全文获取类型
收费全文 | 130篇 |
免费 | 25篇 |
国内免费 | 22篇 |
专业分类
化学 | 67篇 |
晶体学 | 5篇 |
数学 | 39篇 |
物理学 | 66篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 8篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 2篇 |
2015年 | 12篇 |
2014年 | 10篇 |
2013年 | 14篇 |
2012年 | 22篇 |
2011年 | 32篇 |
2010年 | 20篇 |
2009年 | 10篇 |
2008年 | 3篇 |
2007年 | 6篇 |
2006年 | 2篇 |
2002年 | 2篇 |
2001年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1991年 | 1篇 |
排序方式: 共有177条查询结果,搜索用时 31 毫秒
31.
《Radiation Physics and Chemistry》2007,76(3):512-515
We performed temporal as well as frequency-resolved emission spectroscopy of the plasma plume generated in vacuum by 355 nm pulsed laser ablation of a LiYF4:Tm3+ crystal (1% Tm3+ concentration) and a LiYF4:Nd3+ crystal (1.5% Nd3+ concentration). The plume emission spectrum is very rich in features and shows the elemental lines belonging to all the components of the host lattice, either neutral or ionized. The time-resolved analysis of some emission features is discussed and some stream velocities are derived. A possible model for the time evolution of the plume components is reported. The electronic detection technique was used to detect the onset of the plasma plume and to measure the ablation laser fluence threshold. 相似文献
32.
运用模糊数学模型和食品安全指数IFS模型进行安全风险评估,对深圳市新鲜蔬菜批发市场、农贸市场、超市及零售店等常规渠道与其他输入渠道进行模糊评价,得出食品安全风险等级,构建了蔬菜安全风险评估层次结构模型,评估出深圳市新鲜蔬菜安全风险较高。对已有的抽样方案进行改进,设计了两套深圳市新鲜蔬菜抽样检验方案,分别适用于深圳市所有的蔬菜交易市场和销售蔬菜的超市、零售店以及蔬菜产地、蔬菜加工厂的样本抽取及实验室试样的制备。 相似文献
33.
34.
针对修复时间服从任意分布的两不同部件并联可修系统的模型,把系统方程的解转化为Volterra积分方程的形式,用范数指标函数作为衡量控制变量的标准,以及系统在某一时刻T的最优控制问题. 相似文献
35.
An Ambrosetti-Prodi type exact multiplicity result is proved for a diffusive logistic equation with harvesting. We show that a modified diffusive logistic mapping has exactly either zero, or one, or two pre-images depending on the harvesting rate. It implies that the original diffusive logistic equation with harvesting has at most two positive steady state solutions. 相似文献
36.
《中国化学快报》2022,33(8):3903-3908
Fe-N-C structures have been considered as a candidate to replace noble metal catalysts towards oxygen reduction reaction (ORR) due to their excellent electrocatalytic activity and durability. Herein, a zinc-mediated synthesis strategy is proposed for N-doped graphitic porous carbon encapsulated uniform dispersed Fe3C nanoparticles coupled with atomically dispersed Fe-Nx moieties (NPC/Fe-N-C) derived from biomass coconut shell. The introduction of zinc species could be conductive to the dispersion of iron species and formation of porous structures. Density functional theory calculations demonstrate that the N-doped carbon coating structures can weaken the oxygen intermediates adsorption energy barrier of Fe3C. Beside, the graphitic carbon could promote the electron transfer during the electrochemical reaction. These special structures enable NPC/Fe-N-C to have excellent ORR activity with an Eonset of 1.0 V, which is much better than Pt/C. Furthermore, the zinc-air battery assembled by pairing NPC/Fe-N-C with a high-efficiency oxygen evolution reaction (OER) catalyst can continuously and stably operate a charge-discharge potential gap of 0.8 V at 10 mA/cm2 for more than 600 h. More importantly, the assembled batteries could drive overall water splitting device, realizing the effective energy conversion. 相似文献
37.
Low temperature electronic and magneto-transport study across Fe/NiO bilayer on Si substrate has been reported. These bilayer structures have been irradiated by swift heavy ions (~100 MeV Fe7+ ions with a fluence of 5×1012 ions/cm2). The electronic transport study across such bilayer (both unirradiated and irradiated) structures has shown the semiconducting nature of the interface. A significant decrease in current has been observed for the irradiated structure (as compared to unirradiated ones on the irradiation) which could be due to the irradiation induced introduction of defects/disorders in the structure. The magneto-transport study across unirradiated structure has shown the magnetic field sensitivity at low temperatures only whereas the irradiated structure has not shown any perceptible magnetic field sensitivity at low temperatures. Such observed intriguing feature of magnetic field sensitivity across the bilayer structures could be understood due to the motion of thermally assisted magnetic domain walls in the presence of external applied magnetic field. The observed high % MR could be related to spin-dependent electron scattering at the interfaces. 相似文献
38.
An algorithm has been developed based on numerical simulation to relate physical geometry to the Young’s modulus of symmetric and asymmetric single-walled carbon nanotubes (SWCNTs). A large number of finite element results for the stiffness of SWCNTs has been categorized into three main classes (i.e., armchair, zigzag and chiral) and the best curve fitting function has been obtained to describe the relation between the geometry of SWCNTs and their stiffness. For two standard configurations of carbon nanotubes (i.e., armchair and zigzag), four equations referring to geometry parameters (n, m) and diameter (d) have been introduced. To find the size dependence of asymmetric nanotubes, three-dimensional surfaces of stiffness (E(n, m)) have been used. However, since the stiffness of asymmetric nanotubes depends upon n and m, it was impossible to define any diameter dependency. To account for the hidden mechanical behavior of asymmetric SWCNTs, a new physical factor (CF) was introduced as the major novelty in this work. The proposed CF converts any asymmetric geometry (n, m) into a value between 0 and 1. The CF for a chiral nanotube can imply the percentage of similarity in its mechanical properties to the two standard symmetric configurations. Based on the CF concept, a new equation is derived to predict the Young’s modulus of asymmetric carbon nanotubes based on the symmetric prediction of standard models. The new physical factor (CF) which is developed in this study can be useful for the characterization of SWCNTs and the selection of all configurations. 相似文献
39.
N-In codoped ZnO nanobelts were successfully synthesized via high-temperature chemical vapor deposition for the first time, using the mixture of In/ZnO as a precursor. The EDX spectrum showed that In was introduced into ZnO nanobelts. In order to better understand the optical properties of N-In codoped ZnO nanobelts, the Raman and low-temperature PL spectra of the undoped, In-doped and N-In codoped ZnO nanostructures were measured. By contrasting, N is incorporated into the nanobelts. The temperature dependent photoluminescence (PL) spectra were investigated. Their PL spectra in the temperature from 9 K to room temperature were dominated by an AoX emission of excitons bound to 2No-InZn acceptor complexes. The dissociation energy of the acceptor complexes is estimated to be 89-112 meV. 相似文献
40.
The bifurcation of non-trivial steady state solutions of a scalar reaction–diffusion equation with nonlinear boundary conditions is considered using several new abstract bifurcation theorems. The existence and stability of positive steady state solutions are proved using a unified approach. The general results are applied to a Laplace equation with nonlinear boundary condition and bistable nonlinearity, and an elliptic equation with superlinear nonlinearity and sublinear boundary conditions. 相似文献