全文获取类型
收费全文 | 385篇 |
免费 | 16篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 29篇 |
地球物理 | 77篇 |
地质学 | 164篇 |
海洋学 | 43篇 |
天文学 | 43篇 |
综合类 | 1篇 |
自然地理 | 34篇 |
出版年
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 9篇 |
2019年 | 2篇 |
2018年 | 15篇 |
2017年 | 8篇 |
2016年 | 12篇 |
2015年 | 14篇 |
2014年 | 17篇 |
2013年 | 24篇 |
2012年 | 8篇 |
2011年 | 24篇 |
2010年 | 12篇 |
2009年 | 25篇 |
2008年 | 22篇 |
2007年 | 9篇 |
2006年 | 17篇 |
2005年 | 17篇 |
2004年 | 14篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 15篇 |
2000年 | 14篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1967年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有406条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
Analysis of Temporal Environmental Isotopic Variation in Ground Water of the Georgia Piedmont 总被引:2,自引:0,他引:2
Seth Rose 《Ground water》1995,33(4):644-652
35.
N. Stein Dr. 《GeoJournal》1982,6(2):157-164
A re-examination of the biosphere, in particular of the tropical rain forests, is necessary since there are some contradictions in our present knowledge about carbon fluxes and carbon storage in various reservoirs. Traditional land-use systems as well as modern exploitation methods in the tropical rain forest areas need not be necessarily of such a magnitude that the global carbon cycle would undergo a major upset or even a climatic catastrophe. This conclusion is primarily based on the high photosynthesis rates of the humid tropics and on the very important role of tropical river systems for carbon transport between terrestrial and aquatic ecosystems.After careful consideration of all known facts this paper comes to the conclusion that 2 × 1015 g/yr C are released to the atmosphere due to deforestation and burning in the tropical rain forest belt. The same amount is probably being fixed in the temperate forests and the northern ecosystems. A possible steady balance of all terrestrial ecosystems would, therefore, be the result of a particular historical constellation whereby a destruction of vegetation in the tropics would occur simultaneously to an increase of phytomass and also to a humus and peat accumulation in temperate and northern ecosystems. 相似文献
36.
Seth Stein Joseph F. Engeln Douglas A. Wiens Robert C. Speed Kazuya Fujita 《Tectonophysics》1983,99(2-4)
The Lesser Antilles subduction zone is an extreme case of the subduction of old (~ 90 m.y.) lithosphere at a slow (~ 2 cm/y) convergence rate. Focal mechanisms of the largest earthquakes in the area have been obtained using body and surface wave data. During the time period (1950–1978) studied the subduction seismicity appears to represent primarily intraplate rather than interplate deformation. All three large (magnitude seven) earthquakes were from intraplate normal faults; no large thrust faulting earthquakes and few small ones occurred. These observations suggest that the plate boundary is largely decoupled, that subduction is at least partially aseismic, and that the downgoing slab is in a state of extension. 相似文献
37.
A.E. Jennings S. Hagen J. Harðardóttir R. Stein A.E.J. Ogilvie I. Jónsdóttir 《Climatic change》2001,48(1):83-100
Environmental proxies of soil erosion on Iceland, and oceanographic conditions on the adjacent shelf, were measured on a 50 cm box core taken from the southwest Iceland shelf in 1993 during cruise 93030 of the Canadian ship, CSS Hudson. These data, covering the last several centuries, are compared with the documentary record of sea-ice changes around Iceland since A.D. 1600. The site is under the influence of the Irminger Current, which carries warm, saline, Atlantic water northward along the shelf. Because of the relative warmth of this current, sea ice rarely occurs off southwest Iceland, even during the most severe sea-ice intervals of the historical record. In severe sea-ice years, however, the ice drifts clockwise around Iceland from the northeast and east and, in rare cases, reaches the southern coasts (Ogilvie, 1992). The chronology of the core was established by converting the basal radiocarbon date to calendar years and assuming a linear sedimentation rate from the base of the core to the year of collection, 1993. Organic carbon, stable C and O isotope ratios, planktonic foraminiferal assemblages, and sediment magnetic parameters were measured on samples from the core, plotted against calendar years and compared to the Icelandic sea-ice index. The environmental proxies suggest that increased soil erosion, reduced salinity, and, possibly, decreased marine productivity prevailed during the severe sea-ice interval lasting from the last quarter of the eighteenth century to around 1920. Such a situation could develop with climatic cooling, increased storminess, and loss of vegetation cover to stabilise the soil. Although the core site generally lies outside the sea-ice limits, the evidence clearly shows the influence of sea ice and fresh water, and is sensitive to the overall climatic deterioration manifested by the sea-ice record. 相似文献
38.
