全文获取类型
收费全文 | 262篇 |
免费 | 17篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 12篇 |
地球物理 | 74篇 |
地质学 | 102篇 |
海洋学 | 41篇 |
天文学 | 42篇 |
综合类 | 4篇 |
自然地理 | 10篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 3篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 9篇 |
2012年 | 11篇 |
2011年 | 14篇 |
2010年 | 16篇 |
2009年 | 19篇 |
2008年 | 19篇 |
2007年 | 12篇 |
2006年 | 22篇 |
2005年 | 20篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 14篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有291条查询结果,搜索用时 31 毫秒
121.
Tsuyoshi Komiya Shinji Yamamoto Shogo Aoki Keiko Koshida Masanori Shimojo Yusuke Sawaki Kazumasa Aoki Shuhei Sakata Takaomi D. Yokoyama Kenshi Maki Akira Ishikawa Takafumi Hirata Kenneth D. Collerson 《地学前缘(英文版)》2017,8(2):355-385
The Archean continental crusts account for ca.20% of the present volume,but the thermal history of the Earths' mantle suggests much more continental crusts were formed in the early Archean.Because the Archean continental crust underwent severe metamorphism,it is important to avoid influence by the later thermal events.We carried out a comprehensive geochronological work of Cathodoluminescence(CL) observation and U-Pb dating of zircons from orthogneisses and supracrustal rocks over the Saglek Block to obtain their protolith ages.The zircons were classified into three domains of core,mantle and rims,and the cores were further classified into three groups of inherited,altered and zoned cores based on the zonation on the CL images.We estimated the protolith ages from Pb-Pb ages of the zoned-cores of zircons with low U contents.We made a detailed sketch of a small outcrop in St.John's Harbour South(SJHS) area,and classified the orthogneisses and mafic enclaves into seven generations based on the geologic occurrence.The first and second generations comprise mafic rocks and lack magmatic zircons.We conducted CL imaging and U-Pb dating of zircons from the third,sixth and seventh generation of the orthogneisses to estimate the protolith ages at 3902 L 25,3892 ± 33 and 3897 ± 33 Ma for each,supporting the presence of the over 3.9 Ca Iqaluk Gneiss.The geological occurrence that the mafic rocks occur as enclaves within the 3.9 Ga Iqaluk Gneiss indicates that they are the oldest supracrustal rocks in the world.Our geochronological and geological studies show the Uivak Gneiss is quite varied in lithology and age from 3.6 to 3.9 Ga,and tentatively classified into six groups based on their ages.The oldest Uivak Gneiss components including the Iqaluk Gneiss are present around the SJHS area,and the orthogneisses become young as it is away.The lines of evidence of overprinting of younger granitoid on older granitoid in small outcrops and geological-map scale as well as presence of inherited zircons even in the oldest suite suggests that crustal reworking played an important role on erasing the ancient crusts. 相似文献
122.
Masahito Shigemitsu Yutaka W. Watanabe Yasuhiro Yamanaka Hajime Kawakami Makio C. Honda 《Journal of Oceanography》2010,66(5):697-708
We used time-series sediment trap data for four major components, organic matter and ballast minerals (CaCO3, opal, and lithogenic matter) from 150, 540, and 1000 m in the western subarctic Pacific (WSAP), where opal is the predominant
mineral in sinking particles, to develop four simple models for settling particles, including the “ballast model”. The ballast
model is based on the concept that most of the organic matter “rain” in the deep sea is carried by the minerals. These four
models are designed to simultaneously reproduce the flux of each major component of settling particles at 540 and 1000 m by
using the data for each component at 150 m as initial values. Among the four models, the ballast model, which considers the
sinking velocity increase with depth, was identified as the best using the Akaike information criterion as a measure of the
model fit to data. This model successfully reproduced the flux of organic matter at 540 and 1000 m, indicating that the ballast
model concept works well in the shallow zone of the WSAP on a seasonal timescale. This also suggests that ballast minerals
not only physically protect the organic matter from degradation during the settling process but also enhance the sinking velocity
and reduce the degree of decomposition. 相似文献
123.
