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741.
B.G. Manjunath Melanie Frick Rolf-Dieter Reiss 《Journal of multivariate analysis》2012,103(1):107-115
Classical discriminant analysis focusses on Gaussian and nonparametric models where in the second case the unknown densities are replaced by kernel densities based on the training sample. In the present article we assume that it suffices to base the classification on exceedances above higher thresholds, which can be interpreted as observations in a conditional framework. Therefore, the statistical modeling of truncated distributions is merely required. In this context, a nonparametric modeling is not adequate because the kernel method is inaccurate in the upper tail region. Yet one may deal with truncated parametric distributions like the Gaussian ones. Our primary aim is to replace truncated Gaussian distributions by appropriate generalized Pareto distributions and to explore properties and the relationship of discriminant functions in both models. 相似文献
742.
Bradley M Vincent B Warren N Eastoe J Vesperinas A 《Langmuir : the ACS journal of surfaces and colloids》2006,22(1):101-105
Microgel particles are cross-linked polymer particles. When dispersed in a good solvent for the polymer concerned, they are able to respond to a range of external stimuli by changing volume. Hence, microgel particles are suited to numerous applications (for example, controlled uptake and release) in the pharmaceutical, coatings, and water treatment industries. In this work, pH-sensitive, 0.5 wt % cross-linked poly(2-vinylpyridine) (PVP) microgel particles have been prepared and characterized. When the dispersion pH is decreased below 4.5, the pyridine groups become protonated and the microgel network becomes positively charged, causing the particles to expand. To investigate the possibility of using light as a trigger for effecting volume changes, the interaction of these microgel particles with a photodegradable anionic surfactant, 4-hexylphenylazosulfonate (C(6)PAS), has been investigated using dynamic light scattering and electrophoretic mobility measurements. The electrostatic attraction between the positively charged microgel network (at solution pH 3) and the negatively charged headgroups on the surfactant molecules caused a dramatic decrease in particle volume, and charge-reversal of the particles occurred with increasing surfactant concentration. The UV irradiation of phenylazosulfonate surfactants destroys the anionic headgroup of the molecules, and the microgel particles re-swell. The irradiation of PVP dispersions in the presence of C(6)PAS, along with mixed surfactant systems of sodium dodecyl sulfate plus C(6)PAS, has been investigated. 相似文献
743.
Britton MM 《The journal of physical chemistry. A》2006,110(8):2579-2582
This paper presents a magnetic resonance imaging (MRI) method for quantifying the spatial concentrations of the paramagnetic species Mn2+ and Mn3+, during pattern formation, in the manganese-catalyzed 1,4-cyclohexanedione-acid-bromate reaction. The relaxivity of each species was measured, which enabled their concentration to be calculated from nuclear magnetic resonance T2 relaxation times. Images were acquired using the fast spin-echo imaging method RARE. By determining the relation, in these experiments, between signal intensity and T2 relaxation time, it was possible to produce T2 maps from the images. These T2 maps were then used to produce concentration maps for the oxidized (Mn3+) and reduced (Mn2+) states of the catalyst. 相似文献
744.
745.
Ackermann L Gschrei CJ Althammer A Riederer M 《Chemical communications (Cambridge, England)》2006,(13):1419-1421
A palladium complex derived from air-stable TADDOLP(O)H catalyzes efficiently Hiyama, Stille, Kumada and Suzuki cross-coupling reactions of aryl and vinyl chlorides. 相似文献
746.
Han YZ Sanford MS England MD Groves JT 《Chemical communications (Cambridge, England)》2006,(5):549-551
A new and remarkably facile sp3-C-O bond forming reaction of beta-hydroxyalkyl Rh porphyrins to form epoxides has been discovered and its mechanism investigated. 相似文献
747.
A highly efficient and regioselective Pd-catalyzed method for the oxidative coupling of arylpyridine derivatives is reported. Remarkably, the reactions proceed at room temperature and are compatible with diverse functionalities, including aryl halides and thiophenes. Mechanistic studies suggest that these transformations proceed via a previously unprecedented mechanism involving two different pyridine-directed C-H activation reactions-one at a PdII center and one at PdIV. 相似文献
748.
Deprez NR Kalyani D Krause A Sanford MS 《Journal of the American Chemical Society》2006,128(15):4972-4973
This communication describes the rational development of a PdII-catalyzed method for the direct 2-arylation of indoles using [Ar-IIII-Ar]BF4. These reactions proceed under remarkably mild conditions (often at room temperature and in the presence of ambient air and moisture), and these features are believed to be the result of a PdII/IV mechanism operating in these systems. These transformations can be used to prepare functionally diverse 2-arylated indoles and pyrroles, and their potential utility has been expanded by the development of an in situ procedure for generating the iodine(III) arylating reagents. 相似文献
749.
Melanie J. Bugler Stephen T. Grimes Melanie J. Leng Simon D. Rundle Gregory D. Price Jerry J. Hooker Margaret E. Collinson 《Rapid communications in mass spectrometry : RCM》2009,23(18):2939-2951
Experimental measurements of the 18O/16O isotope fractionation between the biogenic aragonite of Viviparus contectus (Gastropoda) and its host freshwater were undertaken to generate a species‐specific thermometry equation. The temperature dependence of the fractionation factor and the relationship between Δδ18O (δ18Ocarb. – δ18Owater) and temperature were calculated from specimens maintained under laboratory and field (collection and cage) conditions. The field specimens were grown (Somerset, UK) between August 2007 and August 2008, with water samples and temperature measurements taken monthly. Specimens grown in the laboratory experiment were maintained under constant temperatures (15°C, 20°C and 25°C) with water samples collected weekly. Application of a linear regression to the datasets indicated that the gradients of all three experiments were within experimental error of each other (±2 times the standard error); therefore, a combined (laboratory and field data) correlation could be applied. The relationship between Δδ18O (δ18Ocarb. – δ18Owater) and temperature (T) for this combined dataset is given by: (T is in °C, δ18Ocarb. is with respect to Vienna Pee Dee Belemnite (VPDB) and δ18Owater is with respect to Vienna Standard Mean Ocean Water (VSMOW). Quoted errors are 2 times standard error). Comparisons made with existing aragonitic thermometry equations reveal that the linear regression for the combined Viviparus contectus equation is within 2 times the standard error of previously reported aragonitic thermometry equations. This suggests there are no species‐specific vital effects for Viviparus contectus. Seasonal δ18Ocarb. profiles from specimens retrieved from the field cage experiment indicate that during shell secretion the δ18Ocarb. of the shell carbonate is not influenced by size, sex or whether females contained eggs or juveniles. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
750.