全文获取类型
收费全文 | 420篇 |
免费 | 15篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 37篇 |
地球物理 | 96篇 |
地质学 | 154篇 |
海洋学 | 49篇 |
天文学 | 58篇 |
综合类 | 1篇 |
自然地理 | 31篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 24篇 |
2012年 | 26篇 |
2011年 | 19篇 |
2010年 | 22篇 |
2009年 | 23篇 |
2008年 | 24篇 |
2007年 | 18篇 |
2006年 | 13篇 |
2005年 | 19篇 |
2004年 | 9篇 |
2003年 | 11篇 |
2002年 | 18篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 5篇 |
1997年 | 14篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1969年 | 1篇 |
1956年 | 1篇 |
1948年 | 2篇 |
1935年 | 1篇 |
1925年 | 1篇 |
排序方式: 共有438条查询结果,搜索用时 27 毫秒
101.
Demersal rockfish are the only fish species that have been found dead in significant numbers after major oil spills, but the link between oil exposure and effect has not been well established. After the 1989 Exxon Valdez oil spill in Prince William Sound, Alaska, several species of rockfish (Sebastes spp.) from oiled and reference sites were analyzed for hydrocarbon metabolites in bile (1989-1991) and for microscopic lesions (1990 and 1991). Biliary hydrocarbons consistent with exposure to Exxon Valdez oil were elevated in 1989, but not in 1990 or 1991. Significant microscopic findings included pigmented macrophage aggregates and hepatic megalocytosis, fibrosis, and lipid accumulation. Site differences in microscopic findings were significant with respect to previous oil exposure in 1991 (P=0.038), but not in 1990. However, differences in microscopic findings were highly significant with respect to age and species in both years (P<0.001). We conclude that demersal rockfish were exposed to Exxon Valdez oil in 1989, but differences in microscopic changes in 1990 and 1991 were related more to age and species differences than to previous oil exposure. 相似文献
102.
Svetlana V. Pakhomova Per O.J. Hall Mikhail Yu. Kononets Alexander G. Rozanov Anders Tengberg Andrei V. Vershinin 《Marine Chemistry》2007
Fluxes of dissolved forms of iron and manganese across the sediment–water interface were studied in situ in the Gulf of Finland and the Vistula Lagoon (Baltic Sea), and in the Golubaya Bay (Black Sea) from 2001 to 2005. Fluxes were measured using chamber incubations, and sediment cores were collected and sliced to assess the porewater and solid phase metal distribution at different depths. Measured and calculated benthic fluxes of manganese and iron were directed out of sediment for all sites and were found to vary between 70–4450 and 5–1000 µmole m− 2 day− 1 for manganese and iron, respectively. The behavior of the studied metals at various redox conditions in the near-bottom water and in the sediment was the main focus in this study. Our results show the importance of bottom water redox conditions for iron fluxes. We measured no fluxes at oxic conditions, intermediate fluxes at anoxic conditions (up to 200 μmole m− 2 day− 1) and high fluxes at suboxic conditions (up to 1000 μmole m− 2 day− 1). Total dissolved iron fluxes were generally dominated by iron(II). Contribution of iron(III) to the total iron flux did not exceed 20%. Obtained fluxes of manganese at all studied regions showed a linear correlation (r2 = 0.97) to its concentration in the porewater of the top sediment layer (0–5 mm) and did not depend on dissolved oxygen concentrations of bottom water. Organically complexed iron and manganese were in most cases not involved in the benthic exchange processes. 相似文献
103.
对取自首都钢铁厂附近的土壤样芯进行了重金属含量、形态分析和的磁学测量.探讨了利用磁参数追踪和指示重金属污染和有机结合态和铁锰氧化结合态重金属的可行性.结果表明:土壤样芯中Cu、Pb、Zn、Fe和Mn的含量与χ、SIRM和ARM存在着十分相似的垂向变化特征,且相关关系显著(0.98>R>0.86).进一步对磁化率和Cu、Pb、Zn、Fe和Mn各结合态进行相关分析表明:五种元素的有机结合态与铁锰结合态和磁化率呈显著相关关系(0.98>R>0.56),而交换态和残渣态重金属与磁化率基本不存在相关关系.反映了磁性矿物和和重金属在赋存状态的本质联系.表明了磁性测量可作为工业区土壤重金属污染及有机结合态与铁锰结合态重金属记录信息提取的辅助手段. 相似文献
104.
