全文获取类型
收费全文 | 1397篇 |
免费 | 29篇 |
国内免费 | 6篇 |
专业分类
化学 | 889篇 |
晶体学 | 12篇 |
力学 | 30篇 |
数学 | 197篇 |
物理学 | 304篇 |
出版年
2021年 | 9篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 6篇 |
2016年 | 18篇 |
2015年 | 20篇 |
2014年 | 24篇 |
2013年 | 52篇 |
2012年 | 45篇 |
2011年 | 75篇 |
2010年 | 54篇 |
2009年 | 52篇 |
2008年 | 73篇 |
2007年 | 74篇 |
2006年 | 59篇 |
2005年 | 79篇 |
2004年 | 66篇 |
2003年 | 59篇 |
2002年 | 51篇 |
2001年 | 18篇 |
2000年 | 26篇 |
1999年 | 13篇 |
1998年 | 20篇 |
1997年 | 16篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 20篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 20篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 21篇 |
1984年 | 18篇 |
1983年 | 13篇 |
1982年 | 25篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 22篇 |
1977年 | 25篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1974年 | 11篇 |
1973年 | 15篇 |
1972年 | 6篇 |
1935年 | 8篇 |
排序方式: 共有1432条查询结果,搜索用时 0 毫秒
21.
22.
Georges Dénès 《Journal of solid state chemistry》1981,37(1):16-23
The kinetics of the reconstructive first order phase transitions α → γ (upon heating) and β, γ → α (upon cooling) of SnF2 were studied by quantitative X-ray powder diffraction. The main feature of the kinetics is that these transformations are incomplete over a wide temperature range. Consequently it is not possible to fit the experimental data using the usual solid state rate expressions. Although these transitions are not reversible (large hysteresis) the empirical use of a kinetic model of a reversible transformation provides a good fit. The α → γ transformation was also investigated by D.T.A.; this transition was found to be greatly influenced by particle size: the transition temperature increases with grain size, and its enthalpy decreases. The X-ray investigation revealed that the process of the α → γ transformation involves an intermediate noncrystalline phase named the “transition phase.” It is suggested that the transition proceeds through a process of fragmentation-reconstruction. 相似文献
23.
Mint Tho Nguyen Georges Leroy Michel Sana Jos Elguero 《Journal of heterocyclic chemistry》1982,19(4):943-944
An ab initio study of the Dimorth rerarrangement of the -amino-1,2,3,4-tetrazole leads to the conclusion teht in vapour phase the rate determining step is not the ring-chain isomerism, but is either the Z-E iomerism around the C?N double bond or the 1,3-sigmatropic shift of the proton. 相似文献
24.
Comparison between the adsorption behaviors of an organic cation and an organic anion on several reversed-phase liquid chromatography adsorbents 总被引:1,自引:0,他引:1
Adsorption data of an organic cation (propranololium chloride) and an organic anion (sodium 1-naphthalene sulfonate) were measured by frontal analysis on two RPLC adsorbents, Symmetry-C18 and XTerra-C18, with aqueous solutions of methanol as the mobile phases. The influence of supporting neutral salts on the adsorption behavior of these two ions are compared. The Henry constants are close (H approximately 5). The four sets of isotherm data are all well accounted for using the bi-Moreau model. However, the isotherms of the two ions behave differently at high concentrations. The initial behaviors of all the isotherms are antilangmuirian but remain so in a much wider concentration range for the cation than for the anion, due to its stronger adsorbate-adsorbate interactions on the low-energy adsorption sites. The retention times of both ions increase with increasing concentration of neutral salt in the mobile phase, suggesting the formation of ion-pair complexes, with Cl- for the cation and with Na+ for the anion. The adsorbate-adsorbate interactions vanish in the presence of salt and the bi-Moreau isotherm model tends toward a bi-Langmuir model. Differences in adsorption behavior are also observed between the cation and the anion when bivalent inorganic anions and cations, respectively, are dissolved in the mobile phase. High concentration band profiles of 1-naphthalene sulfonic acid are langmuirian, except in the presence of a trivalent cation, while those of propranolol are antilangmuirian under certain conditions even with uni- or divalent cations. 相似文献
25.
