全文获取类型
收费全文 | 1461篇 |
免费 | 5篇 |
国内免费 | 15篇 |
专业分类
化学 | 627篇 |
晶体学 | 9篇 |
力学 | 125篇 |
数学 | 276篇 |
物理学 | 444篇 |
出版年
2019年 | 18篇 |
2018年 | 29篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 29篇 |
2013年 | 41篇 |
2012年 | 35篇 |
2011年 | 50篇 |
2010年 | 28篇 |
2009年 | 32篇 |
2008年 | 51篇 |
2007年 | 43篇 |
2006年 | 35篇 |
2005年 | 41篇 |
2004年 | 28篇 |
2003年 | 34篇 |
2002年 | 38篇 |
2001年 | 30篇 |
2000年 | 33篇 |
1999年 | 23篇 |
1998年 | 19篇 |
1997年 | 17篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 27篇 |
1993年 | 23篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 28篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1987年 | 29篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1983年 | 16篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 28篇 |
1977年 | 23篇 |
1976年 | 38篇 |
1975年 | 25篇 |
1974年 | 22篇 |
1973年 | 22篇 |
1972年 | 22篇 |
1971年 | 19篇 |
1970年 | 19篇 |
1969年 | 20篇 |
1968年 | 21篇 |
1967年 | 25篇 |
排序方式: 共有1481条查询结果,搜索用时 15 毫秒
31.
32.
Transgressive dune fields, which are active sand areas surrounded by vegetation, exist on many coasts. In some regions like in Fraser Island in Australia, small dunes shrink while large ones grow, although both experience the same climatic conditions. We propose a general mathematical model for the spatiotemporal dynamics of vegetation cover on sand dunes and focus on the dynamics of transgressive dunes. Among other possibilities, the model predicts growth parallel to the wind with shrinkage perpendicular to the wind, where, depending on geometry and size, a transgressive dune can initially grow although eventually shrink. The larger is the initial area the slower its stabilization process. The model’s predictions are supported by field observations from Fraser Island in Australia. 相似文献
33.
34.
The effect of injection from the blunt surface on the aerodynamic characteristics of long blunt cones inclined at an angle of attack to a supersonic ideal-gas flow is numerically investigated.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 107–113, September–October, 1987. 相似文献
35.
D. V. Kizevetter A. Yu. Savina V. M. Levin G. G. Baskakov 《Optics and Spectroscopy》2013,115(3):396-399
The fluorescence decay constant of a fluorescent polymer optical fiber is measured by two different side illumination methods. Comparative analysis of these methods is performed. It is shown that the difference in the measured parameters is caused by different conditions of energy exchange between the core, cladding, and radiation modes of the fiber waveguide. 相似文献
36.
37.
We explore the mechanism responsible for the ergodicity breaking in systems with long-range forces. In thermodynamic limit such systems do not evolve to the Boltzmann-Gibbs equilibrium, but become trapped in an out-of-equilibrium quasi-stationary-state. Nevertheless, we show that if the initial distribution satisfies a specific constraint-a generalized virial condition-the quasistationary state is very close to ergodic and can be described by Lynden-Bell statistics. On the other hand, if the generalized virial condition is violated, parametric resonances are excited, leading to chaos and ergodicity breaking. 相似文献
38.
E. M. Levin V. K. Pecharsky K. A. Gschneidner Jr. P. Tomlinson 《Journal of magnetism and magnetic materials》2000,210(1-3)
Magnetic field (0–4 T) and temperature dependencies (4.2–320 K) of the electrical resistance of Gd5(Si1.5Ge2.5), which undergoes a reversible first-order ferromagnetic↔paramagnetic phase transition, have been measured. The electrical resistance of Gd5(Si1.5Ge2.5) indicates that the magnetic phase transition can be induced by both temperature and magnetic field. The temperature dependence of the electrical resistance, R(T), for heating at low temperatures in the zero magnetic field has the usual metallic character, but at a critical temperature of Tcr=216 K the resistance shows a 20% negative discontinuity due to the transition from the low-temperature high-resistance state to the high-temperature low-resistance state. The R(T) dependence for cooling shows a similar but positive 25% discontinuity at 198 K. The isothermal magnetic field dependence of the electrical resistance from 212T224 K indicates the presence of temperature-dependent critical magnetic fields which can reversibly transform the paramagnetic phase into the ferromagnetic phase and vice versa. The critical magnetic fields diagram determined from the isothermal magnetic field dependencies of the electrical resistance of Gd5(Si1.5Ge2.5) shows that the FM↔PM transition in zero magnetic field on cooling and heating occurs at 206 and 213 K, respectively. The full isothermal magnetic filed hysteresis for the FM↔PM transition is 2 T, and the isofield temperature gap between critical magnetic fields is 7 K. 相似文献
39.
Jonathan M. Levin Lawrence L. Wald Marc J. Kaufman Marjorie H. Ross Luis C. Maas Perry F. Renshaw 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):292-295
Residual effects of an initial bolus of gadolinium contrast agent have been previously demonstrated in sequential dynamic susceptibility contrast MR experiments. While these residual effects quickly reach a saturation steady state, their etiology is uncertain, and they can lead to spurious estimates of hemodynamic parameters in activation experiments. The possible influence ofT1effects is now investigated with experiments in whichT1weighting is varied as well as with serial regionalT1measurements. Little evidence for significant residualT1effects is found, suggesting instead that susceptibility effects underlie these observations. An initial saturation dose of contrast agent minimizes this effect. 相似文献
40.
We show that pQCD factorization incorporated with pre-hadronization energy-loss effect naturally leads to flatness of the nuclear modification factor RAA for produced hadrons at high transverse momentum pT. We consider two possible scenarios for the pre-hadronization: In scenario 1, the produced gluon propagates through dense QCD medium and loses energy. In scenario 2, all gluons first decay to quark–antiquark pairs and then each pair loses energy as propagating through the medium. We show that the estimates of the energy-loss in these two different models lead to very close values and is able to explain the suppression of high-pT hadrons in nucleus–nucleus collisions at RHIC. We show that the onset of the flatness of RAA for the produced hadron in central collisions at midrapidity is about pT≈15 and 25 GeV at RHIC and the LHC energies, respectively. We show that the smallness (RAA<0.5 ) and the high-pT flatness of RAA obtained from the kT factorization supplemented with the Balitsky–Kovchegov (BK) equation is rather generic and it does not strongly depend on the details of the BK solutions. We show that energy-loss effect reduces the nuclear modification factor obtained from the kT factorization about 30–50% at moderate pT. 相似文献