全文获取类型
收费全文 | 1196篇 |
免费 | 73篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 67篇 |
大气科学 | 128篇 |
地球物理 | 270篇 |
地质学 | 392篇 |
海洋学 | 109篇 |
天文学 | 183篇 |
综合类 | 6篇 |
自然地理 | 123篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 29篇 |
2020年 | 16篇 |
2019年 | 23篇 |
2018年 | 39篇 |
2017年 | 43篇 |
2016年 | 62篇 |
2015年 | 42篇 |
2014年 | 44篇 |
2013年 | 73篇 |
2012年 | 52篇 |
2011年 | 69篇 |
2010年 | 59篇 |
2009年 | 78篇 |
2008年 | 53篇 |
2007年 | 54篇 |
2006年 | 50篇 |
2005年 | 33篇 |
2004年 | 50篇 |
2003年 | 45篇 |
2002年 | 33篇 |
2001年 | 25篇 |
2000年 | 37篇 |
1999年 | 25篇 |
1998年 | 18篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1984年 | 12篇 |
1983年 | 17篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1972年 | 5篇 |
1971年 | 3篇 |
排序方式: 共有1278条查询结果,搜索用时 671 毫秒
1.
The Northland region of New Zealand includes numerous high-value, macrophyte-dominated dune lakes. Recent water policy reforms offer limited guidance on managing for aquatic macrophytes. In addition, dune lake histories are poorly known as regular monitoring dates to 2005 AD. Here, ca. 4000 years of lake functional behaviour is reconstructed from sedimentary archives in two Northland dune lakes (Humuhumu and Rotokawau). Results demonstrated that macrophyte dominance is sensitive to catchment erosion and hydrological drawdown. Degradation of macrophyte communities occurred in the nineteenth and twentieth centuries, earlier at Lake Humuhumu than Lake Rotokawau (post-1880 AD and post-1930 AD, respectively). In both lakes, increased erosional influx reduced macrophyte productivity, before later increases to wider trophic state (post-1970 AD). Lake-level decline is linked to increased nutrient loading at Lake Rotokawau but less so, Lake Humuhumu which is more strongly groundwater-fed. In Northland dune lakes, water-level reduction and erosional influx from land use have driven macrophyte degradation. 相似文献
2.
Impulsive acoustic waveforms are characterized by a different set of derived quantities than are continuous waveforms. This note presents commonly accepted definitions, units, and symbols used to describe the magnitude of impulsive underwater signals 相似文献
3.
Richard T. Jones Jim D. Marshall Stephen F. Crowley Alan Bedford Nigel Richardson Jan Bloemendal Frank Oldfield 《第四纪科学杂志》2002,17(4):329-340
A lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late‐glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake‐system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non‐linear and primarily a function of the antecedent conditions. A significant end‐Devensian isotopic excursion (A) is matched by only minor changes in the cold‐adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
5.
6.
Filippo Fraternali Tom Oosterloo Renzo Sancisi 《Astrophysics and Space Science》2004,289(3-4):377-380
A deep H I survey with the VLA of the spiral galaxy NGC 2403 has revealed the existence of a thick, low density layer of neutral gas surrounding the thin ‘cold’ disk. This layer has a mean rotation velocity 25–50 km s-1 lower than that of the disk and a 10–20 km s-1inflow towards the centre of the galaxy. In the central parts there are velocity differences from rotation of up to 150 km s-1.Chandra observations of NGC 2403 show a diffuse, hot X-ray emitting gas component with a temperature of a few 106 K. These results point at galactic fountain type of flows between disk and halo. ‘Halo’ gas with similar characteristics has also been observed in other spiral galaxies(e.g. NGC 6946, NGC 891). Such gas is probably similar to the IVCs and to some of the HVCs of the Milky Way. 相似文献
7.
8.
9.
10.