全文获取类型
收费全文 | 4660篇 |
免费 | 136篇 |
国内免费 | 22篇 |
专业分类
化学 | 3097篇 |
晶体学 | 20篇 |
力学 | 138篇 |
数学 | 654篇 |
物理学 | 909篇 |
出版年
2023年 | 29篇 |
2022年 | 101篇 |
2021年 | 119篇 |
2020年 | 71篇 |
2019年 | 89篇 |
2018年 | 60篇 |
2017年 | 72篇 |
2016年 | 187篇 |
2015年 | 107篇 |
2014年 | 152篇 |
2013年 | 252篇 |
2012年 | 293篇 |
2011年 | 335篇 |
2010年 | 202篇 |
2009年 | 200篇 |
2008年 | 287篇 |
2007年 | 298篇 |
2006年 | 243篇 |
2005年 | 257篇 |
2004年 | 213篇 |
2003年 | 186篇 |
2002年 | 160篇 |
2001年 | 55篇 |
2000年 | 59篇 |
1999年 | 48篇 |
1998年 | 41篇 |
1997年 | 44篇 |
1996年 | 66篇 |
1995年 | 53篇 |
1994年 | 52篇 |
1993年 | 33篇 |
1992年 | 21篇 |
1991年 | 28篇 |
1990年 | 30篇 |
1989年 | 35篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 27篇 |
1984年 | 39篇 |
1983年 | 18篇 |
1982年 | 24篇 |
1981年 | 30篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1978年 | 19篇 |
1977年 | 12篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1970年 | 7篇 |
排序方式: 共有4818条查询结果,搜索用时 515 毫秒
971.
Franciscus Jozef Vanhecke Antonio Roberto da Silva Cassio Sigaud 《Brazilian Journal of Physics》2012,42(5-6):471-474
In this short communication, we examine the relevance of the signature of the space-time metric in the construction of the product of a pseudo-Riemannian spectral triple with a finite triple describing the internal geometry. We obtain arguments favoring the appearance of SU(2) and U(1) as gage groups in the standard model. 相似文献
972.
Mupparapu R Vynck K Malfanti I Vignolini S Burresi M Scudo P Fusco R Wiersma DS 《Optics letters》2012,37(3):368-370
Metallic nanoparticles are known to enhance nonlinear optical processes due to a local enhancement of the optical field. This strategy has been proposed to enhance downconversion in thin film solar cells, but has various disadvantages, among which is the fact that the enhancement occurs only in a tiny volume close to the particles. We report on a very different physical mechanism that can lead to significant downconversion enhancement, namely, that of resonant light scattering, and which is a large volume effect. We show that only a tiny amount of resonantly scattering metallic (aluminum) nanoparticles is enough to create a significant enhancement of the fluorescence of dye molecules in the visible wavelength range. The strategy can be applied in general to increase the emission of UV-absorbing constituents, and is of particular use for solar energy. 相似文献
973.
P Zhang Y Hu D Cannan A Salandrino T Li R Morandotti X Zhang Z Chen 《Optics letters》2012,37(14):2820-2822
We study linear and nonlinear self-accelerating beams propagating along circular trajectories beyond the paraxial approximation. Such nonparaxial accelerating beams are exact solutions of the Helmholtz equation, preserving their shapes during propagation even under nonlinearity. We generate experimentally and observe directly these large-angle bending beams in colloidal suspensions of polystyrene nanoparticles. 相似文献
974.
Y Hu Z Sun D Bongiovanni D Song C Lou J Xu Z Chen R Morandotti 《Optics letters》2012,37(15):3201-3203
We demonstrate theoretically and experimentally that a finite Airy beam changes its trajectory while maintaining its acceleration in nonlinear photorefractive media. During this process, the spatial spectrum reshapes dramatically, leading to negative (or positive) spectral defects on the initial spectral distribution under a self-focusing (or defocusing) nonlinearity. 相似文献
975.
