全文获取类型
收费全文 | 360篇 |
免费 | 14篇 |
国内免费 | 61篇 |
专业分类
大气科学 | 2篇 |
地球物理 | 171篇 |
地质学 | 17篇 |
海洋学 | 225篇 |
天文学 | 1篇 |
综合类 | 4篇 |
自然地理 | 15篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 12篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 22篇 |
2013年 | 8篇 |
2012年 | 10篇 |
2011年 | 38篇 |
2010年 | 22篇 |
2009年 | 25篇 |
2008年 | 41篇 |
2007年 | 26篇 |
2006年 | 32篇 |
2005年 | 25篇 |
2004年 | 14篇 |
2003年 | 18篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 5篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有435条查询结果,搜索用时 234 毫秒
61.
In June 2003, we conducted a two-part field exercise to examine biogeochemical characteristics of water in the lower Mississippi river during the 4 days prior to discharge and in the Mississippi river plume over 2 days after discharge. Here we describe the fates of materials immediately after their discharge through Southwest Pass of the Mississippi delta into the northern Gulf of Mexico. Changes in surface water properties immediately after discharge were much larger and more rapid than changes prior to discharge. Total suspended matter (TSM) declined, probably due to sinking, dissolved macronutrients were rapidly diminished by mixing and biological uptake, and phytoplankton populations increased dramatically, and then declined. This decline appeared to begin at salinities of approximately 10 and was nearly complete by 15. A large increase in dissolved organic carbon (DOC) occurred over approximately the same salinity range. Weak winds (<2 m s−1) during and preceding this cruise apparently led to the formation of an extensive but thin freshwater lens from the river. This lens spread widely without much mixing, and the bloom of phytoplankton that occurred between discharge and a salinity of 10 was probably a freshwater community seeded from the lower river. Phytoplankton bloomed for a period of about 1–2 days, then declined dramatically, apparently releasing large amounts of DOC. Macronutrients from the river were utilized by the river phytoplankton community in the extensive freshwater lens. This contrasted with the more typical situation in which river nutrients stimulate a marine phytoplankton bloom at salinities in the mid-20s. We concluded that the direct effects of dissolved and particulate bio-reactive materials discharged by the Mississippi river were spatially restricted at this time to low-salinity water, at least as surface phenomena. After being transported through the lower river essentially unaltered, these materials were biogeochemically processed within days and tens of km. More generally, the mixing rate of plume water with receiving oceanic water has profound effects on the food web structure and biogeochemical cycling in the plume. 相似文献
62.
José I. Carreto Nora MontoyaRut Akselman Mario O. CarignanRicardo I. Silva Daniel A. Cucchi Colleoni 《Continental Shelf Research》2008
The composition of phytoplankton assemblages were studied in three sections across the continental shelf between the Río de la Plata and the oceanic waters of the Subtropical Convergence, during late spring. Algal communities were examined using microscopy and HPLC-derived pigment concentrations. The CHEMTAX program was used to estimate the chlorophyll a (chl a) biomass of different algal classes. Trends in pigment ratios due to phytoplankton photo-adaptation and photo-acclimation were also examined. In order to accommodate the natural diversity of phytoplankton assemblages the original data have been split to represent five ecosystems. In addition, the pigment data for the Brazil Current ecosystem has been split by sample depth. 相似文献
63.
The paper describes a finding of photoautotroph cyanobacteria Synechococcus in deep Adriatic waters during the spring of 2006. The maximum abundance in early May was positioned at 800 m, being of order
of the values referred for the surface waters in the Adriatic Sea. The deep abundance maximum has been associated to the fast
ventilation of deep Adriatic waters, usually occurring during wintertime strong cooling events. Two processes were detected:
(1) deep convection in the South Adriatic Pit (SAP) and (2) density current going downslope. The first process was responsible
for bringing the cyanobacteria down to 600-m depth in the area of convection, and the second one triggered the downslope transport
of the cyanobacteria to the SAP very bottom. The depletion rate of Synechoccocus cyanobacteria in an extremely hostile environment has been computed to equal about 1 month. 相似文献
64.
