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991.
992.
993.
Kwang-Hyeon Liu Yun-Kyeong Lee Ji-Young Ryu Dong-Jun Lee Wonku Kang Sang Seop Lee Young-Ran Yoon Jae-Gook Shin 《Chromatographia》2004,60(11-12):639-643
A rapid and sensitive method to assay torasemide in plasma was developed using a simple liquid-liquid extraction technique followed by high-performance liquid chromatography. Torasemide and the internal standard furosemide were extracted from 0.5 mL of plasma using ethyl acetate in the presence of 0.1M HCl. The analysis of the extracts was performed on a monolithic silica column with ultraviolet spectrophotometric detection. The calibration curve was linear over the concentration range of 0.05-5 μg mL?1 in plasma. Recoveries were reasonable for routine analyses (>80%); the limit of quantification was 0.05 μg mL?1 with a signal-to-noise ratio of 5. The coefficient of variation of the assay precision was less than 6.1%, and the accuracy exceeded 98%. This method was used to measure the torasemide concentration in plasma from healthy subjects after a single 20-mg oral dose of torasemide. This method provides a very simple, sensitive, and accurate way to determine torasemide concentrations in plasma. 相似文献
994.
995.
This work examines polyelectrolyte adsorption (exclusively driven by electrostatic attractions) for a model system (DMAEMA, polydimethylaminoethyl methacrylate, adsorbing onto silica) where the adsorbing polycation is more densely charged than the substrate. Variations in the relative charge densities of the polymer and substrate are accomplished by pH, and the polycation is of sufficiently low molecular weight that the adsorbed conformation is generally flat under all conditions examined. We demonstrate, quantitatively, that the charge overcompensation observed on the isotherm plateau can be attributed to the denser positive charge on the adsorbing polycation and that the ultimate coverage obtained corresponds to the adsorption of one oligomer onto each original negative silica charge, when the silica charge is most sparse, at pH 6. This limiting behavior breaks down at higher pHs where the greater silica charge density accommodates single chains adsorbing onto multiple negative sites. As a result of the greater substrate charge density and reduced polycation charge at higher pHs, the extent of charge overcompensation diminishes while the coverage increases on the plateau of the isotherm. Ultimately at the highest pHs, a regime is approached where the coil's excluded surface area, not surface charge, limits the ultimate coverage. In addition to quantifying the crossover from the charge-limiting to the area-limiting behaviors, this paper quantitatively reports adsorption-induced changes in bound counterion density and ionization at the interface, which were generally found to be independent of coverage for this model system. 相似文献
996.
Ho-Sang Shin 《Chromatographia》2006,63(11-12):579-583
A gas chromatography-mass spectrometric GC-MS method has been developed for the determination of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in frog and fish tissues. After homogenization and sonication of 5 g samples, purification was achieved by a liquid phase extraction procedure using methyl-tert-butyl ether. The extract was reacted for 30 min at 80 °C with 10 % H2SO4 in methanol to form the corresponding methyl esters, which were simultaneously extracted with petroleum ether, and analysed by GC-MS in selected ion monitoring mode. Detection limits were 1.0 and 0.5 μg. kg?1 for 2,4-D and 2,4,5-T respectively in tissue samples and the calibration curves showed good linearity (r ≥ 0.999). Twenty-five frog samples and forty-six fish samples from various regions in Korea were analyzed. 2,4,5-T was detected up to a maximum concentration of 16.2 μg kg?1 in frogs and fish. The developed method may be valuable for the national monitoring project of endocrine disruptors (EDs) in biota. 相似文献
997.
