全文获取类型
收费全文 | 1522篇 |
免费 | 37篇 |
国内免费 | 2篇 |
专业分类
化学 | 828篇 |
晶体学 | 13篇 |
力学 | 65篇 |
数学 | 142篇 |
物理学 | 513篇 |
出版年
2023年 | 8篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2016年 | 27篇 |
2015年 | 35篇 |
2014年 | 27篇 |
2013年 | 61篇 |
2012年 | 80篇 |
2011年 | 82篇 |
2010年 | 55篇 |
2009年 | 54篇 |
2008年 | 68篇 |
2007年 | 72篇 |
2006年 | 84篇 |
2005年 | 78篇 |
2004年 | 62篇 |
2003年 | 56篇 |
2002年 | 43篇 |
2001年 | 23篇 |
2000年 | 36篇 |
1999年 | 16篇 |
1998年 | 13篇 |
1997年 | 20篇 |
1996年 | 22篇 |
1995年 | 27篇 |
1994年 | 23篇 |
1993年 | 34篇 |
1992年 | 29篇 |
1991年 | 12篇 |
1990年 | 23篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1943年 | 7篇 |
1934年 | 6篇 |
1933年 | 11篇 |
1931年 | 8篇 |
排序方式: 共有1561条查询结果,搜索用时 15 毫秒
921.
Corbitt T Chen Y Innerhofer E Müller-Ebhardt H Ottaway D Rehbein H Sigg D Whitcomb S Wipf C Mavalvala N 《Physical review letters》2007,98(15):150802
We report on a stable optical trap suitable for a macroscopic mirror, wherein the dynamics of the mirror are fully dominated by radiation pressure. The technique employs two frequency-offset laser fields to simultaneously create a stiff optical restoring force and a viscous optical damping force. We show how these forces may be used to optically trap a free mass without introducing thermal noise, and we demonstrate the technique experimentally with a 1 g mirror. The observed optical spring has an inferred Young's modulus of 1.2 TPa, 20% stiffer than diamond. The trap is intrinsically cold and reaches an effective temperature of 0.8 K, limited by technical noise in our apparatus. 相似文献
922.
Rodenburg JM Hurst AC Cullis AG Dobson BR Pfeiffer F Bunk O David C Jefimovs K Johnson I 《Physical review letters》2007,98(3):034801
We demonstrate a hard-x-ray microscope that does not use a lens and is not limited to a small field of view or an object of finite size. The method does not suffer any of the physical constraints, convergence problems, or defocus ambiguities that often arise in conventional phase-retrieval diffractive imaging techniques. Calculation times are about a thousand times shorter than in current iterative algorithms. We need no a priori knowledge about the object, which can be a transmission function with both modulus and phase components. The technique has revolutionary implications for x-ray imaging of all classes of specimen. 相似文献
923.
Manfra MJ de Picciotto R Jiang Z Simon SH Pfeiffer LN West KW Sergent AM 《Physical review letters》2007,98(20):206804
Anisotropic charge transport is observed in a two-dimensional (2D) hole system in a perpendicular magnetic field at filling factors nu=7/2, nu=11/2, and nu=13/2 at low temperature. In stark contrast, the transport at nu=9/2 is isotropic for all temperatures. Isotropic hole transport at nu=7/2 is restored for sufficiently low 2D densities or an asymmetric confining potential. The density and symmetry dependences of the observed anisotropies suggest that strong spin-orbit coupling in the hole system contributes to the unusual transport behavior. 相似文献
924.
We investigate triplet-triplet annihilation in molecular host-guest systems where triplets are localized on spatially separated guest molecules. Our results indicate that the dominant mechanism of annihilation is single-step long-range (F?rster-type) energy transfer between two excited guests. This mechanism leads to a fundamental limit for the efficiency of phosphorescent organic light emitting diodes at high luminance. Our model is confirmed by photoluminescence decay experiments on 2,3,7,8,12,13,17,18-octaethylporphine platinum as guest in a host matrix of 4,4'-N,N'-dicarbazole-biphenyl. 相似文献
925.
