全文获取类型
收费全文 | 331篇 |
免费 | 18篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 9篇 |
地球物理 | 102篇 |
地质学 | 77篇 |
海洋学 | 62篇 |
天文学 | 71篇 |
综合类 | 2篇 |
自然地理 | 24篇 |
出版年
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 9篇 |
2013年 | 18篇 |
2012年 | 13篇 |
2011年 | 16篇 |
2010年 | 11篇 |
2009年 | 24篇 |
2008年 | 13篇 |
2007年 | 15篇 |
2006年 | 12篇 |
2005年 | 16篇 |
2004年 | 14篇 |
2003年 | 10篇 |
2002年 | 15篇 |
2001年 | 15篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1993年 | 3篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1968年 | 3篇 |
1947年 | 2篇 |
1921年 | 2篇 |
1871年 | 3篇 |
排序方式: 共有352条查询结果,搜索用时 138 毫秒
91.
Evelyn Lawrenz James L. Pinckney Melissa L. Ranhofer Hugh L. MacIntyre Tammi L. Richardson 《Estuaries and Coasts》2010,33(5):1186-1201
We investigated spatial and temporal relationships between spectral irradiance and phytoplankton community composition in
the blackwater-influenced estuary Winyah Bay, South Carolina. Upstream, high concentrations of chromophoric dissolved organic
matter (CDOM) absorbed blue wavelengths, resulting in a predominantly red light field. Green light prevailed downstream near
the lower-CDOM coastal ocean, and phytoplankton community composition was distinct from upstream and mid-estuarine communities.
Diatoms were abundant throughout the estuary in January, August, and October, cryptophytes dominated in July, and chlorophytes
were abundant in December 2006. Only diatoms and chlorophytes showed significant covariation with the spectral attenuation
coefficient (k(λ)): Chlorophytes showed positive relationships with k(442) (blue light) while diatoms were negatively correlated with k(442) and k(490) (violet to blue). Phytoplankton community composition in Winyah Bay appears to be driven by strong horizontal flow rather
than gradients in spectral irradiance, but results indicate that water color is likely to play a greater role in blackwater-influenced
estuaries with longer residence times. 相似文献
92.
Cuauhtémoc Sáenz-Romero Gerald E. Rehfeldt Nicholas L. Crookston Pierre Duval Rémi St-Amant Jean Beaulieu Bryce A. Richardson 《Climatic change》2010,102(3-4):595-623
Spatial climate models were developed for México and its periphery (southern USA, Cuba, Belize and Guatemala) for monthly normals (1961–1990) of average, maximum and minimum temperature and precipitation using thin plate smoothing splines of ANUSPLIN software on ca. 3,800 observations. The fit of the model was generally good: the signal was considerably less than one-half of the number of observations, and reasonable standard errors for the surfaces would be less than 1°C for temperature and 10–15% for precipitation. Monthly normals were updated for three time periods according to three General Circulation Models and three emission scenarios. On average, mean annual temperature would increase 1.5°C by year 2030, 2.3°C by year 2060 and 3.7°C by year 2090; annual precipitation would decrease ?6.7% by year 2030, ?9.0% by year 2060 and ?18.2% by year 2090. By converting monthly means into a series of variables relevant to biology (e. g., degree-days > 5°C, aridity index), the models are directly suited for inferring plant–climate relationships and, therefore, in assessing impact of and developing programs for accommodating global warming. Programs are outlined for (a) assisting migration of four commercially important species of pine distributed in altitudinal sequence in Michoacán State (b) developing conservation programs in the floristically diverse Tehuacán Valley, and (c) perpetuating Pinus chiapensis, a threatened endemic. Climate surfaces, point or gridded climatic estimates and maps are available at http://forest.moscowfsl.wsu.edu/climate/. 相似文献
93.
Sailfish (Istiophorus platypterus) spawning and larval environment in a Florida Current frontal eddy
David E. Richardson Joel K. Llopiz Kevin D. Leaman Peter S. Vertes Frank E. Muller-Karger Robert K. Cowen 《Progress in Oceanography》2009,(4):252-264
Fronts and eddies are widely hypothesized to be critical spawning habitat for large pelagic fishes, due to increased larval and/or adult feeding opportunities at these features. We examined sailfish (Istiophorus platypterus) spawning around a cyclonic, submesoscale (∼13 × 7 km) Florida Current frontal eddy. The temporal progression of eddy dynamics over a 65 h period was determined using ocean color satellite imagery, continuous surface measurements along the cruise track, and non-linear least-squares fitting of the positions of three drifters deployed within the eddy. A peak in larval sailfish densities (n = 2435, stations = 49), composed primarily of yolk-sac and first-feeding larvae, occurred at the eddy frontal zone. A majority of these larvae were estimated to have been spawned during the formation of the eddy. A comparison between the distribution of similar-age sailfish and scombrid larvae indicated that the peak in larval sailfish density likely resulted from spawning directly at the front, rather than transport by convergent flow. The first-feeding prey items of larval sailfish (Farranula and Corycaeus copepods) were most abundant at the frontal zone and to a lesser extent inside the eddy. Egg distributions were used to indirectly assess the distribution of adult sailfish prey items. Euthynnus alleteratus and Auxis spp. eggs were in highest abundance outside the eddy, while the eggs of small carangids were in highest abundance at the eddy frontal zone. Overall, this study indicates that sailfish spawn at small-scale oceanographic features that provide a favorable feeding environment for their larvae and potentially also for the adults. 相似文献
94.
