全文获取类型
收费全文 | 176篇 |
免费 | 8篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 33篇 |
地球物理 | 51篇 |
地质学 | 49篇 |
海洋学 | 21篇 |
天文学 | 16篇 |
综合类 | 2篇 |
自然地理 | 12篇 |
出版年
2023年 | 1篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 11篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 10篇 |
2014年 | 5篇 |
2013年 | 14篇 |
2012年 | 10篇 |
2011年 | 13篇 |
2010年 | 7篇 |
2009年 | 12篇 |
2008年 | 11篇 |
2007年 | 13篇 |
2006年 | 6篇 |
2005年 | 11篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 10篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1979年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有189条查询结果,搜索用时 46 毫秒
181.
A spatial and temporal study on data collected along the longitudinal gradient of the Principal Channel of Bahía Blanca estuary, Argentina, was carried out during 1992–1993. At nine stations, phytoplankton abundance, chlorophyll a (Chl-a) concentration, inorganic nutrient levels, Secchi disk depth, euphotic depth:mixing depth ratio (Zeu:Zm), salinity and temperature were recorded. Phytoplankton abundance, Chl-a concentration and nutrient levels decreased towards the outer zone of the estuary. The inner zone (stations 1 and 2), which was characterized by high turbidity, high nutrient concentrations and high Zeu:Zm (>0.16, [critical mixing ratio]), registered the highest phytoplankton abundance and Chl-a concentrations. Temporal variability of data was also noteworthy in this zone. The highest biomass values thus corresponded to June, July, August and the beginning of spring (18 μg Chl-a L−1 and 9×106 cells L−1) concomitantly with a diatom bloom. In the middle zone (stations 3–6), a strong phytoplankton biomass decrease was observed and it coincided with both deep-mixed depths and low Zeu:Zm (<0.16). The outer zone (stations 7–9), which was characterized by low phytoplankton biomass values and low nutrient levels all along the year, was the area mostly influenced by waters from the adjacent continental shelf. In view of the above, it can be concluded that the most important primary production in the Bahía Blanca would be produced in the shallow inner zone during winter, being the spatial reach of the phytoplankton biomass principally limited to estuarine waters. Presumably, less than 5% of such biomass may reach the coastal area of the estuary. 相似文献
182.
Aída Martínez-López Diana Cecilia Escobedo-Urías Ana Elsi Ulloa-Pérez Raul Aguirre 《Continental Shelf Research》2008
To investigate the relative importance of mesoscale physical events, such as upwellings and physical and chemical variables during an algae bloom of Prorocentrum minimum, 25 sampling sites were established offshore of the Navachiste Lagoon Complex on the east side of the Gulf of California. Samples were analyzed for phytoplankton concentration, water chemistry, and temperature during November 1999, January, March, April, May, and August 2000. Satellite imagery of sea surface temperature (SST) for April 2000 was processed to obtain a synoptic view of the area during the extraordinary bloom of P. minimum in the open waters of the Gulf of California. The bloom was associated with change of oceanographic conditions from moderate winds to calm period, temperature increase and high nitrate (NO3−-N) and ammonia (NH4+-N) content in the offshore waters. Depletion of these nutrients during the bloom suggests that this species uses both types of nitrogen substrates. Cysts in the northernmost sampling stations in January and March indicate that upwelling water, rich in nitrates, also carried a seed stock population of P. minimum. SST patterns in the satellite imagery suggest wind-forcing as the responsible mechanisms triggering the algal bloom offshore of the Navachiste Lagoon Complex. 相似文献
183.
