全文获取类型
收费全文 | 305篇 |
免费 | 56篇 |
国内免费 | 28篇 |
专业分类
测绘学 | 41篇 |
大气科学 | 17篇 |
地球物理 | 159篇 |
地质学 | 84篇 |
海洋学 | 45篇 |
天文学 | 5篇 |
综合类 | 9篇 |
自然地理 | 29篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 14篇 |
2018年 | 3篇 |
2017年 | 15篇 |
2016年 | 13篇 |
2015年 | 23篇 |
2014年 | 29篇 |
2013年 | 28篇 |
2012年 | 8篇 |
2011年 | 25篇 |
2010年 | 21篇 |
2009年 | 30篇 |
2008年 | 37篇 |
2007年 | 26篇 |
2006年 | 16篇 |
2005年 | 18篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1989年 | 1篇 |
排序方式: 共有389条查询结果,搜索用时 15 毫秒
191.
The results of modeling for M2 surface and internal tides in the White Sea are discussed. These results are obtained for the case when shore-fast and drifting ice covers are present concurrently. It is assumed that the interface between ice covers is of non-tidal origin (i.e., it is pre-assigned) and that ice rheology is viscous-elastic, representative of the low temperatures typical of winter conditions. Emphasis is placed on tidal energetics and, in particular, on the averaged (over a tidal cycle) values of the density and the dissipation rate of barotropic/baroclinic tidal energy. It is shown that in the White Sea, unlike in other marginal seas, the averaged (over a tidal cycle) and depth-integrated density of baroclinic tidal energy for the combined ice cover is much less than the same defined density of barotropic tidal energy. Similarly, the averaged and integrated (over the volume of the White Sea) rate of baroclinic tidal energy dissipation is much less than the same defined rate of barotropic tidal energy dissipation. The latter, in turn, is greater than for the shore-fast ice cover, but is smaller than for the drifting ice cover. 相似文献
192.
An environmental capacity model for the petroleum hydrocarbon pollutions (PHs) in Jiaozhou Bay is constructed based on field surveys, mesocosm, and parallel laboratory experiments. Simulated results of PHs seasonal successions in 2003 match the field surveys of Jiaozhou Bay resaonably well with a highest value in July. The Monte Carlo analysis confirms that the variation of PHs concentration significantly correlates with the river input. The water body in the bay is reasonably subjected to self-purification processes, such as volatilization to the atmosphere, biodegradation by microorganism, and transport to the Yellow Sea by water exchange. The environmental capacity of PHs in Jiaozhou Bay is 1500 tons per year IF the seawater quality criterion (Grade Ⅰ/Ⅱ, 0.05 mgL-1) in the region is to be satisfied. The contribution to self-purification by volatilization, biodegradation, and transport to the Yellow Sea accounts for 48%, 28%, and 23%, respectively, which make these three processes the main ways of PHs purification in Jiaozhou Bay. 相似文献
193.
Observed scale effects of runoff on hillslopes and small watersheds derive from complex interactions of time-varying rainfall rates with runoff, infiltration and macro- and microtopographic structures. A little studied aspect of scale effects is the concept of water depth-dependent infiltration. For semi-arid rangeland it has been demonstrated that mounds underneath shrubs have a high infiltrability and lower lying compacted or stony inter-shrub areas have a lower infiltrability. It is hypothesized that runoff accumulation further downslope leads to increased water depth, inundating high infiltrability areas, which increases the area-averaged infiltration rate. A model was developed that combines the concepts of water depth-dependent infiltration, partial contributing area under variable rainfall intensity, and the Green–Ampt theory for point-scale infiltration. The model was applied to rainfall simulation data and natural rainfall–runoff data from a small sub-watershed (0.4 ha) of the Walnut Gulch Experimental Watershed in the semi-arid US Southwest. Its performance to reproduce observed hydrographs was compared to that of a conventional Green–Ampt model assuming complete inundation sheet flow, with runon infiltration, which is infiltration of runoff onto pervious downstream areas. Parameters were derived from rainfall simulations and from watershed-scale calibration directly from the rainfall–runoff events. The performance of the water depth-dependent model was better than that of the conventional model on the scale of a rainfall simulator plot, but on the scale of a small watershed the performance of both model types was similar. We believe that the proposed model contributes to a less scale-dependent way of modeling runoff and erosion on the hillslope-scale. 相似文献
194.
195.
196.
We suggest a quantitative one-dimensional model treating the formation of charge layers near the 0 °C isotherm in stratiform regions of mesoscale convective systems. A number of factors principal for the field generation have been taken into account: both non-inductive and inductive melting charging, light ions, a complicated profile of the vertical air velocity near the 0 °С isotherm, the boundary conditions proper for the horizontally extended systems in the global electric circuit. Non-inductive collisional charging near the 0 °C isotherm was not considered. It was found that both non-inductive and inductive melting mechanisms can contribute; the inductive melting charging of ice aggregates was found more preferable, while the contribution of non-inductive mechanisms might be significant depending on particular conditions. The role of light ions in the formation of the positive charge layer near the 0 °C isotherm may be important. If the advection from the convective region ensures charge inflow to the upper charged layers, the melting charging mechanisms are able to explain an observable electric field structure in the whole stratiform region. It is important that the mutual position of the zero point on the vertical air velocity profile and the point of maximum melting-charge-transfer determines the fine structure of the electric field in the vicinity of the 0 °C isotherm. 相似文献
197.
198.
199.
200.