R. Friedrich B. Wickert P. Blank S. Emeis W. Engewald D. Hassel H. Hoffmann H. Michael A. Obermeier K. Schäfer T. Schmitz A. Sedlmaier M. Stockhause J. Theloke F.-J. Weber 《Journal of Atmospheric Chemistry》2002,42(1):179-206
Measurements and model developments with the objective to improve the quality and resolution of estimations of anthropogenic emissions are described. Measurement results on a chassis dynamometer were used to determine VOC profiles for exhaust gas emissions of passenger cars for different vehicle and fuel types and different driving modes. Further measurements resulted in emission factors and VOC profiles for lignite burning in residential stoves. Using remote sensing techniques benzene emission factors of gas stations and the efficiency of gasoline vapour recovery systems were measured.To improve the quality and the spatial and temporal resolution of emission data, emission models were improved or modified. This was done by elaborating and applying new methods for important emission source categories (e.g., solvent use, road traffic, small combustion) as well as including new data sources in the calculation routines (e.g. emission statements, land use data, import/export indices of solvents). Simultaneously considerable progress was made improving temporal and spatial allocation functions and VOC profiles. With these improvements a large number of anthropogenic emission data sets for 14 different grid projections in Germany and Europe have been generated. An emission scenario for Germany for 2010 suggests that considering air quality directives from the EU and Germany which are in force or in pipeline, German emissions of VOC and NOx will decrease, but still exceed the national emission ceilings of the EU-NEC directive. 相似文献
105.
David W. Dyrssen Per O. J. Hall Conny Haraldsson Melissa Chierici Jens M. Skei H. Göte östlund 《Aquatic Geochemistry》1996,2(2):111-129
Three different layers have been identified in Framvaren, which has a maximum water depth of 184 m. One oxic layer above the redoxcline at 18–20 m. One anoxic layer from 20 to 100 m which is occasionally ventilated by a flow over the sill (which has a depth of 2.5 m), and finally a stagnant layer below 100 m. Using the release rate of silica from the bottom and measurements of the concentration of HTO it is possible to make some calculations on the annual volume of interleaving in the layers 25–50 m, 50–75 m, and 75–100 m together with the advective flows. Reliable values of the sulfide concentration were obtained by precipitating and weighing HgS together with careful protection of all anoxic water samples with argon. The light yellow color of the precipitate in the depth range 25 to 80 m indicates that the occasional ventilation will cause such reactions as 0.502 + H2S S(colloidal) + H2O. The elemental sulfur, being stabilized with HS–, is set free upon the precipitation of HgS. The new data for the concentration of sulfide give an acceptable stoichiometry for the decay reaction of organic matter. This is not the case with the data of Yao and Millero. The mean values for the concentrations of ammonium and phosphate agree with the new data of Yao and Millero. The mol/mol C/N ratio of 10.1 found in trapped material by Naess and coworkers (1988) agrees with the stoichiometry of the dissolved constituents, i.e. C/N = 9.92 ± 0.45. A denitrification reaction is suggested to explain the high values of C/N. The vertical diffusion coefficient at 100 m calculated from the depth profile of silica was 0.92 × 10–6 m2 s–1 which lies in the range of values given by Fröyland. Finally, the 14C age of the total dissolved inorganic carbon (Ct) in the water below 90 m was about 1600 years indicating a bioproduction in the period 8000 years B.P. to A.D. 1853 when a channel was opened between the fjord outside (Helvikfjord) and Framvaren. 相似文献
106.
An Inter-Laboratory Assessment of the Thorium Isotopic Composition of Synthetic and Rock Reference Materials 总被引:2,自引:0,他引:2
Kenneth W.W. Sims James B. Gill Anthony Dosseto Dirk L. Hoffmann Craig C. Lundstrom Ross W. Williams Lary Ball Darren Tollstrup Simon Turner Julie Prytulak Justin J.G. Glessner J.J. Standish Tim Elliott 《Geostandards and Geoanalytical Research》2008,32(1):65-91
We present a concerted international effort to cross-calibrate five synthetic Th isotope reference materials (UCSC Th "A", OU Th "U", WUN, IRMM-35 and IRMM-36), and six rock reference materials (UCSC TML, Icelandic ATHO, USGS BCR-2, USGS W-2, USGS BHVO-2, LV18) using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). We then compare our new values with a compilation of literature mass spectrometric data for these reference materials and derive recommended "consensus"230 Th/232 Th values for each. We also present isotope dilution U and Th concentration data for four rock reference materials (UCSC TML, Icelandic ATHO, USGS BCR-2, USGS W-2). 相似文献
107.
108.
A reconstruction of deglaciation and associated sea-level changes on northern James Ross Island, Antarctic Peninsula, based on lithostratigraphical and geomorphological studies, shows that the initial deglaciation of presently ice-free areas occurred slightly before 7400 14C yr BP. Sea-level in connection with the deglaciation was around 30 m a.s.l. A glacier readvance in Brandy Bay, of at least 7 km, with the initial 3 km over land, reached a position off the present coast at ca. 4600 yr BP. The culmination of the advance was of short duration, and by 4300 yr BP the coastal lowlands again were ice-free. A distinct marine level at 16–18 m a.s.l. was contemporaneous with or slightly post-dates the Brandy Bay advance, thus indicating the relative sea-level around 4600–4500 yr BP. Our results from James Ross Island confirm that over large areas in this part of Antarctica the last deglaciation occurred late. © 1997 John Wiley & Sons, Ltd. 相似文献
109.
