全文获取类型
收费全文 | 646篇 |
免费 | 98篇 |
国内免费 | 128篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 428篇 |
地球物理 | 128篇 |
地质学 | 54篇 |
海洋学 | 147篇 |
天文学 | 27篇 |
综合类 | 5篇 |
自然地理 | 64篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 12篇 |
2020年 | 19篇 |
2019年 | 24篇 |
2018年 | 15篇 |
2017年 | 19篇 |
2016年 | 16篇 |
2015年 | 30篇 |
2014年 | 28篇 |
2013年 | 42篇 |
2012年 | 36篇 |
2011年 | 37篇 |
2010年 | 35篇 |
2009年 | 63篇 |
2008年 | 54篇 |
2007年 | 53篇 |
2006年 | 47篇 |
2005年 | 29篇 |
2004年 | 40篇 |
2003年 | 26篇 |
2002年 | 41篇 |
2001年 | 12篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 20篇 |
1997年 | 27篇 |
1996年 | 22篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有872条查询结果,搜索用时 46 毫秒
101.
Elizabeth A. Masden Daniel T. Haydon Robert W. Furness 《Marine pollution bulletin》2010,60(7):1085-1091
Proposals for wind farms in areas of known importance for breeding seabirds highlight the need to understand the impacts of these structures. Using an energetic modelling approach, we examine the effects of wind farms as barriers to movement on seabirds of differing morphology. Additional costs, expressed in relation to typical daily energetic expenditures, were highest per unit flight for seabirds with high wing loadings, such as cormorants. Taking species-specific differences into account, costs were relatively higher in terns, due to the high daily frequency of foraging flights. For all species, costs of extra flight to avoid a wind farm appear much less than those imposed by low food abundance or adverse weather, although such costs will be additive to these. We conclude that adopting a species-specific approach is essential when assessing the impacts of wind farms on breeding seabird populations, to fully anticipate the effects of avoidance flights. 相似文献
102.
Igor A. Dmitrenko Sergey A. Kirillov Thomas Krumpen Mikhail Makhotin E. Povl Abrahamsen Sascha Willmes Ekaterina Bloshkina Jens A. Hölemann Heidemarie Kassens Carolyn Wegner 《Continental Shelf Research》2010
This paper examines the role of atmospheric forcing in modifying the pathways of riverine water on the Laptev Sea shelf, using summer-to-winter hydrographic surveys from 2007 to 2009. Over the two consecutive winter seasons of 2007–2008 and 2008–2009 in the area of the winter coastal polynya, our data clearly link winter surface salinity fields to the previous summer conditions, with substantially different winter salinity patterns preconditioned by summer atmospheric forcing. In the summer of 2007, dominant along-shore westerly winds in the cyclonic regime force the Lena River runoff to flow eastward. In contrast, in the summer of 2008, dominant along-shore easterly winds over the East Siberian Sea and on-shore northerly winds over the Laptev Sea in the anticyclonic regime lock the riverine water in the vicinity of the Lena Delta. Over the coastal polynya area in the southeastern Laptev Sea these patterns precondition a surface salinity difference of 8–16 psu between the winters of 2008 and 2009. Overall, this indicates a residence time of at least half a year for riverine water on the Laptev Sea shelf. Future climate change associated with an enhanced summer cyclonicity over the eastern Arctic may turn more riverine water eastward along the eastern Siberian coast, resulting in weaker vertical density stratification over the Laptev Sea shelf, with possible impact on the efficiency of vertical mixing and polynya dense water production. 相似文献
103.
Richard P. Mied William J. Schulz Robert A. Handler Charlotte M. Snow Robert A. Fusina John H. Porter 《Continental Shelf Research》2010
The effects of local and remote wind forcing of water level heights in the Virginia Coast Reserve (VCR) are examined in order to determine the significant forces governing estuarine motions over subtidal time scales. Recent (1996–2008) data from tide and wind stations in the lagoon, a tide station to the north at Sandy Hook, NJ, and one offshore wind station at the Chesapeake Light Tower are examined. Sea surface height spectrum calculations reveal significant diurnal and semidiurnal tidal effects along with subtidal variations, but a suppressed inertial signal. Sea-surface heights (SSH) with 2–5 day periods at Wachapreague, VA are coherent with those at Sandy Hook and lag them in time, suggesting that southward-propagating continental shelf waves provide subtidal variability within the lagoon. The coherence between lagoon winds and sea surface height, as well as between winds and cross-lagoon sea height gradient, were significant at a relatively small number of frequency and wind direction combinations. The frequencies at which this wind forcing occurs are the tidal and subtidal bands present to the north, so that lagoon winds selectively augment existing SSH signals, but do not generate them. The impact of the wind direction is closely related to the geometry of the lagoon and bounding landmasses. The effect of wind stress is also constrained by geometry in affecting the cross-lagoon water height gradient. Water levels at subtidal frequencies are likely forced by a combination of local wind forcing, remote wind forcing and oceanic forcing modified by the complex topography of the lagoon, shelf, and barrier islands. 相似文献
104.
