全文获取类型
收费全文 | 292901篇 |
免费 | 3285篇 |
国内免费 | 1244篇 |
专业分类
化学 | 154419篇 |
晶体学 | 4518篇 |
力学 | 12755篇 |
综合类 | 12篇 |
数学 | 31409篇 |
物理学 | 94317篇 |
出版年
2021年 | 2009篇 |
2020年 | 2185篇 |
2019年 | 2463篇 |
2018年 | 2986篇 |
2017年 | 2845篇 |
2016年 | 4627篇 |
2015年 | 3186篇 |
2014年 | 4778篇 |
2013年 | 13375篇 |
2012年 | 10143篇 |
2011年 | 12594篇 |
2010年 | 8443篇 |
2009年 | 8380篇 |
2008年 | 11256篇 |
2007年 | 11234篇 |
2006年 | 10376篇 |
2005年 | 9601篇 |
2004年 | 8587篇 |
2003年 | 7663篇 |
2002年 | 7486篇 |
2001年 | 9662篇 |
2000年 | 7172篇 |
1999年 | 5569篇 |
1998年 | 4486篇 |
1997年 | 4475篇 |
1996年 | 4059篇 |
1995年 | 3810篇 |
1994年 | 3558篇 |
1993年 | 3518篇 |
1992年 | 4120篇 |
1991年 | 4135篇 |
1990年 | 3867篇 |
1989年 | 3752篇 |
1988年 | 3782篇 |
1987年 | 3735篇 |
1986年 | 3510篇 |
1985年 | 4755篇 |
1984年 | 4852篇 |
1983年 | 3883篇 |
1982年 | 4196篇 |
1981年 | 4082篇 |
1980年 | 3942篇 |
1979年 | 4079篇 |
1978年 | 4332篇 |
1977年 | 4183篇 |
1976年 | 4310篇 |
1975年 | 3791篇 |
1974年 | 3958篇 |
1973年 | 4181篇 |
1972年 | 2530篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
Q. Gong R. N tzel P.J. van Veldhoven T.J. Eijkemans J.H. Wolter 《Journal of Crystal Growth》2005,280(3-4):413-418
We report on the shape transition from InAs quantum dashes to quantum dots (QDs) on lattice-matched GaInAsP on InP(3 1 1)A substrates. InAs quantum dashes develop during chemical-beam epitaxy of 3.2 monolayers InAs, which transform into round InAs QDs by introducing a growth interruption without arsenic flux after InAs deposition. The shape transition is solely attributed to surface properties, i.e., increase of the surface energy and symmetry under arsenic deficient conditions. The round QD shape is maintained during subsequent GaInAsP overgrowth because the reversed shape transition from dot to dash is kinetically hindered by the decreased ad-atom diffusion under arsenic flux. 相似文献
94.
R. Centore P. Riccio S. Fusco A. Carella A. Quatela S. Schutzmann F. Stella F. De Matteis 《Journal of polymer science. Part A, Polymer chemistry》2007,45(13):2719-2725
We have prepared new polyesters containing quadratic, nonlinear optical (NLO) active chromophores covalently incorporated into the main chain. In these polymers, the sequence of the chromophore units along the main chain is rigorously head to tail. All the polyesters are processable, both in the melt and in solution. For one polyester, a full second‐order NLO characterization has been performed. An out‐of‐resonance d33 coefficient of 21 pm/V at 1368 nm has been measured. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2719–2725, 2007 相似文献
95.
Daria E. Lonsdale Geoffrey Johnston‐Hall Amanda Fawcett Craig A. Bell Carl N. Urbani Michael R. Whittaker Michael J. Monteiro 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3620-3625
In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (Ctrs) determined using the Mayo method is equal to 3.8 × 10?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the Mn data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007 相似文献
96.
97.
The classical (first integral) methods of studying restrictions on the possible motion of gravitationally interacting bodies are reviewed. The simple and flexible inequality method is extended to a similar approach to the relationship between possible forbidden motion and (asymptotic) symmetries in the relativistic few-body problem. This extended method is used to reproduce the standard results of bounded motion for a test particle in a Schwarzschild geometry. The existence of bounded motion is shown for the general relativistic few-body problem and the difficulties in determining such bounded motion is analysed. The use of this approach to obtaining a relativistic alternative to the classical Roche lobe analysis in contact binaries is discussed. 相似文献
98.
The stationary and the time-dependent homogeneous ordered states in convection may both become unstable against localized perturbations. Defects are then created and they may contribute to the disorganization of the homogeneous state. We present an experimental study of defects in some homogeneous stationary structures as well as in the traveling-wave states of convection of a nematic liquid crystal. We show that the core of the defects is a germ of the unstable state and it can become unstable under the external stress. Then, either fully homogeneous states with the symmetry of the core, or complex disordered states can develop from the local instability of defects in processes quite similar to displacive transitions in solids. Some of the main features are qualitatively similar to numerical simulations of an appropriate Landau-Ginzburg equation. 相似文献
99.
100.