全文获取类型
收费全文 | 380928篇 |
免费 | 4288篇 |
国内免费 | 1319篇 |
专业分类
化学 | 202117篇 |
晶体学 | 6148篇 |
力学 | 16100篇 |
综合类 | 5篇 |
数学 | 44774篇 |
物理学 | 117391篇 |
出版年
2020年 | 2947篇 |
2019年 | 3334篇 |
2018年 | 4124篇 |
2017年 | 4116篇 |
2016年 | 6502篇 |
2015年 | 4158篇 |
2014年 | 6456篇 |
2013年 | 17489篇 |
2012年 | 12720篇 |
2011年 | 15594篇 |
2010年 | 10683篇 |
2009年 | 10655篇 |
2008年 | 14257篇 |
2007年 | 14212篇 |
2006年 | 13315篇 |
2005年 | 12200篇 |
2004年 | 11096篇 |
2003年 | 9899篇 |
2002年 | 9728篇 |
2001年 | 11218篇 |
2000年 | 8425篇 |
1999年 | 6607篇 |
1998年 | 5537篇 |
1997年 | 5458篇 |
1996年 | 5143篇 |
1995年 | 4822篇 |
1994年 | 4628篇 |
1993年 | 4667篇 |
1992年 | 5170篇 |
1991年 | 5125篇 |
1990年 | 4881篇 |
1989年 | 4809篇 |
1988年 | 4861篇 |
1987年 | 4719篇 |
1986年 | 4521篇 |
1985年 | 6113篇 |
1984年 | 6296篇 |
1983年 | 5317篇 |
1982年 | 5732篇 |
1981年 | 5465篇 |
1980年 | 5345篇 |
1979年 | 5504篇 |
1978年 | 5768篇 |
1977年 | 5582篇 |
1976年 | 5790篇 |
1975年 | 5292篇 |
1974年 | 5424篇 |
1973年 | 5862篇 |
1972年 | 3707篇 |
1971年 | 2953篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
951.
F.A. Fernández-Lima C.R. Ponciano E. Pedrero E.F. da Silveira 《Applied Surface Science》2006,252(23):8171-8177
Experimental results of laser sputtering of cesium and rubidium iodide secondary ions are presented. A TOF mass spectrometer, operating in linear mode, continuous extraction for positive or negative ions, was used for the analysis of (CsI)nCs+, (CsI)nI−, (RbI)nRb+ and (RbI)nI− ion emission as a function of the laser irradiance. Experimental data show that the cluster ion emission yields decrease exponentially with n, for all the laser irradiances applied. Theoretical analysis of the clusters structure was performed using density functional theory at the B3LYP/LACV3P level, for the positive and negative cluster series. A quasi-equilibrium evolution of the clusters is proposed to extract a parameter characteristic of the cluster recombination process: the effective temperature. The hypothesis of the atomic species’ recombination (during the expansion of a high density highly ionized cloud) leading to cluster formation is confirmed to some extent in a second set of experiments: the UV laser ablation of a mixed and non-mixed cesium iodide and potassium bromide targets. These experiments show that the emission yields contain contributions from both the recombination process and from the sample stoichiometry, even for high laser irradiances. 相似文献
952.
Phase synchronization in a system of three virtual-cathode microwave oscillators (vircators) simulated by coupled van der Pol oscillators is studied. The phasing dynamics of the vircators is visualized with the phase portraits of the system in the triangular coordinates. Different phasing conditions are found. 相似文献
953.
954.
A planar map is a 2-cell embedding of a connected planar graph, loops and parallel edges allowed, on the sphere. A plane map is a planar map with a distinguished outside (“infinite”) face. An unrooted map is an equivalence class of maps under orientation-preserving homeomorphism, and a rooted map is a map with a distinguished oriented edge. Previously we obtained formulae for the number of unrooted planar n-edge maps of various classes, including all maps, non-separable maps, eulerian maps and loopless maps. In this article, using the same technique we obtain closed formulae for counting unrooted plane maps of all these classes and their duals. The corresponding formulae for rooted maps are known to be all sum-free; the formulae that we obtain for unrooted maps contain only a sum over the divisors of n. We count also unrooted two-vertex plane maps. 相似文献
955.
Chaotic dynamics in open systems produces fractals. This can be seen, for example, in the ionization of an electron from a
hydrogen atom in applied parallel electric and magnetic fields. We summarize some of our recent work on the order that can
be found in these fractals. 相似文献
956.
A. P. Tyutnev R. Sh. Ikhsanov E. L. Grin’ G. P. Safonov A. I. Kononenko A. M. Sorokin I. V. Rudenko 《Polymer Science Series A》2006,48(11):1190-1195
A general theory of the phenomenon of recovered voltage in polymers was considered on the basis of representation of an actual poling process by a discrete set of Debye relaxators. Examples of numerical solution of the direct and inverse problems are given. A correlation expression between intentionally aged polymer specimens and recovered-voltage curves was proposed for use in the assessment of the material state of a polymer under actual service conditions. It was shown that it is sufficient to restrict consideration to three relaxation processes in analysis of the phenomenon. 相似文献
957.
A. Ferreira da Silva I. Pepe S.A. Tomás W.M. de Azevedo R. Ahuja 《Applied Surface Science》2006,252(15):5365-5367
In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO2) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO2 thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO2 absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO2 are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO2 films prepared for undoped sol-gels and by sputtering is performed. 相似文献
958.
959.
960.
N.A. Buznikov A.S. Antonov A.B. Granovsky C.G. Kim C.O. Kim X.P. Li S.S. Yoon 《Journal of magnetism and magnetic materials》2006
The giant magnetoimpedance effect in composite wires consisting of a non-magnetic inner core and soft magnetic shell is studied theoretically. It is assumed that the magnetic shell has a helical anisotropy. The current and field distributions in the composite wire are found by means of a simultaneous solution of Maxwell equations and the Landau–Lifshitz equation. The expressions for the diagonal and off-diagonal impedance are obtained for low and high frequencies. The dependences of the impedance on the anisotropy axis angle and the shell thickness are analyzed. Maximum field sensitivity is shown to correspond to the case of the circular anisotropy in the magnetic shell. It is demonstrated that the optimum shell thickness to obtain maximum impedance ratio is equal to the effective skin depth in the magnetic material. 相似文献