全文获取类型
收费全文 | 1100篇 |
免费 | 51篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 30篇 |
大气科学 | 193篇 |
地球物理 | 262篇 |
地质学 | 453篇 |
海洋学 | 35篇 |
天文学 | 124篇 |
综合类 | 6篇 |
自然地理 | 59篇 |
出版年
2023年 | 6篇 |
2022年 | 2篇 |
2021年 | 27篇 |
2020年 | 27篇 |
2019年 | 25篇 |
2018年 | 39篇 |
2017年 | 30篇 |
2016年 | 61篇 |
2015年 | 46篇 |
2014年 | 62篇 |
2013年 | 86篇 |
2012年 | 64篇 |
2011年 | 76篇 |
2010年 | 62篇 |
2009年 | 73篇 |
2008年 | 65篇 |
2007年 | 45篇 |
2006年 | 57篇 |
2005年 | 49篇 |
2004年 | 31篇 |
2003年 | 24篇 |
2002年 | 27篇 |
2001年 | 24篇 |
2000年 | 14篇 |
1999年 | 20篇 |
1998年 | 14篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1975年 | 2篇 |
1965年 | 1篇 |
1962年 | 1篇 |
1960年 | 1篇 |
1958年 | 1篇 |
1957年 | 2篇 |
1951年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有1162条查询结果,搜索用时 31 毫秒
411.
ABSTRACTClassification of floods is often based on return periods of their peaks estimated from probability distributions and hence depends on assumptions. The choice of an appropriate distribution function and parameter estimation are often connected with high uncertainties. In addition, limited length of data series and the stochastic characteristic of the occurrence of extreme events add further uncertainty. Here, a distribution-free classification approach is proposed based on statistical moments. By using robust estimators the sampling effects are reduced and time series of different lengths can be analysed together. With a developed optimization procedure, locally and regionally consistent flood categories can be defined. In application, it is shown that the resulting flood categories can be used to assess the spatial extent of extreme floods and their coincidences. Moreover, groups of gauges, where simultaneous events belong to the same classes, are indicators for homogeneous groups of gauges in regionalization. 相似文献
412.
413.
ABSTRACTThe groundwater contamination risk in future climates was investigated at three locations in Sweden. Solute transport penetration depths were simulated using the HYDRUS-1D model using historical data and an ensemble of climate projections including two global climate models (GCMs), three emission scenarios and one regional climate model. Most projections indicated increasing precipitation and evapotranspiration until mid-century with a further increase at end-century. Results showed both increasing and decreasing groundwater contamination risks depending on emission scenario and GCM. Generally, the groundwater contamination risk is likely to be unchanged until mid-century, but higher at the end of the century. Soil and site specific relationships between Δ(P – PET) (i.e. change in the difference between precipitation, P, and potential evapotranspiration, PET) and changes in solute transport depths were determined. Using this, changes in solute transport depths for other climate projections can be assessed. 相似文献
414.