Mingjie Shen Shouyun Hu Uli. Blaha Haitao Yan Wolfgang. R?sler Ewin. Appel Viktor. Hoffmann 《Frontiers of Earth Science》2008,2(4):400-407
An expressway-side soil profile 22 cm long was sampled from the grassland of the expressway linking Beijing and the Capital
International Airport. Magnetic measurements, geochemical and multivariate statistic analyses were performed on the soil samples.
The results reveal that the soil profile can be divided into two parts with significant difference in magnetic proxies and
heavy metal concentration. The uppermost soil horizon (0–8 cm) represents the pollution-rich layer with higher concentration
of ferrimagnetic phases and metallic elements. The values of xare very high with an average of 141.60 × 10−8 m3·kg−1 in the layer. We explain that the anthropogenic dust input from traffic is the predominant cause for strong signals of magnetic
phases and heavy metals. Below the profile depth of 8 cm, there is minor pollution in the soil with lower concentration of
magnetic minerals and heavy metals compared to the natural background values. χ remains quite stable and relatively low with
an average of 49.44 × 10−8 m3·kg−1. S-ratio also generally decreases with depth, and it changes from 0.93 in the 0–8 cm layer to 0.87 below the depth of 8 cm.
It indicates that the soil samples are overwhelmingly predominated by ferrimagnetic minerals in the upper part soil, while
the contribution of imperfect antiferromagnetic components is stronger in the lower part. Rock magnetic experiments show MD
magnetite as the main magnetic carrier both in the upper and lower parts. Themagnetic grain size in the upper part is, however,
a bit coarser than that in the lower part. Cluster analysis shows a positive correlation between magnetic properties (χ, ARM,
SIRM) and heavy metal pollutants of Pb, Zn, Cu. Fuzzy C-means cluster analysis can clearly help divide the soil profile into
two different layers and distinguish their characteristics. It can be concluded that these magnetic concentration-related
parameters can be used as proxies for pollution investigation in a fast, sensitive, low-cost and highly efficient approach
to screening heavy metal pollution.
__________
Translated from Quaternary Sciences, 2007, 27(6): 1113-1120 [译自:第四纪研究] 相似文献
110.
Dr. Karl Hoffmann 《International Journal of Earth Sciences》1975,64(1):118-125
Zusammenfassung In den Jahren 1969 bis 1971 wurden in der Morondava-Küstenebene im Westen Madagaskars umfangreiche hydrogeologische Untersuchungen durchgeführt, in deren Zusammenhang mit Hilfe von geoelektrischen Sondierungen der Aufbau der oberen 150 m des quartären bis neogenen Untergrundes der Ebene geklärt werden konnte. Durch die Interpretation der geoelektrischen Sondierprofile und deren Anordnung in einer Profilkarte war eine Korrelation von Schichtkomplexen hohen Widerstandes möglich. Die Untersuchung ergab, da\ der Untergrund der Küstenebene ein Delta darstellt, das von zwei Flu\systemen geschüttet wurde. Die Mündungen der heutigen Flüsse Morondava und Andranomena sind gegenüber den alten Flu\systemen nach Süden verschoben.
Vortrag, gehalten am 28. Februar 1974 in Bochum anlä\lich der 64. Jahrestagung der Geologischen Vereinigung. 相似文献
In 1969 to 1971 comprehensive hydro-geological investigations were carried out in the Morondava Plains in western Madagaskar. In the scope of these investigations, the structure of the upper 150 m of the quaternary and neogene deposits in the coastal plains were determined by means of geo-electrical soundings. The interpretation of the soundings by establishing a profile map, allowed for a correlation of the sequences with high electric resistivity. The investigation showed that the underground of the coastal plains represents a delta, deposited by two rivers. The mouths of the actual Morondava and Andranomena rivers are shifted towards the south in relation to the ancient river systems.
Résumé D'importantes investigations hydro-géologiques ont été effectuées de 1969 à 1971 dans la plaine de Morondava à l'ouest de Madagascar, grâce auxquelles, en procédant également à des sondages géo-électriques, il a été possible de déterminer la structure des 150 m supérieurs du sous-sol quaternaire à néogène.Par l'interprétation des sondages géo-électriques et leur transposition sur une carte des profils, il a été possible d'obtenir une corrélation des couches à haute resistivité. Des recherches ont montré que le sous-sol de la plaine cÔtière représente un delta, remblayé par deux systèmes fluviaux. L'embouchure des fleuves actuels Morondava et Andranomena est déplacée vers le sud par rapport aux anciens systèmes fluviaux.
1969 1971 . . 150 , . , . , , . , .
Vortrag, gehalten am 28. Februar 1974 in Bochum anlä\lich der 64. Jahrestagung der Geologischen Vereinigung. 相似文献