全文获取类型
收费全文 | 122359篇 |
免费 | 12896篇 |
国内免费 | 10372篇 |
专业分类
化学 | 34747篇 |
晶体学 | 550篇 |
力学 | 13490篇 |
综合类 | 2098篇 |
数学 | 53948篇 |
物理学 | 40794篇 |
出版年
2024年 | 207篇 |
2023年 | 1112篇 |
2022年 | 2122篇 |
2021年 | 2373篇 |
2020年 | 2890篇 |
2019年 | 3041篇 |
2018年 | 2671篇 |
2017年 | 3180篇 |
2016年 | 3570篇 |
2015年 | 3094篇 |
2014年 | 4901篇 |
2013年 | 8758篇 |
2012年 | 5345篇 |
2011年 | 6231篇 |
2010年 | 5540篇 |
2009年 | 6947篇 |
2008年 | 7640篇 |
2007年 | 7895篇 |
2006年 | 7139篇 |
2005年 | 6437篇 |
2004年 | 5878篇 |
2003年 | 5681篇 |
2002年 | 5201篇 |
2001年 | 4339篇 |
2000年 | 4136篇 |
1999年 | 3740篇 |
1998年 | 3435篇 |
1997年 | 2892篇 |
1996年 | 2451篇 |
1995年 | 2213篇 |
1994年 | 1911篇 |
1993年 | 1603篇 |
1992年 | 1477篇 |
1991年 | 1265篇 |
1990年 | 1011篇 |
1989年 | 787篇 |
1988年 | 772篇 |
1987年 | 627篇 |
1986年 | 555篇 |
1985年 | 623篇 |
1984年 | 580篇 |
1983年 | 300篇 |
1982年 | 477篇 |
1981年 | 518篇 |
1980年 | 383篇 |
1979年 | 388篇 |
1978年 | 295篇 |
1977年 | 263篇 |
1976年 | 195篇 |
1974年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
981.
982.
Michael S. Kent Matthew Tirrell Timothy P. Lodge 《Journal of Polymer Science.Polymer Physics》1994,32(11):1927-1941
Solution properties for random and diblock copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA) have been measured by dynamic and total intensity light scattering in solvents of differing quality. The results are compared with the corresponding properties for PS and PMMA homopolymers of similar molecular weight, in order to determine if interactions between unlike monomers are significant. The hydrodynamic radius (Rh) and diffusion second virial coefficient (kd) for the random copolymer are found to be larger than the corresponding values for the homopolymers in a solvent which is near-theta for the two homopolymers, whereas no such effect is observed for the block copolymer. This suggests that most intrachain interactions occur a relatively short distance along the chain backbone. In a mutual good solvent Rh and kd of the random copolymer are comparable to the average of the values for the homopolymers, indicating that in a good solvent monomer/solvent interactions dominate over monomer/monomer interactions. For an isolated diblock copolymer in a mutual good solvent, there is no evidence that interactions between unlike monomers lead to additional expansion of the entire molecule, as measured by Rh, nor expansion of the individual blocks as probed by light scattering with one block optically masked. However, at low but finite concentration there is evidence (the coefficients of the binary interaction terms in the viscosity and the mutual diffusion coefficient, and the second and third virial coefficients) that a weak ordering effect may exist in block copolymer solutions, far from the conditions where microphase separation occurs. Finally, measurements of ternary polymer-polymer-solvent solutions show no dependence on monomer composition or monomer distribution for the tracer diffusion of probe PS-PMMA copolymers in a PMMA/toluene matrix. This indicate that the frictional interaction is largely unaffected by interactions between unlike monomers. However, there is evidence that the thermodynamic interaction is more unfavorable between a random copolymer and the homopolymer matrix than between a diblock and the matrix. © 1994 John Wiley & Sons, Inc. 相似文献
983.
We make a thorough non-covariant analysis of the derivation of the equation of motion for a charged particle, including radiation reaction, by means of a simple model for the charge: a dumbbell. This model and our method to expand retarded quantities, based on complex-variable theory, allow us to avoid some of the usual approximations, so we can show several features of the radiation reaction problem. 相似文献
984.
L. Saloff-Coste 《Potential Analysis》1995,4(4):429-467
Old and recent results concerning Harnack inequalities for divergence form operators are reviewed. In particular, the characterization of the parabolic Harnack principle by simple geometric properties -Poincaré inequality and doubling property- is discussed at length. It is shown that these two properties suffice to apply Moser's iterative technique. 相似文献
985.
Ajay K. Saini Clifford M. Carlin Howard H. Patterson 《Journal of polymer science. Part A, Polymer chemistry》1992,30(3):419-427
New model compounds for poly[N,N′-bis(phenoxyphenyl)pyromellitimide] have been synthesized in order to investigate the formation of imine bonds which are proposed to form during the curing process and lead to crosslinking in the bulk polymer. Raman studies show that terminal amines can react with imide carbonyls during curing to form C?N bonds. The Raman band due to C?N appears at 1656 cm?1 and the band due to C?O closest to the imine bond is observed at 1742 cm?1. These results are in agreement with previously published results on vapor deposited polyimide films. 相似文献
986.
The results of the analysis of the stability of stationary solutions of wave equations discribing a behavior of the nonlinear Fabry-Perot interferometer with a saturated paramagnetic filling are presented in this paper. The cases when paramagnetic medium is characterized by a homogeneously and nonhomogeneously broadened line of the magnetic resonance have been considered. Areas of unstable behavior of these characteristics of the resonance structure have been found. 相似文献
987.
988.
The self-diffusion of benzene, toluene, and ethylbenzene in polystyrene have been analyzed using the Vrentas/Duda free-volume diffusion model. Diffusion coefficient predictions suggest an exponential concentration dependence of the activation energy required to overcome attractive forces, E. Without the use of any diffusion data approximating E as zero over the entire concentration range yields self-diffusion coefficient predictions which are in good agreement with experimental data. © 1992 John Wiley & Sons, Inc. 相似文献
989.
K. Gowri Navada 《Proceedings Mathematical Sciences》1995,105(3):281-285
We give an estimate for the number of elements in the intersection of topological Sidon sets inR
n with compact convex subsets and deduce a necessary and sufficient conditions for an orbit of a linear transformation ofR
n to be a topological Sidon set. 相似文献
990.