A hybrid foundation for offshore wind turbines (OWT) is studied, combining a monopile of diameter d and length L with a lightweight circular footing of diameter D. The footing is composed of steel plates and stiffeners forming compartments, backfilled to increase the vertical load. A special pile–footing connection is outlined, allowing transfer of lateral loads and moments, but not of vertical loads. The efficiency of the hybrid foundation is explored through 3D finite element modelling. Hybrid foundations of L=15 m are comparatively assessed to an L=30 m reference monopile. A detailed comparison is performed focusing on a 3.5 MW OWT. While the moment capacity of the monopile is larger, the hybrid foundation exhibits stiffer response, outperforming the monopile in the operational loading range. Under cyclic loading, the hybrid foundation experiences less stiffness degradation and rotation accumulation. Besides installation, the cost savings depend on the design of the footing and buckling can be crucial. The rubble fill is shown to provide lateral restraint to the stiffeners, being beneficial for buckling prevention. Although seismic shaking is not critical in terms of capacity, it may lead to substantial accumulation of rotation and settlement. Combined with cyclic environmental loading, the latter may challenge the serviceability of the OWT, potentially leading to a reduction of its service life. To derive insights on the effect of seismic loading, two scenarios are investigated: (a) seismic loading; and (b) combined environmental and seismic loading. In the first case, even a D=15 m hybrid foundation may outperform the reference monopile. This is not the case for combined environmental and seismic loading, where a D=20 m hybrid system would be required to outperform the reference monopile. 相似文献
105.
Hyunhee Park 《The Cartographic journal》2013,50(1):92-93
Abstract Gamepads and joysticks have the potential to improve spatial navigation in virtual globes, block diagrams and 2D maps. Digital school atlases, in particular, can become more engaging if support for gamepads and joysticks is added, as children and adolescents are very proficient at using these devices. The fusion of gaming devices and interactive school atlases offers interesting new use cases: teachers can control a digital wall map with a remote-control gamepad while lecturing from the front of the classroom, or students can explore maps on their personal computers using an enticing way to interact. This paper presents these use cases, the characteristics of the most common gaming devices, and discusses spatial navigation with gamepads and joysticks for globes, block diagrams and 2D maps. The ideas presented originated from the ongoing development of a new, interactive version of the Swiss World Atlas for schools. 相似文献
106.
107.
108.
利用 POM(Princeton Ocean Model)海洋数值模式建立渤、黄、东海冬季三维环流动力学区域模型。模型在海-气边界使用包括风应力、气压和热通量的大气驱动, 海洋边界使用西太平洋模式提供的环流和潮位驱动, 综合模拟潮波运动、温度、盐度、环流变化和水位低频波动。 模拟了 2001 年 1 月寒潮过境时黄、 渤海水位低频波动及流场变化, 分析了其对大风过程、 气压、降温的响应, 发现冬季强劲的北风和西北风都可以通过抽吸振荡在渤、 黄海诱发水位的低频波动, 东北风则由于地形影响不能诱发渤、黄海的低频波动。气压和降温只是在波动幅度上有一定的影响。波动发源于渤海和北黄海, 最大波幅可以达到 0.6 m。波动进入南黄海后有沿黄海深槽西侧传播的倾向, 波动幅度在传播过程中逐渐减小。 相似文献
109.
Patricia A. Iogna Sandra J. Bucci Fabián G. Scholz Guillermo Goldstein 《Journal of Arid Environments》2011,75(9):763-772
On a local scale, topography influences microclimate, vegetation structure and the morpho-physiological attributes of plants. We studied the effects of microclimatic differences between NE- and SW-facing slopes on the water relations and hydraulic properties of two dominant shrubs of the Patagonian steppe in Argentina (Retanilla patagonica and Colliguaja integerrima). The NE-facing slope had higher irradiance and air saturation deficits and lower soil water availability and wind speed than the SW-facing slope. Predawn and midday ΨL and osmotic potentials were significantly lower in shrubs on the NE-facing slope. Osmotic adjustment and more elastic cell walls helped the plants to cope with a more xeric environment on NE-facing slope. Higher water deficits on NE-facing slope were partially compensated by a higher leaf and stem water storage. While stem hydraulic efficiency did not vary between slopes, leaf hydraulic conductance was between 40% and 300% higher on the NE-facing slope. Changes observed in leaf size and in SLA were consistent with responses to mechanical forces of wind (smaller and scleromorphic leaves on SW-facing slope). Morpho-physiological adjustments observed at a short spatial scale allow maintenance of midday ΨL above the turgor loss point and demonstrate that leaves are more responsive to microclimatic selective pressures than stems. 相似文献
110.
Field measurement and scaled-down wind-tunnel model measurement of airflow field over a barchan dune
Airflow is measured over a barchan dune in the field and over a scaled-down model in a wind tunnel. The change of the flow speed over the stoss side is represented by the change of speed-up ratio. According to the field measurement, the wind profiles within 0-3m above the stoss can be divided into two segments. The lower segment, about 0.66 m thick, is the inner-boundary layer, within which the friction velocities derived from the wind profiles increase from the upwind inter-dune region to the upper stoss, and then decrease near the dune top. This change, together with the changes of airflow field, speed-up ratio and sand flux, is related to the morphological change and contributes to the stable shape and height of a barchan dune. In the wind tunnel, airflow varies in a similar way as in the field, with the speed-up ratios constantly higher than 1.0 and increasing along the stoss slope. While the segmentation of wind profiles also occurs in the wind tunnel, friction velocities derived from the wind profiles decrease along the stoss, indicating a very thin inner-boundary layer above the wind tunnel model where the detailed wind-speed change becomes difficult to measure using the present instruments. 相似文献