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671.
Mojtaba Shamsipur Mehran JavanbakhtVito Lippolis Alessandra GarauGreta De Filippo Mohammad Reza GanjaliAbdullah Yari 《Analytica chimica acta》2002,462(2):225-234
Novel polymeric membrane (PME) and coated graphite (CGE) silver-selective electrodes based on two recently synthesized mixed azathioether crowns containing a 1,10-phenanthroline sub-unit were prepared. The electrodes reveal a Nernstian behavior over quite wide Ag+ ion concentration ranges with a very low limits of detection (LOD) (i.e. down to 1.0×10−8 M for CGEs and 8.0×10−7 M for PMEs). The potentiometric responses are independent of the pH of the test solution in the pH range 3.0-7.0. The electrodes possess advantages of low resistance, very fast response time, relatively long lifetimes and, especially, good selectivities relative to a wide variety of other cations. The electrodes were used, as indicator electrodes, in the potentiometric titration of silver ion and in the determination of Ag+ in waste water, photographic emulsion and radiographic and photographic films. 相似文献
672.
Raymond D. Baechler Lynn James San Filippo Alayne Schroll 《Tetrahedron letters》1981,22(52):5247-5250
Mixtures of sulfides and disulfides are obtained upon reaction of boron trisulfide with a series of allyl aryl suit oxides, with the product distributions dependent upon the structures of the intermediate thiosulfoxides. 相似文献
673.
Van Lier G Ewels CP Zuliani F De Vita A Charlier JC 《The journal of physical chemistry. B》2005,109(13):6153-6158
We present a theoretical investigation on the chemical addition patterns governing the fluorination of single wall carbon nanotubes. Monte Carlo calculations based on a Hückel model suggest that fluorination is stabilized in a bandlike pattern due to electronic confinement effects on the tube bond network topology. Ab initio analysis of the fluorination of small nanotubes show that fluorine addition along the nanotube axis direction is favored by a mechanism of carbon framework distortion. The experimentally observed formation of fluorine bands may be thus explained in terms of multiple axial C(2)F rows expanding by contiguous axial addition. 相似文献
674.
Marina V Braga Filippo Magaraci Silvia Orenes Lorente Ian Gilbert Wanderley de Souza 《Microscopy and microanalysis》2005,11(6):506-515
Trypanosoma cruzi is the ethiological agent of Chagas disease. New compounds are being developed based on the biosynthesis and function of sterols, because T. cruzi has a requirement for specific endogenous sterols for growth and survival. Sterol biosynthesis inhibitors (SBIs) are drugs commonly used against fungal diseases. These drugs act by depleting essential and specific membrane components and/or inducing the accumulation of toxic intermediary or lateral products of the biosynthetic pathway. In this work we present the effects of WSP488, WSP501, and WSP561, specific inhibitors of Delta24(25)-sterol methyl transferase, on the ultrastructure of T. cruzi epimastigotes. All three drugs inhibited parasite multiplication at low concentrations, with IC50 values of 0.48, 0.44, and 0.48 muM, respectively, and induced marked morphological changes including (a) blockage of cell division; (b) swelling of the mitochondrion, with several projections and depressions; (c) swelling of the perinuclear space; (d) presence of autophagosomes and myelin-like figures; (e) enlargement of the flagellar pocket and of a cytoplasmic vacuole located in close association with the flagellar pocket; (f) detachment of the membrane of the cell body; and (g) formation of a vesicle at the surface of the parasite between the flagellar pocket and the cytostome. Our results show that these drugs are potent in vitro inhibitors of growth of T. cruzi. 相似文献
675.
Florio S Perna FM Luisi R Barluenga J Rodríguez F Fañanás FJ 《The Journal of organic chemistry》2004,69(16):5480-5482
Regioselective addition of lithiated oxazoline 2a, easily available from 2-(1-chloroethyl)-4,4-dimethyl-2-oxazoline 1a (LDA, THF, -98 degrees C), to alpha,beta-unsaturated Fischer carbene complexes 3 afforded cyclopropylcarbene complexes 4 as sole diastereoisomers. Exposure of carbene complexes 4a-c (M = Cr) to air and sunlight gave cyclopropane carboxylate derivatives 5a-c. A plausible mechanistic explanation is proposed. Moreover, when lithiated oxazoline 2b was generated from 1b in the presence of the carbene complex 3a,b, the oxazolinylcyclopropane carboxylates 6a,b formed as a 1:1 mixture of diastereoisomers. Chiral lithiated oxazoline 2c added regioselectively and diastereoselectively to chromium complexes 3a,b and to tungsten complexes 3d,e, leading, after oxidation of the metal fragment, to esters 7a,b with good diastereoselectivity (dr = 4:1). The reaction of lithiated oxazoline 2d with chromium complex 3b and tungsten complex 3e proceeded less diastereoselectively, furnishing, in both cases, after oxidation, the ester 7c as a 3:2 diastereoselective mixture. 相似文献
676.