Oxygen can be determined in a perfluorotributylamine emulsion used as a blood substitute by coulometry and polarography. The oxygen uptake of the emulsion (4.3 × 10?3 mol l?1 or 11 ml-% at 25°C and PO2 = 760 mm Hg) is about three times greater than that of water. The adsorption of surfactant on a dropping mercury electrode changes the electrochemical parameters E, α and k3. The marked difference between the diffusion coefficients of oxygen and hydrogen peroxide (ratio 2.6) seems to be proceed from the ejection of oxygen molecules from the perfluorotributylamine droplets and from the insolubility of hydrogen peroxide molecules in the droplets. The constant rate of oxygen release by these droplets was estimated to be 104 s?1 by a stopped-flow spectrophotometric method. This constant rate seems to be linked with the particle diameter (0.2 μm) and the diffusion coefficient in the perfluorotributylamine droplets (1.6 × 10?6 cm2 s?1). 相似文献
26.
Eric Monflier Sbastien Tilloy Georges Fremy Yves Castanet Andr Mortreux 《Tetrahedron letters》1995,36(52):9481-9484
Solvent free biphasic hydroformylalion of various water-insoluble terminal olefins can be achieved in high yields and sclcctivitics by using a water-soluble rhodium/triphenylphosphine trisulfonate catalyst and per(2,6-di-o-mclhyl)-β-cyclodcxtrin as inverse phase transfer catalyst. The catalytic activities were up to ten times higher than those observed without pcr(2,6-di-o-methyl)-β-cyclodextrin. 相似文献
27.
Comparison between adsorption isotherm determination techniques and overloaded band profiles on four batches of monolithic columns 总被引:1,自引:0,他引:1
The adsorption isotherms of 4-tert.-butyl phenol were measured on four different monolithic columns, using three different techniques, classical frontal analysis (FA), the perturbation on a plateau method (PP) and the recently introduced numerical procedure known as the inverse numerical method (IN). This last approach requires only the recording of a few overloaded profiles and has the potential advantage of affording a dramatic decrease of the amounts of compounds, solvent, and time needed to determine accurate estimates of the coefficients of the isotherm. The reproducibility of the adsorption data measured on the four columns is discussed with reference to the specific techniques used for obtaining these data and to the most suitable equation used for modeling them. The data obtained for the different columns were highly consistent. The inverse numerical approach was confirmed to provide a powerful, accurate, and economic method for measuring single component adsorption data. 相似文献
28.
J.Georges Duboudin Michel Petraud Max Ratier Bruno Trouve 《Journal of organometallic chemistry》1985,288(1):C6-C8
Flash pyrolysis of alkyltributyltin acetates, at high temperatures (600–850° C) under a moderate vacuum provides a convenient route to vinyltin derivatives. 相似文献
29.
Garcia-Galdo JE Cobas-Rodriguez J Jáuregui-Haza UJ Guiochon G 《Journal of chromatography. A》2004,1024(1-2):9-14
This work presents a modification to the real adsorbed solution model using a Flory-Huggins type of expression that was reported previously. This modification consists in replacing the Flory-Huggins activity coefficient by the spreading pressure dependent approach. This new model takes into account explicitly the adsorbate-adsorbate interactions taking place in the adsorbed phase. It provides an excellent prediction of the competitive, ternary adsorption equilibrium of benzyl alcohol, 2-phenylethanol and 2-methyl benzyl alcohol observed in a reversed-phase liquid chromatographic system using information merely derived from the single-component adsorption experimental data. 相似文献
30.
Abdeloihid Mellouki Robert Georges Michel Herman Deanne L. Snavely Svetlana Leytner 《Chemical physics》1997,220(3):443-322
We have recorded the infrared absorption spectrum of pyrrole at 0.005 cm−1 spectral resolution using a Fourier transform interferometer. The rotational analysis of the fundamental N---H stretch (110) at 3530.811343(82) cm−1 was performed. A set of 13 upper state rovibrational parameters was determined, allowing the 2715 assigned rovibrational lines to be reproduced with a standard deviation of 1.3 10−3 cm−1. An attempt to record the fundamental band under slit-jet conditions is reported. The role of hot bands accompanying the series of the N---H stretch excitation is investigated. Effective vibrational parameters — ω01, X011, Y111, X1,24 — are obtained. The lower level in the hot band series is unambiguously identified as the V24 = 1 level, by retrieving X1,24 independently, from other spectral data. The observation of the complex band pattern accompanying the N---H series in the higher overtone range is discussed with the help of new data, recorded around the 150 band at different temperatures using intracavity laser optoacoustic spectroscopy. 相似文献