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61.
The structure of the Si3Ox (x=2, 3) cluster is investigated; we find that the geometry of Si3O2 is similar to that of Si3O3 except for the oxygen-deficient defect structure (Si-Si band) which exists only in the Si3O2 cluster. It is known that oxygen-deficient defects are used to explain visible luminescence (especially blue, purple and ultraviolet light) from silicon-based materials, which are directly bound up with the excited states of the molecules. Therefore the excitation properties of the two clusters are also studied. Our results show that the absorption spectrum of Si3O2 is concentrated in the visible light region. In contrast, the absorption spectrum of Si3O3 is mainly located in the ultraviolet light region. The calculations are perfectly consistent with experimental data and also support the theory of oxygen-deficient defects. 相似文献
62.
63.
Zhan-Li Liu Zhuo Zhuang Xiao-Ming Liu Xue-Chuan Zhao Yuan Gao 《Acta Mechanica Sinica》2011,27(2):266-276
The Bauschinger and size effects in the thinfilm plasticity theory arising from the defect-energy of geometrically necessary dislocations (GNDs) are analytically investigated in this paper. Firstly, this defect-energy is deduced based on the elastic interactions of coupling dislocations (or pile-ups) moving on the closed neighboring slip plane. This energy is a quadratic function of the GNDs density, and includes an elastic interaction coefficient and an energetic length scale L. By incorporating it into the work- conjugate strain gradient plasticity theory of Gurtin, an energetic stress associated with this defect energy is obtained, which just plays the role of back stress in the kinematic hardening model. Then this back-stress hardening model is used to investigate the Bauschinger and size effects in the tension problem of single crystal Al films with passivation layers. The tension stress in the film shows a reverse dependence on the film thickness h. By comparing it with discrete-dislocation simulation results, the length scale L is determined, which is just several slip plane spacing, and accords well with our physical interpretation for the defect- energy. The Bauschinger effect after unloading is analyzed by combining this back-stress hardening model with a friction model. The effects of film thickness and pre-strain on the reversed plastic strain after unloading are quantified and qualitatively compared with experiment results. 相似文献
64.
65.
XU Xiaodong CHEN Xiang LI Kaiyuan LIU Xiaojun CHENG Jianchun Christ Glorieux 《声学学报:英文版》2011,(4):391-397
A laser ultrasonics method is used to characterize the propagation properties of surface wave traveling on the surface of materials with sub-surface defect in 2D.Linear and nonlinear propagation properties of ultrasonics caused by the defects have been detected in experiment. A theoretical model is proposed and used to study the linear and nonlinear properties of ultrasonics caused by the defect.The numerical results indicate that the nonlinear ultrasonic wave will be excited when a finite amplitude ultrasonics propagates on the surface of materials with sub-surface defect.The theoretical analysis confirms that the nonlinear wave is caused by the "clapping"of the interface of defect instead of the mode conversions of ultrasonics. 相似文献
66.
The annealing process for boron implantation is a crucial step during large size nuclear radiation detector fabrication. It can reduce the lattice defects and the projection straggling. A two-step annealing process for boron implantation was developed instead of a one-step annealing process, and the reverse body resistance of a silicon micro-strip detector was significantly increased, which means that the performance of the detector was improved. 相似文献
67.
本文采用基于密度泛函理论的第一性原理对zigzag型石墨烯纳米带中含有不同Stone-Wales缺陷的电子结构特性和光学性能进行研究. 考虑了两种模型:不计电子自旋和考虑电子自旋的情况.研究发现:不计电子自旋情况下,含对称Stone-Wales缺陷的石墨烯纳米带在缺陷区域出现了凹凸不平的折皱构型,两种不同的Stone-Wales缺陷都引起了电荷的重新分布.考虑电子自旋时,Stone-Wales缺陷的引入对石墨烯纳米带自旋密度有显著影响,也引起了不同自旋的电子态密度的变化.进一步研究了纳米带的光学性能,发现
关键词:
石墨烯纳米带
Stone-Wales缺陷
电子结构
光学性能 相似文献
68.
应用水热法制备了注射器样纳米结构氧化锌样品,室温下测量其真空场发射特性.根据测量数据,基于Fowler-Nordheim方程,估算了场发射效应增强因子,观察到增强因子随外加电压增加取值的两阶段性;结合样品的光致发光谱和能量散射谱,应用半导体材料中强场效应理论,结合场发射电流密度测量系统的串联电路等效,研究样品中空位对场发射特性影响机理.结果表明,制备过程中形成的锌、氧空位,在样品中产生了相当于杂质态的缺陷能级,缺陷能级与样品形貌共同作用,使样品较大的增强因子随场强增加而阶跃性下降.最后,用电化学沉淀法和气
关键词:
场发射
强场效应
缺陷态
串联等效 相似文献
69.
采用基于密度泛函理论的赝势平面波第一性原理方法,研究了LiNH2缺陷及其掺杂原子交互作用对其释氢影响.通过对其进行优化求得它们的局域最稳定结构并计算了含间隙H原子缺陷的LiNH2及其掺杂合金的结合能、间隙缺陷形成能、态密度和电荷布居.结果表明: 系统结合能不能反映LiNH2及其掺杂合金的释氢性质;平衡时,LiNH2中有一定的间隙氢原子存在,Mg,Ti掺杂使形成能大大降低,大大增大了间隙氢的浓度. 间隙H原子在带隙引入了缺陷能级使带隙大大减小,提高释氢能力.间隙H原子导致[NH2]-中N-H原子间相互作用减弱,容易释氢.间隙H与[NH2]-中N存在共价作用,可以解释LiNH2释氢反应中NH3的放出.当存在掺杂时,N-H键的键强不均衡,部分较弱,部分较强,较弱的N-H键中H容易放出.
关键词:
储氢材料
第一性原理
缺陷
释氢机理 相似文献
70.
对熔体急冷法制备的Fe43Co43Hf7B6Cu1非晶合金进行了200,300,400和500 ℃保温30 min的退火处理,用正电子湮没寿命谱、X射线衍射、穆斯堡尔谱等方法研究了退火后试样的结构及结构缺陷变化.结果表明,在非晶合金的制备态,正电子主要在非晶基体相空位尺寸的自由体积中湮没,湮没寿命τ1为158.4 ps,强度I1关键词:
43Co43Hf7B6Cu1非晶')" href="#">Fe43Co43Hf7B6Cu1非晶
退火处理
正电子湮没寿命
结构与结构缺陷 相似文献