全文获取类型
收费全文 | 30250篇 |
免费 | 4047篇 |
国内免费 | 5716篇 |
专业分类
测绘学 | 3346篇 |
大气科学 | 3863篇 |
地球物理 | 4533篇 |
地质学 | 10704篇 |
海洋学 | 3363篇 |
天文学 | 5610篇 |
综合类 | 2093篇 |
自然地理 | 6501篇 |
出版年
2024年 | 85篇 |
2023年 | 322篇 |
2022年 | 861篇 |
2021年 | 1070篇 |
2020年 | 1123篇 |
2019年 | 1215篇 |
2018年 | 1083篇 |
2017年 | 1176篇 |
2016年 | 1203篇 |
2015年 | 1321篇 |
2014年 | 1742篇 |
2013年 | 2017篇 |
2012年 | 1918篇 |
2011年 | 2070篇 |
2010年 | 1917篇 |
2009年 | 2347篇 |
2008年 | 2206篇 |
2007年 | 2175篇 |
2006年 | 2082篇 |
2005年 | 1782篇 |
2004年 | 1659篇 |
2003年 | 1361篇 |
2002年 | 1179篇 |
2001年 | 1038篇 |
2000年 | 910篇 |
1999年 | 766篇 |
1998年 | 653篇 |
1997年 | 471篇 |
1996年 | 394篇 |
1995年 | 316篇 |
1994年 | 288篇 |
1993年 | 279篇 |
1992年 | 205篇 |
1991年 | 140篇 |
1990年 | 132篇 |
1989年 | 89篇 |
1988年 | 84篇 |
1987年 | 46篇 |
1986年 | 50篇 |
1985年 | 49篇 |
1984年 | 41篇 |
1983年 | 28篇 |
1982年 | 24篇 |
1981年 | 12篇 |
1980年 | 22篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1977年 | 20篇 |
1976年 | 5篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
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
132.
133.
134.
135.
Summary. Multiparameter inversions of multimode dispersion data are performed for two large regions: the Pacific Ocean and North America. Anisotropy is taken into account by considering transversely isotropic structures with a vertical axis of symmetry. Two fundamental questions are studied in detail: (1) how to make the inverted models consistent when using different sets of parameters, (2) what is the significance of transversely isotropic inversion for the actual Earth's structure? It is proved that full consistency of the inverted models can be achieved by properly taking into account some a priori informations on the model and it is shown that the use of transversely isotropic models with vertical axis of symmetry does not cause severe limitations when interpreting the data. The models we have obtained are discussed in the light of these investigations. Considering an olivine-rich upper mantle, we make a tentative interpretation of these models in terms of preferred orientation of the a -axis of the crystals in one fixed horizontal direction. 相似文献
136.
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
137.
138.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1990,11(4):533-540
Photoelectric radial-velocity measurements show that HD 118670 is a double-lined spectroscopic binary in an orbit which is
not quite circular and whose period is about 48 days. Spectral types of K0 V and K7 V would satisfy the photometry and the
mass ratio; the mass function would then suggest the possibility of eclipses. However, actual spectral classification indicates
a luminosity somewhat above the main sequence 相似文献
139.
Miniature gravity corer for recovering short sediment cores 总被引:12,自引:0,他引:12
John R. Glew 《Journal of Paleolimnology》1991,5(3):285-287
140.