全文获取类型
收费全文 | 285篇 |
免费 | 13篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 10篇 |
地球物理 | 56篇 |
地质学 | 116篇 |
海洋学 | 26篇 |
天文学 | 20篇 |
综合类 | 4篇 |
自然地理 | 60篇 |
出版年
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 10篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 13篇 |
2013年 | 26篇 |
2012年 | 9篇 |
2011年 | 15篇 |
2010年 | 15篇 |
2009年 | 18篇 |
2008年 | 13篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 4篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 8篇 |
2000年 | 2篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有301条查询结果,搜索用时 62 毫秒
101.
Populations of the American horseshoe crab (Limulus polyphemus) differ in broad areas of their biology. We observed a non-harvested, marked Florida Gulf coast population during their spring
spawning (March–May) in 11 years across a 17-year period (1992–2009). Long-term changes occurred in the number of spawning
pairs: the population was stable from 1992 to 2000 but increased markedly after 2000. Short-term variation in numbers of spawning
pairs, unpaired females, unpaired males, and operational sex ratios was explained by changes over the season and during each
week of spring tides and by differences in actual (not predicted) maximum high tide height. Wind direction strongly affected
tidal inundation and the number of spawning horseshoe crabs. Tagging individuals revealed that females returned to the nesting
beach less often than males and most females were re-sighted only within 1 week of spring tides. No animals were seen across
more than 6 years. Implications for management are discussed. 相似文献
102.
Patrick Martin Richard S. LampittMary Jane Perry Richard SandersCraig Lee Eric D'Asaro 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(4):338-349
Spring diatom blooms are important for sequestering atmospheric CO2 below the permanent thermocline in the form of particulate organic carbon (POC). We measured downward POC flux during a sub-polar North Atlantic spring bloom at 100 m using thorium-234 (234Th) disequilibria, and below 100 m using neutrally buoyant drifting sediment traps. The cruise followed a Lagrangian float, and a pronounced diatom bloom occurred in a 600 km2 area around the float. Particle flux was low during the first three weeks of the bloom, between 10 and 30 mg POC m−2 d−1. Then, nearly 20 days after the bloom had started, export as diagnosed from 234Th rose to 360-620 mg POC m−2 d−1, co-incident with silicate depletion in the surface mixed layer. Sediment traps at 600 and 750 m depth collected 160 and 150 mg POC m−2 d−1, with a settled volume of particles of 1000-1500 mL m−2 d−1. This implies that 25-43% of the 100 m POC export sank below 750 m. The sinking particles were ungrazed diatom aggregates that contained transparent exopolymer particles (TEP). We conclude that diatom blooms can lead to substantial particle export that is transferred efficiently through the mesopelagic. We also present an improved method of calibrating the Alcian Blue solution against Gum Xanthan for TEP measurements. 相似文献
103.
Climate change adaptation in Australian mining communities: comparing mining company and local government views and activities 总被引:1,自引:0,他引:1
Effective climate change adaptation in mining communities is reliant on action by both local authorities and mining operations. This article reports the findings of two surveys conducted in late 2010, with Australian mining companies and local government authorities respectively, investigating their perceptions and activities related to climate change adaptation. The research identified the main types of weather and climate-related impacts experienced in the past and expected under future climate conditions for the two groups. There were significantly differing levels of concern about weather and climate-related impacts between the two types of organisations. Mining company respondents reported lower levels of severity of impact from both past and (expected) future weather events, as well as lower levels of belief in climate change and of adaptation activities to prepare for it. Interestingly, mining companies generally reported less concern about future impacts than those experienced in the past, suggesting discounting of risks due to climate change scepticism. The article reports on a range of factors relevant to adaptation in mining communities, including perceived barriers, collaboration and further information needs. The research findings are discussed in the context of other recent research on climate change adaptation by Australian organisations and studies of mining industry adaptation in other countries. 相似文献
104.
105.
We present a statistical study of the detectability of lightcurves of Kuiper belt objects (KBOs). Some Kuiper belt objects display lightcurves that appear “flat”; i.e., there are no significant brightness variations within the photometric uncertainties. Under the assumption that KBO lightcurves are mainly due to shape, the lack of brightness variations may be due to (1) the objects having very nearly spherical shapes or (2) their rotation axes coinciding with the line of sight. We investigate the relative importance of these two effects and relate it to the observed fraction of “flat” lightcurves. This study suggests that the fraction of KBOs with detectable brightness variations may provide clues about the shape distribution of these objects. Although the current database of rotational properties of KBOs is still insufficient to draw any statistically meaningful conclusions, we expect that, with a larger dataset, this method will provide a useful test for candidate KBO shape distributions. 相似文献
106.