95.
96.
Hubert Staudigel Karlis Muehlenbachs Stephen H. Richardson Stanley R. Hart 《Contributions to Mineralogy and Petrology》1981,77(2):150-157
18O and87Sr/86Sr isotopic data from smectites, calcites, and whole rocks, together with published isotopic age determinations, alkali element concentration data and petrographic observations suggest a sequential model of ocean floor alteration. The early stage lasts about 3 m.y. and is characterized by palagonite and smectite formation, and solutions with a large basaltic component, increasing with temperature which varies from 15° to 80° C at DSDP site 418A. Most carbonates are depositedafter this stage from solutions with a negligible basaltic Sr component and temperatures of 15° to 40° C. Water of seawater Sr and O isotopic composition is shown to percolate to at least 500 m into the basaltic basement. No evidence was found for continuing exchange of strontium or oxygen after 3 m.y.Lamont-Doherty Geological Observatory Contribution number 3199 相似文献
97.
The solubility of fluorite in NaCl solutions increases with increasing temperature at all ionic strengths up to about 100°C. Above this temperature, the solubility passes through a maximum and possibly a minimum with increasing temperature at NaCl concentrations of 1.0M or less, and increases continuously with increasing temperature at NaCl concentrations above 1.0M. At any given temperature, the solubility of fluorite increases with increasing salt concentration in NaCl, KCl and CaCl2 solutions. The solubility follows Debye-Hückel theory for KCl solutions. In NaCl and CaCl2 solutions, the solubility of fluorite increases more rapidly than predicted by Debye-Hückel theory: the excess solubility is due to the presence of NaFc, CaF+, and possibly of Na2F+. The solubility of fluorite in NaCl-CaCl2 and in NaCl-CaCl2-MgCl2 solutions is controlled by the common ion effect and by the presence of NaFc, CaF+, and MgF+. The solubility of fluorite in NaCl-HCl solutions increases rapidly with increasing initial HCl concentration; the large solubility increase is due to the presence of HFc. It seems likely that complexes other than those identified in this study rarely play a major role in fluoride transport and fluorite deposition at temperatures below 300°C. 相似文献
98.
Fluorite deposition in hydrothermal systems 总被引:1,自引:0,他引:1
During the formation of fluorite deposits fluorite is precipitated either as a consequence of changes in temperature and pressure along the flow path of hydrothermal solutions or due to fluid mixing, or as the result of the interaction of hydrothermal solutions with wall rocks.A decrease in temperature in the flow direction is the most appealing, though still unproven, mechanism of fluorite deposition in Mississippi Valley fluorite deposits.Mixing can produce solutions which are either undersaturated or supersaturated with respect to fluorite. The most important parameters are the temperature, the salinity, and the calcium and fluoride concentration of the fluids prior to mixing.A variety of wall rock reactions can lead to fluorite precipitation. Among these reactions which increase the pH of initially rather acid (pH ≤ 3) hydrothermal solutions are apt to be particularly important. 相似文献
99.
Concentrations of polybrominated diphenyl ethers (PBDEs) in Pearl River Delta sediments 总被引:1,自引:0,他引:1
100.
Confronted by Insurmountable Opportunities: Geography in Society at the AAG's Centennial* 总被引:1,自引:0,他引:1
Geographers at the AAG's centennial are challenged with exceptional opportunities to create a more central place for geography in society and in the university. Realizing these opportunities requires identifying and leveraging key emerging trends in the formation and uses of geographic knowledge. Better integration of geography's profound technological innovations with its core traditions also is necessary to strengthen the discipline's research capacity, and to more effectively engage with and contribute to the needs of society. Trends toward multidisciplinary research and integrative science, and the heightened need for geographic understanding in today's world, hold further promise for advancing the discipline while sustaining its historic strengths and diversity. 相似文献