全文获取类型
收费全文 | 233篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 165篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 19篇 |
物理学 | 47篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 8篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 2篇 |
2016年 | 13篇 |
2015年 | 9篇 |
2014年 | 8篇 |
2013年 | 16篇 |
2012年 | 13篇 |
2011年 | 11篇 |
2010年 | 13篇 |
2009年 | 9篇 |
2008年 | 6篇 |
2007年 | 13篇 |
2006年 | 11篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1996年 | 6篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1988年 | 4篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1869年 | 1篇 |
排序方式: 共有243条查询结果,搜索用时 15 毫秒
41.
42.
Michail Papadourakis Stefano Bosisio Julien Michel 《Journal of computer-aided molecular design》2018,32(10):1047-1058
In the context of the SAMPL6 challenges, series of blinded predictions of standard binding free energies were made with the SOMD software for a dataset of 27 host–guest systems featuring two octa-acids hosts (OA and TEMOA) and a cucurbituril ring (CB8) host. Three different models were used, ModelA computes the free energy of binding based on a double annihilation technique; ModelB additionally takes into account long-range dispersion and standard state corrections; ModelC additionally introduces an empirical correction term derived from a regression analysis of SAMPL5 predictions previously made with SOMD. The performance of each model was evaluated with two different setups; buffer explicitly matches the ionic strength from the binding assays, whereas no-buffer merely neutralizes the host–guest net charge with counter-ions. ModelC/no-buffer shows the lowest mean-unsigned error for the overall dataset (MUE 1.29?<?1.39?<?1.50 kcal mol?1, 95% CI), while explicit modelling of the buffer improves significantly results for the CB8 host only. Correlation with experimental data ranges from excellent for the host TEMOA (R2 0.91?<?0.94?<?0.96), to poor for CB8 (R2 0.04?<?0.12?<?0.23). Further investigations indicate a pronounced dependence of the binding free energies on the modelled ionic strength, and variable reproducibility of the binding free energies between different simulation packages. 相似文献
43.
Michail K Matzi V Maier A Herwig R Greilberger J Juan H Kunert O Wintersteiger R 《Analytical and bioanalytical chemistry》2007,387(8):2801-2814
Hydroxymethylfurfural (HMF), a well-known heterocyclic Maillard reaction product, has often been studied for its potential
toxic, mutagenic, and carcinogenic effects. Recent clinical studies, however, have strongly suggested that HMF might have
exciting antitumor potential. We report on the development and validation of a bioanalytical assay for HMF that could be suitable
as a basis for pharmacokinetic models in cancer patients. Two strategies were tested, i.e., direct and indirect methodologies.
A direct isocratic LC determination at 283 nm was designed. Two indirect attempts involved derivatization coupled to HPLC-UV.
It was possible to resolve the stereoisomers of the HMF derivative, and factors influencing their equilibrium ratio are discussed.
HMF was extracted from the biomatrix by solid-phase extraction using different cartridges. A comparative study was made of
the implemented methods as well as the extraction protocols. Both indirect assays proved to be more sensitive and were used
to assess HMF quantitatively in human plasma. However, the newly introduced derivatization conditions led to the highest sensitivity
with a LOD (S/N ratio = 3) of at least 2 pmol analyte on column. The assay selectivity was satisfactory in pre- and post-dose
real samples. The mean recoveries of the assays were 79% and 89%, with acceptable accuracies and reproducibilities.
Figure Schematic representation of hydroxymethylfurfural (HMF) in human plasma 相似文献
44.
45.
Evangelia Dimitrokalli Stefani Fertaki Michail Lykouras Petros Kokkinos Malvina Orkoula Christos Kontoyannis 《Molecules (Basel, Switzerland)》2021,26(21)
Warfarin sodium is a low-dose pharmaceutical blood thinner that exists in two forms: the clathrate form and the amorphous form. In commercially available warfarin sodium oral suspension, the active pharmaceutical ingredient (API) is added in the amorphous state. This study investigates the apparent instability of the commercially available warfarin liquid oral formulation using Raman and IR spectroscopy, X-ray diffraction, differential scanning calorimetry, UV spectroscopy, and optical microscopy. Warfarin, not its sodium salt, was identified as the undissolved solid existing in the suspension. This was found to be due to the dissociation of sodium salt and the protonation of the warfarin ion in the liquid phase, which triggered the crystallization of the sparingly soluble unsalted form. The coexistence of protonated and unprotonated warfarin ions in the supernatant, as detected by Raman and UV spectroscopy, confirmed this assumption. Study of the dissolution of warfarin sodium amorphous salt and crystalline sodium clathrate in the placebo and pure water verified the results. The effect of pH and temperature on warfarin precipitation was also explored. 相似文献
46.
