全文获取类型
收费全文 | 9232篇 |
免费 | 153篇 |
国内免费 | 57篇 |
专业分类
化学 | 3471篇 |
晶体学 | 232篇 |
力学 | 720篇 |
综合类 | 2篇 |
数学 | 1004篇 |
物理学 | 4013篇 |
出版年
2023年 | 43篇 |
2022年 | 115篇 |
2021年 | 110篇 |
2020年 | 84篇 |
2019年 | 109篇 |
2018年 | 141篇 |
2017年 | 105篇 |
2016年 | 170篇 |
2015年 | 128篇 |
2014年 | 226篇 |
2013年 | 401篇 |
2012年 | 569篇 |
2011年 | 670篇 |
2010年 | 530篇 |
2009年 | 526篇 |
2008年 | 547篇 |
2007年 | 486篇 |
2006年 | 507篇 |
2005年 | 364篇 |
2004年 | 347篇 |
2003年 | 282篇 |
2002年 | 233篇 |
2001年 | 444篇 |
2000年 | 360篇 |
1999年 | 238篇 |
1998年 | 183篇 |
1997年 | 164篇 |
1996年 | 165篇 |
1995年 | 130篇 |
1994年 | 117篇 |
1993年 | 83篇 |
1992年 | 94篇 |
1991年 | 99篇 |
1990年 | 87篇 |
1989年 | 73篇 |
1988年 | 54篇 |
1987年 | 38篇 |
1986年 | 32篇 |
1985年 | 42篇 |
1984年 | 37篇 |
1983年 | 23篇 |
1982年 | 33篇 |
1981年 | 33篇 |
1980年 | 25篇 |
1979年 | 21篇 |
1978年 | 26篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 20篇 |
1974年 | 16篇 |
排序方式: 共有9442条查询结果,搜索用时 15 毫秒
251.
Configurations, stabilities and adsorption mechanisms of ground-state MonN and MonN2 (n?=?1–8) clusters are calculated by using the density functional method within the PBE level. Evidently, N atoms tend to approach more Mo atoms. Doping with two N impurity prefers to occupy symmetrical position of the host Mon (n?=?1–8) cluster except for Mo2N2 clusters. Mo4N, Mo6N, Mo2N2, Mo4N2 and Mo6N2 clusters have higher structural stabilities than their neighbors by the second derivative of total binding energy. Mo2N, Mo4N and Mo7N, Mo2N2, Mo5N2 and Mo7N2 clusters have higher kinetic reactivity than their neighbors by the HOMO–LUMO gaps. The adsorption capacity of a N atom to Mo4 cluster is stronger than the other Mo–N clusters. 相似文献
252.
1D-nanostructural zinc oxide (ZnO) with different shapes have been synthesized on p-type Si(1 0 0) and glass substrates via vapor phase growth by heating pure zinc powder at temperatures between 480 and 570 °C. The different ZnO nanostructures depend on the substrates and the growth temperatures. Scanning electron microscopy and X-ray diffraction revealed that a well-aligned nanowires array, which are vertical to the substrate of Si(1 0 0) with 18 sides on their heads, but six sides on their stems, has been formed at 480 °C. Raman study on the ZnO nanostructures shows that the coupling strength between electron and phonon determined by the ratio of the second- to the first-order Raman scattering cross-sections declines with decreasing diameter of the nanowires. However, a little changes of the coupling strength in terms of the width of the nanobelts have been observed. 相似文献
253.
Q. Zhang G.H. Rao H.Z. Dong Y.G. Xiao X.M. Feng G.Y. Liu Y. Zhang J.K. Liang 《Physica B: Condensed Matter》2005,370(1-4):228-235
The crystal structure and magnetic properties of a series of ordered double perovskite oxides (Sr2−3xLa2xBax)FeMoO6 (0x0.3) have been investigated. X-ray powder diffraction reveals that the crystal structure of the compounds changes from a tetragonal I4/m lattice to a cubic lattice around x=0.2. Though the nominal average size of the A site cation of (Sr2−3xLa2xBax)FeMoO6 is designed to be almost independent of x, the refinements of the crystal structure show that the lattice constants increase with x in both the tetragonal and the cubic phase regions due to electron doping. As the x increases, the degree of cationic ordering on the B site is decreased pronouncedly, while the Curie temperature of the compounds is nearly unchanged. The saturation magnetization of the compounds decreases with x and shows a linear dependence on the degree of cation ordering. The resistivity of the parent compound shows a semiconducting behavior below room temperature, but those of the doped samples exhibit a metal–semiconductor transition. A correlation between the resistivity and metal-semiconducting transition temperature (TM−S) is observed. The resistivity and TM−S of the compounds decrease with x for x0.2 and increase for x0.2. Magnetoresistance of the compounds is reduced by the La/Ba doping. All these observations can be understood based on the interplay of the electron doping, change in bandwidth and the anti-site defect concentration. 相似文献
254.
