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81.
Jeffrey C. Evans Simon K. Jackson Christopher C. Rowlands Martin D. Barratt 《Tetrahedron》1985,41(22):5191-5194
Under acid conditions aqueous solutions of chloramine-T form nitrogen-centred radicals via loss of the chlorine atom. The nitrogen radicals produced have been studied by ESR spectroscopy using the spintrapping method. Adducts of the spin trap phenyl-t-butyl nitrone are oxidized by chloramine-T in acid media to give a paramagnetic product in which the unpaired electron interacts with two inequivalent nitrogen atoms. The spin trap 5,5-dimethyl-2-pyrrolidine-1 -oxide is oxidized rapidly to 5,5-dimethyl-2-pyrrolidone-1-oxyl by chloramine-T under acid onditions. The water soluble trap α-4-pyridyl-1-oxide-N-t-butyl nitrone forms a stable nitroxide adduct with a nitrogen radical of chloramine-T in acid solution. Identical results were obtained with chloramine-B (sodium salt of N-chlorobenzene sulfonamide), indicating the involvement of the N-chloramine group in radical formation. 相似文献
82.
Love JC Urbach AR Prentiss MG Whitesides GM 《Journal of the American Chemical Society》2003,125(42):12696-12697
Metallic rods with submicron diameters that contain disklike ferromagnetic sections self-assemble into highly stable, hexagonally close-packed arrays of rods. The rods were fabricated by electrodeposition in porous alumina membranes and comprised alternating sections of gold and nickel. The thicknesses of the ferromagnetic nickel sections were approximately one-half the diameter of the rods (400 nm); this geometry orients the "easy" axis of magnetization perpendicular to the long axis of the rod. After magnetization of the rods with a rare-earth magnet, followed by sonication of the suspension, the rods spontaneously assembled into three-dimensional (3D) bundles that, on average, contained 15-30 rods. A macroscopic model of the rods suggests that the most stable orientation of the magnetic dipoles for rods in a defect-free, hexagonally close-packed arrangement is in concentric rings with the dipoles oriented head-to-tail. This configuration minimizes the energy of the bundle and does not generate a net dipole for the structure. This work provides a simple demonstration that magnetic interactions between ferromagnetic objects can direct and stabilize the formation of ordered, 3D structures by self-assembly. 相似文献
83.
Robin L.T ChurchillClaudia Sheedy Kerrm Y.F YauJ.Christopher Hall 《Analytica chimica acta》2002,468(2):185-197
Immunoassays are one of the most convenient methods for environmental monitoring, but have been limited so far by low yield and low affinity antibodies (Abs). With the advent of recombinant Ab (rAb) technology and the expression of these Abs in organisms such as yeast, bacteria, insects and plants, widespread monitoring of our food and environment for organic contaminants using immunoassays has become feasible. A multitude of immunoassays have been developed to detect pesticides in soils, ground and river water, foods and biological samples, such as urine and semen. In this paper, we describe advances in Ab production, the move away from using animals, phage-display technologies and the advent of plant-derived Ab expression systems. Finally, we describe future possibilities in Ab technology for environmental monitoring. 相似文献
84.
Christophe Bongars Peter Bougeard Adrian Bury Christopher J. Cooksey Michael D. Johnson Stewart Mitchell Paul A. Owens Famida Rajah 《Journal of organometallic chemistry》1985,289(1):163-171
5-Methylhex-5-enylcobaloxime reacts with carbon tetrachloride and with fluorotrichloromethane at 80–100°C to give substantially pure 1-methyl-1-(β,β,β-trichloroethyl)- and 1-methyl-1-β-fluoro-β,β-dichloroethyl)-cyclopentane. Hex-5-enylco-baloxime also gives trichloroethylcyclopentane from carbon tetrachloride, but the yield is dependent on the concentration of carbon tetrachloride. Similar cyclisation to give trichloroethyl- or fluorodichloroethyltetrahydrofuran is observed in the reactions of hex-3-oxo-5-enylcobaloxime with carbon tetrachloride and fluorotrichloromethane. However, no cyclisation was observed in the reactions of the ester, hex-2-one-3-oxo-5-enylcobaloxime, with carbon tetrachloride. These reactions are believed to take place by attack of a polyhalogenomethyl radical at the terminal unsaturated carbon of the organic ligand, followed either by an intramolecular homolytic displacement in which the carbon radical at position-5 attacks carbon-1 with displacement of cobaloxime(II), or by a halogen atom abstraction. 相似文献
85.
