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771.
Bjørsvik HR Gambarotti C Jensen VR González RR 《The Journal of organic chemistry》2005,70(8):3218-3224
A novel deoxygenation process for N-heteroarene N-oxides is described. The deoxygenation process has been carried out by utilizing some short C-chain alcohols, benzyl alcohol, or 1-phenylethanol as the solvent in the presence of a base, such as sodium alkoxide or sodium hydroxide. A series of N-heteroarene N-oxides was submitted to the developed conditions to provide the corresponding N-heteroarenes with high yield and excellent selectivity. When the deoxygenation is carried out with benzyl alcohol or 1-phenylethanol as the reaction medium, the process can be performed under very mild conditions, at only 30 degrees C. The deoxygenation process is in contrast to several other methods performed without the presence of any transition metal as a catalyst or stoichiometric reagent. DFT calculations suggest that the alkoxide performs a nucleophilic attack on the N-heteroarene in the ortho or para position. This bond is cleaved homolytically with the overall result being that a single electron-transfer step has occurred. The products of this process are an N-heteroarene N-oxide radical anion and an alkoxyl or benzyloxy radical, depending on the solvent that has been used. Successive steps of the mechanism result in an oxygen transfer from the N-oxide to give the deoxygenated N-heteroarene and 1 equiv of the aldehyde, which is the oxidation product of the solvent alcohol. 相似文献
772.
We have studied the generation of arsenic hydride on a fly ash slurry from a thermal power plant burning lignite. The conditions for the formation of the slurry were optimized and the influence of the presence of various surfactants on the formation and stability of slurry (particle size-analytical signal ratio) were investigated.The As content in the ash was 78.7 g/g, with an rsd of 5.6% and a detection limit of 2.8 ng. The proposed method was successfully applied to the determination of arsenic in a certified ash sample (BCR-38). This method was applied to fly ash from a thermal power plant burning anthracite. 相似文献
773.
Raquel Casado Iñigo Uriarte Rita Yolanda Cavero Maria Isabel Calvo 《Chromatographia》2008,67(7-8):665-667
A reversed-phase column liquid chromatographic method for the separation and quantification of mescaline present in “peyote”
has been developed using a Symmetry C18 column and isocratic profile. The method can be utilised for the quantitative determination of other alkaloids. This method
is economical in terms of the time taken and the amount of solvent used for each analysis. The validity of the method with
respect to analysis was confirmed by comparing the UV spectra of peak with the reference compound (mescaline) using a photodiode
array detector. The assay method described is simple, rapid and accurate, and may form part of future drug authentication
protocols. 相似文献
774.
775.
Eder J. Lenardão Elton L. Borges Samuel R. Mendes Gelson Perin Raquel G. Jacob 《Tetrahedron letters》2008,49(12):1919-1921
Acidic ionic liquid butyl ethyl phenyl selenonium tetrafluoroborate, [BEPSe]BF4, was successfully employed as a catalyst for the synthesis of several dithioacetals in the absence of a solvent. The method is general and selectively afforded thioacetals derived from aldehydes and ketones in good yields. 相似文献
776.
777.
Marisa Fernández Stefan Ivanov Luis Ugarte Raquel Villacampa 《Communications in Mathematical Physics》2009,288(2):677-697
We construct new explicit compact supersymmetric valid solutions with non-zero field strength, non-flat instanton and constant
dilaton to the heterotic equations of motion in dimension six. We present balanced Hermitian structures on compact nilmanifolds
in dimension six satisfying the heterotic supersymmetry equations with non-zero flux, non-flat instanton and constant dilaton
which obey the three-form Bianchi identity with curvature term taken with respect to either the Levi-Civita, the (+)-connection
or the Chern connection. Among them, all our solutions with respect to the (+)-connection on the compact nilmanifold M
3 satisfy the heterotic equations of motion. 相似文献
778.
Silva Rosineide G. Cruz Antonio J. G. Hokka Carlos O. Giordano Raquel L. C. Giordano Roberto C. 《Applied biochemistry and biotechnology》2001,91(1-9):341-352
One serious difficulty in modeling a fermentative process is the forecasting of the duration of the lag phase. The usual approach
to model biochemical reactors relies on first-principles, unstructured mathematical models. These models are not able to take
into account changes in the process response caused by different incubation times or by repeated fed batches. Toover come
this problem, we have proposed a hybrid neural network algorithm. Feedforward neural networks were used to estimate rates
of cell growth, substrate consumption, and product formation from on-line measurements during cephalosporin C production.
These rates were included in the mass balance equations to estimate key process variables: concentrations of cells, substrate,
and product. Data from fed-batch fermentation runs in a stirred aerated bioreactor employing the microorganism Cephalosporium acremonium ATCC 48272 were used. On-line measurements strongly related to the mass and activity of the cells used. They include carbon
dioxide and oxygen concentrations in the exhausted gas. Good results were obtained using this approach. 相似文献
779.
Adriana García Forero Diego Armando Villamizar Mantilla Luis A. Núez Raquel Elvira Ocazionez Elena E. Stashenko Jorge Luis Fuentes 《Photochemistry and photobiology》2019,95(4):1010-1018
This work evaluated the photoprotective and antigenotoxic effects against ultraviolet B (UVB) radiation of flavonoid compounds apigenin, naringenin and pinocembrin. The photoprotective efficacy of these compounds was estimated using in vitro photoprotection indices, and the antigenotoxicity against UVB radiation was evaluated using the SOS chromotest and an enzymatic (proteinase K/T4 endonuclease V enzyme) comet assay in UV‐treated Escherichia coli and human (HEK‐293) cells, respectively. Naringenin and pinocembrin showed maximum UV‐absorption peak in UVC and UVB zones, while apigenin showed UV‐absorption capability from UVC to UVA range. These compounds acted as UV filters reducing UV‐induced genotoxicity, both in bacteria and in human cells. The enzymatic comet assay resulted highly sensitive for detection of UVB‐induced DNA damage in HEK‐293 cells. In this work, the photoprotective potential of these flavonoids was widely discussed. 相似文献
780.
Raquel G. Rocha Jssica S. Stefano Iana V. S. Arantes Michelle M. A. C. Ribeiro Mario H. P. Santana Eduardo M. Richter Rodrigo A. A. Munoz 《Electroanalysis》2019,31(1):153-159
Levamisole is the most common adulterant found in cocaine samples and its electrochemical determination in cocaine seized samples is a challenge due to peak overlapping with cocaine. Herein, we propose a deconvolution procedure for levamisole determination in seized cocaine samples using screen‐printed carbon electrodes (SPE). Square‐wave voltammetry in 0.04 mol L?1 Britton Robinson buffered solution (pH 8.0) was selected in combination with optimized SWV parameters (f=8 s?1, a=10 mV and ΔEs=1 mV) to result in the best peak resolution to apply the deconvolution procedure. Deconvoluted responses of levamisole in the presence of cocaine were similar to untreated signals of standard levamisole solutions in absence of cocaine. A linear response was obtained in the range of 20–100 μmol L?1 (r=0.995). The results obtained for the analysis of a seized cocaine sample was statistically similar to that obtained by gas chromatography. Other adulterants found in cocaine street samples (paracetamol, glucose, phenacetin, caffeine, boric acid and lidocaine) did not affect the treated of voltammetric responses of levamisole. A pharmaceutical sample containing levamisole was also analyzed on SPEs and a recovery of 93±2 % was obtained (no deconvolution required for this sample), showing great applicability of SPEs for forensic and pharmaceutical analyses. 相似文献