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61.
62.
Huiyu Bai Yufei Li Wei Wang Guangliang Chen Orlando J. Rojas Weifu Dong Xiaoya Liu 《Cellulose (London, England)》2015,22(6):3877-3894
63.
64.
Majors J. Badgett Barry Boyes Ron Orlando 《Journal of the American Society for Mass Spectrometry》2017,28(5):818-826
Peptides with deamidated asparagine residues and oxidized methionine residues are often not resolved sufficiently to allow quantitation of their native and modified forms using reversed phase (RP) chromatography. The accurate quantitation of these modifications is vital in protein biotherapeutic analysis because they can affect a protein’s function, activity, and stability. We demonstrate here that hydrophilic interaction liquid chromatography (HILIC) adequately and predictably separates peptides with these modifications from their native counterparts. Furthermore, coefficients describing the extent of the hydrophilicity of these modifications have been derived and were incorporated into a previously made peptide retention prediction model that is capable of predicting the retention times of peptides with and without these modifications. 相似文献
65.
Alexey Khakalo Alexey Vishtal Elias Retulainen Ilari Filpponen Orlando J. Rojas 《Cellulose (London, England)》2017,24(1):191-205
The beneficial effect of materials with high aspect ratio as composite reinforcement has prompted continuous interest towards cellulosic fibers. Besides providing stiffness, fibers can potentially contribute to composite extensibility. While mechanical treatments are typically used to adjust the physical and surface properties of fibers, less is known about ensuing effects on their extensibility and that of associated networks. Fiber network dimensional extensibility of 16% was achieved by processing the precursor aqueous fiber dispersions following a simple mechanical treatment with a judicious combination of low (PFI refining) and high concentrations and temperatures (Wing defibrator). Consequently, deformation of fibers and increased inter-fiber bonding resulted in a three-fold increase in strength to rupture of the fiber network leading to the structures with unprecedented toughness. 相似文献
66.
Liu X Vesterinen AH Genzer J Seppälä JV Rojas OJ 《Langmuir : the ACS journal of surfaces and colloids》2011,27(16):9769-9780
We study the adsorption of a symmetric triblock copolymer of ethylene oxide, EO, and propylene oxide, PO, end-capped with quarternized poly(2-dimethylaminoethyl methacrylate), DMAEMA (DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24)). Light scattering and tensiometry are used to measure the relative size of the associated structures and surface excess at the air-liquid interface. The adsorbed amount, the amount of coupled water, and the viscoelasticity of the adsorbed polymer layer are measured on hydrophobic and hydrophilic surfaces (polypropylene, cellulose, and silica) by using quartz crystal microgravimetry (QCM) and surface plasmon resonance (SPR) at different ionic strengths and temperatures. The results of the experiments are compared with those obtained after adsorption of the uncharged precursor copolymer, without the cationic end-caps (EO(132)PO(50)EO(132)). DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) possesses higher affinity with the negatively charged silica and cellulose surfaces while the uncharged copolymer adsorbs to a larger extent on polypropylene surfaces. In this latter case, adsorption increases with increasing solution ionic strength and temperature. Adsorption of EO(132)PO(50)EO(132) on silica surfaces has little effect on the water contact angle (WCA), while adsorption of DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) increases the WCA of silica to 32°, indicating a large density of exposed PPO blocks upon adsorption. After adsorption of EO(132)PO(50)EO(132) and DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) on PP, the WCA is reduced by ≈14° and ≈28°, respectively, due to the exposed hydrophilic EO and highly water-soluble DMAEMA segments on the surfaces. The extent of surface coverage at saturation at the polypropylene/liquid interfaces (≈31 and 40 nm(2)/molecule obtained by QCM and SPR, respectively) is much lower, as expected, when compared with results obtained at the air/liquid interface, where a tighter packing is observed. The percentage of water coupled to the adsorbed cationic polymer decreases with solution ionic strength. Overall, these observations are ascribed to the effects of electrostatic screening, polymer hydrodynamic size, and solvency. 相似文献
67.
