全文获取类型
收费全文 | 4471篇 |
免费 | 671篇 |
国内免费 | 696篇 |
专业分类
测绘学 | 118篇 |
大气科学 | 322篇 |
地球物理 | 570篇 |
地质学 | 2074篇 |
海洋学 | 1051篇 |
天文学 | 16篇 |
综合类 | 279篇 |
自然地理 | 1408篇 |
出版年
2024年 | 29篇 |
2023年 | 94篇 |
2022年 | 196篇 |
2021年 | 184篇 |
2020年 | 183篇 |
2019年 | 229篇 |
2018年 | 174篇 |
2017年 | 191篇 |
2016年 | 168篇 |
2015年 | 141篇 |
2014年 | 257篇 |
2013年 | 259篇 |
2012年 | 238篇 |
2011年 | 218篇 |
2010年 | 217篇 |
2009年 | 241篇 |
2008年 | 246篇 |
2007年 | 263篇 |
2006年 | 305篇 |
2005年 | 257篇 |
2004年 | 231篇 |
2003年 | 205篇 |
2002年 | 233篇 |
2001年 | 217篇 |
2000年 | 155篇 |
1999年 | 129篇 |
1998年 | 123篇 |
1997年 | 92篇 |
1996年 | 86篇 |
1995年 | 58篇 |
1994年 | 49篇 |
1993年 | 36篇 |
1992年 | 33篇 |
1991年 | 22篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 4篇 |
排序方式: 共有5838条查询结果,搜索用时 0 毫秒
1.
《Sedimentology》2018,65(6):2055-2087
This study, conducted in the Catalan Coastal Ranges, north‐east Spain, describes the Upper Devonian Kellwasser event in a shallowing‐upward sequence of black shales, siltstones and quartz arenites. This sequence was deposited in a progradational and regressive coastal system where the sedimentary environment evolved from the inner shelf to a lagoonal pond located landward of the shoreline. Three anomalous succeeding steps have been identified by geochemical analysis. The first one, detected on the inner shelf, was characterized by oxygen depletion and high organic productivity. The second, detected in the nearshore, was caused by hydrothermal activity occurring under normal oxic conditions. The third and most intense step was identified in the muds of the lagoonal pond and has been linked to strong anoxic conditions, elevated clastic input derived from changes in the weathering regime at the source area and moderate hydrothermal activity. The Kellwasser event is thus defined in the study area as stepwise and multi‐causal. This is the first time that the Kellwasser event has been identified in a sedimentary environment behind the shoreline. It is also the first time that it has been reported in the Catalan Coastal Ranges. 相似文献
2.
This paper describes the application of environmental isotopes and injected tracer techniques in estimating the contribution of storms as well as annual precipitation to groundwater recharge and its circulation, in the semi‐arid region of Bagepalli, Kolar district, Karnataka. Environmental isotopes 2H, 18O and 3H were used to study the effect of storms on the hydrological system, and an isotope balance was used to compute the contribution of a storm component to the groundwater. Some of the groundwater samples collected during the post‐storm periods were highly depleted in stable isotope content with higher deuterium excess relative to groundwater from the pre‐storm periods. Significant variation in deuterium excess in groundwater from the same area, collected in two different periods, indicates the different origin of air masses. The estimated recharge component of a storm event of 600 mm to the groundwater was found to be in the range of 117–165 mm. There was no significant variation in environmental tritium content of post‐storm and pre‐storm groundwater, indicating the fast circulation of groundwater in the system. After completion of the environmental isotope work, an injected radiotracer 3H technique was applied to estimate the direct recharge of total precipitation to the groundwater. The estimated recharge to the groundwater is 33 mm of the 550 mm annual precipitation during 1992. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
WANGWei-wu ZHULi-zhong WANGRen-chao SHIYong-jung 《中国地理科学(英文版)》2003,13(1):39-47
Urban heat environmental quality(UHEQ) is affected by the interacting of weather condition and underlying surface framework of urban area .In the last two decades,many researchers from domestic and overseas have studied many problems at the aspect of urban heat environment such as urban heat islands ,urban air temperature and their rela-tion with urban land cover,city population,air pollution etc,In the recent years,Hangzhou,acting as a center city of Zhejiang Province in China,its urbanization quantum and quantity have both changed greatly,in particular ,representing as business affairs building,resident real property and all kins of specialty market having arisen in built-up zone,Based on Landsat TM images data in 1991 and 1999,urban underlying surface temperature value and Normalized Difference Vegetation Index (NDVI) were calculated using image interpreting and supervised classification technique by remote sensing software ERDAS image 8.4,The relation model between urban underlying surface temperature (UUST )and urban air temperature was setup according to the certain correlation patten .Reference to the relational standard of assessing human comfort and other meteorology data of Hangzhou City in summer,the spatial distribution characteristic and the spatial varia-tion degree of human comfort of heat environmental quality are estimated and mapped on a middle scale,that is ,in six districts of Hangzhou City .Then the paper reveals the main characteristic of spatial variation from 1991 to 1999.Lastly,the change mechanism is analyzed and discussed from the viewpoint of city planning,construction and environmental protec-tion. 相似文献
4.
5.
Lock-release gravity currents with a viscous self-similar regime are simulated by use of the renormalization group(RNG) k - ε model for Reynolds-stress closure. Besides the turbulent regime with initially a slumping phase of a conslant current front speed and later an inviseid self-similar phase of front speed decreasing as t^-1/3(where t is the time measured from release), the viseous self-similar regime is satisfactorily reproduced with front speed decreasing as t^-4/5,consistent with well known experimental observations. 相似文献
6.
7.
黄河三角洲地貌环境体系 总被引:4,自引:0,他引:4
黄河三角洲是由三角洲上部冲积平原一下部冲积海积平原(超潮滩)─周边潮滩三个区带的地貌系列构成.它们之间形成三条地貌环境岸线,是一个复杂而统一的陆上─潮滩堆积地貌体系.该体系研究对三角洲发育.环境及其开发利用有一定理论和实践意义. 相似文献
8.
9.
10.