapid communications》2007,28(3):260-264
Nanocomposites based on an ethylene–vinyl acetate copolymer (27 wt.‐% vinyl acetate) and multiwall carbon nanotubes (MWNTs) have been prepared by melt blending and their thermal degradation and flame retardant properties have been evaluated. Special attention has been paid to the influence of the nanotube nature on the flammability properties and more particularly on the time to ignition (TTI) as measured by cone calorimetry. It has been shown that there is a strong influence of the nature of carbon nanotubes on the fire behaviour of the composites, especially previous MWNTs crushing proved to substantially delay the TTI while maintaining much reduced heat release rate (HRR). Such a remarkable behaviour might be explained by the chemical reactivity of radical species present at the surface/extremities of crushed MWNTs during the combustion process.
998.
Stphane Bredeau Laura Boggioni Fabio Bertini Incoronata Tritto Fabien Monteverde Michaël Alexandre Philippe Dubois 《Macromolecular rapid communications》2007,28(7):822-827
Homogeneous surface coating of multi‐walled carbon nanotubes is achieved for the first time by in situ copolymerization of ethylene (E) and 2‐norbornene (N) as catalyzed directly from the nanotube surface previously treated by a highly active metallocene‐based complex, i.e., rac‐Et(Ind)2ZrCl2/MMAO‐3A. The copolymerization reaction allows for the destructuration of the native nanotube bundles, which upon further melt blending with an ethylene–vinyl acetate copolymer (27 wt.‐% vinyl acetate) matrix, leads to high‐performance polyolefinic nanocomposites. The microstructural analysis of the surface‐coating copolymer was carried out by 13C NMR spectroscopy and allowed determination of the actual N content incorporated along the chains. Depending on the experimental conditions used (e.g., E pressure, solvent, feed N concentration) the relative quantity of E–N copolymer can be tuned, as well as the N content in the formed copolymers and accordingly their glass transition temperature.
999.
Anne Siegel Carito Guziolowski Philippe Veber Ovidiu Radulescu Michel Le Borgne 《PAMM》2007,7(1):1121803-1121804
We advocate the use of qualitative models for the analysis of shift equilibria in large biological systems. We present a mathematical method, allowing qualitative predictions to be made of the behaviour of a biological system. These predictions are not dependent on specific values of the kinetic constants. We show how these methods can be used to improve understanding of a complex regulatory system. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
1000.
Abderramane Amgoune Christophe M. Thomas Jean‐Franois Carpentier 《Macromolecular rapid communications》2007,28(6):693-697
Amino‐alkoxy‐bis(phenolate) yttrium complexes act in the presence of an excess of alcohol (up to 50 equiv. vs. Y) as highly active and stereoselective catalysts for rac‐lactide and rac‐β‐butyrolactone polymerizations. These versatile systems enable the production of large quantities of polymer with small amounts of catalyst, optimizing productivity, and also allow the preparation of polymers with functional end groups, which may be employed as intermediates for macromolecular engineering applications.