全文获取类型
收费全文 | 1758篇 |
免费 | 515篇 |
国内免费 | 821篇 |
专业分类
测绘学 | 111篇 |
大气科学 | 1039篇 |
地球物理 | 439篇 |
地质学 | 723篇 |
海洋学 | 447篇 |
天文学 | 24篇 |
综合类 | 66篇 |
自然地理 | 245篇 |
出版年
2024年 | 11篇 |
2023年 | 31篇 |
2022年 | 63篇 |
2021年 | 70篇 |
2020年 | 106篇 |
2019年 | 120篇 |
2018年 | 74篇 |
2017年 | 94篇 |
2016年 | 93篇 |
2015年 | 120篇 |
2014年 | 127篇 |
2013年 | 150篇 |
2012年 | 135篇 |
2011年 | 152篇 |
2010年 | 124篇 |
2009年 | 143篇 |
2008年 | 118篇 |
2007年 | 173篇 |
2006年 | 173篇 |
2005年 | 139篇 |
2004年 | 141篇 |
2003年 | 97篇 |
2002年 | 109篇 |
2001年 | 74篇 |
2000年 | 74篇 |
1999年 | 52篇 |
1998年 | 55篇 |
1997年 | 52篇 |
1996年 | 52篇 |
1995年 | 46篇 |
1994年 | 37篇 |
1993年 | 27篇 |
1992年 | 18篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
排序方式: 共有3094条查询结果,搜索用时 218 毫秒
31.
青藏高原西北缘祁漫塔格山中新世快速抬升
的磷灰石裂变径迹证据 总被引:1,自引:0,他引:1
对祁漫塔格山体不同海拔高度所取的9个磷灰石样品的裂变径迹分析结果表明,东昆仑西段中新世早中期为主要的隆升期且隆升速率较高,早期隆升速率为111m/Ma,晚期隆升速率为98m/Ma,总体隆升速率为100m/Ma。样品显示出磷灰石裂变径迹长度大致分2类,一类磷灰石裂变径迹长度为(12.21±10.20)-(13.75±0.30)μm,径迹长度分布图基本上为窄而对称的正态分布,反映具有快的剥露冷却速率,未受到后期热事件的干扰。另一类磷灰石裂变径迹长度为(11.88±0.33)~(13.32±0.27)μm,较前一类具有稍慢的剥露冷却速率,并且受到了后期热事件的干扰。 相似文献
32.
本文根据层序地层学的基本原理,立足东部箕状断陷盆地的特点,以冀中拗陷和二连盆地为重点研究对象,提炼出陆相断陷盆地层序地层学模式,在缓坡带,以风暴浪基面作为“陆架边角”的参照物,层序地层特征相似于海相被动大陆边缘背景;在陡坡带则截然不同,并以湖面与边界断裂的交点取代“陆架边角”,各体系域所含沉积体系与海相模式不尽相同,在盆地形成初期的层序,低水位体系域发育,湖泊消亡以后,主要发育高水位体系域。此外,本文还探索了层序地层与油气赋存的关系,指出富砂的“盆底扇”是今后勘探开发的重要方向。 相似文献
33.
From source terrains of the Eastern Alps to the Molasse Basin: Detrital record of non-steady-state exhumation 总被引:2,自引:1,他引:2
Fission-track cooling ages of detrital apatite (AFT) in the East Alpine Molasse Basin display age groups corresponding to geodynamic events in the orogen since Jurassic times. These age groups are typical of certain thermotectonic units, which formed a patchwork in the Swiss and Eastern Alps. By a combination of petrographic and thermochronologic data, progressive erosion of source terrains is monitored in different catchments since the Oligocene. The AFT cooling ages show a decrease in lag time until when rapidly cooled debris derived from tectonically exhumed core complexes became exposed. After termination of tectonic exhumation, lag times of debris derived from the core complexes increased. Neither on the scale of the entire Eastern Alps, or on the scale of individual catchments, steady-state exhumation is observed, due to the highly dynamic changes of exhumation rates since Late Eocene collision. 相似文献
34.
