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131.
[structure: see text] A chiral palladium catalyst [(S)-MeObiphep)Pd(NCAr)2(SbF6)2, (S)-4c], has been developed for a variety of asymmetric transformations. (S)-4c is bench-stable and has activity comparable to that of the nitrile free Lewis acid catalyst for Diels-Alder, hetero-Diels-Alder, and glyoxylate-ene reactions. 相似文献
132.
C.R. Sun W.M. Gibson I.J. Kim G.O. Williams M.A. Hasan A.S. Kanofsky R. Allen R.A. Carrigan B.L. Chrisman T.E. Toohig Z. Guzik T.S. Nigmanov E.N. Tsyganov A.S. Vodopianov A.B. Watson J. Kubic D.H. Stork 《Nuclear Physics B》1982,203(1):40-57
Channeling phenomena are observed for positive particles of momentum up to 250 GeV/c in a germanium crystal. The polar angular distributions of the channeled particles are compared with theoretical predictions based on a diffusion model. The results indicate that at high particle energy there may be additional mechanisms besides those operative at low energy leading to dechanneling of the particles. In spite of this, channeling effects are observed for particles incident at up to several times the critical angle, in contrast with the results from low energy channeling. Statistical equilibrium in the azimuthal angular distribution has also been observed at all measured beam momenta to about twice the calculated channeling critical angle. The breakdown of statistical equilibrium for the 2 cm crystal used occurs at an incident angle 2–3 times smaller than predicted theoretically. 相似文献
133.
Mirman D Holt LL McClelland JL 《The Journal of the Acoustical Society of America》2004,116(2):1198-1207
Different patterns of performance across vowels and consonants in tests of categorization and discrimination indicate that vowels tend to be perceived more continuously, or less categorically, than consonants. The present experiments examined whether analogous differences in perception would arise in nonspeech sounds that share critical transient acoustic cues of consonants and steady-state spectral cues of simplified synthetic vowels. Listeners were trained to categorize novel nonspeech sounds varying along a continuum defined by a steady-state cue, a rapidly-changing cue, or both cues. Listeners' categorization of stimuli varying on the rapidly changing cue showed a sharp category boundary and posttraining discrimination was well predicted from the assumption of categorical perception. Listeners more accurately discriminated but less accurately categorized steady-state nonspeech stimuli. When listeners categorized stimuli defined by both rapidly-changing and steady-state cues, discrimination performance was accurate and the categorization function exhibited a sharp boundary. These data are similar to those found in experiments with dynamic vowels, which are defined by both steady-state and rapidly-changing acoustic cues. A general account for the speech and nonspeech patterns is proposed based on the supposition that the perceptual trace of rapidly-changing sounds decays faster than the trace of steady-state sounds. 相似文献
134.
135.
Low-temperature wafer-scale production of ZnO nanowire arrays 总被引:17,自引:0,他引:17
Greene LE Law M Goldberger J Kim F Johnson JC Zhang Y Saykally RJ Yang P 《Angewandte Chemie (International ed. in English)》2003,42(26):3031-3034
136.
Malisza KL Gregorash L Turner A Foniok T Stroman PW Allman AA Summers R Wright A 《Magnetic resonance imaging》2003,21(5):489-496
We examined whether cerebral activation due to secondary hyperalgesia resulting from intrajoint capsaicin injection could be detected using functional magnetic resonance imaging (fMRI) in alpha-chloralose anesthetized rats. We also examined whether we could detect analgesic changes in the central nervous system response to pain as a result of physiotherapy joint manipulation. Robust activation of areas of the brain known to be associated with the processing of pain, namely the anterior cingulate (bilateral), frontal cortex (bilateral) and sensory motor cortex (contralateral), was found in all animals following injection of 25 microl of capsaicin (128 microg/ml in 7.5% DMSO) into the plantar surface of the rat hindpaw (n = 7) and 75 microL into the ankle joint (n = 13). Significantly greater activation was observed when capsaicin was injected into the plantar surface of the hindpaw compared to the ankle joint. Mechanical allodynia and secondary hyperalgesia following capsaicin injection into the ankle joint also resulted in activation of the same brain regions. Trends toward decreased areas of activation in brain regions associated with pain in animals following physiotherapy joint mobilization were observed. 相似文献
137.
