全文获取类型
收费全文 | 9574篇 |
免费 | 2267篇 |
国内免费 | 2520篇 |
专业分类
测绘学 | 414篇 |
大气科学 | 1097篇 |
地球物理 | 2932篇 |
地质学 | 6540篇 |
海洋学 | 1469篇 |
天文学 | 649篇 |
综合类 | 572篇 |
自然地理 | 688篇 |
出版年
2024年 | 43篇 |
2023年 | 130篇 |
2022年 | 336篇 |
2021年 | 363篇 |
2020年 | 363篇 |
2019年 | 511篇 |
2018年 | 406篇 |
2017年 | 406篇 |
2016年 | 488篇 |
2015年 | 502篇 |
2014年 | 613篇 |
2013年 | 599篇 |
2012年 | 584篇 |
2011年 | 700篇 |
2010年 | 596篇 |
2009年 | 762篇 |
2008年 | 674篇 |
2007年 | 696篇 |
2006年 | 704篇 |
2005年 | 637篇 |
2004年 | 576篇 |
2003年 | 532篇 |
2002年 | 470篇 |
2001年 | 351篇 |
2000年 | 392篇 |
1999年 | 279篇 |
1998年 | 301篇 |
1997年 | 256篇 |
1996年 | 216篇 |
1995年 | 155篇 |
1994年 | 143篇 |
1993年 | 126篇 |
1992年 | 109篇 |
1991年 | 76篇 |
1990年 | 60篇 |
1989年 | 37篇 |
1988年 | 39篇 |
1987年 | 22篇 |
1986年 | 25篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 13篇 |
1977年 | 4篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae. 相似文献
22.
Sunetra Giridhar N. Kameswara Rao David L. Lambert 《Journal of Astrophysics and Astronomy》1996,17(1-2):23-40
Two high resolution spectra of the hot RCrB star DY Cen in the red region are compared. The photospheric absorption lines
show a radial velocity variation of 12 kms-1 between 1989 July and 1992 May. Emission components to some CII lines present
in 1989 are almost entirely absent in 1992. Nebular forbidden lines of [OI], [NII] and [SII] appear unchanged from 1989 to
1992 相似文献
23.
1995年7月11日—12日,广西地矿厅和河池地区行署首次联合举办矿产资源勘查成果展销会,会址设在河池市,与会代表130余人。展销会提交大会展销的矿产资源勘查成果38项,引资勘查项目38项。经买卖双方三天的洽谈,涉及到的项目25项,会议期间签订矿产资源勘查成果合同协议4项,愈千万元,取得较好的社会经济效益。为地勘资金多渠道来源开辟了新路子,对促进地勘单位地质找矿工作及勘查成果有偿使用发挥了重要作用 相似文献
24.
We briefly describe an advanced 3D gas dynamical model developed for the simulation of theenvironment of active cometary nuclei.
The model canhandle realistic nucleus shapes and alternative physical models for the gas and dust production mechanism.The
inner gas coma structure is computed by solving self-consistently(a) near to the surface the Boltzman Equation(b) outside
of it, Euler or Navier-Stokes equations.The dust distribution is computed from multifluid ``zero-temperature' Euler equations,extrapolated
with the help of a Keplerian fountain model.The evolution of the coma during the nucleus orbital and spin motion,is computed
as a succession of quasi-steady solutions. Earlier versions of the model using simple,``paedagogic' nuclei have demonstrated
that the surface orographyand the surface inhomogeneity contribute similarly to structuring the near-nucleusgas and dust coma,casting
a shadow on the automatic attribution of such structures to ``active areas'.The model was recently applied to comet P/Halley,
for whichthe nucleus shape is available. In the companion paper of this volume,we show that most near-nucleus dust structuresobserved
during the 1986 Halley flybys are reproduced, assuming that the nucleus is strictly homogeneous. Here, we investigate the
effect of shape perturbations and homogeneityperturbations. We show that the near nucleus gas coma structure is robust vis-a-vissuch
effects. In particular, a random distribution of active and inactive areaswould not affect considerably this structure, suggesting that such areas,even if present, could not be easily identified on images
of the coma. 相似文献
25.
26.
27.
28.
29.
30.