全文获取类型
| 收费全文 | 645篇 |
| 免费 | 49篇 |
| 国内免费 | 66篇 |
专业分类
| 测绘学 | 9篇 |
| 大气科学 | 47篇 |
| 地球物理 | 51篇 |
| 地质学 | 204篇 |
| 海洋学 | 54篇 |
| 天文学 | 371篇 |
| 综合类 | 8篇 |
| 自然地理 | 16篇 |
出版年
| 2024年 | 1篇 |
| 2023年 | 7篇 |
| 2022年 | 7篇 |
| 2021年 | 8篇 |
| 2020年 | 18篇 |
| 2019年 | 12篇 |
| 2018年 | 7篇 |
| 2017年 | 10篇 |
| 2016年 | 16篇 |
| 2015年 | 14篇 |
| 2014年 | 25篇 |
| 2013年 | 26篇 |
| 2012年 | 20篇 |
| 2011年 | 13篇 |
| 2010年 | 12篇 |
| 2009年 | 56篇 |
| 2008年 | 49篇 |
| 2007年 | 42篇 |
| 2006年 | 54篇 |
| 2005年 | 57篇 |
| 2004年 | 44篇 |
| 2003年 | 46篇 |
| 2002年 | 33篇 |
| 2001年 | 32篇 |
| 2000年 | 27篇 |
| 1999年 | 29篇 |
| 1998年 | 39篇 |
| 1997年 | 14篇 |
| 1996年 | 4篇 |
| 1995年 | 4篇 |
| 1994年 | 7篇 |
| 1993年 | 3篇 |
| 1992年 | 4篇 |
| 1991年 | 3篇 |
| 1990年 | 2篇 |
| 1989年 | 8篇 |
| 1988年 | 1篇 |
| 1987年 | 2篇 |
| 1986年 | 1篇 |
| 1985年 | 1篇 |
| 1980年 | 2篇 |
排序方式： 共有760条查询结果，搜索用时 328 毫秒
11.
R. Papoular 《Monthly notices of the Royal Astronomical Society》2005,362(2):489-497
A model is proposed for the formation of water ice mantles on grains in interstellar clouds. This occurs by direct accretion of monomers from the gas, be they formed by gas or surface reactions. The formation of the first monolayer requires a minimum extinction of interstellar radiation, sufficient to lower the grain temperature to the point where thermal evaporation of monomers is just offset by monomer accretion from the gas. This threshold is mainly determined by the adsorption energy of water molecules on the grain material; for hydrocarbon material, chemical simulation places this energy between 0.5 and 2 kcal mol−1 , which sets the (true) visible extinction threshold at a few magnitudes. However, realistic distributions of matter in a cloud will usually add to this an unrelated amount of cloud core extinction, which can explain the large dispersion of observed (apparent) thresholds. Once the threshold is crossed, all available water molecules in the gas are quickly adsorbed, because the grain cools down and the adsorption energy on ice is higher than on bare grain. The relative thickness of the mantle, and, hence, the slope of τ3 ( A v ) depend only on the available water vapour, which is a small fraction of the oxygen abundance. Chemical simulation was also used to determine the adsorption sites and energies of O and OH on hydrocarbons and study the dynamics of formation of water molecules by surface reactions with gaseous H atoms, as well as their chances to stick in situ. 相似文献
12.
13.
14.
15.
Frédéric Zagury 《Monthly notices of the Royal Astronomical Society》2006,370(4):1763-1770
The hypothesis of an extended red emission (ERE) in diffuse Galactic light (DGL) has been put forward in 1998 by Gordon, Witt & Friedmann who found that scattered starlight was not enough to explain the amount of DGL in the R band, in some high Galactic latitude directions. This paper re-investigates, for high Galactic latitudes, the brightnesses and colours of DGL, integrated star and galaxy light (ISGL), and of the total extrasolar light (ISGL+DGL) measured by Pioneer. Under the traditional assumption that DGL is forward scattering of background starlight by interstellar dust on the line of sight, ISGL and Pioneer have very close colours, as it is found by Gordon, Witt & Friedmann. Pioneer observations at high |b| thus accept an alternative and simple interpretation, with no involvement of ERE in DGL. 相似文献
16.
17.
Low-frequency damping of a moored semisubmersible drilling platform was obtained from numerical extinction tests simulated in still water and in regular waves and from mean wave drift forces calculated at zero forward speed. The influence of drag forces was represented by the modified Morison equation. The platform as used for the 18th ITTC Comparative Mooring Study was analyzed in irregular beam waves. The computed time series of sway as well as the corresponding sway response spectrum compared favourably with model test measurements, demonstrating that this procedure to determine low-frequency damping can be effective. 相似文献
18.
19.
20.
Abstract. The major problem in coastal areas of developing countries is disturbance caused by anthropogenic influence. This disturbance can be quantified by analysing the distribution and composition of marine communities using uni- and multivariate techniques and the biotic index. A study of benthic macrofauna was carried out along the São Sebastião Channel, northern coast of São Paulo State, Brazil, in an area with a submarine outfall, a petroleum terminal and a commercial harbour. Sampling was undertaken seasonally, by means of a van Veen grab (0.1 m2 ) at 15 oceanographic stations, from November 1993 to August 1994. A total of 392 species were identified (129 Polychaeta, 127 Mollusca, 98 Crustacea, 28 Echinodermata and 10 other phyla). The sedimentary pattern recorded for the São Sebastião Channel is very heterogeneous, influenced mainly by strong wind-driven currents, and differs from nearby shelf areas. The study area could be divided into three regions based on sediment texture and fauna: one region dominated by medium and coarse sand with low values of organic carbon; a second area where pelitic fractions were dominant with high values of organic carbon and nitrogen; and a third region characterised by fine and very fine sand, presenting intermediate organic carbon values. No temporal significant variation in abundance and species composition was found, except in autumn. The use of the 'marine Biotic Coefficient' showed the same ecological trend as the faunal abundance and demonstrated that the central continental region of the channel is affected by human activities. 相似文献