全文获取类型
收费全文 | 620篇 |
免费 | 21篇 |
专业分类
化学 | 388篇 |
晶体学 | 1篇 |
力学 | 28篇 |
数学 | 97篇 |
物理学 | 127篇 |
出版年
2024年 | 2篇 |
2023年 | 13篇 |
2022年 | 7篇 |
2021年 | 20篇 |
2020年 | 21篇 |
2019年 | 25篇 |
2018年 | 15篇 |
2017年 | 16篇 |
2016年 | 26篇 |
2015年 | 26篇 |
2014年 | 11篇 |
2013年 | 26篇 |
2012年 | 38篇 |
2011年 | 42篇 |
2010年 | 20篇 |
2009年 | 22篇 |
2008年 | 30篇 |
2007年 | 41篇 |
2006年 | 29篇 |
2005年 | 23篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1990年 | 5篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1966年 | 2篇 |
1956年 | 2篇 |
1954年 | 4篇 |
1909年 | 2篇 |
1884年 | 1篇 |
排序方式: 共有641条查询结果,搜索用时 15 毫秒
131.
Giacomo Bruzzone 《Thermochimica Acta》1985,96(2):239-258
The calorimetric methods employed for the study of metal systems (solution, combustion, direct reaction calorimetry) are considered and briefly discussed with respect to each other.The development of apparatus for the calorimetry of metals and alloys is examined as a whole, with particular reference to the progressive increase of the maximum limit of the working temperature.The employment of calorimetric methods for the determination of equilibrium phase diagrams is described according to two different approaches: (1) corresponding to classical DTA, based on the identification of phase boundaries by the exploration of the system as a function of temperature, at constant composition; (2) corresponding to the measurement of partial and integral enthalpies of alloy formation as a function of the composition, at constant temperature.A brief report is given of the utilization of calorimetric data for the computation of equilibrium phase diagrams and equations are also given that allow the equilibrium temperature to be calculated between a liquid solution (binary or multicomponent) and a pure component (or an intermetallic compound) as a function of the thermodynamic parameters obtained by calorimetric methods. 相似文献
132.
133.
A. De Giacomo O. De Pascale 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1405-1407
In this work final results on TiO2 film deposition by Plasma Assisted Pulsed Laser Deposition (PAPLD) with an rf biased substrate are presented. In previous work it has been shown that PAPLD is an improvement over conventional PLD for the elimination of particulates in high refractive index thin film deposition. This paper will give a comparison between conventional PLD and PAPLD on the stoichiometry, morphology, and optical properties of deposited TiO2 films. It will be demonstrated that oxygen rf discharge during the PLD process makes incorporation of oxygen into the depositing films extremely effective. This effect of the rf discharge allows operation of the PLD process at a lower oxygen background pressure while enhancing the deposition rate. Also, the production of a good quality TiO2 film by PAPLD using a pure metal titanium target will be shown. PACS 79.20.Ds; 52.80.Pi 相似文献
134.
135.
Christian Orrenius Torbj rn Norin Karl Hult Giacomo Carrea 《Tetrahedron: Asymmetry》1995,6(12):3023-3030
For further investigation of the kinetic resolutions in transesterification reactions with the highly enantioselective Candida antarctica lipase B, an easy to study model reaction with one typical substrate, the Douglas Fir Beetle pheromone 3-methyl-2-cyclohexen-1-ol (Seudenol), was developed. The influence of the nature of the solvent and thermodynamic water activity was studied. Initial rates showed constant or progressively increasing values with increasing water activity. Enantioselectivity depended on the choice of solvent and descended in most cases with increasing water activity. No general correlations of enantioselectivity or activity with physicochemical constants of the solvent were found. However, at a water activity of 0.11 a tendency toward optimum hydrophobicity (i.elog P ≈ for enantioselectivity was observed. Enantiomeric ratios were in the range 8–32. 相似文献
136.
The enzymatic hydrolysis of methyl 2-fluoro-2-arylpropionates was performed using lipases from Candida rugosa and Candida cylindracea (OF-360). A careful analysis of the reaction products revealed that racemic 2-hydroxy-2-arylpropionic acid and traces of 2-arylacrylic acid are formed, in addition to the expected 2-aryl-2-fluoropropionic acid. The presence of powerful electron-releasing groups in the aromatic ring of the substrate increase the amount of 2-hydroxypropionic acid. A mechanistic hypothesis has been formulated according to which the enzyme facilitates the elimination of fluoride ion from the hydrolysed acid with the formation of an α-carboxy-stabilized carbocation which provides 2-hydroxypropionic acids by nucleophilic attack of H2O and 2-arylacrylic acids by a β-elimination process. 相似文献
137.
The synthesis of 13,15-dihydro-5H-diindeno[1,2-a;1′,2′-h] fluorene in six steps starting from flourenone 4-carboxylic acid and 2,4-dichlorotoluene is described. As an intermediate product the 5, 13, 15-trioxo-derivative is obtained. 相似文献
138.
Giacomo Saielli Gianfranco Scorrano Alessandro Bagno Akihiro Wakisaka 《Chemphyschem》2005,6(7):1307-1315
The solvation of tetramethylammonium chloride (Me4NCl) and tetra-n-butylammonium chloride (Bu4NCl) in water-acetonitrile mixtures was investigated by mass spectrometry of clusters isolated from the solution. As far as the positive ions are concerned, clusters composed of alkylammonium ions and acetonitrile molecules only were observed, even for mixtures with high water content. In contrast, for the negative ions, clusters composed of chloride with both water and/or acetonitrile molecules were observed. For the smaller system (Me4NCl) we performed quantum chemical calculations and molecular dynamics simulations. It was found that even though water is present in the solvation shell of Me4N+, only acetonitrile has a strong electrostatic interaction with the cation. Water molecules around Me4N+ form hydrogen bonds with other water molecules, and they interact with Me4N+ mainly via dispersive interactions. These results indicate that Me4N+ behaves like a hydrophobic solute. On the other hand, the interaction of Cl- with water and acetonitrile is of comparable strength and, in both cases, the electrostatic interaction dominates. Herein we demonstrate experimentally and theoretically that positive and negative ions give rise to characteristic solvation structures in mixed solvents: even a relatively small organic cation, such as Me4N+, exhibits a hydrophobic-like solvation shell. 相似文献
139.
Cacelli I Cinacchi G Prampolini G Tani A 《Journal of the American Chemical Society》2004,126(43):14278-14286
Molecular dynamics atomistic simulations of solid and liquid benzene have been performed, employing a model intermolecular potential derived from quantum mechanical calculations. The ab initio database includes approximately 200 geometries of the benzene dimer with interaction energies computed at the MP2 level of theory. The accuracy of the modeled force field results is satisfactory. The thermodynamic and structural properties, calculated in the condensed phases, are compared with experimental data and previous simulation results. Single particle and collective dynamical properties are also investigated through the calculation of translational and rotational diffusion coefficients, reorientational dynamics, and viscosities. The agreement of these data with experimental measurements confirms the reliability of the proposed force field. 相似文献
140.
Giacomo Lorenzini 《Applied biochemistry and biotechnology》1994,48(1):1-4
A new miniaturized kit based on very young supersensitive tobacco Bel-W3 plantlets, which can be easily used to detect phytotoxic
levels of ozone in ambient air in large scale surveys, is described. It has been developed in laboratory as well as field
studies. The optimal sampling time is 5–7 d. The advantages of the kit are its user-friendliness, low cost, and reliability.
The kit may be integrated by a passive sampling tube set and may be also proposed for educational programs. 相似文献