首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   794篇
  免费   12篇
  国内免费   11篇
测绘学   12篇
大气科学   99篇
地球物理   187篇
地质学   229篇
海洋学   69篇
天文学   147篇
综合类   6篇
自然地理   68篇
  2021年   6篇
  2020年   7篇
  2019年   6篇
  2018年   7篇
  2017年   8篇
  2016年   14篇
  2015年   15篇
  2014年   17篇
  2013年   43篇
  2012年   28篇
  2011年   32篇
  2010年   28篇
  2009年   37篇
  2008年   60篇
  2007年   30篇
  2006年   26篇
  2005年   30篇
  2004年   31篇
  2003年   26篇
  2002年   32篇
  2001年   23篇
  2000年   17篇
  1999年   22篇
  1998年   20篇
  1997年   15篇
  1996年   15篇
  1995年   7篇
  1994年   14篇
  1993年   10篇
  1992年   8篇
  1991年   11篇
  1990年   9篇
  1989年   8篇
  1988年   8篇
  1987年   6篇
  1986年   9篇
  1985年   13篇
  1984年   7篇
  1983年   17篇
  1982年   13篇
  1981年   11篇
  1980年   9篇
  1979年   8篇
  1978年   4篇
  1977年   8篇
  1976年   6篇
  1975年   5篇
  1974年   5篇
  1973年   5篇
  1970年   3篇
排序方式: 共有817条查询结果,搜索用时 15 毫秒
91.
92.
A simplistic study of the dynamics of a falling particle ensemble is described. It shows the effect created by the introduction of particle size distributions on precipitation onset and duration and compares it to the case where air motions or pressure fields triggered by the particles are neglected. The assumption of homogeneously sized raindrops seems adequate if precipitation rates and total rainfall are considered. As soon as timing is involved a more refined treatment is required.  相似文献   
93.
We take issue with the claim by Tavoni and Tol (Clim Chang 100:769–778, 2010) that reviews of the macroeconomic costs of achieving the 2 °C climate target have been affected by selection bias and have underestimated the costs. Although many more cost estimates are available in the literature, they have restricted their survey to the data in the EMF22 study, with a limited set of model solutions for the 2 °C target. They have applied the methodology of observational meta-analysis inappropriately to policy meta-analysis, where the number of results is often very small and the basis for imputing a statistical distribution does not usually exist. They have mixed direct costs with net costs in terms of %GDP. Their method of “correcting” for missing data with (high) costs of stringent mitigation could equally be applied to correcting the data for omission of mitigation options such as biomass energy with carbon capture so reducing the cost estimates. And finally they implicitly assume that the same policy combinations and mitigation options are applied for all climate scenarios, when more stringent scenarios may require more stringent policies and options, such as regulation or BECCS. The conclusion from the literature is more appropriately that the costs are highly uncertain, that they can equally be positive or negative (gains) and that models which fail to solve for stringent mitigations are not fit for purpose.  相似文献   
94.
We present spatially resolved intermediate-resolution spectroscopy of a sample of 12 E+A galaxies in the   z = 0.32  rich galaxy cluster AC 114, obtained with the FLAMES multi-integral field unit system on the Very Large Telescope (VLT) of the European Southern Observatory. Previous integrated spectroscopy of all these galaxies by Couch & Sharples had shown them to have strong Balmer line absorption and an absence of [O  ii ]λ3727 emission – the defining characteristics of the 'E+A' spectral signature, indicative of an abrupt halt to a recent episode of quite vigorous star formation. We have used our spectral data to determine the radial variation in the strength of Hδ absorption in these galaxies and hence map out the distribution of this recently formed stellar population. Such information provides important clues as to what physical event might have been responsible for this quite dramatic change in star formation activity in the recent past of these galaxies. We find a diversity of behaviour amongst these galaxies in terms of the radial variation in Hδ absorption: four galaxies show little Hδ absorption across their entire extent; it would appear they were misidentified as E+A galaxies in the earlier integrated spectroscopic studies. The remainder show strong Hδ absorption, with a gradient that is either negative (Hδ equivalent width decreasing with radius), flat or positive . By comparison with numerical simulations we suggest that the first of these different types of radial behaviour provides evidence for a merger/interaction origin, whereas the latter two types of behaviour are more consistent with the truncation of star formation in normal disc galaxies with the Hδ gradient becoming increasingly positive with time after truncation. It would seem therefore that more than one physical mechanism is responsible for E+A formation in the same environment.  相似文献   
95.
96.
97.
The dates of recession of eleven outlet glaciers of the Hielo Patagónico Norte (Northern Patagonian Icefield) from their recent maximum positions have been inferred from dendrochronology, lichenometry, radiocarbon dating and historical sources. We have refined the dating for part of the Little Ice Age period in this area placing a glacial advance to between AD 1650 and 1766 with the latter date favoured as conformable with historical records and an uncalibrated radiocarbon determination. Glacier recession from maximal positions began in the early 1860s–1870s. Recession was largely synchronous on the western and eastern sides of the Icefield. This synchronicity suggests that climate forcing over-rides second-order controls on glacier behaviour such as the nature of the terminal environment (e.g. calving/non-calving) or differences in glacier drainage basin area. We argue that this icefield-wide glacier recession represents a response to post-Little Ice Age warming, and provides further evidence for the global extent and near synchronous termination of the Little Ice Age.  相似文献   
98.
99.
Palaeoclimates across Europe for 6000 y BP were estimated from pollen data using the modern pollen analogue technique constrained with lake-level data. The constraint consists of restricting the set of modern pollen samples considered as analogues of the fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration (PE) is consistent with the regional change in moisture balance as indicated by lakes. An artificial neural network was used for the spatial interpolation of lake-level changes to the pollen sites, and for mapping palaeoclimate anomalies. The climate variables reconstructed were mean temperature of the coldest month (T c ), growing degree days above 5  °C (GDD), moisture availability expressed as the ratio of actual to equilibrium evapotranspiration (α), and PE. The constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies, especially for PE. The reconstructions indicate clear spatial and seasonal patterns of Holocene climate change, which can provide a quantitative benchmark for the evaluation of palaeoclimate model simulations. Winter temperatures (T c ) were 1–3 K greater than present in the far N and NE of Europe, but 2–4 K less than present in the Mediterranean region. Summer warmth (GDD) was greater than present in NW Europe (by 400–800 K day at the highest elevations) and in the Alps, but >400 K day less than present at lower elevations in S Europe. PE was 50–250 mm less than present in NW Europe and the Alps, but α was 10–15% greater than present in S Europe and PE was 50–200 mm greater than present in S and E Europe. Received: 3 January 1996 / Accepted: 15 July 1996  相似文献   
100.
Celestial Mechanics and Dynamical Astronomy - The increasing availability of computing machines capable of parallel computation has accelerated interest in numerical methods that exhibit natural...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号