全文获取类型
收费全文 | 528篇 |
免费 | 20篇 |
国内免费 | 2篇 |
专业分类
化学 | 351篇 |
晶体学 | 3篇 |
力学 | 10篇 |
数学 | 79篇 |
物理学 | 107篇 |
出版年
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 8篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 18篇 |
2015年 | 10篇 |
2014年 | 16篇 |
2013年 | 36篇 |
2012年 | 43篇 |
2011年 | 27篇 |
2010年 | 27篇 |
2009年 | 25篇 |
2008年 | 34篇 |
2007年 | 33篇 |
2006年 | 26篇 |
2005年 | 25篇 |
2004年 | 20篇 |
2003年 | 17篇 |
2002年 | 14篇 |
2001年 | 15篇 |
2000年 | 15篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有550条查询结果,搜索用时 46 毫秒
101.
Jeanne Crassous Jos Rivera Nicolette S. Fender Lianhe Shu Luis Echegoyen Carlo Thilgen Andreas Herrmann Franois Diederich 《Angewandte Chemie (International ed. in English)》1999,38(11):1613-1617
The pure enantiomers of D 2 -C 84 as well as a third constitutional isomer of this higher fullerene were produced by a retro-Bingel reaction on the first organic derivatives of C84 (see scheme). These derivatives were synthesized by Bingel cyclopropenation of C84, separated, and unambiguously structurally characterized. 相似文献
102.
The dependence of Li mobility on structure and composition of Li0.5 − xNaxLa0.5TiO3 perovskites (0 ≤ x ≤ 0.5) has been investigated by means of neutron diffraction, nuclear magnetic resonance and impedance spectroscopy. At 300 K, all samples display a rhombohedral superstructure (R-3c S.G.), where octahedra are out of phase tilted along [111] direction of the ideal cubic cell. The elimination of the octahedral tilting is responsible for the rhombohedral–cubic transformation, detected near 1000 K. In these perovskites, La and Na cations are randomly distributed in A sites, but Li ions are fourfold coordinated at unit cell faces of the cubic perovskite. Lithium conductivity, σ300 K, decreases with the sodium content, decreasing from values typical of fast ionic conductors, 10− 3 S/cm, to those of good insulators, 10− 10 S/cm, when the interconnectivity between vacant A sites is lost (x > 0.3). In samples with x < 0.3, dc conductivity displays a non-Arrhenius behaviour, decreasing activation energy from ~ 0.37 to 0.25 eV when the sample is heated between 77 and 500 K. The temperature dependence of BLi factors shows the existence of two regimes for Li motion. Below 373 K, Li ions remain partially located near square oxygen windows that connect contiguous A sites, but above 400 K, extended Li motions become dominant. The additional decrease of activation energy from 0.25 to 0.16 eV (low-temperature 7Li NMR value), should require the full elimination of octahedral tilting which is only produced above 1000 °C. 相似文献
103.
V. A. G. Rivera S. Sergeenkov C. Stari L. Cichetto C. A. Cardoso E. Marega F. M. Araujo-Moreira 《JETP Letters》2009,90(5):365-369
By applying a highly sensitive homemade AC susceptibility technique to Pr
x
Y1 − x
Ba2Cu3O7 − δ polycrystals (with x = 0.0, 0.1, and 0.3), we observed very sharp Fraunhofer type low-field periodic oscillations of the real part of the AC susceptibility
which were attributed to Josephson vortices penetrating intergranular regions of grain-boundary Josephson network in our samples.
Assuming the Lorentz type distribution of single-junction contact areas, we were able to successfully fit the experimental
data. 相似文献
104.
The first 3-fold multicomponent macrocyclizations of trifunctional building blocks were developed to produce, in one pot, cryptands, cages, and cryptophanes with peptoid tethers carrying additional recognition motifs. The straightforward, efficient, and diversity-oriented fashion by which these complex macromulticycles are obtained is suitable for building combinatorial libraries of synthetic receptors with potential applicability in catalysis and supramolecular and coordination chemistry. The strategy also easily allows creation of asymmetric macromulticyclic cavities, with up to 20 new bonds formed in one pot. 相似文献
105.
