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51.
The combination of valence band photoemission and inverse photoemission spectroscopy is applied to study the densities of occupied and unoccupied states of perylene derivative and phthalocyanine organic layers on inorganic semiconductors. The ionisation energies and electron affinities are determined and it is proposed that the transport gap of the materials can be evaluated from the distance of the HOMO and LUMO edges. The resulting values for the transport gap which are somewhat smaller than other published data are in good agreement with e.g. electrical measurements. The experimental spectra are compared with simulated ones obtained by density functional theory calculations. 相似文献
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53.
L. C. Oliveira C. B. Zamboni F. A. Genezini A. M. G. Figueiredo G. S. Zahn 《Journal of Radioanalytical and Nuclear Chemistry》2005,263(3):783-786
Summary In this study we show that the NAA technique can be used to perform clinical analyses of blood and urine, with many advantages towards the conventional methods. From the knowledge of the neutron flux and the induced activity, the concentration ofelements were obtained. In comparison to the conventional techniques, this methodology uses smaller quantities of biological material and allows the simultaneous evaluation of the concentrations of several elements in biological samples at once, something not always possible in the conventional clinical analysis. Another important advantage is that it eliminates the use of standard materials, thus making the analyzing process practical and economic. 相似文献
54.
Investigation of the surfactant type and concentration effect on the retention factors of glutathione and its analogues by micellar electrokinetic chromatography 下载免费PDF全文
Jana Kazarjan Riina Mahlapuu Mats Hansen Ursel Soomets Mihkel Kaljurand Merike Vaher 《Journal of separation science》2015,38(19):3461-3468
In the present study, a micellar electrokinetic chromatographic method was used to determine the retention factors of hydrophilic monomeric and homodimeric forms of glutathione analogues. Ionic‐liquid‐based surfactant, 1‐tetradecyl‐3‐methylimidazolium chloride, as well as cetyltrimethylammonium bromide and phosphate buffer (pH 7.4) were employed in the experiments. Since the studied peptides possess a negative charge under physiological conditions, it is expected that the peptides interact with the oppositely charged 1‐tetradecyl‐3‐methylimidazolium chloride and cetyltrimethylammonium bromide micelles via hydrophobically assisted electrostatic forces. The dependence of the retention factor on the micellar concentration of 1‐tetradecyl‐3‐methylimidazolium chloride and cetyltrimethylammonium bromide is nonlinear and the obtained curves converge to a limiting value. The retention factor values of GSH analogues were in the range of 0.36–2.22 for glutathione analogues and –1.21 to 0.37 for glutathione when 1‐tetradecyl‐3‐methylimidazolium chloride was used. When cetyltrimethylammonium bromide was employed, the retention factor values were in the range of 0.27–2.17 for glutathione analogues and –1.22 to 0.06 for glutathione. If sodium dodecyl sulfate was used, the retention factor values of glutathione analogues with carnosine moiety were in the range of –1.54 to 0.38. 相似文献
55.
We make the link between the size-dependent phase stability of a nanocrystal and the phase-transition behavior of emerging crystallites during the earliest stages of crystallization, by using the former as a proxy for the latter. We outline an extension of the classical nucleation theory to describe crystal nucleation and subsequent transformations of competing polymorphic phases that characterize Ostwald's rule of stages. The theoretical framework reveals that the relative stability of the competing phases is a function of cluster size, which in turn varies with time, and therefore explains the complex transformation behavior observed for some systems. We investigated the stability of a nanocrystal of dl-norleucine by means of molecular simulation as a proxy for post-nucleation phase-transformation behavior in emerging crystallites. The simulations reveal that, for nanocrystals, the surface energy of the transition state of a transformation can dominate the barrier to phase change, thus causing metastable phases to be stabilized, not because they are thermodynamically stable, but rather due to kinetic hindering. Therefore, in the context of the earliest stages of crystal growth, not only does phase stability vary as a function of cluster size, and hence time, but thermodynamically feasible transformations are also prone to kinetic hindering. 相似文献
56.
Heretsch P Büttner A Tzagkaroulaki L Zahn S Kirchner B Giannis A 《Chemical communications (Cambridge, England)》2011,47(26):7362-7364
The combination of theoretical and computational studies with organic synthesis and biological investigations has led to exo-cyclopamine. This stable and highly potent derivative of cyclopamine promises big potential as an experimental drug against several types of human cancer. 相似文献
57.
di Dio PJ Brüssel M Muñiz K Ray RS Zahn S Kirchner B 《Angewandte Chemie (International ed. in English)》2011,50(37):A40-A45
We investigated the key step of Pd-N to Pd-O rearrangement from a model catalytic cycle for the activation of carbon dioxide and methane with static quantum chemical calculations and metadynamics simulation. Our calculations show that different bottlenecks appear in the catalytic cycle but that the investigated rearrangement of the Pd-N to Pd-O bounded complex has a barrier ΔG(#)/ΔF(#) of approximately 20 kJ mol?1 and is therefore accessible at ambient reaction conditions. 相似文献
58.
The mechanisms of ionic conductivity in BaLiF(3) are investigated using molecular simulations. Direct molecular dynamics simulations of (quasi) single crystalline super cell models hint at the preferred mobility mechanism which is based on fluoride interstitial (and to a smaller extent F(-) vacancy) migration. Analogous to previous modeling studies, the energy related to Frenkel defect formation in the ideal BaLiF(3) crystal was found as 4-5 eV which is in serious controversy to the experimentally observed activation barrier to ionic conductivity of only 1 eV. However, this controversy could be resolved by incorporating Ba(2+)? Li(+) exchange defects into the elsewise single crystalline model systems. Indeed, in the neighborhood of such cation exchange defects the F(-) Frenkel defect formation energy was identified to reduce to 1.3 eV whilst the cation exchange defect itself is related to a formation energy of 1.0 eV. Thus, our simulations hint at the importance of multiple defect scenarios for the ionic conductivity in BaLiF(3). 相似文献
59.
60.
The nonkeratinous proteins of wool can be partly or completely dissolved by controlled enzymatic digestion. A comparison between the keratose content of intact wool and that of wool which has been hydrolysed for 96 h with pronase confirms that specifically all the nonkeratinous components are dissolved out of the wool composite by pronase. The influence of microbial infection can be excluded.The residue of wool after the hydrolysis, i. e., a wool low in nonkeratinous proteins, has a higher internal volume, as measured by mercury porosimetry. The centrifugal swelling test shows that these wool samples also have increased hygroscopy. 相似文献