首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   532篇
  免费   17篇
  国内免费   9篇
测绘学   14篇
大气科学   23篇
地球物理   132篇
地质学   184篇
海洋学   24篇
天文学   126篇
综合类   1篇
自然地理   54篇
  2022年   2篇
  2021年   11篇
  2020年   12篇
  2019年   12篇
  2018年   17篇
  2017年   8篇
  2016年   20篇
  2015年   14篇
  2014年   11篇
  2013年   31篇
  2012年   26篇
  2011年   22篇
  2010年   20篇
  2009年   25篇
  2008年   27篇
  2007年   12篇
  2006年   21篇
  2005年   17篇
  2004年   12篇
  2003年   15篇
  2002年   19篇
  2001年   10篇
  2000年   18篇
  1999年   7篇
  1998年   11篇
  1997年   10篇
  1996年   12篇
  1995年   10篇
  1994年   10篇
  1993年   13篇
  1992年   12篇
  1991年   3篇
  1990年   4篇
  1989年   2篇
  1988年   2篇
  1987年   5篇
  1986年   5篇
  1985年   12篇
  1984年   5篇
  1983年   4篇
  1982年   4篇
  1981年   5篇
  1980年   3篇
  1979年   5篇
  1978年   6篇
  1977年   4篇
  1976年   6篇
  1975年   5篇
  1970年   2篇
  1969年   2篇
排序方式: 共有558条查询结果,搜索用时 15 毫秒
131.
Derek R. Hall 《GeoJournal》1998,46(3):283-287
This paper examines the prospects for Albanian rural diversification with particular reference to rural tourism. In the early 1990s, tourism was identified by the Albanian government and Western development consultants as a likely vehicle for an appropriate and sustainable development strategy, given the relative wealth generated by international tourism in neighbouring Greece, Italy and Croatia. Pressure has been exerted by commercial developers for mass coastal tourism and permission for around 40 new tourist development has been granted. But Albania embraces a considerable wealth of natural and cultural heritage, which provides opportunities for the development of small scale rural tourism carefully integrated into the local economy with respect to organic farming, quality wine production and sustainable fishing. But sensitive social integration is vital where it is difficult to identify rural communities where there is a conspicuous absence of local consensus. The resurgence of traditional social systems and the empowerment of local actors in cases where organised crime has taken root pose major problems for rural diversification. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
132.
We present 10 in situ cosmogenic exposure ages from two moraines on the Isle of Skye. The Strollamus medial moraine was deposited during deglaciation of the Devensian ice sheet and yields a mean exposure age from five samples of 14.3 ± 0.9 ka. The moraine age indicates that a significant ice mass existed on Skye at the time of a regional readvance recorded in Wester Ross, northwest Scotland. Taken at face value the ages suggest that deglaciation did not occur until well into Greenland Interstade 1. The Slapin moraine represents the local limit of the Loch Lomond Readvance (LLR) and yields a mean exposure age from five samples of 11.5 ± 0.7 ka, which is consistent with deposition relating to the LLR. These ages suggest that the maximum extent may have been reached late in the stadial and that some glaciers may have remained active until after the climatic amelioration that marks its end. This scenario is considered unlikely given the nature of the climate during this period, which leads us to call for a locally calibrated production rate. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
133.
