全文获取类型
收费全文 | 3535篇 |
免费 | 771篇 |
国内免费 | 742篇 |
专业分类
化学 | 2437篇 |
晶体学 | 221篇 |
力学 | 23篇 |
综合类 | 13篇 |
数学 | 4篇 |
物理学 | 2350篇 |
出版年
2024年 | 26篇 |
2023年 | 77篇 |
2022年 | 142篇 |
2021年 | 158篇 |
2020年 | 182篇 |
2019年 | 148篇 |
2018年 | 119篇 |
2017年 | 139篇 |
2016年 | 188篇 |
2015年 | 177篇 |
2014年 | 236篇 |
2013年 | 321篇 |
2012年 | 258篇 |
2011年 | 313篇 |
2010年 | 234篇 |
2009年 | 276篇 |
2008年 | 214篇 |
2007年 | 319篇 |
2006年 | 292篇 |
2005年 | 171篇 |
2004年 | 166篇 |
2003年 | 148篇 |
2002年 | 86篇 |
2001年 | 110篇 |
2000年 | 84篇 |
1999年 | 88篇 |
1998年 | 110篇 |
1997年 | 66篇 |
1996年 | 38篇 |
1995年 | 28篇 |
1994年 | 30篇 |
1993年 | 24篇 |
1992年 | 16篇 |
1991年 | 9篇 |
1990年 | 13篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1966年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有5048条查询结果,搜索用时 15 毫秒
991.
Hiroyuki Yoshida Hiroshi Deguchi Kazuhiro Miura Masaki Horiuchi Toru Inagaki 《Solid State Ionics》2001,140(3-4):191-199
The oxide ionic conductivity measurements of singly and doubly doped ceria compounds were carried out. Singly and doubly doped ceria used in this study were Ce0.8Ln0.2O1.9 (Ln=Y, Sm, Nd, or La) and Ce0.8La0.1Y0.1O1.9, respectively. Lattice constants of these compounds were in proportion to the ionic radius of the dopant(s). The doubly doped ceria compound showed oxide ionic conductivity comparative to the average of that of each corresponding singly doped sample. This finding indicates that the conductivity is influenced by both dopants in the doubly doped compounds. The extended X-ray absorption fine structure (EXAFS) study showed that the coordination number of oxide ions at the nearest neighbor of cation was related to the ionic conductivity. It was found that the conductivity gave the highest value when oxygen vacancies were randomly distributed in the lattice. This indicates that the local structure seriously affects oxide ionic conduction in singly and doubly doped ceria compounds. 相似文献
992.
基于密度泛函理论的第一性原理研究Fe,Ni单掺杂和(Fe,Ni)共掺杂纤锌矿型ZnO的能带结构、电子态密度分布、介电函数、光学吸收系数,分析了掺杂后电子结构与光学性质的变化.计算结果表明:掺杂体系的费米能级附近电子态密度主要来源于Fe 3d,Ni 3d态电子的贡献;与纯净ZnO相比,Fe,Ni单掺杂和(Fe,Ni)共掺杂ZnO的介电函数虚部均在0.46eV左右出现了一个新峰;Fe,Ni单掺杂和共掺杂ZnO的吸收光谱均发生明显的红移,并都在1.3eV处出现较强吸收峰.结合他人的计算和实验结果,给出了定性的讨
关键词:
氧化锌
掺杂
第一性原理
光学性质 相似文献
993.
Plasma doping is the candidate for semiconductor doping. Accurate simulation of the doping technology is needed for the advanced integrated circuit manufacturing. In this paper, the plasma doping process simulation is performed by using the localized molecular dynamics method. Models that involve the statistics of the implanted compositions, angles and energies are developed. The effect of the model on simulation results is studied. The simulation results about the doping concentration profile are supported by experimental data. 相似文献
994.
Donald F. Gerson 《Journal of Dispersion Science and Technology》2013,34(1):91-108
The physical properties of the intimal surfaces of both natural and artificial arteries are important In the prevention of thrombosis and clotting. It Is expected thati a) the interface between the blood plasma and the intima should be highly negatively charged, to repel negatively charged platelets and other blood constituents, and b) the interfacial free energy at the plasma-intima interface should be as low as possible, to prevent adhesion If the charge barrier is breached. Few measurements of either the zeta potential or the interfacial free energy at the intimal surface can be found in the literature. Zeta potentials of natural and cross-linked bovine carotid intima, and of an expanded Teflon prosthesis were determined by a streaming potential method in 0.9% (w/v) NaC1. Interfacial free energies of both bovine and ovine carotid intima, and of an expanded Teflon prosthesis were also determined by a contact-angle method using water immiscible liquid drops on the intimal surface Immersed in 0.9% (w/v) NaC1. 相似文献
995.