Q.-Y. Shao A.-D. Li J.-B. Cheng H.-Q. Ling D. Wu Z.-G. Liu N.-B. Ming C. Wang H.-W. Zhou B.-Y. Nguyen 《Applied Physics A: Materials Science & Processing》2005,81(6):1181-1185
LaAlO3 (LAO) gate dielectric films were deposited on Si substrates by low-pressure metalorganic chemical vapor deposition. The interfacial structure and composition distribution were investigated by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectroscopy (SIMS), and Auger-electron spectroscopy (AES). HRTEM confirms that there exists an interfacial layer between LAO and Si in most samples. AES, SIMS, and XPS analyses indicate that the interfacial layer is compositionally graded La–Al silicate and the Al element is severely deficient close to the Si surface. Electrical properties of LAO films were evaluated. No evident difference in electrical properties between samples with and without native SiO2 layers was observed. The electrical properties are discussed in terms of LAO growth mechanisms, in relation to the interfacial structure. PACS 73.40.Qv; 81.15.Gh; 77.55.+f; 68.35.-p 相似文献
255.
S. H. Li C. Wang J. S. Liu X. X. Wang R. X. Li G. Q. Ni Z. Z. Xu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,34(1-3):215-218
Using time-of-flight spectrometry, the interaction of intense femtosecond
laser pulses with argon clusters has been studied by measuring the energy
and yield of emitted ions. With two different supersonic nozzles, the
dependence of average ion energy
on cluster size
in a large range of
has been measured. The experimental results indicate that
when the cluster size
, the average ion
energy
Coulomb explosion is the
dominant expansion mechanism. Beyond this size, the average ion energy gets
saturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamic
expansion behavior. We also find that with the increasing gas backing
pressure, there is a maximum ion yield, the ion yield decreases as the gas
backing pressure is further increased. 相似文献
256.
Q. Liu B. Poumellec C. Haut D. Dragoe R. Blum G. Girard J.-E. Bourée A. Kudlinski Y. Quiquempois G. Blaise 《Applied Physics A: Materials Science & Processing》2005,81(6):1213-1219
Amorphous N- or Ge-doped H:SiO2 films deposited on silica by the matrix distributed electron cyclotron resonance-PECVD method were irradiated by an electron-beam with different doses in order to pole the material and induce second harmonic generation (SHG). SHG was measured using the Maker-fringe method. When irradiated at an acceleration voltage of 25 kV, an incident current of 5 nA during 480 s, the N-doped H:SiO2 films exhibited a maximum second harmonic signal in the order of 0.003 pm/V, but when irradiated with an acceleration voltage of 30 kV, at 5 nA during 240 s, the films exhibited a maximum second harmonic signal of 0.006 pm/V. With a smaller current of 0.5 nA during 25 s and 25 kV acceleration voltage, the Ge-doped H:SiO2 films (3.8 at. % Ge) showed a maximum second-order nonlinearity of 0.0005 pm/V. But an H:SiO2 films with a smaller Ge content (1.0 at. % Ge), showed a large SHG: d33=0.09 pm/V when irradiated at 25 kV, 0.5 nA during 15 s. PACS 78.66.J; 42.65.K; 68.60.D 相似文献
257.
X.Q. Yan 《Journal of Physics and Chemistry of Solids》2005,66(5):701-705
In this paper, we report that amorphous silicon oxide nanowires can be grown in a large quantity by chemical vapor deposition with molten gallium as the catalyst in a flow of mixture of SiH4, H2 and N2 at 600 °C. Meanwhile, when we grow these nanowires under the same conditions but without H2, octopus-like silicon oxide nanostructures are obtained. The reasons and mechanisms for the growth of these nanowires and nanostructures are discussed. Blue light emission is observed from SiOx nanowires, which can be attributed to defect centers of high oxygen deficiency. These SiOx nanowires may find applications in nanodevices and reinforcing composites. 相似文献
258.
The traditional diffusion theory, often used for isotropic sources, becomes inaccurate at short source-detector spacings and cannot be applied to media with large absorption or with small scattering strengths. We show that for any type of source anisotropy, a Green's-function-based procedure can remove these limitations. The accuracy of the new approach is examined through a comparison with the numerical solution to the radiative transfer equation. 相似文献
259.
H. Wang S.R. Foltyn L. Civale B. Maiorov Q.X. Jia 《Physica C: Superconductivity and its Applications》2009,469(23-24):2033-2036
Numerous experimental results have suggested that the Jc of YBa2Cu3O7 (YBCO) films is significantly higher near the film–substrate interface than in the remainder of the film. We previously proposed that this effect is due to interfacial pinning enhancement caused by stress and the resulting misfit dislocations at the heteroepitaxial interface. To test this hypothesis we have used a non-superconducting PrBa2Cu3O7?δ (PrBCO) buffer layer to minimize the lattice mismatch with YBCO. We find that the PrBCO layers lower Jc of the 0.4 μm YBCO films in a predictable way, and that, if sufficiently thick (~0.5 μm), they eliminate interfacial enhancement altogether. Our interpretation of this result is that the defects responsible for interfacial enhancement of flux pinning originate at the bottom of the non-superconducting PrBCO layer, which screens the pinning centers from vortices in YBCO. This result demonstrates that the pinning enhancement arises from stress at the film–substrate interface. 相似文献
260.
In this article we have studied the nonlinear interaction between ellipticity and dissipation in a set of model equations (1.1) and established the relation between this interaction and chaos. In addition to theoretical investigations, extensive numerical simulations with these equations have been made, and different routes to chaos have been found. The numerical studies have revealed the chaotic nature of the solutions. 相似文献