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571.
Mirko Dreßler Thomas Hübener Solvig Görs Petra Werner Uwe Selig 《Journal of Paleolimnology》2007,37(2):205-219
During monthly investigations from 1996 to 2000, a hypolimnetic layer of phototrophic sulphur bacteria (Chromatium spp.) were observed in Lake Dudinghausen, a small dimictic lake in northern Germany. This paleolimnological study was initiated
to detect if the occurrence of sulphur bacteria was related to cultural eutrophication or reflected natural conditions. Therefore,
diatoms, algal pigments, okenone, geochemical proxies, and 210Pb and 137Cs were used in four sediment cores to investigate historical changes in trophic development, hypolimnetic redox conditions,
anoxia and phototrophic sulphur bacteria abundances. Fossil diatoms, pigments, the ratio of chlorophyll derivatives to total
carotenoids and the ratio of chlorophyll a to its derivatives suggest two phases of eutrophication coupled with hypolimnetic anoxia over the last ~80 years: a first
phase from about 1923–1932 and a second from 1952 to 1982. In the first phase the ratios of Fe–Mn as well as Fe–Ca increased,
suggesting seasonal anoxia. However, hypolimnetic anoxia was only weak because low levels of okenone suggest no mass development
of sulphur bacteria. In contrast, sulphur bacteria increased during the early stages of the second eutrophication phase, suggesting
increased temporal and spatial hypolimnetic anoxia. Surprisingly, the ratios of Fe–Mn as well as Fe–Ca decreased during this
time. Possibly Fe, Mn and Ca were equally reduced through the intense anoxia. In the final stage, sulphur bacteria decreased
again. As these bacteria need both anoxic conditions and a certain amount of light, the increased nutrient load probably led
to low Secchi depth and therefore insufficient light conditions. In more recent years, diatoms and pigments suggest a decrease
in nutrient levels. A second mass development of sulphur bacteria occurred, probably due to improved light conditions and
continued anoxia in the upper hypolimnion. We conclude that the recent development of phototrophic sulphur bacteria do not
represent natural conditions in Lake Dudinghausen. Furthermore, the upper sediments contain a completely new diatom flora
that never occurred in older sediments of Lake Dudinghausen. Therefore, nutrient levels may eventually reach natural conditions,
however they may not represent biological background reference conditions. 相似文献
572.
Role of pigments on algal communities and photosynthesis 总被引:2,自引:0,他引:2
A. Lami P. Guilizzoni D. Ruggiu B. Polli M. Simona A. Barbieri 《Aquatic Sciences - Research Across Boundaries》1992,54(3-4):321-330
A one-year study of phytoplankton, primary production and related physical and chemical factors was made in a Swiss basin of Lake Lugano (Lago di Lugano). The chlorophylls and 12 carotenoids were analyzed with a TLC technique. The carotenoid monitoring was considered to be particularly interesting, because the role of these pigments in freshwater algae is still very poorly documented by field studies. The dependence of photosynthesis on several factors was statistically evaluated. Evidence was found of light-adaptation phenomena. The variations of photosynthetic activity and efficiency largely depended on the light regime in the few days before the field observations and on the cellular content of chlorophylls and single carotenoids, whose concentrations in their turn were closely linked with light, temperature, average cell size, and with the actual species assemblage. 相似文献
573.
鲁西、苏北地区中寒武统张夏组上部主要是藻灰岩与鲕粒灰岩互层沉积。根据藻类的宏观结构可划分为藻礁、藻叠层石、藻丘及藻斑块。显微镜下观察藻类主要由Epiphyton组成。根据沉积相分析,研究区自东南而西北张夏组上部可划分为藻礁相、鲕粒滩相及藻坪相。藻灰岩的沉积与环境条件是密切相关的,其主要影响因素有海平面变化、沉积速率、碎屑物源供应及水动力条件等。 相似文献
574.
