全文获取类型
收费全文 | 1884篇 |
免费 | 48篇 |
国内免费 | 6篇 |
专业分类
化学 | 1178篇 |
晶体学 | 9篇 |
力学 | 45篇 |
数学 | 231篇 |
物理学 | 475篇 |
出版年
2021年 | 15篇 |
2020年 | 20篇 |
2019年 | 23篇 |
2017年 | 14篇 |
2016年 | 35篇 |
2015年 | 29篇 |
2014年 | 25篇 |
2013年 | 77篇 |
2012年 | 75篇 |
2011年 | 84篇 |
2010年 | 40篇 |
2009年 | 37篇 |
2008年 | 85篇 |
2007年 | 88篇 |
2006年 | 76篇 |
2005年 | 87篇 |
2004年 | 86篇 |
2003年 | 66篇 |
2002年 | 63篇 |
2001年 | 47篇 |
2000年 | 49篇 |
1999年 | 34篇 |
1998年 | 30篇 |
1997年 | 19篇 |
1996年 | 39篇 |
1995年 | 32篇 |
1994年 | 22篇 |
1993年 | 26篇 |
1992年 | 40篇 |
1991年 | 23篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1988年 | 32篇 |
1987年 | 22篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 19篇 |
1983年 | 29篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 24篇 |
1979年 | 26篇 |
1978年 | 20篇 |
1977年 | 20篇 |
1976年 | 27篇 |
1975年 | 25篇 |
1974年 | 21篇 |
1973年 | 16篇 |
1972年 | 9篇 |
1970年 | 14篇 |
排序方式: 共有1938条查询结果,搜索用时 15 毫秒
991.
Brillouin scattering of laser light has been used to study the temperature dependence of phonon velocity in a variety of amorphous polymeric systems, particularly internally and externally plasticized methacrylates. Discontinuities in the temperature coefficient of the hypersound velocities are observed at the glass transition temperatures (Tg). This phenomenon is related to changes in the temperature behavior of the specific volume accompanied by corresponding discontinuities in certain second-order thermodynamic quantities. This method was also used to examine the temperature dependence of the Landau-Placzek ratio. This ratio is relatively large in polymer systems and appears to be independent of temperature in the region of the glass transition, provided that there are no internal strains in the sample at the temperature of measurement. Evidence is presented which suggests that the abrupt changes in this ratio at Tg reported by earlier workers were due to kinetic effects related to the relaxation of internal strains above Tg, and the results of recent studies by other investigators, both corroborating and supplementing the present work, are reviewed. 相似文献
992.
993.
The Petrov-Galerkin projection method is outlined for the solution of the linear elliptic equation Lu = f with homogeneous boundary conditions. By choosing appropriate finite dimensional trial and test spaces, the methods of weighted residuals, collocation, and H1 Galerkin can be interpreted within the Petrov-Galerkin projection method framework. The important question of how best to choose the trial and test functions to suit a particular type of problem is then discussed. Objective criteria associated with the matrix which governs the Petrov-Galerkin numerical process are proposed. 相似文献
994.
995.
P.A. Forsyth S. Marčelia D.J. Mitchell B.W. Ninham 《Advances in colloid and interface science》1978,9(1):37-60
The role played by statistical mechanics in the ordering of colloidal systems is examined. This role is made explicit through a study of phase (order-disorder) transitions in 1, 2 and 3 dimensions which exist in the examples provided by clay plate, tobacco mossaic virus and latex sphere suspensions. Essentially the statement is that the extrapolation of DLVO theory which attributes stability to a balance between attractive and repulsive two-body forces is not always a panacea. The ideas of Langmuir and Onsager who dealt with statistical mechanics and repulsive forces and considered that attractive long-range forces are not always important are paramount for some systems and must be built into existing theories. 相似文献
996.
997.
998.
999.
Terence N. Mitchell 《Magnetic resonance in chemistry : MRC》1975,7(12):610-614
The proton and carbon-13 NMR spectra of thirteen trialkylmetal derivatives of pyridine, several of which were previously unknown, have been recorded and analysed. The proton NMR spectra show variations in proton chemical shifts but not in proton-proton coupling constants when the metal substituent is changed; the ring proton-metal coupling constants nJ(M? H) in the tin and lead derivatives correspond closely with the corresponding proton-proton couplings nJ(H? H) in pyridine. The carbon-13 chemical shifts of the carbons bound to the metal can apparently be correlated with the electron-donating ability of the trialkylmetal group. In the trimethylstannylpyridines the value of 1J(Sn? Cring) varies greatly with the position of the Me3Sn group. 相似文献
1000.
The phosphorescence lifetimes of ω-alkenyl esters of p-benzophenone-carboxylic acid have been measured in dilute solution in degassed acetic acid solution. The lifetimes were extrapolated to infinite dilution. Intramolecular quenching was not very significant in benzophenone-4-CO2(CH2)nCHCH2 for n = 1, 2 or 4. For n = 9 the phosphorescence lifetime was found to be 2 μs compared to 70 μs for n = 1, 2. These results are interpreted to mean that the quenching complex has a specific geometric requirement with the CHCH2 group approaching within a van der Waals distance of the ketone carbonyl group. 相似文献