全文获取类型
| 收费全文 | 6582篇 |
| 免费 | 984篇 |
| 国内免费 | 824篇 |
专业分类
| 测绘学 | 396篇 |
| 大气科学 | 268篇 |
| 地球物理 | 1608篇 |
| 地质学 | 2387篇 |
| 海洋学 | 515篇 |
| 天文学 | 2431篇 |
| 综合类 | 262篇 |
| 自然地理 | 523篇 |
出版年
| 2024年 | 19篇 |
| 2023年 | 59篇 |
| 2022年 | 120篇 |
| 2021年 | 157篇 |
| 2020年 | 176篇 |
| 2019年 | 195篇 |
| 2018年 | 157篇 |
| 2017年 | 181篇 |
| 2016年 | 223篇 |
| 2015年 | 248篇 |
| 2014年 | 343篇 |
| 2013年 | 344篇 |
| 2012年 | 312篇 |
| 2011年 | 308篇 |
| 2010年 | 289篇 |
| 2009年 | 500篇 |
| 2008年 | 466篇 |
| 2007年 | 596篇 |
| 2006年 | 477篇 |
| 2005年 | 401篇 |
| 2004年 | 372篇 |
| 2003年 | 350篇 |
| 2002年 | 287篇 |
| 2001年 | 264篇 |
| 2000年 | 251篇 |
| 1999年 | 243篇 |
| 1998年 | 241篇 |
| 1997年 | 122篇 |
| 1996年 | 141篇 |
| 1995年 | 89篇 |
| 1994年 | 82篇 |
| 1993年 | 74篇 |
| 1992年 | 67篇 |
| 1991年 | 42篇 |
| 1990年 | 58篇 |
| 1989年 | 34篇 |
| 1988年 | 33篇 |
| 1987年 | 16篇 |
| 1986年 | 15篇 |
| 1985年 | 12篇 |
| 1984年 | 3篇 |
| 1983年 | 1篇 |
| 1982年 | 3篇 |
| 1981年 | 4篇 |
| 1980年 | 5篇 |
| 1978年 | 4篇 |
| 1977年 | 1篇 |
| 1954年 | 5篇 |
排序方式： 共有8390条查询结果，搜索用时 234 毫秒
961.
962.
963.
964.
965.
966.
967.
968.
969.
A. G. Polnarev N. J. Miller B. G. Keating 《Monthly notices of the Royal Astronomical Society》2008,386(2):1053-1063
We examine the use of the TE cross-correlation power spectrum of the cosmic microwave background (CMB) as a complementary test to detect primordial gravitational waves (PGWs). The first method used is based on the determination of the lowest multipole, ℓ0 , where the TE power spectrum, C TE ℓ , first changes sign. The second method uses Wiener filtering on the CMB TE data to remove the density perturbations contribution to the TE power spectrum. In principle this leaves only the contribution of PGWs. We examine two toy experiments (one ideal and another more realistic) to see their ability to constrain PGWs using the TE power spectrum alone. We found that an ideal experiment, one limited only by cosmic variance, can detect PGWs with a ratio of tensor to scalar metric perturbation power spectra r = 0.3 at 99.9 per cent confidence level using only the TE correlation. This value is comparable with current constraints obtained by the Wilkinson Microwave Anisotropy Probe based on the 2σ upper limits to the B-mode amplitude. We demonstrate that to measure PGWs by their contribution to the TE cross-correlation power spectrum in a realistic ground-based experiment when real instrumental noise is taken into account, the tensor-to-scalar ratio, r , should be approximately three times larger. 相似文献
970.
Eric G. Blackman George B. Field 《Monthly notices of the Royal Astronomical Society》2008,386(3):1481-1486
The magnetic Reynolds number, R M , is defined as the product of a characteristic scale and associated flow speed divided by the microphysical magnetic diffusivity. For laminar flows, R M also approximates the ratio of advective to dissipative terms in the total magnetic energy equation, but for turbulent flows this latter ratio depends on the energy spectra and approaches unity in a steady state. To generalize for flows of arbitrary spectra we define an effective magnetic dissipation number, R M,e , as the ratio of the advection to microphysical dissipation terms in the total magnetic energy equation, incorporating the full spectrum of scales, arbitrary magnetic Prandtl numbers, and distinct pairs of inner and outer scales for magnetic and kinetic spectra. As expected, for a substantial parameter range R M,e ∼ O (1) ≪ R M . We also distinguish R M,e from where the latter is an effective magnetic Reynolds number for the mean magnetic field equation when a turbulent diffusivity is explicitly imposed as a closure. That R M,e and approach unity even if R M ≫ 1 highlights that, just as in hydrodynamic turbulence, energy dissipation of large-scale structures in turbulent flows via a cascade can be much faster than the dissipation of large-scale structures in laminar flows. This illustrates that the rate of energy dissipation by magnetic reconnection is much faster in turbulent flows, and much less sensitive to microphysical reconnection rates compared to laminar flows. 相似文献