Vincenzo Piccialli Sabrina Zaccaria Roberto Centore Angela Tuzi Nicola Borbone Giorgia Oliviero Stefano D’Errico Valentina D’Atri 《Journal of chemical crystallography》2012,42(4):360-365
Abstract
The conformational arrangement of an all-threo bis-THF diol compound, synthesized through the RuO4-catalysed oxidative bis-cyclization of farnesyl acetate, was determined via crystallographic analysis and detailed 2D-NMR solution studies. The bis-THF compound crystallizes in the orthorhombic Pbca space group, with unit cell parameters a = 10.496(1), b = 17.974(1), c = 19.777(2) ?, Z = 8. The final refinement converged to R 1 = 0.0484 for 4714 independent observed reflections having I > 2σ(I). There is a good agreement between the solution molecular conformation determined by 2D-NMR and the X-ray molecular conformation. The molecule adopts a folded, horse shoe-type conformation both in solution and in the crystal, that suggests aptitude to coordinate cations. Additionally, in the crystals, the molecular conformation is stabilized by intramolecular and intermolecular H-bonding. 相似文献976.
Bellussi G Millini R Montanari E Carati A Rizzo C Parker WO Cruciani G de Angelis A Bonoldi L Zanardi S 《Chemical communications (Cambridge, England)》2012,48(59):7356-7358
ECS-14, a crystalline microporous hybrid organic-inorganic aluminosilicate, has been synthesized by using 1,4-bis-(triethoxysilyl)-benzene (BTEB) as a source of silica. Its structure contains a system of linear channels with 12-membered ring openings, running along the [001] direction, resembling the pore architecture of the AFI framework type. 相似文献
977.
Castriciano MA Romeo A Zagami R Micali N Scolaro LM 《Chemical communications (Cambridge, England)》2012,48(40):4872-4874
The kinetics of growth for chiral J-aggregates of H(4)TPPS(4) porphyrin have been investigated under different experimental conditions in the presence of tartaric acid. The observed rate constants and the anisotropy factor g show a defined dependence on the enantiomer used as a chiral templating agent. 相似文献
978.
Curcio A Marotta R Riedinger A Palumberi D Falqui A Pellegrino T 《Chemical communications (Cambridge, England)》2012,48(18):2400-2402
We here exploit pH-responsive nanogels as carriers to deliver functional anti-GFP siRNA and superparamagnetic IONPs to HeLa-GFP cells. The siRNA release via pH-mediated endosomal escape is shown. The IONPs act first as magnetofection agents to boost cellular uptake and then as probes to track the release mechanism by electron microscopy. 相似文献
979.
Mashinsky VM Karatun NM Bogatyrev VA Sigaev VN Golubev NV Ignat'eva ES Lorenzi R Mozzati MC Paleari A Dianov EM 《Microscopy and microanalysis》2012,18(2):259-265
A spectroscopic protocol is proposed to implement confocal microfluorescence imaging to the analysis of microinhomogeneity in the nanocrystallization of the core of fibers belonging to a new kind of broadband fiber amplifier based on glass with embedded nanocrystals. Nanocrystallization, crucial for achieving an adequate light emission efficiency of transition metal ions in these materials, has to be as homogeneous as possible in the fiber to assure optical amplification. This requirement calls for a sensitive method for monitoring nanostructuring in oxide glasses. Here we show that mapping microfluorescence excited at 633 nm by a He-Ne laser may give a useful tool in this regard, thanks to quasi-resonant excitation of coordination defects typical of germanosilicate materials, such as nonbridging oxygens and charged Ge-O-Ge sites, whose fluorescence are shown to undergo spectral modifications when nanocrystals form into the glass. The method has been positively checked on prototypes of optical fibers--preventively characterized by means of scanning electron microscopy and energy dispersive spectroscopy--fabricated from preforms of Ni-doped Li?O-Na?O-Sb?O?-Ga?O?-GeO?-SiO? glass in silica cladding and subjected to heat treatment to activate gallium oxide nanocrystal growth. The method indeed enables not only the mapping of the crystallization degree but also the identification of drawing-induced defects in the fiber cladding. 相似文献
980.
Venturoni F Gioiello A Sardella R Natalini B Pellicciari R 《Organic & biomolecular chemistry》2012,10(20):4109-4115
A multi-gram scale protocol for the N-acyl amidation of bile acids with glycine and taurine has been successfully developed under continuous flow processing conditions. Selecting ursodeoxycholic acid (UDCA) as the model compound and N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) as the condensing agent, a modular mesoreactor assisted flow set-up was employed to significantly speed up the optimization of the reaction conditions and the flow scale-up synthesis. The results in terms of yield, in line purification, analysis, and implemented flow set-up for the reaction optimization and large scale production are reported and discussed. 相似文献