Cooper SM Laosripaiboon W Rahman AS Hothersall J El-Sayed AK Winfield C Crosby J Cox RJ Simpson TJ Thomas CM 《Chemistry & biology》2005,12(7):825-833
Mupirocin, a polyketide-derived antibiotic from Pseudomonas fluorescens NCIMB10586, is a mixture of pseudomonic acids (PA) that target isoleucyl-tRNA synthase. The mup gene cluster encodes both type I polyketide synthases and monofunctional enzymes that should play a role during the conversion of the product of the polyketide synthase into the active antibiotic (tailoring). By in-frame deletion analysis of selected tailoring open-reading frames we show that mupQ, mupS, mupT, and mupW are essential for mupirocin production, whereas mupO, mupU, mupV, and macpE are essential for production of PA-A but not PA-B. Therefore, PA-B is not simply produced by hydroxylation of PA-A but is either a precursor of PA-A or a shunt product. In the mupW mutant, a new metabolite lacking the tetrahydropyran ring is produced, implicating mupW in oxidation of the 16-methyl group. 相似文献
86.
Nicolai D. Knfel Hannah Rothfuss Pavleta Tzvetkova Bragavie Kulendran Christopher Barner-Kowollik Peter W. Roesky 《Chemical science》2020,11(38):10331
We introduce the formation and characterization of heterometallic single-chain nanoparticles entailing both catalytic and luminescent properties. A terpolymer containing two divergent ligand moieties, phosphines and phosphine oxides, is synthesized and intramolecularly folded into nanoparticles via a selective metal complexation of Pt(ii) and Eu(iii). The formation of heterometallic Eu(iii)/Pt(ii) nanoparticles is evidenced by size exclusion chromatography, multinuclear NMR (1H, 31P{1H}, 19F, 195Pt) as well as diffusion-ordered NMR and IR spectroscopy. Critically, we demonstrate the activity of the SCNPs as a homogeneous and luminescent catalytic system in the amination reaction of allyl alcohol.A bifunctional terpolymer containing two orthogonal ligand moieties was synthesized, giving way to the facile formation of heterometallic Eu(iii)/Pt(ii) single-chain nanoparticles, which display both catalytic and luminescent properties. 相似文献
87.
Wender PA Baryza JL Bennett CE Bi FC Brenner SE Clarke MO Horan JC Kan C Lacôte E Lippa B Nell PG Turner TM 《Journal of the American Chemical Society》2002,124(46):13648-13649
Macrocycle 1 is a new highly potent analogue of bryostatin 1, a promising anti-cancer agent currently in human clinical trials. In vitro, 1 displays picomolar affinity for PKC and exhibits over 100-fold greater potency than bryostatin 1 when tested against various human cancer cell lines. Macrocycle 1 can be generated in clinically required amounts by chemical synthesis in only 19 steps (LLS) and represents a new clinical lead for the treatment of cancer. 相似文献
88.
