全文获取类型
收费全文 | 150篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 10篇 |
地球物理 | 31篇 |
地质学 | 71篇 |
海洋学 | 16篇 |
天文学 | 9篇 |
综合类 | 1篇 |
自然地理 | 20篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 3篇 |
2012年 | 11篇 |
2011年 | 6篇 |
2010年 | 7篇 |
2009年 | 15篇 |
2008年 | 10篇 |
2007年 | 7篇 |
2006年 | 14篇 |
2005年 | 7篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有160条查询结果,搜索用时 15 毫秒
21.
Jacqueline Michel 《Geochimica et cosmochimica acta》1984,48(6):1249-1255
Previous studies of the distribution of U and Th in parent versus weathered granites have shown both depletion and enrichment of these elements during weathering. In this study, the distribution of U and Th decay series isotopes was determined in a weathering profile of a granitic saprolite, which showed textural preservation indicating isovolumetric weathering. Two types of dissolution methods were used: a whole-rock dissolution and a sodium-citrate dithionite leach to preferentially attack noncrystalline phases of weathering products. Using volume-based activities, 45–70 percent of the total 232Th was gradually removed during weathering. Although the whole-rock activity ratios were in equilibrium, there were large excesses of 228Th in the leachable fraction of both parent rock () and partially weathered saprolite (), due to alpha recoil and release of daughter 228Th to the weathering rind of the mineral grain. For the most weathered sample, 81 percent of the thorium was in the teachable fraction and , indicating that even the more resistant minerals were attacked.The total U activities showed as much variation in the six parent rock samples as in the weathered profile, and were in equilibrium in both the whole-rock and leachable fractions. 230Th was deficient relative to 234U and 226Ra in both fractions, suggesting recent addition of U and Ra to the entire profile. The large variation in U was not from absorption onto the intermediate weathering products, because only 11–23 percent of the U was in the leachable fraction. 相似文献
22.
23.
Jacqueline Flückiger Reto Knutti James W. C. White Hans Renssen 《Climate Dynamics》2008,31(6):633-645
Greenland ice cores, as well as many other paleo-archives from the northern hemisphere, recorded a series of 25 warm interstadial
events, the so-called Dansgaard-Oeschger (D-O) events, during the last glacial period. We use the three-dimensional coupled
global ocean–atmosphere–sea ice model ECBILT-CLIO and force it with freshwater input into the North Atlantic to simulate abrupt
glacial climate events, which we use as analogues for D-O events. We focus our analysis on the Northern Hemisphere. The simulated
events show large differences in the regional and seasonal distribution of the temperature and precipitation changes. While
the temperature changes in high northern latitudes and in the North Atlantic region are dominated by winter changes, the largest
temperature increases in most other land regions are seen in spring. Smallest changes over land are found during the summer
months. Our model simulations also demonstrate that the temperature and precipitation change patterns for different intensifications
of the Atlantic meridional overturning circulation are not linear. The extent of the transitions varies, and local non-linearities
influence the amplitude of the annual mean response as well as the response in different seasons. Implications for the interpretation
of paleo-records are discussed. 相似文献
24.
Lucien von Gunten Oliver Heiri Christian Bigler Jacqueline van Leeuwen Carlo Casty André F. Lotter Michael Sturm 《Journal of Paleolimnology》2008,39(3):283-299
We analysed a 42 cm long sediment record from Lej da la Tscheppa, a high-altitude lake (2,616 m a.s.l.) in the Upper Engadine
valley (Switzerland) for subfossil diatoms, chironomids and pollen. The chronology of the top 21 cm of the record was established
using 210Pb analysis using a constant-rate-of-supply model, and validated with 137Cs measurements and the content of spheroidal carbonaceous particles. A tentative chronology for the lower part of the core
was obtained through extrapolation of the sedimentation rates in the uppermost part of the record. Pollen assemblages in the
record reflect regional changes in forestation and land-use patterns in the Upper Engadine valley and show no evidence of
significant local human activity in the lake’s catchment. Diatom assemblages record a distinct increase in planktonic taxa
since the early 19th century, suggesting a decrease in the duration of ice-cover. In contrast, chironomid assemblages remained
stable during a large part of the record. We applied an established chironomid-based July air temperature transfer function
and a newly developed diatom-based spring air temperature transfer function to reconstruct past seasonal air temperature changes
at Lej da la Tscheppa. The reconstructions indicate a diatom-inferred warming trend in spring temperatures during the past
ca. 400 years, whereas chironomid-inferred summer temperatures suggest a slight cooling trend. These biota-based reconstructions
are in good agreement with the centennial-scale temperature trend in an independent reconstruction of regional temperatures
in the Upper Engadine region based on instrumental records and documentary proxy evidence from the Alps. Our results suggest
that, in high-altitude lakes, independent chironomid- and diatom-based seasonal temperature reconstruction is possible and
can be successfully used to track seasonal temperature trends. 相似文献
25.
26.
