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排序方式: 共有209条查询结果,搜索用时 703 毫秒
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Summary In this paper we analize the reversibility of the diffusion property for the solution of certain infinite-dimensional systems of stochastic differential equations. Necessary and sufficient conditions ensuring this reversibility are given. The proofs use the techniques of the stochastic calculus of variations.This work was partly done when the first author was visiting the Centre de Recerca Matemàtica at Barcelona 相似文献
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In the previous paper in this issue we have demonstrated that it is possible to measure the five different relaxation rates of a deuteron in (13)CH(2)D methyl groups of (13)C-labeled, fractionally deuterated proteins. The extensive set of data acquired in these experiments provides an opportunity to investigate side-chain dynamics in proteins at a level of detail that heretofore was not possible. The data, acquired on the B1 domain of peptostreptococcal protein L, include 16 (9) relaxation measurements at 4 (2) different magnetic field strengths, 25 degrees C (5 degrees C). These data are shown to be self-consistent and are analyzed using a spectral density mapping procedure which allows extraction of values of the spectral density function at a number of frequencies with no assumptions about the underlying dynamics. Dynamics data from 31 of 35 methyls in the protein for which data could be obtained were well-fitted using the two-parameter Lipari-Szabo model (Lipari, G.; Szabo, A. J. Am. Chem. Soc. 1982, 104, 4546). The data from the remaining 4 methyls can be fitted using a three-parameter version of the Lipari-Szabo model that takes into account, in a simple manner, additional nanosecond time-scale local dynamics. This interpretation is supported by analysis of a molecular dynamics trajectory where spectral density profiles calculated for side-chain methyl sites reflect the influence of slower (nanosecond) time-scale motions involving jumps between rotameric wells. A discussion of the minimum number of relaxation measurements that are necessary to extract the full complement of dynamics information is presented along with an interpretation of the extracted dynamics parameters. 相似文献
6.
A chromatographic approach was proposed to describe the existence of surfactant micelles in a surfactant/hydroorganic phosphate buffer mobile phase. Using this mixture as a mobile phase, a novel mathematical theory is presented to describe the inclusion mechanism of imidazole derivatives in surfactant micelles. Using this model, enthalpy, entropy and the Gibbs free energy were determined for two chromatographic chemical processes: (i) the transfer of the imidazole derivative from the mobile phase to the stationary phase; and (ii) the imidazole derivative inclusion in surfactant micelles. These thermodynamic data indicate that the main parameter determining chromatographic retention is distribution of the imidazole derivatives to micelles of surfactant while the interaction with the stationary phase play a minor role. 相似文献
7.
Morin N. Chilouet A. Millet J. Rouland J.-C. 《Journal of Thermal Analysis and Calorimetry》2000,62(1):187-201
The complexation of bifonazole, an antimycotic hydrophobic imidazole derivative, with β-cyclodextrin (β-CD) was investigated
in solid phase, using the following complementary techniques: differential scanning calorimetry (DSC), thermogravimetric analysis
(TG) and X-ray powder diffractometry. The β-CD-bifonazole samples were prepared in both aqueous medium by coprecipitation
and in solid state by kneading method and the β-CD-bifonazole binary diagrams were drawn. The experimental results demonstrate
the formation of two binary compounds, β-CD-bifonazole and (β-CD)x bifonazole (x =2 or 4). The first compound may be an inclusion compound and the second a crystallized compound, in which the bifonazole
is not necessarily included in the cyclodextrin internal cavity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Millet O Muhandiram DR Skrynnikov NR Kay LE 《Journal of the American Chemical Society》2002,124(22):6439-6448
New pulse sequences are presented for the measurement of the relaxation of deuterium double quantum, quadrupolar order, and transverse antiphase magnetization in (13)CH(2)D methyl groups of (15)N-, (13)C-labeled, fractionally deuterated proteins. Together with previously developed experiments for measuring deuterium longitudinal and transverse decay rates [Muhandiram, D. R.; Yamazaki, T.; Sykes, B. D.; Kay, L. E. J. Am. Chem. Soc. 1995, 117, 11536], these schemes allow measurement of the five unique decay constants of a single deuteron, providing an unprecedented opportunity to investigate side-chain dynamics in proteins. All five deuterium relaxation rates have been measured for deuterons in the methyl groups of the B1 immunoglobulin binding domain of peptostreptococcal protein L and the N-terminal SH3 domain from the protein drk. Since values of the spectral density function at only three different frequencies contribute to the five relaxation rates, the self-consistency of the relaxation data is readily established. Very good agreement is obtained between calculated parameters describing the amplitudes and time scales of motion when different subsets of the relaxation data are employed. 相似文献
9.
A method using GC-MS and derivatization with N-(t-butyldimethylsilyl)-N-ethyltrifluoroacetamide (MTBSTFA) was developed for the analysis of 19 chlorophenols compounds in atmospheric samples (gas
and particles). Air sampling was carried out using a Hi-Vol sampler with glass fibre filter and XAD-2 resin at a flow rate
of 60 m3 h−1. The particle and gas phases were collected separately over a period of 4 h. Samples were Soxhlet extracted, evaporated to
dryness under nitrogen and refilled with acetonitrile. 100 mL of these extracts were derivatized with 100 μL of MTBSTFA at
80 °C for 1 h under strong stirring. Sylylated chlorophenols were injected into a GC-MS in splitless mode and quantified as
their TBDMS derivatives in the SIM mode. Mass spectral analysis of the derivatives of the 19 compounds studied indicates that
the spectra are highly specific showing an ion at [M - 57]+ which is useful for structure confirmation or analysis at low levels using selected ion monitoring. Quantification limits
varied between 5 μg L−1 and 10 μg L−1 which correspond to 20 pg m−3 and 40 pg m−3 for 250 m3 of air sampled. This method was successfully applied to atmospheric samples collected simultaneously in winter 2004 in an
urban (Strasbourg) and rural (Erstein) areas in east of France. 相似文献
10.
Sara Bertuzzi Dr. Ana Gimeno Reyes Núñez-Franco Dr. Ganeko Bernardo-Seisdedos Sandra Delgado Dr. Gonzalo Jiménez-Osés Dr. Oscar Millet Prof. Dr. Jesús Jiménez-Barbero Dr. Ana Ardá 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(67):15643-15653
The interaction of human galectin-1 with a variety of oligosaccharides, from di-(N-acetyllactosamine) to tetra-saccharides (blood B type-II antigen) has been scrutinized by using a combined approach of different NMR experiments, molecular dynamics (MD) simulations, and isothermal titration calorimetry. Ligand- and receptor-based NMR experiments assisted by computational methods allowed proposing three-dimensional structures for the different complexes, which explained the lack of enthalpy gain when increasing the chemical complexity of the glycan. Interestingly, and independently of the glycan ligand, the entropy term does not oppose the binding event, a rather unusual feature for protein-sugar interactions. CLEANEX-PM and relaxation dispersion experiments revealed that sugar binding affected residues far from the binding site and described significant changes in the dynamics of the protein. In particular, motions in the microsecond-millisecond timescale in residues at the protein dimer interface were identified in the presence of high affinity ligands. The dynamic process was further explored by extensive MD simulations, which provided additional support for the existence of allostery in glycan recognition by human galectin-1. 相似文献