Hamilton BH Cardon TB Lorigan GA Ziegler CJ 《Dalton transactions (Cambridge, England : 2003)》2005,(17):2941-2944
Metal-organic frameworks based on the Pb[B(Im)(4)](+) unit form layered structures analogous to those observed in clays and double layered hydroxide minerals. These layers can act as scaffolds for the organization of anionic organic guests. In this report, we use this scaffold to assemble TEMPO and PROXYL carboxylates in the interlayer spacings of Pb[B(Im)(4)](4-carboxy-TEMPO) 1 and Pb[B(Im)(4)](3-carboxy-PROXYL)(H(2)O)2, respectively. The resultant materials are paramagnetic, and the organization of the radical units differs between the two compounds. This results in changes in electronic structure of the radical unit, as observed by EPR spectroscopy. 相似文献
89.
Pandey S Redden RA Hendricks AE Fletcher KA Palmer CP 《Journal of colloid and interface science》2003,262(2):579-587
Solubilization environment afforded by several of the novel allyl glycidyl ether-modified methylhydrosiloxane polymers are investigated using a common polycyclic aromatic hydrocarbon fluorescence probe, pyrene. The backbone of the polymer has been modified by the addition of an alkyl chain of varying length (either C8, C12, or C18) and to differing degrees of substitution. The nomenclature adopted for the purposes of these studies is as follows: "AGENT" represents the backbone polymer with no alkyl substitution, and "OAGENT", "DAGENT", and "SAGENT" are substituted with n-octyl, n-dodecyl, and n-octadecyl, respectively. The percentage of alkyl substitution is designated as 10, 15, and 20%. The pyrene polarity scale (defined as the ratio of the intensity of peak I to peak III) was used to determine the relative dipolarity of the cybotactic region provided by approximately 1 w/w% aqueous polymer solutions compared to 10 mM sodium dodecylsulfate (SDS) micellar solution. Results indicate that 10-15% DAGENT afforded the most hydrophobic solubilization site, followed by 15% OAGENT and 15% SAGENT. In addition, as the degree of alkyl substitution of DAGENT increased from 10 to 20%, the cybotactic region appeared to become more hydrophobic. Furthermore, a deeper investigation into the relative size of the solubilization site revealed that all alkyl-substituted polymers promoted excimer formation at relatively low pyrene concentrations, indicating the possibility of localized concentration enhancement within the solvation pockets and/or compartmentalization of the solute molecules. The pyrene fluorescence excitation data strongly indicates ground-state heterogeneity that is most prominent in AGENT and decreases as the alkyl chain length is increased. This provides a relative sense of the size and shape of the solvation pockets afforded by each polymer solution. An overall analysis of the collected data indicated that these alkyl-substituted polymers may provide a more selective and efficient pseudostationary phase in electrokinetic chromatography with better solvation capacity for hydrophobic compounds compared to SDS. 相似文献
90.
The type 1 copper sites of cupredoxins typically have a His(2)Cys equatorial ligand set with a weakly interacting axial Met, giving a distorted tetrahedral geometry. Natural variations to this coordination environment are known, and we have utilized paramagnetic (1)H NMR spectroscopy to study the active-site structure of umecyanin (UMC), a stellacyanin with an axial Gln ligand. The assigned spectra of the Cu(II) UMC and its Ni(II) derivative [Ni(II) UMC] demonstrate that this protein has the typical His(2)Cys equatorial coordination observed in other structurally characterized cupredoxins. The NMR spectrum of the Cu(II) protein does not exhibit any paramagnetically shifted resonances from the axial ligand, showing that this residue does not contribute to the singly occupied molecular orbital (SOMO) in Cu(II) UMC. The assigned paramagnetic (1)H NMR spectrum of Ni(II) UMC demonstrates that the axial Gln ligand coordinates in a monodentate fashion via its side-chain amide oxygen atom. The alkaline transition, a feature common to stellacyanins, influences all of the ligating residues but does not alter the coordination mode of the axial Gln ligand in UMC. The structural features which result in Cu(II) UMC possessing a classic type 1 site as compared to the perturbed type 1 center observed for other stellacyanins do not have a significant influence on the paramagnetic (1)H NMR spectra of the Cu(II) or Ni(II) proteins. 相似文献