Shizuko Hirata 《Marine Chemistry》1985,16(1):23-46
Phosphorus and metals bound to organic matter were separated from coastal sediments of Harima Sound in Seto Inland Sea, Japan by extraction with NaOH and fractionated by Sephadex G-25 chromatography. Phosphorus and metals were determined in the eluates by a multi-channel, inductively coupled plasma-atomic emission spectrometer. Phosphorus and Cu, Zn, Fe, Mn, Ni, Cr, Co and Ti bound to organic matter with high molecular weights (OMHMW) (MW ? 5000) were found to be present in the sediments, but no Mo or V were found. The technique provides minimum estimates of the amounts of P and metals bound to organic matter. These organic complexes show surface enrichment in a sediment core (0–20 cm) and their contents decrease with depth. Also, the amounts of eighteen elements, namely: P, Fe, Mn, Zn, Cu, Si, Al, Ti, Pb, Co, Ni, Cr, Mo, V, Na, K, Ca and Mg, in H2O, ammonium acetate at pH 7 and 5, hydrogen peroxide, hydroxylamine hydrochloride and hydrogen fluoric acid soluble fractions have been determined with a selective chemical leaching technique for the 210Pb-dated sediment core sample. Considerable amounts of P (6–19%) and Cu (5–21%) were associated with organic matter, in contrast to other metals such as Fe, Mn, Zn, Ni, Cr, Co and Ti which were associated with sulfide and silicate. 相似文献
124.
After the establishment of the seismic observation network of southern Okinawa in August,1988 by the JMA(Japan Meteorological Agency),many hypocenters of earthquakes have been located.However,due to the small number of observation stations and narrow configuration of the array,the hypocenters lo-cated contain some systematic errors.Numerical experiments on the extent of the errors and the reliabilityof the JMA seismic observation network showed that the obtained hypocenters deeper than 100 km werereliable,but that for the obtained hypocenters shallower than 100 km,only the epicenters were reliable. 相似文献
125.
Simulated biogeochemical responses to iron enrichments in three high nutrient, low chlorophyll (HNLC) regions 总被引:1,自引:0,他引:1
To fill temporal gaps in iron-enrichment experimental data and gain further understanding of marine ecosystem responses to iron enrichments, we apply a fifteen-compartment ecosystem model to three iron-enrichment sites, namely SEEDS (the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study; 48.5°N, 165°E) in the western North Pacific, SOIREE (the Southern Ocean Iron RElease Experiment; 61°S, 140°E) in the Southern Ocean, and IronExII (the second mesoscale iron enrichment experiment; 3.5°S, 104°W) in the Equatorial Pacific. The ecological effects of iron in the model are represented by changing two photosynthetic parameters during the iron-enrichment period. The model results successfully reproduce the observed biogeochemical responses inside and outside the iron patch at each site, such as rapid increases in plankton biomass and biological productivity, and decreases in surface nutrients and pCO2, inside the patch. However, the modeled timing and magnitude of changes differ among the sites because of differences in both physical environments and plankton species. After the iron enrichment, the diatom productivity is strongly controlled by light at SOIREE and by silicate at IronExII and SEEDS. Light limitation due to self-shading by the phytoplankton is significant during the bloom at all sites. Sensitivity analysis of the model results to duration of the iron enrichment reveals that long-term multiple infusions over more than a week would not be effective at SEEDS because of strong silicate limitation on diatom growth. Sensitivity of the model to water temperature shows that export production is higher at lower temperatures, because of slower recycling of particulate organic carbon. Therefore, the e-ratio (the ratio of export production to primary production) is inversely correlated with temperature, and the relationship can be described with a linear function. Through this study, we conclude that ecosystem modeling is a powerful tool to help design future iron-enrichment experiments and observational plans. 相似文献
126.
Vertical distribution of underwater scattering radiances of the first, the second and the third order is estimated by the Jerlov's method. In the estimation the volume attenuation coefficient and the volume scattering function are assumed to be constant in near surface layer, and the sky radiation separated from solar radiation to be a parallel beam and to fall into the sea in the vertical direction only.In the zenith direction the second scattering radiance is more intense than the first scattering radiance in near surface layer. As for the total radiance which is a sum of radiances up to the third order, the zenith radiation is largest, the nadir radiation is moderate and the horizontal radiation is least. 相似文献
127.
