全文获取类型
收费全文 | 3996篇 |
免费 | 765篇 |
国内免费 | 1224篇 |
专业分类
测绘学 | 200篇 |
大气科学 | 2080篇 |
地球物理 | 1075篇 |
地质学 | 1763篇 |
海洋学 | 288篇 |
天文学 | 8篇 |
综合类 | 197篇 |
自然地理 | 374篇 |
出版年
2024年 | 25篇 |
2023年 | 56篇 |
2022年 | 111篇 |
2021年 | 153篇 |
2020年 | 148篇 |
2019年 | 175篇 |
2018年 | 159篇 |
2017年 | 143篇 |
2016年 | 156篇 |
2015年 | 137篇 |
2014年 | 226篇 |
2013年 | 227篇 |
2012年 | 229篇 |
2011年 | 218篇 |
2010年 | 217篇 |
2009年 | 292篇 |
2008年 | 279篇 |
2007年 | 350篇 |
2006年 | 350篇 |
2005年 | 307篇 |
2004年 | 288篇 |
2003年 | 295篇 |
2002年 | 207篇 |
2001年 | 186篇 |
2000年 | 209篇 |
1999年 | 175篇 |
1998年 | 128篇 |
1997年 | 100篇 |
1996年 | 106篇 |
1995年 | 75篇 |
1994年 | 77篇 |
1993年 | 51篇 |
1992年 | 39篇 |
1991年 | 22篇 |
1990年 | 16篇 |
1989年 | 22篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有5985条查询结果,搜索用时 15 毫秒
201.
Local Modeling模式及其在月径流预测中的应用 总被引:5,自引:2,他引:5
Local Modeling方法是一种动力系统预测方法,将其应用于河西内陆区黑河干流出山口莺落峡水文站月平均流量的中长期预测预报,取得了较为理想的成果。预测试验的结果表明,该预测模型有较高计算精度,尤其适用于非主汛期各月的月平均流量的预测;对于主汛期6~9月的月平均流量的预测,在考虑前期来水与预见期内降水的影响后,亦可获到较为理想的预测结果。可以认为,该方法的预报精度达到了水文情报预报规范的要求,Local Modeling方法的应用,将为西北干旱地区河川径流的中长期预报提供了一个新的途径。 相似文献
202.
203.
204.
205.
206.
207.
Structural and geotechnical impacts of surface rupture on highway structures during recent earthquakes in Turkey 总被引:4,自引:0,他引:4
The most significant damage on highway bridges during the recent earthquakes in Turkey (Kocaeli and Duzce earthquakes) and Taiwan (Chi–Chi earthquake) was the result of fault ruptures traversing transportation infrastructure. This phenomenon and its consequences accentuate the need to examine surface rupture hazards and to identify those areas at risk. This understanding can help to develop remedial measures for both structural and geotechnical engineering. For that purpose, damage to highway bridges during the recent events was reviewed. The total collapse of the highway overpass in Arifiye, during the Kocaeli earthquake, was investigated. The major problems under consideration (in Arifiye) were: (i) dislodging of the bridge spans, and consequently, the total separation of the reinforced concrete girders from the piers; and (ii) the stability of a mechanically stabilized earth wall (MSEW) system under extreme loading conditions. The results of the structural and geotechnical investigations presented herein can be taken in consideration to improve transportation infrastructure against surface rupture hazards. 相似文献
208.
During the 20th century many floods of different intensity and extent have occurred on the Odra River and its tributaries. On the basis of long-term water level observations five major floods, that affected the entire upper and middle Odra River basin, were chosen for further analysis: June 1902, July 1903, August 1977, August 1985 and July 1997. However, hazardous floods were not only those that covered the whole upper and middle Odra River basin, so several local floods were also studied. Detailed historical analysis was made of meteorological conditions, with special emphasis on precipitation patterns and amounts. Then, on the basis of flood peak time occurrence, the stages of flood wave formation were formulated. The natural flood wave of the Odra River is often modified by hydro-technical infrastructure, the development and improvement of which is briefly described in this paper. In conclusion, a comparison of flood wave characteristics such as rising time, falling time, duration, peak flow and volume is presented. 相似文献
209.
Delayed Geochemical Hazard (DGH briefly) presents the whole process of a kind of serious ecological and environmental hazard caused by sudden reactivation and sharp release of long-term accumulated pollutant from stable species to active ones in soil or sediment system due to the change of physical-chemical conditions (such as temperature, pH, Eh, moisture, the concentrations of organic matters, etc.) or the decrease of environment capacity. The characteristics of DGH are discussed. The process of a typical DGH can be expressed as a nonlinear polynomial. The points where the derivative functions of the first and second orders of the polynomial reach zero, minimum and maximum are keys for risk assessment and harzard pridication.The process and mechanism of the hazard is due to the transform of pollutant among different species principally. The concepts of "total releasable content of pollutant", TRCP, and "total concentration of active specie", TCAS, are necessarily defined to describe the mechanism of DGH. The possibility of the temporal and spatial propagation is discussed. Case study shows that there exists a transform mechanism of "gradual release" and "chain reaction" among the species of the exchangeable and the bounds to carbonate, iron and manganese oxides and organic matter, thus causing the delayed geochemical hazard. 相似文献
210.
A granitic rock avalanche, one of the largest Quaternary landslides in Arizona outside the Grand Canyon with a volume of approximately 5.25 M m3 and a width a little under 0.5 km, ran 1 km from the eastern McDowell Mountains. With lateral levees and pressure ridges, the rock avalanche deposit displays many features found on classic sturzstroms. Failure occurred along a major joint plane paralleling the slope with a dip of 44°, when a major base level lowering event in the Salt River system would have undermined the base of the failed slope, and probably during a period of more moisture than normally available in the present-day arid climate. Failure at the subsurface weathering front highlights the importance of the dramatic permeability change between grussified regolith and relatively fresh bedrock. Rock varnish microlaminations (VMLs) dating, in concert with other geomorphic evidence, suggests that the rock avalanche deposit is slightly older than 500 ka. The rock vanish results also have important implications for sampling strategies designed to use cosmogenic nuclide to date Quaternary landslide deposits. Discovery of a large landslide in close proximity to the extending urban fringe of metropolitan Phoenix argues for a more careful analysis of landslide hazards in the region, especially where rapid development excavates bedrock at the base of steep mountain slopes and where the subsurface weathering front is near the surface. 相似文献