We have functions expressed as antisymmetrized products of strongly orthogonal geminals have been evaluated for some three membered ring molecules. GF results are compared with previously computed SCF-MO results, obtained employing the same atomic basis. Transferability features of bonds and inner shells are shown. 相似文献
677.
Filippo?De Angelis Simona?Fantacci Antonio?SgamellottiEmail author Nazzareno?Re 《Theoretical chemistry accounts》2003,110(3):196-204
The energetics and reaction mechanism of the migratory insertion of carbon monoxide and methyl isocyanide into the zirconium–carbon and titanium–carbon bonds in [calix[4](OMe)2(O)2–M–Me2], (M=Zr, Ti), have been investigated by combining static and dynamic density functional calculations. Two steps have been characterized: the coordination of the incoming nucleophilic moiety leading to relatively stable facial adducts; its subsequent insertion into the M–C bond, leading to 2-bound acyl or iminoacyl complexes, providing a rationale for the different behavior of CO and MeNC towards both insertion and deinsertion reactions. Our results indicate that the rate-determining step for the overall MeNC insertion into the M–C bond is its coordination to the electron-deficient metal center, with the titanium system featuring a higher energy barrier (12.7 versus 5.5 kcal mol–1). Ab initio molecular dynamics simulations have been performed on the Zr system by means of the Car–Parrinello method, to study the hitherto inaccessible mechanistic features of the insertion reactions.Contribution to the Björn Roos Honorary Issue 相似文献
678.
679.
The reaction of M(η6-1,3,5-Me3C6H3)2, M = Cr, Mo, with the tetrahalides of Groups 4 and 5 elements proceeds with the monoelectronic oxidation of the metal bis-arene to the [M(η6-Me3C6H3)2]+ cation. In the case of MX4, M = Ti, X = Cl, Br, M = V, X = Cl, and of Nb2Cl10 the reduction products are the titanium(III), vanadium(III) halides and the niobium(IV) chloride, isolated as the solvate anions [MCl4(THF)2]− and [NbCl4(CH3CN)]−. The reaction of the tetrachloro complexes MCl4(THF)2, M = Zr, Hf, with Cr(η6-1,3,5-Me3C6H3)2 in THF produces the ionic [Cr(η6-1,3,5-Me3C6H3)2][MCl5(THF)], which has been characterized by single-crystal X-ray diffraction in the case of hafnium. 相似文献
680.
Stefania Della Sciucca Gloria Spagnoli Maurizio Penco Salvatore Battiato Filippo Samperi Raniero Mendichi 《Journal of Polymer Science.Polymer Physics》2009,47(6):596-607
The structural relaxation of poly(methyl‐methacrylate) (PMMA)‐based copolymers with different chain flexibility has been studied by DSC with the classical procedure of the isothermal and dynamical approach. Modified PMMA with different chain flexibility have been prepared by free radical polymerization in solution using a mixture of monomers containing 10 mol % of alkyl methacrylate (i.e., ethyl, buthyl, and hexyl methacrylate). The molecular characteristics of all the prepared copolymers have been performed by a multiangle laser light scattering (MALS) photometer on‐line to a size exclusion chromatography (SEC) system (SEC‐MALS) after and before the thermal treatments, NMR (1H and 13C) and MALDI‐TOF mass spectrometry. A comparison of the apparent relaxation rate (RH) was appraised from the enthalpy loss by annealing the different samples at the same level of undercooling (Ta = Tg ? 18 °C). It was found an increase of RH increasing the chain flexibility in the copolymers. Dynamical tests, performed at different cooling rates, have been used to estimate the apparent activation energy of the relaxation process. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 596–607, 2009 相似文献