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101.
Marianne Spittel 《Fresenius' Journal of Analytical Chemistry》1964,203(6):463
Ohne Zusammenfassung 相似文献
102.
Analytical and Bioanalytical Chemistry - 相似文献
103.
Marianne Spittel 《Fresenius' Journal of Analytical Chemistry》1965,214(5):378
Ohne Zusammenfassung 相似文献
104.
Marianne E. Van Dommelen Jan W. De Haan Henk M. Buck 《Magnetic resonance in chemistry : MRC》1980,14(6):497-501
The usefulness and some of the limitations of the linear electric field (LEF) effect in 13C NMR are illustrated by means of model calculations on the 13C NMR chemical shifts of C-1 and C-2 in 5-chloro-1-pentene in nine different conformations. Two different concepts are used in order to calculate the electric fields near C-1 and C-2 caused by the C-5? Cl dipole. It is also demonstrated that, when using charges calculated by CNDO/2, the influences of the hydrogen atoms at C-5 cannot be neglected. The use of the dipole–dipole interaction formula is advocated. The consequences of taking into account the additional contributions of the vinylic bonds to the accumulated charges at C-1 and C-2 are described. The results with the dipole–dipole formula show that the same signs and similar magnitudes of the LEF effects are calculated in seven out of nine conformations of 5-chloro-1-pentene. This reduces the LEF to a means of confirming, rather than deducing, conformational equilibria in acylic flexible compounds. The usefulness of some recently published applications of the LEF concept to explain some short range substituent effects is critically discussed, mainly in view of the inhomogeneities of the calculated electric fields. 相似文献
105.
Marianne Spittel H. Blaha und Doris Rittweger-Heiligmann 《Fresenius' Journal of Analytical Chemistry》1965,212(3):432-434
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106.
Marianne Spittel 《Fresenius' Journal of Analytical Chemistry》1964,203(5):384
Ohne Zusammenfassung 相似文献
107.
Marianne Spittel 《Fresenius' Journal of Analytical Chemistry》1964,204(4):281
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108.
Tinnemans SJ Kox MH Sletering MW Nijhuis TA Visser T Weckhuysen BM 《Physical chemistry chemical physics : PCCP》2006,8(20):2413-2420
In continuation of our previous work on the applicability of the G(R(infinity)) correction factor for the quantification of Raman spectra of coke during propane dehydrogenation experiments (Phys. Chem. Chem. Phys., 2005, 7, 211), research has been carried out on the potential of this correction factor for the quantification of supported metal oxides during reduction experiments. For this purpose, supported chromium oxide catalysts have been studied by combined in situ Raman and UV-Vis spectroscopy during temperature programmed reduction experiments with hydrogen as reducing agent. The goal was to quantify on-line the amount of Cr(6+) in a reactor based on the measured in situ Raman spectra. During these experiments, a significant temperature effect was observed, which has been investigated in more detail with a thermal imaging technique. The results revealed a temperature 'on the spot' that can exceed 100 degrees C. It implies that Raman spectroscopy can have a considerable effect on the local reaction conditions and explains observed inconsistencies between the in situ UV-Vis and Raman data. In order to minimize this heating effect, reduction of the laser power, mathematical matching of the spectroscopic data, a different cell design and a change in reaction conditions has been evaluated. It is demonstrated that increasing the reactor temperature is the most feasible method to solve the heating problem. Next, it allows the application of in situ Raman spectroscopy in a reliable quantitative way without the need of an internal standard. 相似文献
109.
Monte Carlo simulations have been used to study two different models for a weak linear polyelectrolyte in the presence of nanoparticles: (i) a rodlike and (ii) a flexible polyelectrolytes. The use of simulated annealing has made it possible to simulate a polyelectrolyte chain in the presence of several nanoparticles by improving conformation sampling and avoiding multiple minima problems when dense conformations are produced. Nanoparticle distributions along the polymer backbone were analyzed versus the ionic concentration, polyelectrolyte stiffness, and nanoparticle surface charge. Titration curves were calculated and the influences of the ionic concentration, solution pH, and number of adsorbed nanoparticles on the acid/base polyelectrolyte properties have been systematically investigated. The subtle balance of attractive and repulsive interactions has been discussed, and some characteristic conformations are presented. The comparison of the two limit models provides a good representation of the stiffness influence on the complex formation. In some conditions, overcharging was obtained and presented with respect to both the polyelectrolyte and nanoparticle as the central element. Finally, the charge mobility influence along the polyelectrolyte backbone was investigated by considering annealed and quenched polyelectrolyte chains. 相似文献
110.
Michael Zech Marianne Benesch Johannes Hepp Steven Polifka Bruno Glaser 《Isotopes in environmental and health studies》2013,49(4):394-403
ABSTRACTInspired by a previous ‘Sauna, sweat and science’ study [Zech et al. Isot Environ Health Stud. 2015;51(3):439–447] and out of curiosity and enthusiasm for stable isotope and sauna research we aimed at answering the question ‘do we sweat (isotopically) what we drink’? We, therefore, pulse-labelled five test persons in a sauna experiment with beverages that were 2H-enriched at about +25,600?‰. Sweat samples were collected during six sauna rounds and the hydrogen isotope composition δ2Hsweat was determined using an isotope ratio mass spectrometer. Before pulse labelling, δ2Hsweat – reflecting by approximation body water – ranged from –32 to –22?‰. This is ~35?‰ enriched compared to usual mid-European drinking water and can be explained with hydrogen-bearing food as well as with the respiratory loss of 2H-depleted vapour. The absence of a clearly detectable 2H pulse in sweat after pulse labelling and δ2Hsweat results of ≤+250?‰ due to a fast 2H equilibration with body water are moreover a clearly negative answer to our research question also in a short-term consideration. Given that the recovery of the tracer based on an isotope mass balance calculation is clearly below 100?%, we finally answer the question ‘where did the rest of the tracer go?’ 相似文献