Olanrewaju BO Herring-Captain J Grieves GA Aleksandrov A Orlando TM 《The journal of physical chemistry. A》2011,115(23):5936-5942
The interaction and autoionization of HCl on low-temperature (80-140 K) water ice surfaces has been studied using low-energy (5-250 eV) electron-stimulated desorption (ESD) and temperature programmed desorption (TPD). There is a reduction of H(+) and H(2)(+) and a concomitant increase in H(+)(H(2)O)(n=1-7) ESD yields due to the presence of submonolayer quantities of HCl. These changes are consistent with HCl induced reduction of dangling bonds required for H(+) and H(2)(+) ESD and increased hole localization necessary for H(+)(H(2)O)(n=1-7) ESD. For low coverages, this can involve nonactivated autoionization of HCl, even at temperatures as low as 80 K; well below those typical of polar stratospheric cloud particles. The uptake and autoionization of HCl is supported by TPD studies which show that for HCl doses ≤0.5 ± 0.2 ML (ML = monolayer) at 110 K, desorption of HCl begins at 115 K and peaks at 180 K. The former is associated with adsorption of a small amount of molecular HCl and is strongly dependent on the annealing history of the ice. The latter peak at 180 K is commensurate with desorption of HCl via recombinative desorption of solvated separated ion pairs. The activation energy for second-order desorption of HCl initially in the ionized state is 43 ± 2 kJ/mol. This is close to the zero-order activation energy for ice desorption. 相似文献
68.
Djenaine De Souza Lucia Helena Mascaro Orlando Fatibello-Filho 《Journal of Solid State Electrochemistry》2011,15(9):2023-2029
The main purpose of this work was to evaluate the effect of the silver to mercury ratio on the voltammetric responses of silver
solid amalgam electrodes (AgSAE’s). For this, the AgSAE were prepared by mechanical mixing the metals in the following mass
ratios of silver to mercury: 30/70, 40/60, 50/50, 60/40, and 70/30. The resulting AgSAE’s were physically characterized by
energy dispersive X-ray analysis, X-ray diffraction and scanning electron microscopy, confirming the mass percentages of the
silver and mercury, the total absence of liquid mercury and a globular structure of all AgSAE’s. Furthermore, it was observed
that the AgSAE 30/70 contained only one single phase (Ag2Hg3), and no metallic silver or mercury oxides. Additionally, the resulting AgSAE’s were chemically characterized with respect
to the influence of the electrode composition on the reproducibility and electrochemical signals of a hexamine-ruthenium (III)
chloride solution by use of electrochemical impedance spectroscopy and cyclic voltammetry. The separation between anodic and
cathodic peaks, and consequently, the charge transfer resistance across the electrode/solution interface, and the electroactive
area were calculated demonstrating that the 30/70 composition is the best surface for practical applications. Finally, square-wave
voltammetry experiments were performed in 4-nitrophenol solution, with a previous optimization of the experimental and voltammetric
parameters. The calculated detection limit shows that the AgSAE 30/70 is suitable for determining any contamination by p-nitrophenol, minimizing the toxic residues in case of using liquid mercury electrodes. 相似文献
69.
The strict application of IUPAC rules for the numbering of tropane alkaloids is not always applied by authors and there is hence a lot of confusion in the literature. In most cases, the notation of 3, 6/7-disubstituted derivatives has been chosen arbitrarily, based on NMR and MS data, without taking into account the absolute configuration of these two carbons. This paper discusses the problem and the relevance of CD and NMR to determine molecular configurations. We report on the use of (1)H-NMR anisochrony (Δδ) induced by the Mosher's chiral auxiliary reagents (R)-(-)- and (S)-(+)-α-methoxy-α-trifluoromethyl-phenylacetyl chlorides (MTPA-Cl), to determine the absolute configuration of (3R,6R)-3α-hydroxy-6β-senecioyloxytropane, a disubstituted tropane alkaloid isolated from the aerial parts of Schizanthus grahamii (Solanaceae). These analytical tools should help future works in correctly assigning the configuration of additional 3, 6/7 disubstituted tropane derivatives. 相似文献
70.
Journal of Nonlinear Science - We study the existence of quasistatic evolutions for a family of gradient damage models which take into account fatigue, that is the process of weakening in a... 相似文献