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81.
Alp H. Alidedeoglu Adam W. York Dale A. Rosado Charles L. McCormick Sarah E. Morgan 《Journal of polymer science. Part A, Polymer chemistry》2010,48(14):3052-3061
The synthesis of well‐defined carboxylic acid‐functionalized glycopolymers prepared via one‐step postpolymerization modification of poly(N‐[3‐aminopropyl] methacrylamide) (PAPMA), a water‐soluble primary amine methacrylamide, in aqueous medium is demonstrated. PAPMA was first polymerized via aqueous reversible addition‐fragmentation chain transfer polymerization in aqueous buffer using 4‐cyanopentanoic acid dithiobenzoate as the chain transfer agent and 4,4′‐azobis(4‐cyanovaleric acid) (V‐501) as the initiator at 70 °C. The resulting well‐defined PAPMA was then conjugated with D ‐glucuronic acid sodium salt through reductive amination in alkaline medium (pH 8.5) at 45 °C. The successful bioconjugation was proven through proton (1H) and carbon (13C) nuclear magnetic resonance spectroscopy and matrix‐assisted laser desorption/ionization time of flight mass spectrometry analysis, which indicated near quantitative conversion. A similar bioconjugation reaction was conducted with poly(2‐aminoethyl methacrylate) (PAEMA) and poly(2‐aminoethyl methacrylate‐b‐poly(N‐[2‐hydroxypropyl]methacrylamide) (PAEMA‐b‐PHPMA). For the PAEMA homopolymers and block copolymers, however, lower conversion was obtained, most likely because of degradation reactions of PAEMA in alkaline medium. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3052–3061, 2010 相似文献
82.
Bartels JW Cauët SI Billings PL Lin LY Zhu J Fidge C Pochan DJ Wooley KL 《Macromolecules》2010,43(17):7128-7138
Two RAFT-capable PEO macro-CTAs, 2 and 5 kDa, were prepared and used for the polymerization of isoprene which yielded well-defined block copolymers of varied lengths and compositions. GPC analysis of the PEO macro-CTAs and block copolymers showed remaining unreacted PEO macro-CTA. Mathematical deconvolution of the GPC chromatograms allowed for the estimation of the blocking efficiency, about 50% for the 5 kDa PEO macro-CTA and 64% for the 2 kDa CTA. Self assembly of the block copolymers in both water and decane was investigated and the resulting regular and inverse assemblies, respectively, were analyzed with DLS, AFM, and TEM to ascertain their dimensions and properties. Assembly of PEO-b-PIp block copolymers in aqueous solution resulted in well-defined micelles of varying sizes while the assembly in hydrophobic, organic solvent resulted in the formation of different morphologies including large aggregates and well-defined cylindrical and spherical structures. 相似文献
83.
A family of guanidinate-supported imido metal complexes are novel, effective catalysts for C=N metathesis of alkyl and aryl carbodiimides and evidence suggests that this reaction proceeds via a sequential addition/elimination pathway. 相似文献
84.
Density functional calculations of thio effects on the in-line mechanism of methanolysis of ethylene phosphate (a reverse reaction model for RNA phosphate transesterification) are presented. A total of 12 reaction mechanisms are examined using the B3LYP functional with large basis sets, and the effects of solvation were treated using the PCM, CPCM, and SM5 solvation models. Single thio substitutions at all of the distinct phosphoryl oxygen positions (2', 3', 5', pro-R) and a double thio substitution at the nonbridging (pro-R/pro-S) positions were considered. Profiles for each reaction were calculated in the dianionic and monoanionic/monoprotic states, corresponding to reaction models under alkaline and nonalkaline conditions, respectively. These models provide insight into the mechanisms of RNA transesterification thio effects and serve as a set of high-level quantum data that can be used in the design of new semiempirical quantum models for hybrid quantum mechanical/molecular mechanical simulations and linear-scaling electronic structure calculations. 相似文献
85.