Basnayake R Li Z Katar S Zhou W Rivera H Smotkin ES Casadonte DJ Korzeniewski C 《Langmuir : the ACS journal of surfaces and colloids》2006,22(25):10446-10450
Properties of PtRu nanoparticles prepared using high-intensity sonochemistry are reported. Syntheses were carried out in tetrahydrofuran (THF) containing Ru3+ and Pt4+ in a fixed mole ratio of either 1:10 or 1:1. X-ray diffraction measurements confirmed sonocation produces an alloy phase and showed that the composition of the nanometer scale metal particles is close to the mole fraction of Ru3+ and Pt4+ in solution with deviations that tend toward Ru enrichment in the alloy phase. The materials gave responses that are similar in terms of peak potential and current density, referenced to the catalyst active surface area, to those of bulk alloys in voltammetry experiments involving CO stripping and CH3OH electrochemical oxidation in 0.1 M H2SO4. The results show that sonochemical methods have the potential to produce nanometer scale bimetallic electrocatalysts that possess alloy properties. The materials have application in mechanistic studies of fuel cell reactions and as platforms for the development of CO tolerant fuel cell catalyst. 相似文献
106.
Alvaro Valencia Francisco Muñoz Sebastián Araya Rodrigo Rivera Eduardo Bravo 《International Journal of Computational Fluid Dynamics》2013,27(9):649-666
Haemodynamically induced stress plays an important role in the progression and rupture of cerebral aneurysms. The current work describes computational fluid dynamics (CFD), fluid–structure interaction (FSI) and computational structural dynamics (CSD) simulations in an anatomically realistic model of a carotid artery with two saccular cerebral aneurysms in the ophthalmic region. The model was obtained from three-dimensional (3D) rotational angiographic imaging data. CFD and FSI were studied under a physiologically representative waveform of inflow. The arterial wall was assumed elastic or hyperelastic, as a 3D solid or as a shell depending on the type of modelling used. The flow was assumed to be laminar, non-Newtonian and incompressible. The CFD, FSI and CSD models were solved with the finite elements package ADINA. Predictions of velocity field and wall shear stress (WSS) on the aneurysms made using CFD and FSI were compared. The CSD model of the aneurysms using complete geometry was compared with isolated aneurysm models. Additionally, the effects of hypertensive pressure on CSD aneurysm models are also reported. The vortex structure, WSS, effective stress, strain and displacement of the aneurysm walls showed differences, depending on the type of modelling used. 相似文献
107.
108.
Systematic data on the effect of irradiation with swift ions (Zn at 735 MeV and Xe at 929 MeV) on NaCl single crystals have been analysed in terms of a synergetic two-spike approach (thermal and excitation spikes). The coupling of the two spikes, simultaneously generated by the irradiation, contributes to the operation of a non-radiative exciton decay model as proposed for purely ionization damage. Using this scheme, we have accounted for the π-emission yield of self-trapped excitons and its temperature dependence under ion-beam irradiation. Moreover, the initial production rates of F-centre growth have also been reasonably simulated for irradiation at low temperatures ( < 100 K), where colour centre annealing and aggregation can be neglected. 相似文献
109.
Humberto Bustos Rodríguez Dagoberto Oyola Lozano Yebrayl Antonio Rojas Martínez Marlene Rivera Pinilla German Antonio Pérez Alcázar 《Hyperfine Interactions》2012,206(1-3):13-18
Friedreich ataxia is a disease that is associated with defects in the gene coding for a small protein frataxin. Several different roles have been proposed for the protein, including iron chaperoning and iron storage. M?ssbauer spectroscopy was used to probe these hypotheses. Iron accumulation in mutant mitochondria unable to assemble iron sulfur clusters proved to be insensitive to overexpression of frataxin, ruling out its potential involvement as an iron storage protein similar to ferritin. Rather, it was found that frataxin negatively regulates iron sulfur cluster assembly. 相似文献
110.
Ch. Jesús F. Socorro M. Rodríguez de Rivera 《Journal of Thermal Analysis and Calorimetry》2012,110(3):1523-1532
In the calorimeters used for the determination of thermodynamical properties of liquid environments, the mixture takes place when injecting liquid in the mixture zone, this injection incorporates an additional calorific power that is a function of the volumetric heat capacity of the injected liquid and the injection flow. In this article, it is rewritten Tian??s equation including this additional power to relate correctly the experimental output to the mixture enthalpy. It is applied Tian??s equation, once it has been corrected, to two types of calorimeters: flow-microcalorimeters and isothermal titration calorimeters. In this second case, it has been taken into account the classical operating mode (titration) and the continuous liquid injection mode. Tian??s equation, completed with all the energetic terms additional to the mixture process, is of great interest for the scientific and academic community because it allows to explain, in a simple and effective way, the operation of these instruments. 相似文献