Transport of oceanic nitrate from the continental shelf to the coastal basin in relation to the path of the Kuroshio 总被引:1,自引:0,他引:1
Ryo Sugimoto Akihide Kasai Toshihiro Miyajima Kouichi Fujita 《Continental Shelf Research》2009,29(14):1678-1688
Hydrographic and biogeochemical observations were conducted along the longitudinal section from Ise Bay to the continental margin (southern coast of Japan) to investigate changes according to the Kuroshio path variations during the summer. The strength of the uplift of the cold deep water was influenced by the surface intrusion of the Kuroshio water to the shelf region. When the intrusion of the Kuroshio surface water to the shelf region was weak in 2006, the cold and NO3−-rich shelf water intruded into the bottom layer in the bay from the shelf. This bottom intrusion was intensified by the large river discharge. The nitrogen isotope ratio (δ15N) of NO3− (4–5‰) in the bottom bay water was same as that in the deeper NO3− over the shelf, indicating the supply of new nitrogen to the bay. The warm and NO3−-poor shelf water intruded into the middle layer via the mixing region at the bay mouth when the Kuroshio water distributed in the coastal areas off Ise Bay in 2005. The regenerated NO3− with isotopically light nitrogen (δ15N=−1‰) was supplied from the shelf to the bay. This NO3− is regenerated by the nitrification in the upper layer over the shelf. The contribution rate of regenerated NO3− over the shelf to the total NO3− in the subsurface chlorophyll maximum layer in the bay was estimated at 56% by a two-source mixing model coupled with the Rayleigh equation. 相似文献
65.
Phytoplankton biomass size structure and its regulation in the Southern Yellow Sea (China): Seasonal variability 总被引:7,自引:0,他引:7
Mingzhu Fu Zongling Wang Yan Li Ruixiang Li Ping Sun Xiuhua Wei Xuezheng Lin Jingsong Guo 《Continental Shelf Research》2009,29(18):2178-2194
Phytoplankton size structure plays a significant role in controlling the carbon flux of marine pelagic ecosystems. The mesoscale distribution and seasonal variation of total and size-fractionated phytoplankton biomass in surface waters, as measured by chlorophyll a (Chl a), was studied in the Southern Yellow Sea using data from four cruises during 2006–2007. The distribution of Chl a showed a high degree of spatial and temporal variation in the study area. Chl a concentrations were relatively high in the summer and autumn, with a mean of 1.42 and 1.27 mg m−3, respectively. Conversely, in the winter and spring, the average Chl a levels were only 0.98 and 0.99 mg m−3. Total Chl a showed a clear decreasing gradient from coastal areas to the open sea in the summer, autumn and winter cruises. Patches of high Chl a were observed in the central part of the Southern Yellow Sea in the spring due to the onset of the phytoplankton bloom. The eutrophic coastal waters contributed at least 68% of the total phytoplankton biomass in the surface layer. Picophytoplankton showed a consistent and absolute dominance in the central region of the Southern Yellow Sea (>40%) in all of the cruises, while the proportion of microphytoplankton was the highest in coastal waters. The relative proportions of pico- and nanophytoplankton decreased with total biomass, whereas the proportion of the micro-fraction increased with total biomass. Relationships between phytoplankton biomass and environmental factors were also analysed. The results showed that the onset of the spring bloom was highly dependent on water column stability. Phytoplankton growth was limited by nutrient availability in the summer due to the strong thermocline. The combined effects of P-limitation and vertical mixing in the autumn restrained the further increase of phytoplankton biomass in the surface layer. The low phytoplankton biomass in winter was caused by vertical dispersion due to intense mixing. Compared with the availability of nutrients, temperature did not seem to cause direct effects on phytoplankton biomass and its size structure. Although interactions of many different environmental factors affected phytoplankton distributions, hydrodynamic conditions seemed to be the dominant factor. Phytoplankton size structure was determined mainly by the size-differential capacity in acquiring resource. Short time scale events, such as the spring bloom and the extension of Yangtze River plume, can have substantial influences, both on the total Chl a concentration and on the size structure of the phytoplankton. 相似文献
66.
The ecohydrodynamics of the Gibraltar Strait and the Western Alboran Sea is investigated using a 3-D, two-way nested, coupled
hydrodynamic/plankton ecosystem model, exploiting the MEDATLAS climatological database. A high-resolution model (~1 km) of
the Gibraltar/Western Alboran region embedded within a coarse-resolution model of the West Mediterranean (~5 km) is implemented.
The model seasonal climatology of the 3-D circulation and the flow characteristics at the Gibraltar Strait and the Alboran
Sea are discussed, and their impact on the plankton ecosystem evolution is explored. An important ecohydrodynamic feature
produced by the model is a permanent upwelling zone in the northwestern part of the Alboran Sea in agreement with observations.
Model results show that both horizontal and vertical current intensity of the Atlantic Jet increases progressively at the
strait to obtain maximum values in the northeastern Mediterranean entrance, inducing an upward displacement of the nitracline.
The nutrient-rich water transport through the strait along with the generation of cyclonic vorticity in the northwestern Alboran
Sea result in the accumulation of nutrients there and thus induce a permanent fertilisation of this area. 相似文献
67.
