全文获取类型
收费全文 | 202篇 |
免费 | 3篇 |
专业分类
化学 | 153篇 |
晶体学 | 3篇 |
力学 | 5篇 |
数学 | 7篇 |
物理学 | 37篇 |
出版年
2023年 | 2篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 8篇 |
2012年 | 9篇 |
2011年 | 5篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 10篇 |
2007年 | 15篇 |
2006年 | 13篇 |
2005年 | 17篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 18篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有205条查询结果,搜索用时 15 毫秒
101.
Ralf Koppert Dirk Goettel Olivia Freitag-Weber Guenter Schultes 《Solid State Sciences》2009,11(10):1797-1800
Diamond like carbon (DLC) coatings are well established for multiple applications. The electrical conductivity of DLC or amorphous carbon can be influenced by several orders of magnitude via doping with different metals. Depending on the deposition process hydrogen may be incorporated as well, thereby decreasing the conductivity. Recent investigations of DLC disclose nice piezoresistive properties.Our work was focused on Ni:a-C:H thin films on different substrates by reactive sputtering from a nickel target. Several carbon precursors were added to the sputtering gas to create an amorphous carbon hydrogen network with embedded crystal clusters. In order to optimize the piezoresistive properties we varied various process parameters. The piezoresistive response was monitored by measuring the resistance change during bending. Our Ni:a-C:H films develop gauge factors of approx. 12 in a wide range of process parameters.For sensor applications the temperature coefficient of resistance (TCR) is important as well. It depends on the metal concentration in the thin film and can be adjusted by the concentration of the incorporated nickel. It can be set to approximately zero in a wide temperature range of 80–400 K. The combination of a high gauge factor and a very small TCR is achieved and described in this paper.XRD measurements reveal nickel or nickel carbide clusters with diameters of approx. 8–30 nm depending on the metal concentration. The clusters crystallize in the hexagonal hcp structure which could be transformed into the cubic fcc structure of nickel by thermal annealing in a vacuum. 相似文献
102.
Using compressed gases with Prandtl numbers near 0.7, we obtained flow visualizations of turbulent Rayleigh-Bénard convection in a cylindrical sample with an aspect ratio Γ≡D/L?10 (D is the diameter and L the height) by the shadowgraph method. Focusing on the plumes under the top plate, we found that their length had a log-normal distribution, suggesting a fragmentation process. Fragmentation events could be visually identified in the images and involved plume interactions with bulk fluctuations or upwelling domain walls. We found the mean spacing between plumes to vary with the Rayleigh number in proportion to the volume-averaged Kolmogorov length of the turbulent bulk fluctuations, providing further evidence for plume-bulk interactions. 相似文献
103.
N-Benzyl-substituted complexes [(triazacyclohexane)Ni(NCMe)3](BF4)2 and their diamagnetic zinc analogues have been prepared and characterized by X-ray crystallography. The T1 spin decoupling observed in their paramagnetic 13C NMR spectra can be quantitatively described by newly derived expressions that allow an independent determination of T2 of the 13C signal, T1 of the attached H or F, and the 1J coupling constant by line shape analysis. 相似文献
104.
联合FTIR,FT-拉曼表征了乐果的振动光谱,获得了固态及不同酸碱条件下饱和液态乐果的振动特征信息;以金/银核-壳复合粒子为基底,获得了乐果在酸碱条件下一系列浓度的表面增强拉曼散射(SERS)光谱,考察了乐果分子在该基底表面的吸附状态及其酸碱影响,推测了乐果与金/银核-壳复合粒子作用机理;结果表明:νas(NH),νas(CH3),ν(O=C-N),τ(O=C-N),ν(P—O),ν(P S),ν(C—C),δ(P—O—C)为乐果分子特征振动;酸、碱条件下,在1.0×10-3mol.L-1为乐果与基底作用的最佳浓度;乐果主要以P—O—C,O=C-C,(S—CH2),P=S,CH3与金/银核-壳复合粒子基底相作用,探讨了酸碱条件下磷酸酯键不同离解历程对吸附的影响。为研究有机磷农药的形态变化提供有益参考。 相似文献
105.
Steffens S Oldendorf J Haufe G Galla HJ 《Langmuir : the ACS journal of surfaces and colloids》2006,22(4):1428-1435
Monolayers of enantiomeric compounds as well as diastereomeric mixtures and racemic/diastereomeric mixtures of ethyl 2-azido-4-fluoro-3-hydroxystearates have been investigated using surface pressure-area isotherms and Brewster angle microscopy. All monolayers collapse out of the liquid-expanded phase, forming 3D collapse structures which were visualized with scanning force microscopy. The enantiomeric compound and the diastereomeric mixtures form unique fiber-like network structures with heights between 20 and 40 nm. Interestingly, the shape of the enantiomeric fiber structures is straight, whereas the diastereomeric mixtures exhibit curved fibers of different sizes. The racemic mixture however forms circular 10 nm high and 20-50 microm broad structures. The shape of unconventional collapse structures could be changed by using distinct ratios of diastereomeric or racemic/diastereomeric mixed compounds. 相似文献
106.
