全文获取类型
收费全文 | 192篇 |
免费 | 18篇 |
国内免费 | 67篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 4篇 |
地球物理 | 39篇 |
地质学 | 179篇 |
海洋学 | 24篇 |
天文学 | 1篇 |
综合类 | 2篇 |
自然地理 | 27篇 |
出版年
2024年 | 4篇 |
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 12篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 10篇 |
2014年 | 15篇 |
2013年 | 15篇 |
2012年 | 13篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 28篇 |
2008年 | 11篇 |
2007年 | 22篇 |
2006年 | 15篇 |
2005年 | 8篇 |
2004年 | 13篇 |
2003年 | 4篇 |
2002年 | 12篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
排序方式: 共有277条查询结果,搜索用时 15 毫秒
51.
Selection of coherent deposit-type locations and their application in data-driven mineral prospectivity mapping 总被引:2,自引:1,他引:1
Data-driven prospectivity mapping can be undermined by dissimilarity in multivariate spatial data signatures of deposit-type locations. Most cases of data-driven prospectivity mapping, however, make use of training sets of randomly selected deposit-type locations with the implicit assumption that they are coherent (i.e., with similar multivariate spatial data signatures). This study shows that the quality of data-driven prospectivity mapping can be improved by using a training set of coherent deposit-type locations. Analysis and selection of coherent deposit-type locations was performed via logistic regression, by using multiple sets of deposit occurrence favourability scores of univariate geoscience spatial data as independent variables and binary deposit occurrence scores as dependent variable. The set of coherent deposit-type locations and three sets of randomly selected deposit-type locations were each used in data-driven prospectivity mapping via application of evidential belief functions. The prospectivity map based on the training set of coherent deposit-type locations resulted in lower uncertainty, better goodness-of-fit to the training set, and better predictive capacity against a cross-validation set of economic deposits of the type sought. This study shows that explicit selection of training set of coherent deposit-type locations should be applied in data-driven prospectivity mapping. 相似文献
52.
Eighteen lakes were added to a published training set of 46 British Columbia (BC) lakes in order to expand the original range of total phosphorus (TP) concentrations. Canonical correspondence analysis (CCA) was used to analyze the relationship between diatom assemblages and environmental variables. Specific conductivity and [TP] each explained significant (P0.05) directions of variance in the distribution of the diatoms. The relationship between diatom assemblages and [TP] was sufficiently strong to warrant the development of a weighted-averaging (WA) regression and calibration model that can be used to infer past trophic status from fossil diatom assemblages.The relationship between observed and inferred [TP] was not improved by the addition of more eutrophic lakes, however the [TP] range and the number of taxa used in the transfer function are now superior to the original model. Diatom species assemblages changed very little in lakes with TP concentrations greater than 85 µg 1–1, so we document the development of a model containing lakes with TP85 µg 1–1. The updated model uses 59 training lakes and covers a range of species optima from 6 to 41.9 µg 1–1 TP, and a total of 150 diatom taxa.The updated inference model provided a more realistic reconstruction of the anthropogenic history of a highly eutrophic BC lake. The model can now be used to infer past nutrient conditions in other BC lakes in order to assess changes in trophic status. 相似文献
53.
From 1998 to 2003, we observed large fluctuations in the abundance and distribution of four pelagic predatory (piscivorous) fishes off northern Oregon and southern Washington, USA. Fluctuations in predatory fish species composition and abundance were strongly linked to the date of the spring transition and to ocean temperatures. Predatory fishes, forage fishes, and juvenile salmonids had distinct spatial distributions, with predators distributed primarily offshore and forage fish and salmonids onshore, but this varied depending on ocean conditions. We suggest that predatory and forage fish distributions respond to ocean temperatures, predator/prey interactions, and possibly turbidity. A shift in ocean conditions in 1999 decreased overall predator fish abundance in the Columbia River plume, particularly for Pacific hake. Marine survival of juvenile salmon started to increase in 1999, and forage fish densities increased in 2000, lagging by one year. 相似文献
54.
Chrysophyte cysts and scales and sponge spicules were enumerated, along with diatoms, from the surface sediments of 102 western
Canadian lakes. The salinities of these lakes ranged from 0.042 to 369 g L−1 in late summer. Sponge spicules and chrysophyte cysts and scales were more common in fresher waters, although chrysophyte
cysts were also present in subsaline and hyposaline waters at lower relative percentages. These siliceous microfossils can
easily be distinguished and counted along with diatom valves, with little extra effort. It is likely that using these additional
indicators will strengthen paleolimnological inferences of past lakewater salinity. 相似文献
55.
