全文获取类型
| 收费全文 | 43961篇 |
| 免费 | 8051篇 |
| 国内免费 | 10252篇 |
专业分类
| 测绘学 | 3389篇 |
| 大气科学 | 4854篇 |
| 地球物理 | 7541篇 |
| 地质学 | 29339篇 |
| 海洋学 | 4936篇 |
| 天文学 | 3391篇 |
| 综合类 | 2723篇 |
| 自然地理 | 6091篇 |
出版年
| 2024年 | 171篇 |
| 2023年 | 565篇 |
| 2022年 | 1442篇 |
| 2021年 | 1701篇 |
| 2020年 | 1599篇 |
| 2019年 | 1854篇 |
| 2018年 | 1518篇 |
| 2017年 | 1790篇 |
| 2016年 | 1904篇 |
| 2015年 | 2005篇 |
| 2014年 | 2549篇 |
| 2013年 | 2619篇 |
| 2012年 | 2737篇 |
| 2011年 | 2957篇 |
| 2010年 | 2514篇 |
| 2009年 | 3117篇 |
| 2008年 | 3036篇 |
| 2007年 | 3113篇 |
| 2006年 | 3130篇 |
| 2005年 | 2853篇 |
| 2004年 | 2515篇 |
| 2003年 | 2387篇 |
| 2002年 | 2104篇 |
| 2001年 | 1841篇 |
| 2000年 | 1894篇 |
| 1999年 | 1611篇 |
| 1998年 | 1354篇 |
| 1997年 | 1037篇 |
| 1996年 | 850篇 |
| 1995年 | 724篇 |
| 1994年 | 642篇 |
| 1993年 | 537篇 |
| 1992年 | 379篇 |
| 1991年 | 313篇 |
| 1990年 | 227篇 |
| 1989年 | 169篇 |
| 1988年 | 160篇 |
| 1987年 | 85篇 |
| 1986年 | 59篇 |
| 1985年 | 45篇 |
| 1984年 | 30篇 |
| 1983年 | 16篇 |
| 1982年 | 18篇 |
| 1981年 | 13篇 |
| 1980年 | 9篇 |
| 1979年 | 6篇 |
| 1978年 | 19篇 |
| 1977年 | 7篇 |
| 1976年 | 5篇 |
| 1954年 | 9篇 |
排序方式： 共有10000条查询结果，搜索用时 109 毫秒
131.
We briefly describe an advanced 3D gas dynamical model developed for the simulation of theenvironment of active cometary nuclei.
The model canhandle realistic nucleus shapes and alternative physical models for the gas and dust production mechanism.The
inner gas coma structure is computed by solving self-consistently(a) near to the surface the Boltzman Equation(b) outside
of it, Euler or Navier-Stokes equations.The dust distribution is computed from multifluid ``zero-temperature' Euler equations,extrapolated
with the help of a Keplerian fountain model.The evolution of the coma during the nucleus orbital and spin motion,is computed
as a succession of quasi-steady solutions. Earlier versions of the model using simple,``paedagogic' nuclei have demonstrated
that the surface orographyand the surface inhomogeneity contribute similarly to structuring the near-nucleusgas and dust coma,casting
a shadow on the automatic attribution of such structures to ``active areas'.The model was recently applied to comet P/Halley,
for whichthe nucleus shape is available. In the companion paper of this volume,we show that most near-nucleus dust structuresobserved
during the 1986 Halley flybys are reproduced, assuming that the nucleus is strictly homogeneous. Here, we investigate the
effect of shape perturbations and homogeneityperturbations. We show that the near nucleus gas coma structure is robust vis-a-vissuch
effects. In particular, a random distribution of active and inactive areaswould not affect considerably this structure, suggesting that such areas,even if present, could not be easily identified on images
of the coma. 相似文献
132.
The purpose of this work was to reinvestigate the existing hydrogeological conceptual model of the basin of Madrid, Spain. A cumulative chemical isotopic diagram which enabled the distinction between different groups of water as well as calculation of the mode of their blending was used for this investigation. It was found that the groups of discharge were lighter in their isotopic composition than that of recharge. The previous explanation of this fact, backed by carbon-14 dating, was the long residence time due to flow lines going down to depths of more than 1000 m. This flow model assumes homogenous conditions to these depths. This assumption can not be supported by evidence from deep wells. Thus a modified model is suggested which maintains homogenous conditions only to about 300 m and a deep confined aquifer below containing paleowater. The higher degree of depletion of this water has been explained by a colder climate on top of an altitude effect. Another interesting observation was the correlation between the isotopic composition of the rains, the month of the rain event and the composition of the recharge group groundwater. It could be seen that the winter rains resemble the groundwater composition, which shows that practically all the spring and summer rains were evapotranspirated. 相似文献
133.
Antony J. Long Sarah A. Woodroffe Sue Dawson David H. Roberts Charlotte L. Bryant 《第四纪科学杂志》2009,24(4):345-359
In West Greenland, early and mid Holocene relative sea level (RSL) fall was replaced by late Holocene RSL rise during the Neoglacial, after 4–3 cal. ka BP (thousand calibrated years before present). Here we present the results of an isolation basin RSL study completed near to the coastal town of Sisimiut, in central West Greenland. RSL fell from 14 m above sea level at 5.7 cal. ka BP to reach a lowstand of ?4.0 m at 2.3–1.2 cal. ka BP, before rising by an equivalent amount to present. Differences in the timing and magnitude of the RSL lowstand between this and other sites in West and South Greenland record the varied interplay of local and non‐Greenland RSL processes, notably the reloading of the Earth's crust caused by a Neoglacial expansion of the Greenland Ice Sheet (GIS) and the subsidence associated with the collapse of the Laurentide Ice Sheet forebulge. This means that the timing of the sea level lowstand cannot be used to infer directly when the GIS advanced during the Neoglacial. The rise in Late Holocene RSL is contrary to recently reported bedrock uplift in the Sisimiut area, based on repeat GPS surveys. This indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late Holocene, and that there has been a switch from subsidence to uplift at some point in the last thousand years or so. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
134.
135.
136.
137.
138.
139.
从胶东所处的板块构造位置和区域控热构造入手,根据地热传导理论,对胶东温泉的地热属性进行分析研究,认为胶东半岛温泉地热属性为毗邻板块边缘高温地热带的板内中低温地热系统,它以偏高的大地热流值为地热背景,以局部控热构造聚敛的大地热流为热源,以地形高差影响和相应的水力压差作用为动力,入渗的大气降水被岩石中的热量加热,并沿断裂出露形成温泉地热水。根据山东半岛温泉地热属性的特点和地热水开发中所面临的问题,提出保持胶东温泉可持续开发的相关对策。 相似文献
140.