Shizuko Hirata 《Journal of Oceanography》1983,39(5):203-210
Molecular weight and trace metal distributions of fulvic and humic acid fractions of marine sediments from the Seto Inland Sea were investigated by using a gel filtration technique in combination with atomic absorption and emission spectrometries. A binary molecular weight distribution was found both in the fulvic acid fraction and in the humic acid fraction. The fulvic acid fractions with molecular weights of less than 1.5×103 and of 5×103?104 accounted for 38–57 % and 25–41 % of the total fulvic acids, respectively, and the humic acid fractions with molecular weights of 102?104 and of over 2×105 accounted for 58–73 % and 16–27 % of the total humic acids, respectively. The components with molecular weights of over 1.5×103 contained 54 %, on average, of the Fe, Zn and Cu in the fulvic acid fraction, and the components with molecular weights of over 104 contained 58 %, on average, of these metals in the humic acid fraction. 相似文献
128.
The mid-Cretaceous is well known for its ocean anoxic events. The causal mechanisms are controversial: stagnant deepwater, high biological productivity in the surface waters, and other possibilities have been suggested. Our study simulated the mid-Cretaceous ocean, using general circulation models combined with a marine biogeochemical cycle model to explore the relationship between thermohaline circulation and biogeochemical cycles and investigate the causes of ocean anoxic events. The simulated thermohaline circulation shows an unsteady inactive state. Oxygen concentrations in the deepwater decrease under the inactive state, but a horizontal gradient develops, with higher oxygen concentrations in the Tethys and lower concentrations in eastern Panthalassa. This is not due to the different ages of the deepwater but rather to the differences in biological productivity in the surface water, meaning that the relationship between thermohaline circulation and biogeochemical cycles under the inactive state is different from that in the present ocean. In the standard simulation, assuming the present level of the total amount of phosphate in the ocean, 29% of the bottom water is anoxic. The experiments increasing the amount of phosphate show its high sensitivity for extending the anoxic region with global-scale anoxia simulated under the doubled amount of phosphate. The high amount of phosphate would be reasonable because the inactive state would induce an imbalance of phosphate between riverine input and sediment output. Therefore, both the inactive thermohaline circulation and the increase in the total amount of phosphate in the ocean induce the global-scale anoxic condition in the deepwater. 相似文献
129.
Evolution of the composition of seawater through geologic time, and its influence on the evolution of life 总被引:2,自引:2,他引:0
Tsuyoshi Komiya Takafumi Hirata Kouki Kitajima Shinji Yamamoto Takazo Shibuya Yusuke Sawaki Tomoko Ishikawa Degan Shu Yong Li Jian Han 《Gondwana Research》2008,14(1-2):159
The redox state of the surface environment of the early Earth is still controversial, and a detailed and quantitative estimate is still lacking. We carried out in-situ analyses of major, trace, and rare-earth elements of carbonate minerals in rocks with primary sedimentary structures in shallow and deep sea-deposits, in order to eliminate secondary carbonate and contamination of detrital materials, and to estimate the redox condition of seawater through time. Based on the Ce content and anomalies of the carbonate minerals at given parameters of atmospheric CO2 content (pCO2) and Ca content of seawater, we calculated the oxygen contents of shallow and deep seawater, respectively. The results show that the oxygen content of the deep sea was low and constant until at least 1.9 Ga. The oxygen content of shallow seawater increased after 2.7 Ga, but fluctuated. It became quite high at 2.5 and 2.3 Ga, but eventually increased after the Phanerozoic. In addition, the calculation of a high pCO2 condition shows that seawater was more oxic even in the Archean than at present, suggesting a relatively low pCO2 through geologic time.Our detailed calculations from compositions of carbonate minerals in Three Gorge area, south China show a low oxygen content of seawater after the Snowball Earth until the late Ediacaran, an increase in the late Ediacaran, and a significant decrease around the Precambrian–Cambrian and Nemakit/Daldynian–Tommotian boundaries. These variations were possibly caused by global regression and dissolution of methane hydrates. 相似文献
130.