Samples of a type 3.4 chondrite have been annealed at 400–1000°C for 1–200 hours, their thermoluminescence properties determined and analyzed for K, Na, Mn, Sc and Ca by instrumental neutron activation analysis. After annealing at ?900°C, the samples showed a 50% decrease in TL sensitivity, while after annealing at 1000°C it fell to 0.1-0.01 times its unannealed value and loss of Na and K occurred. The TL and compositional changes resemble those observed for the equilibrated Kernouve chondrite after similar annealing treatments, except that the sharp TL decrease, and element loss, occurred at ~ 1100°C; this difference is presumably due to petrographic differences in the feldspar of the two meteorites. The temperature and the width of the TL peak showed a discontinuous increase after annealing at 800°C; peak temperature jumped from 130 to 200°C and peak width increased from 90 to 150°C. The activation energies for these TL changes are 7–10 kcal/mole. Similar increases in the TL peak temperature have been reported in TL studies of Amelia, VA, albite, where they were associated with the low to high-temperature transformation. However, the activation energy for the transformation is ~80 kcal/mole. These changes in TL emission characteristics resemble trends observed in type 3 ordinary chondrites and it is suggested that type 3.3–3.5 chondrites have a low-feldspar as TL phosphor and > 3.5 have high-feldspar as the phosphor. Thermoluminescence therefore provides a means of palaeothermometry for type 3 ordinary chondrites.  相似文献   
134.
Adsorption and precipitation reactions often dictate the availability of phosphorus in soil environments. Tripolyphosphate (TPP) is considered a form of slow release P fertilizer in P limited soils, however, investigations of the chemical fate of TPP in soils are limited. It has been proposed that TPP rapidly hydrolyzes in the soil solution before adsorbing or precipitating with soil surfaces, but in model systems, TPP also adsorbs rapidly onto mineral surfaces. To study the adsorption behavior of TPP in calcareous soils, a short-term (48 h) TPP spike was performed under laboratory conditions. To determine the fate of TPP under field conditions, two different liquid TPP amendments were applied to a P limited subsurface field site via an in-ground injection system. Phosphorus speciation was assessed using X-ray absorption spectroscopy, total and labile extractable P, and X-ray diffraction. Adsorption of TPP to soil mineral surfaces was rapid (< 48 h) and persisted without fully hydrolyzing to ortho-P. Linear combination fitting of XAS data indicated that the distribution of adsorbed P was highest (~ 30–40%) throughout the site after the first TPP amendment application (high water volume and low TPP concentrations). In contrast, lower water volumes with more concentrated TPP resulted in lower relative fractions of adsorbed P (15–25%), but a significant increase in total P concentrations (~ 3000 mg P kg soil) and adsorbed P (60%) directly adjacent to the injection system. This demonstrates that TPP application increases the adsorbed P fraction of calcareous soils through rapid adsorption reactions with soil mineral surfaces.  相似文献   
135.
Summary Barometric anomalies for stations near the Indian Ocean since 1841 are tabulated and combined for years and half-years. Early records for India yield a further series back to 1796. Regional anomalies for the west Indian Ocean correlate inversely with Nile Flood data, and those for the east Indian Ocean inversely with Java tree-rings. Combined values (including Australia), if reversed, correlate well with such rainfall indicators and at the same time provide good indicators of the half-yearly anomalies of the Southern Oscillation and the yearly anomalies of the Pressure Parameter. The Pressure Parameter is an index linked also with tropical temperature changes and with climatic fluctuations in various parts of the world.
Zusammenfassung Luftdruckwerte für Orte im Gebiete des Indischen Ozeans seit 1841 wurden zusammengestellt in Tabellen jährlicher und halbjährlicher Anomalien. Frühe Aufzeichnungen in Indien sind erhältlich seit 1796. Regionale Anomalien des Luftdruckes im westlichen Indischen Ozean sind umgekehrt korreliert mit der Nilflut, solche im östlichen Indischen Ozean mit den Jahresringbreiten von Bäumen auf Java. Kombinierte Luftdruckanomalien (Australien eingeschlossen) sind umgekehrt korreliert mit solcherart Indikatoren des Niederschlags und ergeben zur gleichen Zeit gute Anweisungen für die halbjährlichen Anomalien der sogenannten Südlichen Schwankung und der jährlichen Anomalien eines gewissen Luftdruckparameters. Der Luftdruckparameter ist verbunden mit tropischen Temperaturänderungen und klimatischen Schwankungen in verschiedenen Weltteilen.
  相似文献   
136.
