全文获取类型
收费全文 | 1940篇 |
免费 | 80篇 |
国内免费 | 6篇 |
专业分类
化学 | 1286篇 |
晶体学 | 11篇 |
力学 | 70篇 |
综合类 | 2篇 |
数学 | 210篇 |
物理学 | 447篇 |
出版年
2023年 | 12篇 |
2022年 | 21篇 |
2021年 | 38篇 |
2020年 | 35篇 |
2019年 | 19篇 |
2018年 | 28篇 |
2017年 | 16篇 |
2016年 | 50篇 |
2015年 | 44篇 |
2014年 | 57篇 |
2013年 | 100篇 |
2012年 | 135篇 |
2011年 | 131篇 |
2010年 | 79篇 |
2009年 | 85篇 |
2008年 | 132篇 |
2007年 | 127篇 |
2006年 | 114篇 |
2005年 | 96篇 |
2004年 | 71篇 |
2003年 | 72篇 |
2002年 | 85篇 |
2001年 | 30篇 |
2000年 | 43篇 |
1999年 | 20篇 |
1998年 | 20篇 |
1997年 | 25篇 |
1996年 | 31篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 21篇 |
1992年 | 23篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 8篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1974年 | 12篇 |
1973年 | 6篇 |
1972年 | 7篇 |
排序方式: 共有2026条查询结果,搜索用时 15 毫秒
991.
Silsesquioxane-based nanocomposite dendrimers with photo-luminescent and charge transport properties
The synthesis and characterization of octavinylsilsesquioxane (OVS)-based nanocomposite dendrimers with luminescent and charge transport properties are reported. The nanocomposite dendrimers were prepared in high yield using mild Heck chemistry of mono-haloaromatic compounds with the peripheral vinylsilane groups of OVS. Attachment of 2-naphthalene, 2-(9,9-dimethyl)fluorene, and 2-(4-phenyl)-5-(1-naphthyl)-1,3,4-oxadiazole resulted in materials with blue-violet emission (360-380 nm) and photo-luminescent quantum efficiencies (PLQEs) from 1 to 26%. Blue-green emission was observed for attachment of 1-pyrene, 9-anthracene, and N1-(4-phenyl)-N1,N4,N4-triphenylbenzene-1,4-diamine with PLQEs ranging from 23 to 50%. Despite the planar characteristics of the organic dendrons, the nanocomposite dendrimers are completely amorphous and have high glass transition temperatures (Tg) ranging from 115 to 186 degrees C with decomposition temperatures (Td) exceeding 450 degrees C. Matrix-assisted laser desorption ionization-time of flight shows that unlike traditional Heck chemistry, haloaromatic compounds are adding twice across the vinylsilane groups. Finally, organic light emitting diodes using the aromatic amine-based dendrimer as hole injection layers show 55% improvement in device efficiency over traditional materials (5.16 vs. 3.24 cd A(-1)) with brightness levels exceeding 40,000 cd m(-2). 相似文献
992.
Emel Sungur Lo?c Mager Alex Boeglin Min-Hui Li Patrick Keller Kokou D. Dorkenoo 《Applied Physics A: Materials Science & Processing》2010,98(1):119-122
We have investigated the behaviour of temperature dependent periodic-index gratings fabricated in a nematic elastomer. The
gratings have been obtained by photopolymerisation under a microscopy apparatus. Contraction properties, as well as diffraction
properties, have been studied as a function of temperature. Unidirectional contraction has been demonstrated by means of circular
figure deformation and the polarisation dependency of the diffraction by the gratings has been determined. 相似文献
993.
Wimmer K Kröll T Krücken R Bildstein V Gernhäuser R Bastin B Bree N Diriken J Van Duppen P Huyse M Patronis N Vermaelen P Voulot D Van de Walle J Wenander F Fraile LM Chapman R Hadinia B Orlandi R Smith JF Lutter R Thirolf PG Labiche M Blazhev A Kalkühler M Reiter P Seidlitz M Warr N Macchiavelli AO Jeppesen HB Fiori E Georgiev G Schrieder G Das Gupta S Lo Bianco G Nardelli S Butterworth J Johansen J Riisager K 《Physical review letters》2010,105(25):252501
The "island of inversion" nucleus 32 Mg has been studied by a (t, p) two neutron transfer reaction in inverse kinematics at REX-ISOLDE. The shape coexistent excited 0+ state in 32 Mg has been identified by the characteristic angular distribution of the protons of the Δ L=0 transfer. The excitation energy of 1058 keV is much lower than predicted by any theoretical model. The low γ-ray intensity observed for the decay of this 0+ state indicates a lifetime of more than 10 ns. Deduced spectroscopic amplitudes are compared with occupation numbers from shell-model calculations. 相似文献
994.
