全文获取类型
收费全文 | 299860篇 |
免费 | 2436篇 |
国内免费 | 1054篇 |
专业分类
化学 | 137066篇 |
晶体学 | 4173篇 |
力学 | 16480篇 |
综合类 | 14篇 |
数学 | 56446篇 |
物理学 | 89171篇 |
出版年
2021年 | 2014篇 |
2020年 | 2121篇 |
2019年 | 2289篇 |
2018年 | 13116篇 |
2017年 | 12776篇 |
2016年 | 10155篇 |
2015年 | 3568篇 |
2014年 | 4396篇 |
2013年 | 10197篇 |
2012年 | 11896篇 |
2011年 | 19902篇 |
2010年 | 12104篇 |
2009年 | 12342篇 |
2008年 | 15200篇 |
2007年 | 17347篇 |
2006年 | 8805篇 |
2005年 | 9397篇 |
2004年 | 9206篇 |
2003年 | 8440篇 |
2002年 | 7049篇 |
2001年 | 7119篇 |
2000年 | 5668篇 |
1999年 | 4201篇 |
1998年 | 3435篇 |
1997年 | 3408篇 |
1996年 | 3294篇 |
1995年 | 2992篇 |
1994年 | 2812篇 |
1993年 | 2719篇 |
1992年 | 3028篇 |
1991年 | 2965篇 |
1990年 | 2825篇 |
1989年 | 2628篇 |
1988年 | 2651篇 |
1987年 | 2649篇 |
1986年 | 2486篇 |
1985年 | 3200篇 |
1984年 | 3434篇 |
1983年 | 2826篇 |
1982年 | 2999篇 |
1981年 | 2959篇 |
1980年 | 2822篇 |
1979年 | 2887篇 |
1978年 | 3013篇 |
1977年 | 2958篇 |
1976年 | 3015篇 |
1975年 | 2788篇 |
1974年 | 2768篇 |
1973年 | 2914篇 |
1972年 | 1824篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
M. M. Eisl B. M. Reichl S. D. Böhmig H. Störi 《Fresenius' Journal of Analytical Chemistry》1994,349(1-3):194-196
Using a discrete model for the segregation kinetics based on the Darken theory of diffusion and on the regular solution model (RSM), one and two dimensional simulations of interface segregation in binary and ternary systems have been performed. The aim of the calculations was to investigate the kinetics of segregation sequences in ternary systems, the segregation kinetics in discrete systems during the initial phase and finally the kinetics of surface segregation in the region of a grain boundary intersected by the surface. 相似文献
992.
993.
R. D. Patel 《国际化学动力学杂志》1994,26(4):403-406
Pseudo-first-order rate constants and activation parameters have been measured for the solvolysis of 2-chloroquinoxaline in various aquo-organic mixtures using methanol, ethanol, and isopropanol as the organic solvent. Excellent linear correlations are found between lnk and the mol fraction of cosolvent and ln[H2O]. The medium effect on the rates of solvolysis is assessed by Grunwald–Winstein's mY correlationship. The estimated values of m (0.55–0.72) and the entropy of activation (148–212 J deg?1 mol?1) for the reactions are well in the range for a bimolecular aromatic substitution reactions. © 1994 John Wiley & Sons, Inc. 相似文献
994.
The kinetics of the thermal decomposition reaction of gaseous 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (ACDP) in the presence of n-octane was studied in the 403.2–523.2 K temperature range. This reaction yields acetone as the organic product. Under optimum conditions, first-order kinetics were observed, included when the S/V ratio of the Pyrex reaction vessel was increased by a nearly six-fold factor. In the range 443.2–488.2 K the temperature dependence of the rate constants for the unimolecular reaction in conditioned vessels is given by In k1/(s?1) = (31.8 ± 2.5) ? [(39.0 ± 2.5)/RT]. The value of the energy of activation in kcal/mol correspond to one O? O bond homolysis of the ACDP molecule in a stepwise biradical initiated decomposition mechanism. At the lower reaction temperatures as well in preliminary experiments participation of a surface catalyzed ACDP decomposition process could be detected. © 1994 John Wiley & Sons, Inc. 相似文献
995.
996.
An asymptotic formula is obtained for the number of representations of an element of a finite field as a weighted sum of two prescribed powers of primitive elements. This generalises previous work on sums of primitive elements, including that relating to some conjectures of Golomb. 相似文献
997.
We study infinite-dimensional systems of ordinary differential equations having applications in some popular and important physical problems. The appearance of infinite-dimensional space–time chaos is considered, namely, the bifurcations and critical phenomena that occur in the phase space of the systems and explain some physical problems are described. 相似文献
998.
X.T Zhang Y.C LiuZ.Z Zhi J.Y ZhangY.M Lu D.Z ShenW Xu X.W FanX.G Kong 《Journal of luminescence》2002,99(2):149-154
The properties of the excitonic luminescence for nanocrystalline ZnO thin films are investigated by using the dependence of excitonic photoluminescence (PL) spectra on temperature. The ZnO thin films are prepared by thermal oxidation of ZnS films prepared by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique. The X-ray diffraction (XRD) indicates that ZnO thin films have a polycrystalline hexagonal wurtzite structure with a preferred (0 0 2) orientation. A strong ultraviolet (UV) emission peak at 3.26 eV is observed, while the deep-level emission band is barely observable at room temperature. The strength of the exciton-longitudinal-optical (LO) phonon coupling is deduced from the temperature dependence of the full-width at half-maximum (FWHM) of the fundamental excitonic peak, decrease in exciton-longitudinal-optical (LO) phonon coupling strength is due to the quantum confinement effect. 相似文献
999.
S. I. Pesotskii R. B. Lyubovskii W. Biberacher M. V. Kartsovnik V. I. Nizhankovskii N. D. Kushch H. Kobayashi A. Kobayashi 《Journal of Experimental and Theoretical Physics》2002,94(2):431-433
Behavior of the de Haas-van Alphen (dHvA) oscillations depending on the angle between the magnetic field direction and the perpendicular to conducting layers in the quasi-two-dimensional organic metal α-(BETS)2 KHg(SCN)4 was studied in detail. The angular dependence of the dHvA oscillation amplitude exhibits a series of minima (at ±43.2°, ±64.6°, and ±72.0°) related to the “zero spin” effect, through which it is possible to estimate the splitting factor. An analysis of this value suggests that many-body interactions in the compound studied are either absent or at least radically weakened. 相似文献
1000.
A. Thomasson S. Geffroy E. Frejafon D. Weidauer R. Fabian Y. Godet M. Nominé T. Ménard P. Rairoux D. Moeller J.P. Wolf 《Applied physics. B, Lasers and optics》2002,74(4-5):453-459
Continuous mapping of an ozone episode in Paris in June 1999 has been performed using a differential absorption lidar system.
The 2D ozone concentration vertical maps recorded over 33 h at the Champ de Mars are compiled in a video clip that gives access
to local photochemical dynamics with unprecedented precision. The lidar data are compared over the whole period with point
monitors located at 0-, 50-, and 300-m altitudes on the Eiffel Tower. Very good agreement is found when spatial resolution,
acquisition time, and required concentration accuracy are optimized. Sensitivity to these parameters for successful intercomparison
in urban areas is discussed.
Received: 11 February 2002 / Published online: 14 March 2002 相似文献