全文获取类型
收费全文 | 585330篇 |
免费 | 4174篇 |
国内免费 | 1298篇 |
专业分类
化学 | 285421篇 |
晶体学 | 8291篇 |
力学 | 30801篇 |
综合类 | 17篇 |
数学 | 85046篇 |
物理学 | 181226篇 |
出版年
2021年 | 5036篇 |
2020年 | 5480篇 |
2019年 | 6223篇 |
2018年 | 13030篇 |
2017年 | 13429篇 |
2016年 | 13905篇 |
2015年 | 6581篇 |
2014年 | 10514篇 |
2013年 | 23573篇 |
2012年 | 20897篇 |
2011年 | 29145篇 |
2010年 | 20578篇 |
2009年 | 20559篇 |
2008年 | 26786篇 |
2007年 | 28894篇 |
2006年 | 18748篇 |
2005年 | 20053篇 |
2004年 | 17206篇 |
2003年 | 16104篇 |
2002年 | 14816篇 |
2001年 | 14836篇 |
2000年 | 11597篇 |
1999年 | 8787篇 |
1998年 | 7630篇 |
1997年 | 7487篇 |
1996年 | 7084篇 |
1995年 | 6361篇 |
1994年 | 6346篇 |
1993年 | 6098篇 |
1992年 | 6444篇 |
1991年 | 6939篇 |
1990年 | 6645篇 |
1989年 | 6565篇 |
1988年 | 6409篇 |
1987年 | 6209篇 |
1986年 | 5954篇 |
1985年 | 7495篇 |
1984年 | 7867篇 |
1983年 | 6615篇 |
1982年 | 6907篇 |
1981年 | 6417篇 |
1980年 | 6094篇 |
1979年 | 6607篇 |
1978年 | 6841篇 |
1977年 | 6660篇 |
1976年 | 6645篇 |
1975年 | 6360篇 |
1974年 | 6175篇 |
1973年 | 6512篇 |
1972年 | 4746篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
V. A. Zayats A. N. Nikolaevskii T. A. Filippenko O. P. Kniga G. A. Tikhonova 《Russian Journal of Applied Chemistry》2006,79(10):1651-1654
Specific features of the initiated oxidation of polyethylene and its low-molecular-weight analogue tridecane, associated with the occurrence of the process in the short-chain mode, were studied. 相似文献
992.
993.
Michael A. Mandell 《Publications Mathématiques de L'IHéS》2006,103(1):213-246
Finite type nilpotent spaces are weakly equivalent if and only if their singular cochains are quasi-isomorphic as E∞ algebras. The cochain functor from the homotopy category of finite type nilpotent spaces to the homotopy category of E∞ algebras is faithful but not full. 相似文献
994.
The not-sufficient-enough conductance of semioxidized protonated polyaniline (PANI) is usually attributed to the presence of ordered quasi-metallic domains surrounded by a poorly conducting amorphous phase. The paper presents experimental results testifying to the existence, in semioxidized PANI, of multilevel redox heterogeneity that crucially effects the conductance magnitude in view of specific topology at which higher-oxidized (conducting) domains are surrounded by less oxidized (poorly conducting) domains and because the PANI conduction is extremely sensitive to the oxidation degree. It is shown experimentally that the interphase doping with metals and degenerate semiconductors of a semioxidized salt of PANI and poly(2-acrylamide-2-methyl-1-propanesulfonic acid) (PAMPSA) with a 1: 2 ratio between PANI and PAMPSA raises the PANI-PAMPSA conductivity by 3–8 orders of magnitude due to the formation near the interface of thin layers whose conductance depends on the work function of the material in contact with PANI-PAMPSA and in extreme cases substantially exceeds the conductance of gold and copper at room temperature. 相似文献
995.
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
996.
A. Shaporenko A. Terfort M. Grunze M. Zharnikov 《Journal of Electron Spectroscopy and Related Phenomena》2006
Analysis of photoemission spectra of complex thioaromatic self-assembled monolayers (SAMs) requires the knowledge and understanding of such spectra for the basic systems. Keeping this goal in mind, synchrotron-based high-resolution X-ray photoelectron spectroscopy was used to characterize SAMs formed from the simplest thioaromatic compounds, namely thiophenol, 1,1′-biphenyl-4-thiol and 1,1′;4′,1″-terphenyl-4-thiol on evaporated Au(1 1 1) and Ag(1 1 1) substrates. The acquired S 2p and C 1s spectra were analyzed in terms of fine structure and initial and final state effects in the photoemission process. The assignment of the individual spectral features was considered in detail. Conclusions on quality and chemical and structural homogeneity of the investigated SAMs were derived. 相似文献
997.
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
998.
The discovery of the neutrino oscillation pattern with solar and atmospheric neutrinos has stimulated systematic studies with long-baseline accelerator experiments. Precise neutrino beamline calculations have demonstrated the importance and paucity of existing hadroproduction data needed to shape the primary meson production in targets and tune available Monte Carlo codes for hadronic shower simulation. After a brief introduction to the physics of neutrino beams, available hadron production data will be reviewed with regards to their parametrization. Fast simulations based on such parameterizations and full Monte Carlo simulations of neutrino beamlines will then be illustrated. The prospective impact of new hadroproduction experiments, such as HARP at CERN and MIPP at Fermilab, will be shown together with some neutrino beamline simulations. 相似文献
999.
For any finite dimensional control system with arbitrary cost, Pontryagin's Maximum Principle (PMP) [N. Bensalem, Localisation des courbes anormales et problème d'accessibilité sur un groupe de Lie hilbertien nilpotent de degré 2, Thèse de doctorat, Université de Savoie, 1998. [6]] gives necessary conditions for optimality of trajectories. In the infinite dimensional case, it is well known that these conditions are no more true in general. The purpose of this paper is to establish an “approached” version of PMP for infinite dimensional bilinear systems, with fixed final time and without constraints on the final state. Moreover, if the set of control is contained in a closed bounded convex subset with operators defining its dynamics are compact, or if it is contained in a finite dimensional space, we get an “exact” version of PMP. We also give two applications of these results. The first one deals with sub-Riemannian geometry on nilpotent Hilbertian Lie groups for which we can define a sub-Riemannian distance. The second one deals with heat equation for which we analyse the necessary conditions to give the optimal controls. 相似文献
1000.