Neetu Agnihotri P. Chittibabu Indu Jain P. C. Sinha A. D. Rao S. K. Dube 《Natural Hazards》2006,39(1):83-101
The paper describes a two-dimensional bay–river coupled numerical model for storm surges along the Andhra coast of India.
The effect of the Krishna and Godavari rivers on the surge development is analysed. A comparative study of the surge generated
by a tropical cyclone with and without the inclusion of rivers is done in detail. Three cyclones that struck the Andhra coast
in November 1977, May 1990 and November 1996 were used for the simulation studies. It is found that the idealized model without
a river overestimates the sea-level elevation as compared to a more realistic bay–river coupled model. The temporal variation
of surge values at the mouth of the rivers is also studied for all three cyclone cases. It is found that the effect of the
presence of rivers depends on the strength of the cyclone, its point of landfall and the location of the rivers with respect
to the landfall point. 相似文献
35.
The degree to which dust emissions are controlled by geomorphic conditions, wind environments and land use was investigated using the dust storm frequency (DSF) and data from more than 300 meteorological stations throughout northern China. Our analysis showed that most dust emissions originated in gobi deserts that developed in piedmont alluvial fans of the Kunlun, Qilian and Helan mountains. Dust emissions are low from other gobi desert regions, such as the northern Gurbantunggut and eastern Taklimakan, where high vegetation coverage restrained dust emissions or where dust-size particles are not abundant after a long period of strong wind erosion. Sandy deserts with relatively high vegetation coverage or an extensive cover by mobile sands are not a major dust source. Although the highest dust emissions did not appear in regions with the highest wind energy, DSF trends in each region from 1960 to 2003 were closely related to local wind activity. DSF was low in regions with high levels of human activity, where the mean DSF from 1960 to 2003 did not exceed 4 days/year; even from the 1960s to the early 1970s, the period with the greatest DSF, frequency did not exceed 8 days/year, which indicates that extensive land use did not contribute to DSF. The low DSF in these areas might result from the fact that although land use could produce abundant fine soil fractions, vegetation coverage and soil moisture remained higher than in the gobi deserts of arid China, thereby decreasing dust-storm occurrence. 相似文献
36.
1 IntroductionThe Mesozoic-Cenozoic tectonic evolution and ki-netics mechanism of the intracontinental orogen are thekey subjects of continental dynamics (Ma Zongjin andGao Xianglin, 2004) and the key to understanding theregional geological tectonics (Qia… 相似文献
37.
38.
2004年全球重大气候事件概述 总被引:1,自引:3,他引:1
2004年全球气候持续偏暖。年初,暴雪席卷欧洲多国,美国受到罕见大雪袭击,南亚和墨西哥遭遇低温严寒。北半球夏秋季,西太平洋、大西洋热带风暴活动频繁。日本、菲律宾和美国受灾严重。年内,非洲、亚洲部分国家发生严重干旱;同时,南亚、南美洲及非洲多国暴雨致洪。年内,欧洲伊比利亚半岛、日本和澳大利亚遭遇高温热浪。 相似文献
39.
40.
2001年全球重大气候事件概述 总被引:1,自引:0,他引:1
全球气候仍持续偏暖。亚洲大部出现异常冷冬,许多地区遇到数十年未见的风雪严寒;美国冬季也连续遭受暴风雪袭击。东亚、南亚、中亚有西亚发生了大范围的持久干旱,南亚、东南亚夏季暴雨频繁,造成严重洪涝灾害。欧洲、非洲及南美洲的许多国家和地区降水异常偏多,导致不同程度的洪水,俄罗斯西伯利亚地区发生百年不遇的大洪水。北大西洋飓风较常年显著偏多,西北太平洋台风也给沿海地区带来严重灾害。 相似文献