Fast removal and recovery of Cr(VI) using surface-modified jacobsite (MnFe2O4) nanoparticles 总被引:1,自引:0,他引:1
In this work, the effectiveness of surface-modified jacobsite (MnFe2O4) nanoparticles was investigated for the removal and recovery of Cr(VI) from synthetic wastewater. Ten nanometer modified MnFe2O4 nanoparticles were produced to be a new adsorbent using a co-precipitation method followed by a surface redox reaction. The equilibrium time for Cr(VI) adsorption onto modified MnFe2O4 nanoparticles was as short as 5 min, and the adsorption data fit the Langmuir model well. The maximum uptake of 31.5 mg of Cr(VI)/g of modified MnFe2O4 was obtained at pH 2, which was comparable with other common adsorbents such as activated carbon and sawdust. The effects of ligands (EDTA, SO4(2-), NH4+) and ionic strength were studied in a pH range of 2-10. EDTA and SO4(2-) inhibited the adsorption of Cr(VI) over the entire pH range studied, whereas NH4+ enhanced the uptake of Cr(VI) at pH greater than 6.5. The mechanisms leading to Cr(VI) adsorption by modified MnFe2O4 nanoparticles were determined by X-ray diffraction and X-ray photoelectron spectroscopy to be a combination of electrostatic interaction and ion exchange. Regeneration studies indicated the potential reuse of the modified MnFe2O4 nanoparticles without sacrificing adsorption capacity and the possible recycling of Cr(VI) without changing the valence. 相似文献
995.
Esteban Malel Dr. Roland Ludwig Prof. Dr. Lo Gorton Prof. Dr. Daniel Mandler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(38):11697-11706
Cellobiose dehydrogenase (CDH) is a fascinating extracellular fungal enzyme that consists of two domains, one carrying a flavin adenine dinucleotide (FAD) and the other a cytochrome‐type heme b group as cofactors. The two domains are interconnected by a linker and electrons can shuttle from the FAD to the heme group by intramolecular electron transfer. Electron transfer between CDH and an electrode can occur by direct electron transfer (DET) and by mediated electron transfer (MET). This characteristic makes CDH an interesting candidate for integration in systems such as biosensors and biofuel cells. Moreover, it makes CDH an alternative for the reduction of metal ions through DET and MET. In this work we have explored the localized deposition of gold on Pd substrates by CDH through DET and MET. For this purpose we exploited the advantage of scanning electrochemical microscopy (SECM) as a patterning tool. We first demonstrated that gold nanoparticles can be formed in homogenous solution. Then we showed that Au nanoparticles can also be locally formed and deposited on surfaces through DET at low pH and by MET at neutral pH using benzoquinone/hydroquinone as mediator. 相似文献
996.
This paper proposes an improved image coding scheme based on vector quantization. It is well known that the image quality
of a VQ-compressed image is poor when a small-sized codebook is used. In order to solve this problem, the mean value of the
image block is taken as an alternative block encoding rule to improve the image quality in the proposed scheme. To cut down
the storage cost of compressed codes, a two-stage lossless coding approach including the linear prediction technique and the
Huffman coding technique is employed in the proposed scheme. The results show that the proposed scheme achieves better image
qualities than vector quantization while keeping low bit rates. 相似文献
997.
998.
The conditions for vanishing of the coherent component of radiation transmitted through a monolayer of polymer-dispersed ferroelectric liquid-crystal droplets are found. The influence of polydispersity and disorientation of axes of semispherical droplets on the conditions of interference quenching is studied. It is shown that these factors cause a change in the average size and concentration of droplets for which the quenching effect is realized. Data on the contrast ratio and the modulation depth of a monolayer, determined from the coherent component of transmitted radiation, are presented. It is shown that these characteristics can be considerably improved under quenching conditions for a film of polymer-dispersed ferroelectric liquid-crystal droplets. 相似文献
999.
The alternating direction method is an attractive method for a class of variational inequality problems if the subproblems can be solved efficiently. However, solving the subproblems exactly is expensive even when the subproblem is strongly monotone or linear. To overcome this disadvantage, this paper develops a new alternating direction method for cocoercive nonlinear variational inequality problems. To illustrate the performance of this approach, we implement it for traffic assignment problems with fixed demand and for large-scale spatial price equilibrium problems. 相似文献
1000.
N. Blasi G. Lo Bianco Ch. Protochristov D. Bazzacco G. Falconi N. H. Medina G. De Angelis D. R. Napoli 《Zeitschrift für Physik A Hadrons and Nuclei》1996,356(1):233-234
The10Be(12C,14O)8He-reaction has been used to study the levels of8He. In addition to the known excited state of8He at E x =3.6MeV, withJ π=2+, three additional states were found at excitation energies of 4.54(25)MeV, 6.03(10)MeV and 7.16(4)MeV. 相似文献