D. Vaughan Griffiths Helen J. Groombridge Stephen P. Swetnam David C. York 《Tetrahedron》2005,61(19):4595-4600
The synthesis of a range of new phosphine-containing polydentate ligands has been achieved by addition of sulfur and nitrogen nucleophiles to dimethylvinylphosphine sulfide, followed by reduction of the resulting phosphine sulfides with lithium aluminium hydride. 相似文献
86.
A series of primary amido gallium alkyl complexes that includes a base free dimer, [tBu2Ga(μ-N(H)tBu)]2 (1), Lewis base stabilized monomeric complexes, nBu2Ga(N(H)tBu)(THF) (2) and nBu2Ga[NH(2,6-Me2C6H3)]py (3) and an anionic complex, nBu2Ga[NH(2,6-Me2C6H3)]2[Li(Et2O)] (4) is reported. Complex 1 crystallizes in the triclinic space group P-1 (a = 10.265(5) Å, B = 15.752(6) Å, C = 8.932(4) Å, = 90.32(3)°, β = 105.61(3)°, γ = 88.24(4)°) with two molecules, each residing on an inversion center, in the asymmetric unit. Structural analysis revealed a planar Ga2N2 core with both the bridging N and the Ga centers in distorted tetrahedral environments (Ga---C distances 2.052(3)-2.065(3) Å and Ga---N distances 2.060(3)-2.069(3) Å). The use of excess amido ligand allowed the isolation and crystallization of 4. Complex 4 crystallized in the monoclinic space group P21/n (a = 8.666(2) Å, B = 22.305(3) Å, C = 15.570(3) Å, β = 103.47(2)) with Z = 4. The pseudotetrahedral gallium center has a coordination sphere composed of two amido ligands (Ga---N1 = 2.011(8) Å, Ga---N2 = 2.006(7) Å), and two nBu ligands (Ga---C17 = 2.002(9) Å Ga---C21 = 1.985(12) Å). A bridging interaction of the lithium cation with the lone pair of electrons on each of amido nitrogen atoms generates a molecular core which is made up of a planar Ga---N1---Li---N2 distorted square (N1---Gal---N2 94.4°, Gal---N2---Lil 86.2°, N1---Li1---N2 92.2°, Gal---N1---Li1 87.1°). 相似文献
87.
Silva López C Nieto Faza O York DM de Lera AR 《The Journal of organic chemistry》2004,69(11):3635-3644
Density-functional calculations in the gas phase and solvent (PCM) at the B3LYP/6-311++G(3df,2p)//B3LYP/6-31++G(d,p) level were performed to study a series of six reactions that involve the rearrangement of vinyl allene oxides to cyclopent-2-en-1-ones along two distinct mechanistic pathways, namely concerted and stepwise. Calculations predict that stepwise pathways are highly competitive processes that occur via biradical/zwitterionic intermediates. Torquoselectivity is predicted to result from the concerted pathway leading to a stereodefined 4,5-disubstituted cyclopent-2-en-1-ones that should have memory of the starting terminal double-bond geometry and oxide configuration. The stepwise pathway cannot show torquoselectivity as cyclization of the planar oxidopentadienyl zwitterion can follow enantiomorphous conrotations. The concerted/stepwise mechanistic preference depends mainly on the olefin geometry and is further modulated by epoxide substitution. The influence of the solvent (PCM model for dichloromethane or water) is moderate, although the greater (de)stabilization of the polarized oxidopentadienyl zwitterions along the stepwise mechanism does alter the kinetic preferences exhibited by the systems in vacuo. Results with system 1e suggest that, if vinyl allene oxide II having a double bond with Z-geometry, an intermediate in the biogenesis of epi-jasmonic acid IV, is processed along an in stepwise mechanism following ring opening, the enzyme allene oxide cyclase must enforce enantiofacial torquoselectivity. 相似文献
88.
89.
90.
Primary and secondary kinetic and equilibrium isotope effects are calculated with density-functional methods for the dianionic methanolysis of the native (unsubstituted) and thio-substituted ethylene phosphates. 相似文献