全文获取类型
收费全文 | 4510篇 |
免费 | 196篇 |
国内免费 | 64篇 |
专业分类
测绘学 | 165篇 |
大气科学 | 461篇 |
地球物理 | 941篇 |
地质学 | 1446篇 |
海洋学 | 437篇 |
天文学 | 945篇 |
综合类 | 13篇 |
自然地理 | 362篇 |
出版年
2023年 | 22篇 |
2022年 | 20篇 |
2021年 | 64篇 |
2020年 | 83篇 |
2019年 | 83篇 |
2018年 | 162篇 |
2017年 | 126篇 |
2016年 | 190篇 |
2015年 | 137篇 |
2014年 | 162篇 |
2013年 | 250篇 |
2012年 | 188篇 |
2011年 | 254篇 |
2010年 | 211篇 |
2009年 | 278篇 |
2008年 | 257篇 |
2007年 | 244篇 |
2006年 | 207篇 |
2005年 | 166篇 |
2004年 | 179篇 |
2003年 | 153篇 |
2002年 | 143篇 |
2001年 | 112篇 |
2000年 | 127篇 |
1999年 | 102篇 |
1998年 | 105篇 |
1997年 | 68篇 |
1996年 | 62篇 |
1995年 | 43篇 |
1994年 | 36篇 |
1993年 | 43篇 |
1992年 | 37篇 |
1991年 | 39篇 |
1990年 | 21篇 |
1989年 | 22篇 |
1988年 | 11篇 |
1987年 | 21篇 |
1986年 | 20篇 |
1985年 | 30篇 |
1984年 | 32篇 |
1983年 | 28篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 14篇 |
1976年 | 18篇 |
1975年 | 16篇 |
1973年 | 12篇 |
排序方式: 共有4770条查询结果,搜索用时 15 毫秒
1.
Hydrological trends and the evolution of catchment research in the Alptal valley,central Switzerland
Manfred Stähli Jan Seibert James W. Kirchner Jana von Freyberg Ilja van Meerveld 《水文研究》2021,35(4):e14113
When the observation of small headwater catchments in the pre-Alpine Alptal valley (central Switzerland) started in the late 1960s, the researchers were mainly interested in questions related to floods and forest management. Investigations of geomorphological processes in the steep torrent channels followed in the 1980s, along with detailed observations of biogeochemical and ecohydrological processes in individual forest stands. More recently, research in the Alptal has addressed the impacts of climate change on water supply and runoff generation. In this article, we describe, for the first time, the evolution of catchment research at Alptal, and present new analyses of long-term trends and short-term hydrologic behaviour. Hydrometeorological time series from the past 50 years show substantial interannual variability, but only minimal long-term trends, except for the ~2°C increase in mean annual air temperature over the 50-year period, and a corresponding shift towards earlier snowmelt. Similar to previous studies in larger Alpine catchments, the decadal variations in mean annual runoff in Alptal's small research catchments reflect the long-term variability in annual precipitation. In the Alptal valley, the most evident hydrological trends were observed in late spring and are related to the substantial change in the duration of the snow cover. Streamflow and water quality are highly variable within and between hydrological events, suggesting rapid shifts in flow pathways and mixing, as well as changing connectivity of runoff-generating areas. This overview illustrates how catchment research in the Alptal has evolved in response to changing societal concerns and emerging scientific questions. 相似文献
2.
3.
4.
5.
6.
R. J. Beswick A. Pedlar M. S. Clemens P. Alexander 《Monthly notices of the Royal Astronomical Society》2003,346(2):424-432
We present subarcsec angular resolution observations of the neutral gas in the nearby starburst galaxy NGC 520. The central kpc region of NGC 520 contains an area of significantly enhanced star formation. The radio continuum structure of this region resolves into ∼10 continuum components. By comparing the flux densities of the brightest of these components at 1.4 GHz with published 15-GHz data we infer that these components detected at 1.4 and 1.6 GHz are related to the starburst and are most likely to be collections of several supernova remnants within the beam. None of these components is consistent with emission from an active galactic nuclei. Both neutral hydrogen (H i ) and hydroxyl (OH) absorption lines are observed against the continuum emission, along with a weak OH maser feature probably related to the star formation activity in this galaxy. Strong H i absorption ( N H ∼ 1022 atoms cm−2 ) traces a velocity gradient of 0.5 km s−1 pc−1 across the central kpc of NGC 520. The H i absorption velocity structure is consistent with the velocity gradients observed in both the OH absorption and in CO emission observations. The neutral gas velocity structure observed within the central kpc of NGC 520 is attributed to a kpc-scale ring or disc. It is also noted that the velocity gradients observed for these neutral gas components appear to differ with the velocity gradients observed from optical ionized emission lines. This apparent disagreement is discussed and attributed to the extinction of the optical emission from the actual centre of this source hence implying that optical ionized emission lines are only detected from regions with significantly different radii to those sampled by the observations presented here. 相似文献
7.
8.
Flavio Scappini Cesare Cecchi-Pestellini Harvey Smith William Klemperer Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2003,341(2):657-661
We consider sulphur depletion in dense molecular clouds, and suggest hydrated sulphuric acid, H2 SO4 · n H2 O, as a component of interstellar dust in icy mantles. We discuss the formation of hydrated sulphuric acid in collapsing clouds and its instability in heated regions in terms of the existing hot core models and observations. We also show that some features of the infrared spectrum of hydrated sulphuric acid have correspondence in the observed spectra of young stellar objects. 相似文献
9.
10.