Francis W.N. Nsubuga O.J. Botai Jane M. Olwoch C.J. deW Rautenbach Yvette Bevis Adebayo O. Adetunji 《水文科学杂志》2013,58(2):278-299
AbstractA study of rainfall trends and temporal variations within seven sub-basins of Uganda spanning from 1940 to 2009 has been made. Rainfall climatologies are constructed from observational data, using 36 station records which reflect hydroclimatic conditions. Long-term changes in rainfall characteristics were determined by non-parametric tests (Mann-Kendall and Sen’s T tests), coefficient of variation (CV), precipitation concentration index and drought severity index. Magnitude of change was estimated by applying Sen’s estimator of slope. Decadal variability of rainfall with marked seasonal cycles is evident. Temporal variability of drought patterns is detected. Variations in annual rainfall are low with no significant trends observed in the main drainage sub-basins. Significant trends occur in October, November, December and January. A noticeable decrease in the annual total rainfall was observed mostly in northwestern and southwestern sub-basins. Rainfall trend in the second normal of June–July–August (JJA) was decreasing in all the main drainage sub-basins.Editor Z.W. Kundzewicz; Associate editor S. YueCitation Nsubuga, F.W.N., Botai, O.J., Olwoch, J.M., Rautenbach, C.J.deW., Bevis, Y., and Adetunji, A.O., 2014. The nature of rainfall in the main drainage sub-basins of Uganda. Hydrological Sciences Journal, 59 (2), 278–299. 相似文献
107.
108.
Angélica Goldoni Camila Golfeto Jane B. Teixeira Gislaine Blumm Camila M. Wilhelm Franko Telöken Eloisa Bianchi Jairo L. Schmitt Günther Gehlen Marco Antonio S. Rodrigues Luciano Basso da Silva 《Environmental Earth Sciences》2014,72(5):1503-1509
This study was conducted to evaluate the chemical parameters and the cytotoxic and genotoxic potential of raw domestic sewage and effluents from treatment with activated sludge and a floating emergent-macrophyte filter from a domestic wastewater treatment plant in the city of Novo Hamburgo, Rio Grande do Sul, Brazil. The physicochemical analysis revealed that both treatment systems achieved the legal emission pattern for biochemical oxygen demand, chemical oxygen demand, and suspended solids, but ammoniacal nitrogen and E. coli values were above the limits in the macrophyte treatment effluent. Phosphorous values were above the maximum permitted for both treatments. The results obtained from the Allium cepa test and the micronuclei test in fish did not demonstrate any significant differences in both cytotoxicity (mitotic index) and genotoxicity (chromosome aberration and micronucleus) endpoints between the negative control group and the exposed groups. However, the comet assay in fish revealed a DNA damage increase in animals exposed to the 30 % concentration of the macrophyte effluent and two concentrations of the activated sludge treatment effluent (10 and 75 %), which suggests that these two treatment systems may increase wastewater genotoxicity. 相似文献
109.
Jane M. Chewings Cliff B. Atkins Gavin B. Dunbar Nicholas R. Golledge 《Sedimentology》2014,61(6):1535-1557
Aeolian sand and dust in polar regions are transported offshore over sea ice and released to the ocean during summer melt. This process has long been considered an important contributor to polar sea floor sedimentation and as a source of bioavailable iron that triggers vast phytoplankton blooms. Reported here are aeolian sediment dispersal patterns and accumulation rates varying between 0·2 g m?2 yr?1 and 55 g m?2 yr?1 over 3000 km2 of sea ice in McMurdo Sound, south‐west Ross Sea, adjacent to the largest ice free area in Antarctica. Sediment distribution and the abundance of southern McMurdo Volcanic Group‐derived glass, show that most sediment originates from the McMurdo Ice Shelf and nearby coastal outcrops. Almost no sediment is derived from the extensive ice free areas of the McMurdo Dry Valleys due to winnowed surficial layers shielding sand‐sized and silt‐sized material from wind erosion and because of the imposing topographic barrier of the north‐south aligned piedmont glaciers. Southerly winds of intermediate strength (ca 20 m sec?1) are primarily responsible for transporting sediment northwards and offshore. The results presented here indicate that sand‐sized sediment does not travel more than ca 5 km offshore, but very‐fine sand and silt grains can travel >100 km from source. For sites >10 km from the coast, the mass accumulation rate is relatively uniform (1·14 ± 0·57 g m?2 yr?1), three orders of magnitude above estimated global atmospheric dust values for the region. This uniformity represents a sea floor sedimentation rate of only 0·2 cm kyr?1, well below the rates of >9 cm kyr?1 reported for biogenic‐dominated sedimentation measured over much of the Ross Sea. These results show that, even for this region of high‐windblown sediment flux, aeolian processes are only a minor contributor to sea floor sedimentation, excepting areas proximal to coastal sources. 相似文献
110.
Torben C. Rick Leslie A. Reeder‐Myers C. Jane Cox Stephanie T. Sperling Alex Jansen Anson H. Hines 《Geoarchaeology》2014,29(5):371-388
North America's Atlantic Coast has been a focus of human settlement and subsistence for millennia, but sea‐level rise, sedimentation, and other processes pose significant challenges for archaeological research. Radiocarbon dating of 31 shell middens near the Rhode River Estuary, Maryland provides an opportunity to evaluate human land use, settlement, and cultural chronologies on the Chesapeake Bay. Sixty calibrated radiocarbon dates on eastern oyster (Crassostrea virginica) shell and charcoal demonstrate that Native Americans, colonial, and historic peoples harvested oysters and other shellfish from at least 3200 years ago through the 19th century. The number of dated sites increases during the Late Woodland period after about 1000 cal yr B.P., a factor probably related to greater site visibility and preservation, as well as increased human exploitation of the watershed. Accumulation rates for five of the shell middens provide preliminary indications that some of the sites accumulated rapidly suggesting, along with other evidence, that many of the region's shell middens were logistical or perhaps seasonal camps. Our study demonstrates the importance of regional watershed surveys and radiocarbon dating programs to help build and refine cultural chronologies in coastal regions threatened by sea‐level rise and other processes. 相似文献