Severe droughts in the middle-12th and late-13th centuries appear to have affected Anasazi (pre-Columbian Native American)
populations. During the first drought most of the great houses in the central San Juan Basin were vacated; the second drought
resulted in the abandonment of the Four Corners region. During the first drought, villages may not have been completely abandoned.
The multi-year drought periods probably were characterized by reductions in both winter and summer precipitation. Maize is
dependent on winter precipitation for its germination and initial growth and on summer (monsoonal) precipitation for its continued
growth. Reductions in precipitation are hypothesized to have resulted in low yields of maize, the dietary staple of the Anasazi.
A comparison of historic climate data and tree-ring-based reconstructions of precipitation in the Four Corners region with
tree-ring-based reconstructions of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) indicate
that severe and persistent drought in the Four Corners region occurs when the PDO is negative and the AMO is positive. Historic
climate data from the greater San Juan Basin indicate that a negative PDO is characterized by reductions in both water-year
and summer precipitation, reinforcing the concept that at least some multi-year droughts involved weakening of the summer
monsoon with attendant decreases in the yields of maize. 相似文献
39.
Robert J. Kieber Joan D. Willey Robert F. Whitehead Seth N. Reid 《Journal of Atmospheric Chemistry》2007,58(3):219-235
Significant photodegradation of chromophoric dissolved organic matter (CDOM) in rainwater was observed after exposure to simulated
sunlight. Fluorescence excitation emission spectra (EEMS) of precipitation revealed the presence of four major peaks all of
which degraded upon photolysis with the greatest loss in the region characteristic of marine CDOM. Photobleaching of absorbance
also occurred in the wavelength region between 250 and 375 nm with the greatest loss of absorbance in the upper end of the
UV-A region near 275 nm. There was a strong positive correlation between absorbance loss and total integrated fluorescence
loss suggesting these optical properties and the degree to which they are photobleached in rainwater are directly related.
The quantum yield of CDOM photodegradation in rainwater decreased dramatically with increasing wavelength and decreasing energy
of incoming radiation with the average quantum yield at 325 nm approximately an order of magnitude greater than at 460 nm.
The similarity of photolytic response between rainwater and Cape Fear estuarine CDOM indicates that some fraction of the compounds
that make up rainwater CDOM may be derived from surface sources and/or that the processes that produce or modify humic-like
substances in the atmosphere result in similar types of compounds as non-atmospheric processes. 相似文献
40.
Sm-Nd data for the Archean granulite and amphibolite facies migmatites of Langøy and Hinnøy in Vesterålen are presented which indicate that their protoliths formed ~2.6 AE ago. Rubidium and U loss during a granulite facies metamorphism at ~1.8 AE caused serious disturbance of total-rock U-Pb and Rb-Sr systems. Therefore these systems do not provide any precise age information for the granulite facies migmatites. For the amphibolite facies migmatites of Vesterålen both SmNd, RbSr and PbPb total-rock systems give model ages of ~2.6 AE. The results on both granulite and amphibolite facies rocks are thus in agreement. Previous interpretations based on PbPb data, which indicated an age of 3.41 AE for the Archean terrane of Vesterålen, are not valid.One SmNd model age from the granulite facies migmatites at Moskenesøy in Lofoten indicates that the protoliths of these migmatites formed ~2.0 AE ago and are thus not related to the Vesterålen migmatites. 相似文献