全文获取类型
收费全文 | 230篇 |
免费 | 13篇 |
国内免费 | 9篇 |
专业分类
化学 | 121篇 |
力学 | 60篇 |
数学 | 21篇 |
物理学 | 50篇 |
出版年
2019年 | 9篇 |
2018年 | 6篇 |
2017年 | 11篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 13篇 |
2012年 | 9篇 |
2011年 | 7篇 |
2010年 | 5篇 |
2009年 | 8篇 |
2008年 | 7篇 |
2007年 | 10篇 |
2006年 | 14篇 |
2005年 | 17篇 |
2004年 | 12篇 |
2003年 | 22篇 |
2002年 | 21篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有252条查询结果,搜索用时 15 毫秒
121.
Lei Zhou Dawa Shen Junquan He Yuhui Wei Qinglin Ma Zhide Hu 《Journal of Raman spectroscopy : JRS》2012,43(10):1504-1509
Five resinous incense materials excavated from the underground palace of Bao'en Temple, Nanjing, were studied by a multianalytical approach of near infrared, midinfrared, and Fourier transform Raman spectroscopies. By comparing the multispectroscopic features of five specimens, these incense materials were identified to the same substance. Subsequent analysis and comparison of the ancient incense materials and three modern reference specimens were carried out, and the results indicated that the excavated incense materials were frankincense, with its major component of triterpenoids. This work performs, for the first time, a comprehensive spectroscopic study for the Chinese excavated incense materials, demonstrating that a combined use of near infrared, midinfrared, and Fourier transform Raman spectroscopies is an efficient technique to identify an excavated incense. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
122.
We study the large time asymptotic behavior, in Lp (1p∞), of higher derivatives Dγu(t) of solutions of the nonlinear equation(1) where the integers n and θ are bigger than or equal to 1, a is a constant vector in with . The function ψ is a nonlinearity such that and ψ(0)=0, and is a higher order elliptic operator with nonsmooth bounded measurable coefficients on . We also establish faster decay when . 相似文献
123.
《Comptes Rendus Physique》2015,16(5):531-539
The distribution and the comparison of an ultra-stable optical frequency and accurate time using optical fibres have been greatly improved in the last ten years. The frequency stability and accuracy of optical links surpass well-established methods using the global navigation satellite system and geostationary satellites. In this paper, we present a review of the methods and the results obtained. We show that public telecommunication network carrying Internet data can be used to compare and distribute ultra-stable metrological signals over long distances. This novel technique paves the way for the deployment of a national and continental ultra-stable metrological optical network. 相似文献
124.
cis,cis,cis‐1,2,3,4‐Tetrakis(diphenylphosphinomethyl)cyclopentane–[PdCl(C3H5)]2 efficiently catalyses the Heck reaction of alk‐1‐en‐3‐ol with a variety of aryl halides. In the presence of hex‐1‐en‐3‐ol or oct‐1‐en‐3‐ol, the β‐arylated carbonyl compounds were selectively obtained. Turnover numbers up to 84 000 can be obtained for this reaction. Linalool and 2‐methylbut‐3‐en‐2‐ol led regio‐ and stereoselectively to the corresponding (E)‐1‐arylalk‐1‐en‐3‐ol derivatives. A minor electronic effect of the substituents of the aryl bromide was observed. Quite similar reaction rates were generally observed in the presence of activated aryl bromides such as bromoacetophenone and deactivated aryl bromides such as bromoanisole, indicating that, with these alkenols and this catalyst, the oxidative addition of aryl bromides to palladium is not the rate‐limiting step. It should be noted that this reaction also proceeds with sterically very congested aryl bromides such as 9‐bromoanthracene or 2,4,6‐triisopropylbromobenzene or with a vinyl bromide. On the other hand, low yields were obtained with aryl chlorides. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
125.