Nam-Suk Lee Hoon-Kyu Shin Young-Soo Kwon 《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,290(1-3):77-81
Recently, research on conducting molecules containing thiol functional groups such as benzenethiol has been progressing [X. Xiao, B. Xu, N.J. Tao, Nano Lett. 4 (2004) 267]. This conducting molecule is applicable to the study of the negative differential resistance (NDR) and switching properties of logic device. The 4-{4[4-(4-{1-[4-(4-acetylsulfanyl-phenylethynyl)-phenyl]-2,6-diphenyl-pyridinium-4-yl}-phenyl)-2,6-diphenyl-pyridinium-1-yl]-phenylethynyl}-phenylthioacetate (dipyridinium) molecule contains thiol functional groups such as benzenethiol. Thus, we have studied an NDR property of a dipyridinium molecule using the self-assembly method in scanning tunneling microscopy (STM). The Au substrate was exposed to a 1 mM solution of 1-dodecanethiol in ethanol for 24 h to form a monolayer. After thorough rinsing of the sample, it was exposed to a 0.1 μM solution of dipyridinium in dimethylformamide (DMF) for 30 min. After the assembly, we measured the electrical properties of the self-assembly monolayers (SAMs) using ultra high vacuum scanning tunneling microscopy (UHV-STM) and scanning tunneling spectroscopy (STS). As a result, we confirmed the properties of NDR in a negative region at −1.67 V and a positive region at 1.78 V. The energy gap (Eg) was found to be 3.12 eV [C. Arena, B. Kleinsorge, J. Robertson, W.I. Milne, M.E. Welland, J. Appl. Phys. 85 (1999) 1609]. This molecule is applicable to the fabrication of molecular junctions. 相似文献
998.
The observation that ascorbate known to retain pro-oxidant properties induces cell death in a number of immortal cell lines, led us to examine its mechanism and whether it is involved in oxidative stress injury in such asocorbate-enriched tissue cells as hepatocytes. In rat liver homogenates, higher concentrations (1 and 3 mM) of ascorbate suppressed lipid peroxide productions but lower concentrations (0.1 and 0.3 mM) did not. In contrast to the homogenate, ascorbate increased lipid peroxide production in liver slices in a concentration dependant manner. Iso-ascorbate, the epimer of ascorbate did not cause an increase the oxidative stress in liver slices. This differential effect between homogenates and liver slices implies that cellular integrity is required for ascorbate to induce oxidative stress. Wortmannin, an inhibitor of the GLUT (glucose transporter) thought to transport dehydroascorbate into cells, inhibited [(14)C]-ascorbate uptake and suppressed oxidative stress in liver slices. Wortmannin suppressed that [(14)C]-ascorbate uptake by GLUT following oxidation to [(14)C]dehydroascorbate. Taken together, these observations support our hypothesis that ascorbate is oxidized to dehydroascorbate by molecular oxygen in solution (i.e., plasma and culture medium) which is then carried into hepatocytes (via a GLUT) where it is reduced back to ascorbate causing oxidative stress. 相似文献
999.
A general method for the asymmetric synthesis of α-substituted β-amino secondary alcohols is described, which comprises the four-reaction sequence (1) the proline-mediated, asymmetric, three-component Mannich reaction of two different aldehydes, (2) nucleophilic carbon addition to aldehyde, (3) oxidation of the resulting alcohol to the corresponding ketone, and (4) diastereoselective reduction with LiAlH(O-t-Bu)3 or catecholborane. The former reductant afforded the 1,2-syn isomer, while the latter gave the 1,2-anti isomer stereoselectively. The present method was successfully applied to the efficient asymmetric synthesis of the N-terminal amino acid moiety of nikkomycin B and BX. 相似文献
1000.
Fujio Mizukami Yoshimichi Kiyozumi Tsuneji Sano Shu-ich Niwa Makoto Toba Shigemitsu Shin 《Journal of Sol-Gel Science and Technology》1998,13(1-3):1027-1031
Amorphous alumina-silicas were prepared from a tetra-alkoxysilane and anhydrous aluminum trichloride or an aluminum alkoxide by a sol-gel process using 2-methyl-2,4-pentanediol, pinacol, 1,2-propanediol, 2,3-butanediol or ethylene glycol as the solvent or complexing agent, and the effect of diols and alkoxy groups on the physical and chemical properties of the alumina-silicas was examined. When the diol or the alkoxy group was bulky, the alumina-silicas had relatively larger micropores, a larger pore volume and higher surface areas. In the conversion of methanol catalyzed by the alumina-silicas, the bulkier diols and alkoxides gave catalysts that produced dimethyl ether in higher yield and hydrocarbons in lower yield. Thus, when ethylene glycol was used as the diol, the best catalyst for the production of hydrocarbons, especially the production of olefins such as ethylene, propylene and butene, was obtained. Furthermore, in comparison with alumina-silica prepared by a traditional kneading process, it was found that the sol-gel alumina-silica could efficiently convert methanol to dimethyl ether and hydrocarbons, but the material prepared by kneading had a very low conversion of methanol to other compounds. 相似文献