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101.
Benavente F Vescina MC Hernández E Sanz-Nebot V Barbosa J Guzman NA 《Journal of chromatography. A》2007,1140(1-2):205-212
The use of solid-phase extraction coupled on-line to capillary electrophoresis using electrospray mass spectrometry detection (SPE-CE-ESI-MS) is described for the analysis of peptides in dilute solutions. A SPE microcartridge or analyte concentrator containing C(18) derivatized silica particles as the extraction sorbent was easily constructed near the inlet of the separation capillary using commercially available materials. The reversed-phase sorbent selectively retained the target peptides, enabling large volumes of the sample to be introduced (>100muL). The captured analytes were eluted in a small volume of an appropriate solution (20-50nL). This resulted in sample clean-up and concentration enhancement, with minimum sample handling. As the SPE-CE conditions were compatible with on-line ESI-MS detection, the potential for identifying and characterizing the preconcentrated analytes by SPE-CE-ESI-MS using a sheath-flow CE-ESI-MS interface is also shown. Using separation electrolytes containing N-[carbamoylmethyl]-2-aminoethanesulfonic acid (ACES) at pH 7.4, an elution plug of 80:20 (v/v) (25mM of formic acid in MeCN):H(2)O and a sheath liquid of 20mM of acetic acid in 50:50 (v/v) methanol:H(2)O the concentration limits of detection for the analyzed peptides in the positive ion mode were lowered to nanogram per milliliter levels. The systematic optimization of the operational parameters involved in the development of the SPE-CE method is described in detail, in order to promote robust and quantitative SPE-CE-ESI-MS analysis and facilitate the widespread use of the technique. 相似文献
102.
In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed. 相似文献
103.
The geometrical picture of gauge theories must be enlarged when a gauge potentialceases to behave like a connection, as it does in electroweak interactions. Whenthe gauge group has dimension four, the vector space isomorphism betweenspacetime and the gauge algebra is realized by a tetrad-like field. The objectmeasuring the deviation from a strict bundle structure has the formal behaviorof a spacetime connection, of which the deformed gauge field strength is thetorsion. A generalized derivative emerges in terms of which the two Bianchiidentities are formally recovered. Effects of gravitational type turn up. Thedynamical equations obtained correspond to a broken gauge model on acurved spacetime. 相似文献
104.
Joo Henrique Zimnoch Dos Santos Marcelo Barbosa Da Rosa Cristiano Krug Fernanda Chiarello Stedile Monica Carcuchinski Haag Jairton Dupont Madalena De Camargo Forte 《Journal of polymer science. Part A, Polymer chemistry》1999,37(13):1987-1996
The effects of polymerization conditions were evaluated on the production of polyethylene by silica-supported (n-BuCp)2ZrCl2 grafted under optimized conditions and cocatalyzed by methylaluminoxane (MAO). The Al : Zr molar ratio, reaction temperature, monomer pressure, and the age and concentration of the catalyst were systematically varied. Most reactions were performed in toluene. Hexane, with the addition of triisobutilaluminum (TIBA) to MAO, was also tested as a polymerization solvent for both homogeneous and heterogeneous catalyst systems. Polymerization reactions in hexane showed their highest activities with MAO : TIBA ratios of 3 : 1 and 1 : 1 for the homogeneous and supported systems, respectively. Catalyst activity increased continuously as Al : Zr molar ratios increased from 0 to 2000, and remained constant up to 5000. The highest activity was observed at 333 K. High monomer pressures (≈ 4 atm) appeared to stabilize active species during polymerization, producing polyethylenes with high molecular weight (≈ 3 × 105 g mol−1). Catalyst concentration had no significant effect on polymerization activity or polymer properties. Catalyst aging under inert atmosphere was evaluated over 6 months; a pronounced reduction in catalyst activity [from 20 to 13 × 105 g PE (mol Zr h)−1] was observed only after the first two days following preparation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1987–1996, 1999 相似文献
105.
JürgenF.K. Müller Margareta Zehnder Frdrique Barbosa Bernhard Spingler 《Helvetica chimica acta》1999,82(9):1486-1501
The theoretical structure of a cyclic phosphoric triamide 3 and of its monolithiated isomers 4 – 6 was calculated by ab initio methods (Fig. 1, Tables 1 and 2). The global minimum in 4 consists of a five-membered Li−C−N−P−O chelate. The intermediates 5 and 6 are, relative to 4 , energetically unfavorable by 15 and 18 kcal mol−1, respectively, due to distortion in order to accommodate the N-complexation of the Li+ ions. NMR Investigations (1H, 13C, 31P, and 7Li) of the lithiated bicyclic phosphoric triamide 1 were performed (Tables 3 – 5). The lithium aminomethanide 2 is characterized by a sp3-hybridized anion supporting Li−C contacts. The anions exist in a monomer-dimer equilibrium in solution (Scheme 2). Trapping reactions of rac- 2 with carbonyl compounds generated the corresponding amino-alcohol derivatives with high diastereoselectivities (Scheme 3, Table 6). A rational for the stereochemical outcome is given (Fig. 4). In the presence of LiBr, a P−N bond cleavage occurred on reaction of rac- 2 with aldehydes, which allowed the synthesis of (1-hydroxylalkyl)phosphonic diamides (Scheme 5, Table 7). 相似文献
106.