Understanding the pace and drivers of marine-based ice-sheet retreat relies upon the integration of numerical ice-sheet models with observations from contemporary polar ice sheets and well-constrained palaeo-glaciological reconstructions. This paper provides a reconstruction of the retreat of the last British–Irish Ice Sheet (BIIS) from the Atlantic shelf west of Ireland during and following the Last Glacial Maximum (LGM). It uses marine-geophysical data and sediment cores dated by radiocarbon, combined with terrestrial cosmogenic nuclide and optically stimulated luminescence dating of onshore ice-marginal landforms, to reconstruct the timing and rate of ice-sheet retreat from the continental shelf and across the adjoining coastline of Ireland, thus including the switch from a marine- to a terrestrially-based ice-sheet margin. Seafloor bathymetric data in the form of moraines and grounding-zone wedges on the continental shelf record an extensive ice sheet west of Ireland during the LGM which advanced to the outer shelf. This interpretation is supported by the presence of dated subglacial tills and overridden glacimarine sediments from across the Porcupine Bank, a westwards extension of the Irish continental shelf. The ice sheet was grounded on the outer shelf at ~26.8 ka cal bp with initial retreat underway by 25.9 ka cal bp. Retreat was not a continuous process but was punctuated by marginal oscillations until ~24.3 ka cal bp. The ice sheet thereafter retreated to the mid-shelf where it formed a large grounding-zone complex at ~23.7 ka cal bp. This retreat occurred in a glacimarine environment. The Aran Islands on the inner continental shelf were ice-free by ~19.5 ka bp and the ice sheet had become largely terrestrially based by 17.3 ka bp. This suggests that the Aran Islands acted to stabilize and slow overall ice-sheet retreat once the BIIS margin had reached the inner shelf. Our results constrain the timing of initial retreat of the BIIS from the outer shelf west of Ireland to the period of minimum global eustatic sea level. Initial retreat was driven, at least in part, by glacio-isostatically induced, high relative sea level. Net rates of ice-sheet retreat across the shelf were slow (62–19 m a−1) and reduced (8 m a−1) as the ice sheet vacated the inner shelf and moved onshore. A picture therefore emerges of an extensive BIIS on the Atlantic shelf west of Ireland, in which early, oscillatory retreat was followed by slow episodic retreat which decelerated further as the ice margin became terrestrially based. More broadly, this demonstrates the importance of localized controls, in particular bed topography, on modulating the retreat of marine-based sectors of ice sheets.  相似文献   
137.
The timing of eustatic sea level fluctuations over the vertical range + 15 to ?11 m has been deduced from 230Th234U dating of Bermudan corals and speleothems. On this tectonically stable carbonate island, interglacial periods are characterized by platform submergence, development of patch reefs, and the deposition of littoral and eolian carbonates, whereas glacial periods are times of platform emergence, carbonate diagenesis, soil development, and the deposition of speleothems in caves extending below present sea level. Interglacial periods are observed at about 200,000, 130,000 to 90,000, and 10,000 yr BP to present. The sea level history of the last interglacial period (130,000 to 90,000 yr BP) is complex, consisting of at least two short, distinct episodes of high sea stand (at 125,000 and 97,000 yr BP) superimposed on a longer period of general platform submergence. The sea level data derived from this study are compatible with those from other stable areas such as the Bahamas, but in addition suggest that eustatic sea level changes can be rapid, on the order of 5 to 10 m/1000 yr.  相似文献   
138.
Cell parameters, ranging from 8.447 to 9.331 Å, are given for 13 synthetic aluminosilicate-sodalites. Correlations between the cell edge of aluminosilicate-sodalites and the sizes of the cavity ions are established and discussed. The principal infrared absorption bands for 6 synthetic and 4 natural aluminosilicate-sodalites are also correlated with the cell edge and discussed in terms of the bonding theory of linked TO4 tetrahedra (T=Si, Al).  相似文献   
139.
For the love of pipes and cables: a response to Deborah Thien   总被引:2,自引:0,他引:2  
Derek McCormack 《Area》2006,38(3):330-332
  相似文献   
140.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号