Donald T. Rodbell Holli M. Frey Matthew R.F. Manon Jacqueline A. Smith Nicholas A. McTurk 《Quaternary Research》2012,77(1):149-158
Mylonite textures in granodiorite boulders are responsible for higher rates of surface denudation of host rocks and the progressive development of unusual rock weathering features, termed weathering posts. These textures are characterized by smaller grain sizes, higher biotite content, and a higher biotite axial ratio in host rocks relative to weathering posts. Elemental concentrations do not show a significant difference between weathering posts and the host rocks in which they are found, and this reflects the absence of a weathering residue on the rock surfaces. Chemical weathering loosens the bonds between mineral grains through the expansion of biotite, and the loosened grains fall off or are blown off the boulder surface and continue their chemical alteration in the surrounding soil. The height of weathering posts on late Quaternary moraines increases at a linear rate of ~ 1.45 ± 0.45 cm (1000 yr)? 1 until post heights reach the diameter of host rocks. Such a rate of boulder denudation, if unrecognized, would generate significant errors (> 20%) in cosmogenic exposure ages for Pleistocene moraines. Given the paucity of boulders with diameters that significantly exceed 1.5 m, the maximum age of utility of weathering posts as a numeric age indicator is ~ 100 ka. 相似文献
27.
Juliet G. Crider David Frank Stephen D. Malone Michael P. Poland Cynthia Werner Jacqueline Caplan-Auerbach 《Bulletin of Volcanology》2011,73(2):175-189
Mount Baker volcano displayed a short interval of seismically-quiescent thermal unrest in 1975, with high emissions of magmatic
gas that slowly waned during the following three decades. The area of snow-free ground in the active crater has not returned
to pre-unrest levels, and fumarole gas geochemistry shows a decreasing magmatic signature over that same interval. A relative
microgravity survey revealed a substantial gravity increase in the ~30 years since the unrest, while deformation measurements
suggest slight deflation of the edifice between 1981–83 and 2006–07. The volcano remains seismically quiet with regard to
impulsive volcano-tectonic events, but experiences shallow (<3 km) low-frequency events likely related to glacier activity,
as well as deep (>10 km) long-period earthquakes. Reviewing the observations from the 1975 unrest in combination with geophysical
and geochemical data collected in the decades that followed, we infer that elevated gas and thermal emissions at Mount Baker
in 1975 resulted from magmatic activity beneath the volcano: either the emplacement of magma at mid-crustal levels, or opening
of a conduit to a deep existing source of magmatic volatiles. Decadal-timescale, multi-parameter observations were essential
to this assessment of magmatic activity. 相似文献
28.
Benoît Thibodeau Moritz F. Lehmann Jacqueline Kowarzyk Alfonso Mucci Yves Gélinas Denis Gilbert Roxane Maranger Mohammad Alkhatib 《Estuarine, Coastal and Shelf Science》2010
Water column concentrations and benthic fluxes of dissolved inorganic nitrogen (DIN) and oxygen (DO) were measured in the Gulf of St. Lawrence and the Upper and Lower St. Lawrence Estuary (USLE and LSLE, respectively) to assess the nitrogen (N) budget in the St. Lawrence (SL) system, as well as to elucidate the impact of bottom water hypoxia on fixed-N removal in the LSLE. A severe nitrate deficit, with respect to ambient phosphate concentrations (N*∼−10 μmol L−1), was observed within and in the vicinity of the hypoxic bottom water of the LSLE. Given that DO concentrations in the water column have remained above 50 μmol L−1, nitrate reduction in suboxic sediments, rather than in the water column, is most likely responsible for the removal of fixed N from the SL system. Net nitrate fluxes into the sediments, derived from pore water nitrate concentration gradients, ranged from 190 μmol m−2 d−1 in the hypoxic western LSLE to 100 μmol m−2 d−1 in the Gulf. The average total benthic nitrate reduction rate for the Laurentian Channel (LC) is on the order of 690 μmol m−2 d−1, with coupled nitrification-nitrate reduction accounting for more than 70%. Using average nitrate reduction rates derived from the observed water column nitrate deficit, the annual fixed-N elimination within the three main channels of the Gulf of St. Lawrence and LSLE was estimated at 411 × 106 t N, yielding an almost balanced N budget for the SL marine system. 相似文献
29.
Jacqueline D’Souza Annamma Mathew R. Rajamohan 《Journal of Astrophysics and Astronomy》1992,13(1):109-128
The effect of rotation on the observed colours of stars has been considered as a possible cause for the blue straggler phenomenon
in clusters listed by Mermilliod (1982). It appears that this phenomenon is definitely not real in the case of the late B
and early A spectral type blue stragglers that are intrinsic slow rotators. Among clusters containing the early B type blue
stragglers it is found that the anomalous position of the stragglers in NGC 6633, NGC 6475 and NGC 2516 cannot be accounted
for by rotation effects alone.
on leave from Assumption College, Changanacherry, Kerala. 相似文献
30.
Jacqueline Tivers 《Area》1997,29(4):344-356
Summary Many sports landscapes are said to have become increasingly 'artificial' over time. Landscapes of dry skiing have not exhibited this trend, but instead have become more 'realistic' or 'authentic'. 1 This paper discusses the results of a new study of dry ski centres in England and Wales. 相似文献