In December 2001, acid mine drainage (AMD) from an abandoned copper mine at Britannia Beach (British Columbia, Canada) was diverted to flow from Britannia Creek into an outfall at 30 m depth in Howe Sound. Britannia Beach was studied in early 2003 to determine whether AMD diversion resulted in improved conditions for intertidal organisms. Species number and abundance have increased at the intertidal zone since AMD diversion, although they were still lower than at an unpolluted control site nearby (Furry Creek). Survivorship and growth rates of transplanted Mytilus trossulus (mussel) have increased since AMD diversion, although they were still significantly lower than at the control site. Transplanted Fucus gardneri (seaweed) performed better than before the AMD diversion; at Britannia Beach the chlorophyll a concentration in tissues was not significantly different from that at the control site, although the concentration of chlorophyll c in tissues and the chlorophyll c to a ratio was lower than at the control site six weeks after transplantation. Britannia Beach is still subject to leaching of metals from surrounding soils, low levels of AMD coming down the creek, and AMD discharge from the deep outfall. Although there has been an improvement, the intertidal environment at Britannia Beach still seems unable to support normal growth and survival of organisms. 相似文献
56.
The geochemistry of selenium associated with coal waste in the Elk River Valley,Canada 总被引:1,自引:0,他引:1
Selenium (Se) concentrations more than 12 times greater than the provincial freshwater quality guideline (2 µg/L) were detected in the Elk River downstream from the five open-pit coal mines in southeastern British Columbia's Elk River Valley. To identify possible sources of Se to the Elk River, samples from the coal-bearing Mist Mountain Formation were studied using X-ray diffraction, elemental and oxide analyses, sequential extractions and heavy liquid separation. Between 2.5 and 21.3% of the total Se in the five types of materials studied is water-soluble and 1.0 to 10.6% is associated with hydrous ferric and manganese oxides. Se associated with sulphides and organic material varies between 60 and 84% of the total Se and Se in the silicate structure varies from 5.9 to 24.7%. The ratio of sulphides to the total of organic carbon is well-correlated with the amount of Se in materials closely associated with coal seams containing less than 6 mg/kg of Se (r=0.916). This may suggest that the amount of organic matter present during deposition affects the amount of Se incorporated into sulphides. 相似文献
57.
IGCP440"罗迪尼亚超大陆汇聚与裂解"项目2003年度工作进展 总被引:2,自引:0,他引:2
借助于最新的地质、同位素年代学、地球化学和航空地球物理资料,对全球各地原属于罗迪尼亚大陆组成单元的构造环境、地质事件特征及其演化历史进行了探讨,并提出一些新见解和成因模式.认为东欧克拉通在1.7~0.9Ga有复杂的演化历史一个新的劳仑古陆和西伯利亚的重建发生在1 050~1 000Ma;中、新元古代南美洲造山拼贴的岩石构造历程构成南美陆台的西部边界非洲克拉通是古元古代/太古宙陆块汇聚收敛的结果;东南极的一部分在中元古时期附属于非洲南部;印度西北的新元古代长英质岩浆事件构成了罗迪尼亚大陆的西部边缘;前格林威尔时期的劳仑古陆已被确定为古元古代末期的一个主要大陆;在罗迪尼亚大陆中,华南可能位于劳仑古陆南部和澳大利亚东部之间;塔里木克拉通和扬子克拉通相连接或邻近.据此检验了关于Pisarevsky提出的罗迪尼亚超大陆汇聚和裂解的新模式.新模式提出初始裂解是沿着劳仑古陆的西部边缘,与大西洋北部相类似.同时认为一些大陆(印度、刚果/圣·弗朗西斯科)可能不是罗迪尼亚超大陆的组成部分. 相似文献
58.
59.
Relative sea level at Vancouver, British Columbia rose from below the present datum about 30,000 cal yr B.P. to at least 18 m above sea level 28,000 cal yr B.P. In contrast, eustatic sea level in this interval was at least 85 m lower than at present. The difference in the local and eustatic sea-level positions is attributed to glacio-isostatic depression of the crust in the expanding forefield of the Cordilleran ice sheet during the initial phase of the Fraser Glaciation. Our findings suggest that about 1 km of ice was present in the northern Strait of Georgia 28,000 cal yr B.P., early during the Fraser Glaciation. 相似文献
60.
Large, rapid, low-gradient landslides are common in clay-rich glacial sediments in northeastern British Columbia. Many of the landslides create upstream impoundments that may persist for years in small watersheds in the region. We have documented such events in the Halden Creek watershed, 60 km southeast of Fort Nelson. The events are recorded geologically in two ways. First, trees are drowned in lakes dammed by the landslides and subsequently buried by deltaic sediments, where they are protected from decay. Bank erosion later exhumes the drowned trees. Second, landslide deposits with entrained wood are exposed along stream banks. We have reconstructed the recent history of landslide damming at Halden Creek by performing radiocarbon dating on exhumed trees and wood in and beneath landslide deposits at 13 sites in the watershed. Drowned trees range in age from 169±59 to 274±49 14C year bp. Wood in and below landslide deposits yielded radiocarbon ages ranging from modern to 965±49 14C year bp. 相似文献