Anatomical information on most lichen species, including Parmeliaceae species, is scarce and superficial. This is partially due to the technical difficulties found during the preparation of samples and sections suitable for optical microscopy analysis. There is a lack of pictures of anatomical sections as well as detailed anatomical protocols related to the sample processing made by specialized plant anatomists in literature. This work aimed to look for a standardized histological technique and to develop a protocol for histological studies of foliose Parmeliaceae under light microscopy. Four common pantropical species of Parmeliaceae, abundant in the Brazilian cerrado vegetation, were processed in several ways in relation to fixing and inclusion media, sectioning thicknesses, and staining, including both fresh and 2-year-old herbarium specimens. The best technique found for anatomical studies of Parmeliaceae under light microscopy is represented by 2 or 3 microm thick sections of fresh or herbarium samples, desiccated and fixed in FAA 50, infiltrated and embedded in glycol-methacrylate resin (Leica), and stained by Toluidine Blue or Methylene Blue. 相似文献
107.
Marjorie C. L. C. Freire Gabriela D. Noske Natlia V. Bitencourt Paulo R. S. Sanches Norival A. Santos-Filho Victor O. Gawriljuk Eduardo P. de Souza Victor H. R. Nogueira Mariana O. de Godoy Aline M. Nakamura Rafaela S. Fernandes Andre S. Godoy Maria A. Juliano Bianca M. Peres Cecília G. Barbosa Carolina B. Moraes Lucio H. G. Freitas-Junior Eduardo M. Cilli Rafael V. C. Guido Glaucius Oliva 《Molecules (Basel, Switzerland)》2021,26(16)
The COVID-19 outbreak has rapidly spread on a global scale, affecting the economy and public health systems throughout the world. In recent years, peptide-based therapeutics have been widely studied and developed to treat infectious diseases, including viral infections. Herein, the antiviral effects of the lysine linked dimer des-Cys11, Lys12,Lys13-(pBthTX-I)2K ((pBthTX-I)2K)) and derivatives against SARS-CoV-2 are reported. The lead peptide (pBthTX-I)2K and derivatives showed attractive inhibitory activities against SARS-CoV-2 (EC50 = 28–65 µM) and mostly low cytotoxic effect (CC50 > 100 µM). To shed light on the mechanism of action underlying the peptides’ antiviral activity, the Main Protease (Mpro) and Papain-Like protease (PLpro) inhibitory activities of the peptides were assessed. The synthetic peptides showed PLpro inhibition potencies (IC50s = 1.0–3.5 µM) and binding affinities (Kd = 0.9–7 µM) at the low micromolar range but poor inhibitory activity against Mpro (IC50 > 10 µM). The modeled binding mode of a representative peptide of the series indicated that the compound blocked the entry of the PLpro substrate toward the protease catalytic cleft. Our findings indicated that non-toxic dimeric peptides derived from the Bothropstoxin-I have attractive cellular and enzymatic inhibitory activities, thereby suggesting that they are promising prototypes for the discovery and development of new drugs against SARS-CoV-2 infection. 相似文献
108.
R.R. Teixeira L.C.A. Barbosa J.W.de M. Carneiro J. Ellena 《Journal of Molecular Structure》2009,917(1):1-9
The synthesis and structural analysis of a set of nostoclide analogues with potential herbicide activity is described. The influence of intra- and intermolecular hydrogen bonding, as well as other interactions on the conformation and packing of the compounds is thoroughly described using DFT calculations and single crystal X-ray diffraction analyses. All lactones exhibited the Z configuration as confirmed by NOESY experiments and by single crystal X-ray diffraction measurements. 相似文献
109.
110.
Phabyanno Rodrigues Lima Paulo Rogério Barbosa de Miranda Adriano Bof de Oliveira Marília Oliveira Fonseca Goulart Lauro Tatsuo Kubota 《Electroanalysis》2009,21(21):2311-2320
The present work explores, for the first time, the electrocatalytic oxidation of ascorbic acid (AscH2) and its determination in the presence of uric acid (UA) on the in situ activated 4‐nitrophthalonitrile modified carbon paste electrode. The kinetic constant κ for the catalytic reaction for the electrocatalytic oxidation of ascorbic acid, evaluated by cyclic voltammetry, chronoamperometry and RDE voltammetry provided values around 106 L mol?1 s?1. The sensor provided a linear response range for AscH2 and UA from 5.0 up to 120.0 μmol L?1 with detection limits of 1.6 μmol L?1and 1.3 μmol L?1, respectively. The sensor was applied for the simultaneous determination of AscH2 and UA in urine samples and the average recoveries for these samples were 99.8 (±3.1)% and 99.9 (±2.1)%, respectively . 相似文献