The dynamics of theCeratium hirundinella population and the abundance of dinocysts in the plankton and sediments were studied in Lake Sempach in 1988. In 1987, a rich population ofCeratium (380 cells ml–1) accompanied byPeridinium spp. developed in the lake. The dinocysts were found entrapped in a kind of flocs, in the deepest part of the lake, in the upper flocculent layer. The number of viable cysts ofCeratium in the sediments decreased gradually from April to July 1988. TheCeratium population increased slowly starting in April, and reached a maximum number in August (31 cells ml–1).Peridinium willei reached 100 cells ml–1. Newly formed cysts ofCeratium were recorded in the plankton and sediments at the end of July — beginning of August. They appear in the sediments as separate cells. Their number increased gradually, reaching a maximum of 600 cysts l–1 at the end of October.Ceratium formed more cysts than didPeridinium, but the rate of survival of theCeratium cysts appears to be lower than that ofPeridinium cysts. In addition to their biological functions, the cysts also have an impact on the ecosystem as carriers of nutrients from down to up and from up to down. 相似文献
575.
Abstract Through microscopic and SEM observations and X-ray diffraction and energy spectrum analyses, the oldest sponge spicules and radiolarians have been found in bedded cherts and it is proposed that microbial activity of algae and bacteria played an important role in silica precipitation. The microbial activity resulted in the formation of a series of single crystals and crystal aggregates with peculiar shapes. Biogenic single crystals usually occur in spherical, rod, platy, colloidal and granular forms. The most common aggregates are framboidal aggregates composed of dense spherical quartz crystals, which are considered to be of typical bacterial origin. Other aggregates, such as favositic, double-spherical, chain -spherical and coccoid ones, are considered to be probably the result of silicification of algal cells and mainly of primary sedimentary origin. This paper also discusses the ultrastructural features and diagnostic indications of jasper rocks formed in a submarine hydrothermal environment and cherts formed by replacement and diagenetic recrystallisation. 相似文献
576.
The northward migration of spring bloom was observed in the Sea of Japan from April to May 1997 by the Ocean Color and Temperature
Scanner (OCTS) on board the Advanced Earth Observing Satellite (ADEOS). This phenomenon is well simulated with a numerical
ecosystem model coupled with a hydrodynamic model. The hydrodynamic model is the Geophysical Fluid Dynamics Laboratory (GFDL)
Modular Ocean Model (MOM). The ecosystem model consists of five components: dissolved inorganic nitrogen (DIN), dissolved
inorganic phosphorus (DIP), phytoplankton, zooplankton and detritus. Results of the numerical ecosystem model suggest that
the mesoscale development of the spring bloom in the Sea of Japan is related to that of sea water temperature, and that the
bloom is limited by the depletion of DIN.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
577.
Argo drifters provide information of the vertical structure in the water column and have a potential for the improvement of
understanding phytoplankton primary production and biogeochemical cycles in combination with ocean color satellite data, which
can obtain the horizontal distribution of phytoplankton biomass in the surface layer. Our examples show that using Argo drifters
with satellite-measured horizontal distribution of phytoplankton biomass at the sea surface allow an improved understanding
of the development of the spring bloom. The other possible uses of Argo drifter are discussed. 相似文献
578.
Naoki Yoshie Yasuhiro Yamanaka Michio J. Kishi Hiroaki Saito 《Journal of Oceanography》2003,59(5):563-571
A one-dimensional ecosystem model has been used to investigate the processes relevant to the spring diatom bloom which play
important roles in the biogeochemical cycle in the western subarctic Pacific. The model represents the plankton dynamics and
the nutrient cycles in the spring diatom bloom; its results show the importance of dilution by deep mixing in winter. It is
supposed that the vertically integrated biomass of phytoplankton decreases in the winter due to the decrease of photosynthesis,
because the deep mixing transports phytoplankton to a layer with a low light level. However, the observed integrated diatom
biomass increases as the mixed layer deepens. This is because the decrease of concentration due to dilution by mixing causes
the diatom grazed pressure to be less significant than diatom photosynthesis. In other words, the effect of dilution on the
grazed rate is more significant than the effect on the photosynthesis rate because the grazed rate depends on the concentrations
of both diatom and grazer, whereas the photosynthesis rate depends only diatom concentration. The average specific diatom
grazed rate, defined as grazed rate divided by diatom biomass, decreases by 35% associated with the deepening, while the average
specific photosynthesis rate of diatom decreases by 11%. As a result, the average specific net diatom growth rate during the
deep mixing is about 70% of its maximum during the spring diatom bloom. The deep mixing significantly affects the amplitude
of the spring diatom bloom not only by the supply of nutrients but also by the dilution which drastically decreases the grazed
pressure.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
579.
580.