Stable carbon isotope distribution of particulate organic matter in the ocean: a model study 总被引:4,自引:0,他引:4
Matthias Hofmann Dieter A. Wolf-Gladrow Taro Takahashi Steward C. Sutherland Katharina D. Six Ernst Maier-Reimer 《Marine Chemistry》2000,72(2-4)
The stable carbon isotopic composition of particulate organic matter in the ocean, δ13CPOC, shows characteristic spatial variations with high values in low latitudes and low values in high latitudes. The lowest δ13CPOC values (−32‰ to −35‰) have been reported in the Southern Ocean, whereas in arctic and subarctic regions δ13CPOC values do not drop below −27‰. This interhemispheric asymmetry is still unexplained. Global gradients in δ13CPOC are much greater than in δ13CDIC, suggesting that variations in isotopic fractionation during organic matter production are primarily responsible for the observed range in δ13CPOC. Understanding the factors that control isotope variability is a prerequisite when applying δ13CPOC to the study of marine carbon biogeochemistry. The present model study attempts to reproduce the δ13CPOC distribution pattern in the ocean. The three-dimensional (3D) Hamburg Model of the Oceanic Carbon Cycle version 3.1 (HAMOCC3.1) was combined with two different parametrizations of the biological fractionation of stable carbon isotopes. In the first parametrization, it is assumed that the isotopic fractionation between CO2 in seawater and the organic material produced by algae, P, is a function of the ambient CO2 concentration. The two parameters of this function are derived from observations and are not based on an assumption of any specific mechanism. Thus, this parametrization is purely empirical. The second parametrization is based on fractionation models for microalgae. It is supported by several laboratory experiments. Here the fractionation, P, depends on the CO2 concentration in seawater and on the (instantaneous) growth rates, μi, of the phytoplankton. In the Atlantic Ocean, where most field data are available, both parametrizations reproduce the latitudinal variability of the mean δ13CPOC distribution. The interhemispheric asymmetry of δ13CPOC can mostly be attributed to the interhemispheric asymmetry of CO2 concentration in the water. However, the strong seasonal variations of δ13CPOC as reported by several authors, can only be explained by a growth rate-dependent fractionation, which reflects variations in the cellular carbon demand. 相似文献
68.
J. F. Read M. I. Lucas S. E. Holley R. T. Pollard 《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(12):2341-2367
A survey was made of the Southwest Indian Ocean frontal region between 30 and 50°E containing the Agulhas Return, Subtropical and Subantarctic Fronts. From CTD, SeaSoar and extracted samples the distribution of nitrate, silicate and chlorophyll a is shown to be strongly linked to the front and water mass structure, varying zonally and meridionally. Surface chlorophyll a concentrations were low to the north and south leaving a band of elevated chlorophyll between the Subtropical and Subantarctic Fronts. The low concentration of chlorophyll a to the north, in Subtropical Water, was clearly due to nitrate limitation. Between the Subtropical and Subantarctic Fronts, where the chlorophyll a concentrations were highest, the surface layer showed silicate depletion limiting diatom growth. South of the Subantarctic Front there were deep extending, low concentrations of chlorophyll a, but despite plentiful supplies of macro-nutrients and a well-stratified surface layer, high concentrations of chlorophyll a were absent. Changes from west to east were associated with the meandering of the Southern Ocean Fronts, especially the Subtropical Front, and their strength and proximity to each other. Concentrations of chlorophyll a peaked where the Agulhas Return, Subtropical and Subantarctic Fronts were in close proximity. Combined frontal structures appear to have particularly pronounced vertical stability and are associated with enhanced upwelling of nutrients and leakage of nutrients across the front. Light levels are high within the shallow stable layer. Such conditions are clearly favourable for biological growth and support the development of larger-celled phytoplankton communities. 相似文献
69.
应用特征光合色素研究东海和南海北部浮游植物的群落结构 总被引:23,自引:0,他引:23
应用高效液相色谱并结合二极管阵列检测器分析技术,研究了东海与南海北部典型断面浮游植物的光合色素组成,进而由CHEMTAX软件估算浮游植物群落结构。结果表明:东海断面浮游植物叶绿素a生物量大于南海北部断面。受海水层化结构影响,东海PN断面浮游植物群落结构形成上层和下层两种类型,上层以蓝藻为主要优势类群;下层以硅藻为主要优势类群。南海北部S断面浮游植物群落形成近岸与离岸两种类型,近岸以硅藻、隐藻、绿藻为主要优势类群;离岸以定鞭金藻、蓝藻、原绿球藻为主要优势类群。初步分析了研究海区浮游植物群落结构与环境因子的关系。 相似文献
70.