A. Lachal S. Leorato E. Orsingher 《Annales de l'Institut Henri Poincaré (B) Probabilités et Statistiques》2006,42(6):753-772
We obtain the explicit distribution of the position of a particle performing a cyclic, minimal, random motion with constant velocity c in . The n+1 possible directions of motion as well as the support of the distribution form a regular hyperpolyhedron (the first one having constant sides and the other expanding with time t), the geometrical features of which are here investigated.The distribution is obtained by using order statistics and is expressed in terms of hyper-Bessel functions of order n+1. These distributions are proved to be connected with (n+1)th order p.d.e. which can be reduced to Bessel equations of higher order.Some properties of the distributions obtained are examined. This research has been inspired by a conjecture formulated in Orsingher and Sommella [E. Orsingher, A.M. Sommella, A cyclic random motion in R3 with four directions and finite velocity, Stochastics Stochastics Rep. 76 (2) (2004) 113–133] which is here proved to be false. 相似文献
126.
127.
128.
The symmetry-breaking in a swirling flow generated inside a cylindrical tank of aspect ratio h=1 by the rotation of one lid is studied numerically. Beyond a critical Reynolds number, the flow undergoes a bifurcation to three-dimensional solutions. The spatial and temporal behaviour on these branches are examined. To cite this article: E. Barbosa, O. Daube, C. R. Mecanique 330 (2002) 791–796. 相似文献
129.
Xiaoying Xu Xiang Li Anjie Wang Yinyong Sun W. Bernd Schweizer Roel Prins 《Helvetica chimica acta》2011,94(10):1754-1763
1,2,3,4‐Tetrahydro‐4,6‐dimethyldibenzothiophene was prepared by coupling 2‐bromo‐3‐methylcyclohexanone with 2‐methylbenzenethiol and annulating the product with the aid of polyphosphoric acid. A mixture of 1,2,3,4‐tetrahydro‐4,6‐dimethyldibenzothiophene and 4,6‐dimethyldibenzothiophene was prepared by coupling 2‐bromo‐3‐methylcyclohex‐2‐en‐1‐one with 2‐methylbenzenethiol and annulating the product with the aid of polyphosphoric acid. 2‐Bromo‐3‐methylcyclohexanone was synthesized by conjugate addition of Me3Al to 2‐bromocyclohex‐2‐en‐1‐one with CuBr as catalyst and 2‐bromo‐3‐methylcyclohex‐2‐en‐1‐one by bromination? elimination of 3‐methylcyclohex‐2‐en‐1‐one. 1,2,3,4,4a,9b‐Hexahydro‐4,6‐dimethyldibenzothiophene was prepared by reduction of 1,2,3,4‐tetrahydro‐4,6‐dimethyldibenzothiophene with Zn and CF3COOH. 相似文献
130.
《Comptes Rendus Physique》2013,14(7):578-589
Spontaneous dewetting of solid thin films proceeds by edge retraction of film edges and/or by heterogeneous void growth. Classical 1D and 2D continuous models of the evolution of a dewetting film, based on surface diffusion mechanisms, predict that in the long-time limit dewetting obeys universal scaling laws. In this paper, we review 1D and 2D predictions and recent experimental results. For this purpose, using Si(001)/SiO2 and Ge(001)/SiO2 single-crystalline thin films in different geometries, we have been able to compare theoretical predictions to experimental results obtained by combining in situ LEEM and ex situ AFM measurements. For dewetting from film edges, experimental results partially differ from continuous models predictions. More precisely, because of the crystallographic anisotropy: (i) the facetted edges remain stable during dewetting (they simply recede at constant shape) while poorly or un-facetted edges are unstable (they recede by finger formation); (ii) rim formation, induced by mass-conservation condition, proceeds in a layer-by-layer mode and is limited by 2D nucleation properties on the top of the rim; (iii) the island generation mechanism differs from the mass shedding behaviour predicted by 1D models. For dewetting mechanisms involving void growth, different behaviours are reported and discussed. For thin Si(001)/SiO2 films, the corners of the opening square-shaped voids lead to a local destabilisation of the growing voids. For thin Ge(001)/SiO2 films, the side of the voids invariably turns instable and forms tip dendrites whose branch density depends on the temperature and the initial film thickness. Finally, ultra-thin films, more sensitive to local fluctuations, dewet in a fractal geometry. 相似文献