Lori Manoukian José A. Correa Robin S. Stein Dominic Frigon Sidney Omelon 《Electrophoresis》2022,43(20):2014-2022
Inorganic polyphosphates (polyPs) have been identified in eukaryotic and prokaryotic cells alike. Various extraction methods have been optimized as a necessary step before identification and measurement of these polymers. Three commercially available sodium polyP glasses were either dissolved or dissolved and extracted by two commonly used polyP extraction techniques – perchloric acid or buffered phenol–chloroform. The products were separated by polyacrylamide gel electrophoresis (PAGE), stained with toluidine blue O, and the migration results quantitatively compared. Both extraction processes reduced the relative migration distances of the peak and leading edges, and the stained band lengths, suggesting reduced polyP migration and dispersion. 31P diffusion-ordered spectroscopy nuclear magnetic resonance confirmed that polyP extraction by perchloric acid or phenol–chloroform processes reduced polyP diffusion coefficients and suggested hydrolytic degradation with stronger end-chain signals. Reduced polyP diffusivity after extraction makes possible an overestimation of synthetic polyP chain length assignment when compared to unextracted polyP ladders with PAGE. The mechanism(s) for reduced synthetic polyP diffusion after extraction and intracellular chemical environment effects on migration are not known. 相似文献
138.
Leibold et al.[J. Acoust. Soc. Am. 121, 2822-2831 (2007)] examined the perceptual weight subjects assigned to individual components of a multitone complex while performing a loudness-matching task. Weights agreed with the Moore et al. loudness model [J. Audio Eng. Soc. 45, 224-237 (1997)], except when components were widely spaced in frequency. In an effort to account for the data, the just-noticeable-difference (jnd) for intensity discrimination was measured for each component and compared to the weight for that component. The model predicts greater improvement in intensity discrimination with increasing bandwidth than was observed in the data. jnds were not correlated with weights in the widest frequency-spacing condition. 相似文献
139.
Karbiwnyk CM Carr LE Turnipseed SB Andersen WC Miller KE 《Analytica chimica acta》2007,596(2):257-263
The quinolones, oxolinic acid (OXO), flumequine (FLU), and nalidixic acid (NAL), are antibacterial drugs effective against Gram-negative bacteria. Quinolones are used in both human and veterinary medicine, but are currently not approved by the U.S. Food and Drug Administration for use in food fish. A liquid chromatography-fluorescence (LC-FL) method was developed to determine OXO, FLU, and NAL residues in shrimp. An additional liquid chromatography-mass spectrometry (LC-MSn) method was created to confirm these residues using the same sample extract. Samples were prepared with a simple ethyl acetate extraction followed by solvent exchange into 0.2% formic acid and cleaned-up with hexane. Reverse phase chromatography was used to separate the three compounds in both procedures. For the LC-FL determinative method, fluorescence emission was monitored at 369 nm with excitation at 327 nm. With electrospray ionization, the three most abundant ions from the MS3 product ion spectrum were used to identify OXO, FLU, and NAL in the confirmation procedure. Shrimp samples fortified at levels ranging from 7.5 to 100 ng g−1 were used to validate both methods. 相似文献
140.
A series of four complete factorial experiments were performed to determine the major parameters affecting the trapping efficiencies of fat-soluble vitamins after supercritical fluid extraction. The parameters varied were the collection solvent, extraction flow rate, collection temperature, restrictor temperature, and collection pressurization. The identity of the collection solvent was found to have the most profound effect. The viscosity and surface tension of the collection solvent appeared to have great significance. 相似文献