In this study, a one-dimensional ensemble-average model is used to simulatethe Atlantic Stratocumulus Transition Experiment firstLagrangian, where the same airmass was followed from the subtropical high pressure region en route towards the trade wind region. The airmass experiences increasing sea-surface temperature and achange from subsidence to weak ascent on its way south. Thiscauses the marine boundary layer (MBL)to grow and the cloud deck to change from a solid stratocumulus deck tomore broken stratocumulus clouds with cumulus cloudsdeveloping beneath, and reaching up into the stratocumulus clouds.A control run is analyzed and compared in detail with theobservations. Both a statistical evaluation and a more subjective evaluation are performed, where both establish confidencein the model performance. The model captures the MBL growth and the cloudliquid water, as well as the drizzle flux, is well predicted by the model.A sensitivity study was performed with the objective of examining theMBL and the cloud response to external and internal 'forces'.The results show that, if drizzle formation is not allowed,unrealistically high cloud liquid water mixing ratios are predicted. Even though the drizzle flux is very small, it is still important for the water budget of the MBL and for the boundary-layer dynamics.We also found that the sea-surface temperature increase is more important for the increasing cloud top height than the synoptic-scale divergence fields. However, the synoptic-scale subsidence is crucial during the first day, when the sea-surface temperature was constant, in keepingthe cloud top at a constant height. Drizzle evaporation below the cloud base seems to be important for below-cloud condensation. The drizzle predictions are significantly altered when the prescribed cloud droplet and/or drizzle drop numbers are altered. 相似文献
184.
185.
This article contributes to research on how climate change will impact crops in China by moving from ex-post empirical analysis to forecasting. We construct a multiple regression model, using agricultural observations and meteorological simulations by GCMs, to simulate the possible planting boundaries and suitable planting regions of spring wheat under RCP4.5 scenario for the base period 2040s and 2070s. We find that the south boundary of possible planting region for spring wheat spreads along the belt: south Shandong-north Jiangsu-north Anhui-central Henan-north Hubei-southeast Sichuan-north Yunnan provinces, and will likely move northward under RCP4.5 scenario in 2040s and 2070s, resulting in the decrease of possible planting area in China. Moreover, the sowing and harvest date of spring wheat in the base period shows a gradually delayed phenomenon from the belt: south Xinjiang - Gansu, to the Tibet Plateau. As a result, the growth period of spring wheat in China will shorten because of the impacts of climate change. These results imply that a variety of adaptations measures should be set up in response to changing climatic conditions, including developing the planting base for spring wheat, restricting the planting area of spring wheat in sub-suitable areas at risk while expanding the planting area of optimal crops. 相似文献
186.
‘Modelling the Arctic Boundary Layer: An Evaluation of Six Arcmip Regional-Scale Models using Data from the Sheba Project’ 总被引:3,自引:0,他引:3
Michael Tjernström Mark Žagar Gunilla Svensson John J. Cassano Susanne Pfeifer Annette Rinke Klaus Wyser Klaus Dethloff Colin Jones Tido Semmler Michael Shaw 《Boundary-Layer Meteorology》2005,117(2):337-381
A primary climate change signal in the central Arctic is the melting of sea ice. This is dependent on the interplay between
the atmosphere and the sea ice, which is critically dependent on the exchange of momentum, heat and moisture at the surface.
In assessing the realism of climate change scenarios it is vital to know the quality by which these exchanges are modelled
in climate simulations. Six state-of-the-art regional-climate models are run for one year in the western Arctic, on a common
domain that encompasses the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment ice-drift track. Surface variables,
surface fluxes and the vertical structure of the lower troposphere are evaluated using data from the SHEBA experiment. All
the models are driven by the same lateral boundary conditions, sea-ice fraction and sea and sea-ice surface temperatures.
Surface pressure, near-surface air temperature, specific humidity and wind speed agree well with observations, with a falling
degree of accuracy in that order. Wind speeds have systematic biases in some models, by as much as a few metres per second.