Cyclotron resonance at microwave frequencies is used to measure the band mass (mb) of the two-dimensional holes (2DHs) in carbon-doped (100) GaAs/ AlxGa1−xAs heterostructures. The measured mb shows strong dependences on both the 2DH density (p) and the GaAs quantum well width (W). For a fixed W, in the density range (0.4×1011 to 1.1×1011 cm−2) studied here, mb increases with p, consistently with previous studies of the 2DHs on the (311)A surface. For a fixed , mb increases from 0.22me at to 0.50me at , and saturates around 0.51me for . 相似文献
926.
Nikitin K Müller-Bunz H Ortin Y McGlinchey MJ 《Organic & biomolecular chemistry》2007,5(12):1952-1960
The indenyltriptycenes, and , where the 3- or 2-indenyl, respectively, is attached at the 9-position of the triptycene, are attractive prototypes of molecular gearing systems that can also incorporate a brake. These molecules have been prepared from their respective indenylanthracenes, and , by the [4 + 2] cycloaddition of benzyne to the anthracene fragment, and the rotational barriers about the indenyl-triptycenyl single bonds in (12 kcal mol(-1)) and (<9 kcal mol(-1)) have been measured. The precursor anthracenes, and , were prepared by using palladium-catalysed coupling reactions. Unexpectedly, the Heck-type reaction of 9-bromoanthracene, , with indene leads to the formation of 3-indenylanthracene ; moreover, this process is accompanied by a novel palladium-catalysed carbocyclisation reaction leading to the indenophenanthrylene . The addition of benzyne to 9-(3-indenyl)anthracene, , yields the corresponding indenyltriptycene, , and, surprisingly, the anthracenyl methano-bridged phenanthrene . It has been demonstrated that 2-arylindenes can act as 1,3-dienes in the [4 + 2] cycloadditions of benzyne. The products , , and have been characterised by X-ray crystallography. 相似文献
927.
Finze M Bernhardt E Willner H 《Angewandte Chemie (International ed. in English)》2007,46(48):9180-9196
The synthesis of salts with the [B(CF3)4]− anion has been the starting point for new developments in the field of trifluoromethylboron chemistry. In contrast to the previous syntheses of (CF3)nB derivatives (n=1–3), achieved exclusively by CF3 transfer, the synthesis of the [B(CF3)4]− anion was accomplished by fluorination of the [B(CN)4]− anion with ClF or ClF3 in anhydrous HF. Owing to its thermal and chemical stability, [B(CF3)4]− is an attractive weakly coordinating anion. However, in concentrated sulfuric acid one of the four CF3 groups is solvolyzed to a CO ligand to yield the neutral borane carbonyl (CF3)3BCO. It has been shown that the borane carbonyl compound is a versatile synthetic building block, and numerous reactions have been investigated. The addition of nucleophiles to the C atom of the CO ligand is favored, and examples for new derivatives are the anions [(CF3)3BCPnic]− (Pnic=N, P, As). Under certain conditions, ligand-exchange reactions are also observed, for example, the formation of (CF3)3BNCH. Finally, the borane carbonyl compound is a component of the conjugated Brønsted–Lewis superacid HF/(CF3)3BCO. 相似文献
928.
929.
Eduard Bernhardt Helge Willner Friedhelm Aubke 《Angewandte Chemie (International ed. in English)》1999,38(6):823-825
The first carbonyl halogen cation in the condensed phase , the superelectrophilic [ClCO]+ ion, has been clearly and unambiguously established by its complete, fully assigned vibrational spectrum. The cation is obtained by the reaction of COCl2 with SbF5 at room temperature in the form of a suspension, in which it is stabilized by oligomeric fluoroantimonate ions. 相似文献
930.
Beng Sim Chuah Florence Geneste Andrew B. Holmes Rainer E. Martin Henning Rost Franco Cacialli Richard H. Friend Hans‐Heinrich Hrhold Steffen Pfeiffer Do‐Hoon Hwang 《Macromolecular Symposia》2000,154(1):177-186
The synthesis of the highly fluorescent mono‐ and bis‐silylated poly(1,4‐phenylene vinylene) derivatives 1 and 2 is reported. The Gilch dehydrohalogenation polycondensation and the Horner synthesis of strictly alternating copolymers have been used to prepare the copolymers 8‐11 and 14, 16‐18 , respectively, in which the tunability of various optoelectonic properties may be examined systematically. 相似文献