Márcia F. Mesko Paola A. Mello Cezar A. Bizzi Valderi L. Dressler Guenter Knapp Érico M. M. Flores 《Analytical and bioanalytical chemistry》2010,398(2):1125-1131
Iodine determination in food samples was performed by inductively coupled plasma mass spectrometry (ICP-MS) after digestion
by microwave-induced combustion (MIC). Sample masses up to 500 mg of bovine liver, corn starch, milk powder, or wheat flour
were completely combusted using the MIC system. Ammonium nitrate (6 mol l−1 solution, 50 μl) was used as an aid for ignition and vessels were charged with 15 bar of O2. The use of H2O, 0.9 mmol l−1 H2O2, 10 to 50 mmol l−1 (NH4)2CO3 and 56 mmol l−1 tetramethylammonium hydroxide was investigated as absorbing solutions, as well as the suitability of performing a reflux
step after the combustion process. Digestion of food samples by pressurized microwave-assisted acid digestion, microwave-assisted
extraction and conventional extraction of iodine in alkaline solution were also evaluated. Iodine recoveries higher than 99%
were obtained using MIC and 50 mmol l−1 (NH4)2CO3 or 56 mmol l−1 tetramethylammonium hydroxide as absorbing solution and with 5 min for the reflux step. Accuracy was evaluated using certified
reference materials (bovine muscle, corn bran, and milk powder) and agreement better than 97% was obtained. The limit of quantification
by MIC and further ICP-MS determination was 0.002 μg g−1. Blanks were always low and no memory effects were observed. Digestion by MIC allowed the processing of up to eight samples
by each run in 25 min with high efficiency of digestion (residual carbon content lower than 1%) providing a suitable medium
for further iodine determination by ICP-MS. 相似文献
107.
The first representative of a new class of TcN complexes with thiacrown ethers have been prepared by ligand exchange reaction of NBu4[TcNCl4] with 1,4,8,11-tetrathiacyclotetradecane (14S4), 1,5,9,13-tetrathiacyclohexadecane (16S4), 1,5,9,13-tetrathiacyclohexadecane-3,11-diole (16S4-(OH)2) and 1,4,7,10,13,16-hexathiacyclooctadecane (18S6). The crystal structure of [TcNCl(14S4)]TcNCl4 1) consists of couples of independent cations with the metal in the oxidation state + 5 and hexavalent TcNCl4− anions. In the complex cation the metal is six-coordinated in a rather distorted octahedral geometry, being directly bound to four sulphur atoms from the macrocyclic ligand in the equatorial plane and to the nitrido atom and to one chlorine atom in the axial positions. The strong trans influence of the nitrido ligand causes an extreme lengthening of the Tc---Cl bond distance to 2.718 Å. The octahedral molecular structure of [TcNCl(18S6)]TcNCl4 (3) is comparable with that of 1, but only four sulphur atoms of the thiacrown ether form the equatorial plane, two sulphur atoms remain non-coordinated, and the nitrido and Cl− ligands are in axial positions. The most interesting feature in the structure of [TcNCl(16S4-(OH)2)]Cl (5) is the observation of an exceptionally long Tc---N distance of 1.95 Å. 相似文献
108.
Angulo G Grampp G Rosspeintner A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,65(3-4):727-731
This paper presents a critical discussion on the representation of UV-vis-NIR light absorption and fluorescence emission spectra of polyatomic molecules in liquid solution. A general overview how to handle the experimental spectra in order to extract physical data from them is presented together with some simulations to show the errors that can arise from unfortunate manipulation. 相似文献
109.
Patrick Hoffmann Ricardo P. Mikalo Alexandros Yfantis David R. Batchelor Guenter Appel Dimitrios Yfantis Dieter Schmeißer 《Mikrochimica acta》2001,136(3-4):109-113
Synchrotron radiation based spectro-microscopy is shown to be an exciting tool for elemental analysis in the field of heterogeneous
interfaces, thin films, and device technology. Results are reported, taken with a spectrometer that enables the combination
of a photoemission electron microscope (PEEM) with photoelectron spectroscopies (XPS, UPS) operated at a high brilliance undulator
beam line at BESSY.
The properties of mc-Si (multi crystalline silicon) are of interest because of their applications in low priced photovoltaic
devices. An example of how to analyze the surface potentials of such surfaces without removing the native oxide is given.
Tin nano-scale particles are shown to be the decisive factor affecting the corrosion prevention of passivated tinplate surfaces. 相似文献
110.
The first ring-closing olefin metatheses of alkenyl α-fluoroacrylamides or acrylates incorporating a fluorinated double bond are reported. Several N-benzyl-N-alkenyl-α-fluoroacrylamides were cyclized in the presence of 2 mol % of Grubbs II catalyst at room temperature to form an unsaturated γ-lactam, and at 80 °C to form the corresponding δ-lactams bearing a fluoro vinyl moiety. At elevated temperature, cyclization of an N-methallyl 2-fluoroacrylamide to form a fluorinated, tetrasubstituted double bond was achieved. Similarly, 3-fluorocoumarin was prepared from (2-vinylphenyl)-α-fluoroacrylate. 相似文献