The surface radiation fluxes are also surprisingly accurate, given the complexity of the problem. The turbulent momentum flux
is acceptable, on average, in most models, but the turbulent heat fluxes are, however, mostly unreliable. Their correlation
with observed fluxes is, in principle, insignificant, and they accumulate over a year to values an order of magnitude larger
than observed. Typical instantaneous errors are easily of the same order of magnitude as the observed net atmospheric heat
flux. In the light of the sensitivity of the atmosphere–ice interaction to errors in these fluxes, the ice-melt in climate
change scenarios must be viewed with considerable caution. 相似文献
187.
Anders Svensson Katrine K. Andersen Matthias Bigler Henrik B. Clausen Dorthe Dahl-Jensen Siwan M. Davies Sigfus J. Johnsen Raimund Muscheler Sune O. Rasmussen Regine Rthlisberger Jrgen Peder Steffensen Bo.M. Vinther 《Quaternary Science Reviews》2006,25(23-24):3258
A new Greenland Ice Core Chronology (GICC05) based on multi-parameter counting of annual layers has been obtained for the last 42 ka. Here we compare the glacial part of the new time scale, which is based entirely on records from the NorthGRIP ice core, to existing time scales and reference horizons covering the same period. These include the GRIP and NorthGRIP modelled time scales, the Meese-Sowers GISP2 counted time scale, the Shackleton–Fairbanks GRIP time scale (SFCP04) based on 14C calibration of a marine core, the Hulu Cave record, three volcanic reference horizons, and the Laschamp geomagnetic excursion event occurring around Greenland Interstadial 10. GICC05 is generally in good long-term agreement with the existing Greenland ice core chronologies and with the Hulu Cave record, but on shorter time scales there are significant discrepancies. Around the Last Glacial Maximum there is a more than 1 ka age difference between GICC05 and SFCP04 and a more than 0.5 ka discrepancy in the same direction between GICC05 and the age of a recently identified tephra layer in the NorthGRIP ice core. Both SFCP04 and the tephra age are based on 14C-dated marine cores and fixed marine reservoir ages. For the Laschamp event, GICC05 agrees with a recent independent dating within the uncertainties. 相似文献
188.
Results from radiosoundings, performed both over land and over sea, show that the ascent rate of a radiosounding balloon, the vertical velocity of the balloon, can be used to determine the height of the boundary layer. In many cases the balloon has a higher ascent rate in the boundary layer and a lower, less variable, ascent rate above. The decrease in ascending velocity appears as a jump at the top of the boundary layer. Two examples of potential temperature profiles for unstable stratification and one profile for stable conditions are shown with the corresponding ascent rates. A comparison between the boundary-layer height determined from potential temperature profiles and from ascent rates is presented for a larger dataset. The different ascent rates of the balloon in the boundary layer and above can be explained by a decrease in drag on the balloon in combination with a lowering of the critical Reynolds number in the boundary layer caused by turbulence. Hence, by simply logging the time from release of a radiosonde, it is possible to obtain additional information that can be used to estimate the height of both the unstable and stable boundary layers. 相似文献
189.
High-T torsion experiments on lizardite + chrysotile serpentinites produced mineralogical and micro/nanostructural changes,
with important implications in rheological properties. High-resolution TEM showed that specimens underwent ductile [by microkinking
and (001) interlayer glide] and brittle deformation (by microfracturing), together with dehydration and break-down reactions.
Lizardite is affected by polytypic disorder and microkinking [kink axial planes at high angle with respect to (001) planes],
that were not present in the initial ordered 1T-lizardite. Chrysotile fibres are deformed, resulting in elliptical cross-sections,
with strong loss of interlayer cohesion. Both lizardite and chrysotile break down to a fine intergrowth of olivine (up to
200 nm), talc (up to 30 nm) and poorly-crystalline material. Lizardite-out reaction preferentially occurs at kink axial planes,
representing sites of preferential strain and enhanced reactivity; conversely, chrysotile break-down is a bulk process, resulting
in large healed olivine aggregates, up to micrometric in size. Overall observations suggest that dehydration and break-down
reactions are more advanced in chrysotile than in lizardite. 相似文献