Irina YU. Gorbunova Michail L. Kerber Svetlana I. Vladimirova Reem R. Musleh Nickolay N. Avdeev 《Macromolecular Symposia》1998,127(1):187-192
Miscibility of polypropylene with some oligoesters was evaluated by optical wedge interference microscopy. Mechanical, thermal, rheological and relaxation properties were studied. Compatibility between the polymers and modifying agents was shown to have a marked effect on stress-strain properties as well as on the structure and melting characteristics of the modified polymers. 相似文献
47.
Alexander S. Lyakhov Pavel N. Gaponik Michail M. Degtyarik Ludmila S. Ivashkevich 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(6):m204-m206
In the polymeric title complex, [CuCl2(C3H6N4)2]n, there are two ligands in the asymmetric unit. The Cu atom adopts an elongated octahedral geometry, with two 2‐ethyltetrazole ligands [Cu—N = 2.0037 (16) and 2.0136 (16) Å] and two Cl atoms [Cu—Cl = 2.2595 (6) and 2.2796 (6) Å] in equatorial positions. A Cl atom and a symmetry‐related 2‐ethyltetrazole molecule [Cu—Cl = 2.8845 (8) Å and Cu—N = 2.851 (2) Å] lie in the axial positions of the octahedron. One of the two 2‐ethyltetrazole ligands of the asymmetric unit exhibits bidentate binding to two Cu atoms through two N atoms of the tetrazole ring, whereas the other ligand is coordinated in a monodentate fashion via one tetrazole N atom. The Cu‐atom octahedra form dimer entities by sharing edges with equatorial and axial Cl atoms. The dimers are linked together through the 2‐ethyltetrazole ligands to form one‐dimensional polymeric zigzag chains extending along the b axis. The chains are connected into infinite layers parallel to the (10) plane via the 2‐ethyltetrazole ligands. 相似文献
48.
Michail Pivovarov 《Regular and Chaotic Dynamics》2012,17(6):506-511
A nonlinear time-varying one-degree-of-freedom system, which is used for the modelling of the buckling of a loaded beam in Euler??s problem, is considered. For a slowly changing load, the deterministic approach in this problem fails if the trajectories pass through the separatrix. An expression for the probability of possible outcomes of the evolution of the oscillations is obtained. The analytical and numerical results are compared. 相似文献
49.
3-Methylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)acrylonitriles do not enter into [4+2]-cycloaddition reactions with maleimides to form the expected pyrrolo-pyridazines. Instead the formation of novel pyrrolo-pyridazines of type 4 takes place via a formal [3+2]-cycloaddition of initially formed pyrrolidine-derived azomethine ylides 7. The mechanism leading to the final product is discussed. 相似文献
50.
N. Kalyvas I. Valais S. David Ch. Michail G. Fountos P. Liaparinos I. Kandarakis 《Optics and Spectroscopy》2014,116(5):743-747
Single crystal scintilators are used in various radiation detectors applications. The efficiency of the crystal can be determined by the Detector Optical Gain (DOG) defined as the ratio of the emitted optical photon flux over the incident radiation photons flux. A parameter affecting DOG is the intrinsic conversion efficiency (n C ) giving the percentage of the X-ray photon power converted to optical photon power. n C is considered a constant value for X-ray energies in the order of keV although a non-proportional behavior has been reported. In this work an analytical model, has been utilized to single crystals scintillators GSO:Ce, LSO:Ce and LYSO:Ce to examine whether the intrinsic conversion efficiency shows non proportional behavior under X-ray excitation. DOG was theoretically calculated as a function of the incident X-ray spectrum, the X-ray absorption efficiency, the energy of the produced optical photons and the light transmission efficiency. The theoretical DOG values were compared with experimental data obtained by irradiating the crystals with X-rays at tube voltages from 50 to 140 kV and by measuring the light energy flux emitted from the irradiated screen. An initial value for n C (calculated from literature data) was assumed for the X-ray tube voltage of 50 kV. For higher X-ray tube voltages the optical photon propagation phenomena was assumed constant and any deviations between experimental and theoretical data were associated with changes in the intrinsic conversion efficiency. The experimental errors were below 7% for each experimental setup. The behavior of n C values for LSO:Ce and LYSO:Ce were found very similar, i.e., ranging with values from 0.089 at 50 kV to 0.015 at 140 kV, while for GSO:Ce, n C demonstrated a peak at 80 kV. 相似文献