The development of technology of new semiconductor devices requires fundamental studies of a number of phenomena taking place in semiconductors during the doping process or accompanying the doping process. These studies are concerned with the following problems: 1. Diffusion of gold in silicon and the effect of diffusion layers (particularly phosphorus layers) and epitaxial silicon layers on the distribution of gold in thin silicon plates. 2. Distribution of admixtures in silicon introduced with the aid of the ion implantation technique. Our studies concerned with the second of the above mentioned problems comprised an autoradiographic examination of the homogeneity of the beam of phosphorus ions implanted in silicon, and a study of some apparatus factors and of the purity of the basic material on the implantation. 相似文献
996.
S. A. Gevelyuk I. K. Doycho L. P. Prokopovich E. Rysiakiewics-Pasek E. D. Safronsky 《辐射效应与固体损伤》2013,168(1-6):427-432
We have studied the influence of multiple carbon treatments on the properties of silica porous glasses. Each step of each carbon treatment started with filling the voids of porous glass with carbon. During the following anneal carbon interacted with the walls of the voids. It was shown that low dimensional silicon clusters were formed inside the voids as a result of this reaction. In the experiments the photoluminescence spectra and conductivity of carbon-processed specimens were measured. The size-distribution of voids in porous glasses was calculated from absorption—desorption isotherms. An original technique was proposed that allowed to obtain the size-distribution of silicon clusters from the positions of peaks in the photoluminescence spectra. Correlation between the photoluminescence intensity and the sizes of pores was revealed. The observed oscillations in the shapes of the photoluminescence spectra in subsequent cycles of carbon treatment are explained by changes of the number of clusters corresponding to definite peaks in the size distribution spectra. 相似文献
997.
通过光刺激放电(PSD)技术研究了纳米粉末掺杂低密度聚乙烯(LDPE)中的陷阱能级.利用连续扫描法得到了不同掺杂比例的Al2O3,MgO纳米粉末掺杂试样以及相同掺杂比例的多种纳米粉末掺杂试样的PSD电流谱,定性地得出了试样陷阱能级的深浅变化.分步扫描法定量地描述了LDPE试样在Al2O3纳米掺杂前后陷阱能量分布的变化.结果表明,掺杂比例大于0.2%的Al2O3纳米粉末掺杂、大于0.5%的MgO纳米粉末掺杂能够显著地使得LDPE陷阱能级变深.结合纳米掺杂对LDPE空间电荷注入影响的相关报道,可推测纳米掺杂对空间电荷注入的抑制与试样中陷阱能级变深存在密切的关联. 相似文献
998.
Heavily n‐type doped and several nanometres thick In0.485Ga0.515P layers are necessary for various devices. We studied the delta‐doping of this ternary with tellurium; the layers were grown by metalorganic vapour phase epitaxy (MOVPE), and diethyltelluride was used as the precursor. A maximum Hall sheet concentration of 2.75 × 1013 cm–2 was achieved in our samples grown at 560 °C. The Te profiles were analyzed with secondary ion mass spectrometry (SIMS), and a very narrow spectrum with a full width at half maximum of 7.5 nm was measured. This value indicates that the memory effect, referred to in the literature, was practically eliminated with appropriate growth conditions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
999.
Geometries, relative energies, and stabilities of endo- and exohedral complexes, X@Si20H20 and XSi20H20, (X = H+, H, N, P, C?, and Si?) are calculated at B3LYP/6-31G* level. The energy minimum structure of Si20H21 + shows that the proton cannot be positioned in the Si20H20 centre, but prefers attach to Si20H20 exohedrally with C2v symmetry. Most investigated Ih endohedral complexes X@Si20H20 (X = H, N, P, C?, and Si?) are local minima, except for 2N@Si20H20, which is a high-order saddle point. Inclusions energies of the endohedral complexes are calculated, and it reveals that energy penalties caused by encapsulation are rather small. Exohedral complexes XSi20H20 (X = H, N, P, C?, and Si?) have C2v or Cs local minima, and most of them are more stable than their endohedral isomers with the exception of C2v 4PSi20H20 and 4Si?Si20H20. 相似文献
1000.
DC Electrical Conductivity of the Direct Electrochemically Synthesized Polythiophene Metal Complexes
Electrochemical anodic oxidation of a metal anode in an acetone solution of 2,5-diamino-3,4-dicyanothiophene gave the polythiophene metal complexes of Co, Ni, Cu, Zn, Cd, and Sn. Chemical analyses, as well as FTIR and electronic spectral data, are presented to confirm the formulation of the isolated materials. DC electrical conductivity measurements of the polymer complexes were measured in the range 300–500 K in the annealed and 5% doped forms. The products gave electrical conductivity in the semi-conducting region that increased by heat. 相似文献