Ulrike Kienel Heinz Vos Peter Dulski Andreas Lücke Robert Moschen Norbert R. Nowaczyk Markus J. Schwab 《Journal of Paleolimnology》2013,50(4):561-575
Paleolimnological data from varved sediments in Lake Holzmaar (Eifel, Germany) were combined with documentary data on human activities, long-term data from the Historical Climate Database (HISKLID) for Germany and with recent monitoring data to evaluate changes in deposition that arose from climatic and human influences. The sediment data included seasonal layer thickness in an established varve chronology (1608–1942 AD), subannual chemical element counts, and multiannual organic matter data (TOC, TN, δ13Corg), all combined on an annual scale. Indicators for detritus deposition (lithogenic element counts and detritus layers) determined the first principal component (PC1) of the sediment data. This detritus PC1 was compared to the first PCs of the seasonal precipitation and temperature from HISKLID. While no relation was found to precipitation, the correlation with the temperature PC1 determined by spring to fall temperatures was significant. From 1608 to 1870, a positive correlation of the PCs suggests an increase of detritus deposition in the lake center with increasing non-winter temperatures. These may be linked by lake-internal sediment redeposition that increases when the periods of winter stratification become shorter and that of lake circulation longer. The detritus deposition is modulated by external detritus input depending on the intensity of erosion-conducive land use (wood pasture, wood cutting, and rotational slash-and-burn cultivation). Detritus input diminished when land use slowed down with population decrease as the consequence of plague epidemics, warfare and emigration. After 1870, forest regeneration and improving agricultural practices led to a stabilization of the catchment. Erosion and detritus deposition decreased progressively. The negative correlation of detritus deposition with the gradually increasing temperature presumably mimics a cause-effect relation, although a link with decreasing freeze–thaw action is possible. The modernization of agriculture proceeded with manuring and fertilizing, which caused an increase of lake productivity as indicated by summer blooms of diatoms with enhanced nutrient demand, increased δ13Corg values and sulfur concentrations. Within this well established data base we found combinations of criteria that may be used to deduce natural climatic or anthropogenic influences. The quantitative attribution of these influences remains a challenging task in paleolimnology because their interaction makes the detection of linking mechanisms difficult even at high degree of detail and the processes themselves remain debatable. 相似文献
415.
Andreas Bachmann Britta Allgöwer 《International journal of geographical information science》2013,27(2):115-127
Rothermel's model is the most widely used fire behaviour model in wildland fire research and management. It is a complex model that considers 17 input variables describing fuel type, fuel moisture, terrain and wind. Uncertainties in the input variables can have a substantial impact on the resulting errors and have to be considered, especially when the results are used in spatial decision making. In this paper it is shown that the analysis of uncertainty propagation can be carried out with the Taylor series method. This method is computationally cheaper than Monte Carlo and offers easy-to-use, preliminary sensitivity estimations. 相似文献
416.
Locating, monitoring, and characterizing typhoon-linduced landslides with real-time seismic signals 总被引:1,自引:0,他引:1
Honn Kao Chih-Wen Kan Rong-Yuh Chen Chien-Hsin Chang Andreas Rosenberger Tzay-Chyn Shin Pei-Ling Leu Kai-Wen Kuo Wen-Tzong Liang 《Landslides》2012,9(4):557-563
Landslides induced by typhoon Morakot during its passage across Taiwan on 7–9 Aug 2009 claimed more than 700 lives and caused heavy economic loss. Unlike earthquake monitoring, precise locations of landslides could not be determined in near-real time because their seismic phases are difficult to identify. Here, we show that large, damaging landslide events are characterized seismically by a distinct waveform pattern of frequent intermixes of P and S waves over a time window of several tens of seconds. The predominant frequency band during these time windows ranges from 0.5 to 5?Hz. The high-frequency content is clearly deficient relative to that of local earthquakes by about one to two orders. We also demonstrate that large landslide events can be located and monitored with algorithms specifically designed for real-time seismic applications. This near-real-time monitoring capability would be particularly useful for emergency responders and government organizations to coordinate effective relief-and-rescue operations. 相似文献
417.
Geochemistry of surface sediments and heavy metal contamination assessment: Messolonghi lagoon complex,Greece 总被引:2,自引:2,他引:0
Aristomenis P. Karageorgis Andreas Sioulas Evangelia Krasakopoulou Christos L. Anagnostou George A. Hatiris Harikleia Kyriakidou Konstantinos Vasilopoulos 《Environmental Earth Sciences》2012,65(6):1619-1629
The Messolonghi lagoon complex in Western Greece receives agricultural and domestic effluents both from point and diffused
sources. Surface sediments were analyzed for grain size, organic carbon, total nitrogen, total sulfur, major and minor elements,
aiming at the identification of geochemical relationships between all variables. Enrichment factors and the modified degree
of contamination methods were applied to assess potential heavy metal enrichment related to human activities. Sediment texture
was highly variable, with muddy sediments prevailing. In the central sector of the Messolonghi lagoon, organic carbon contents
were high. Principal factor analysis revealed the following main groups of variables with common geochemical behavior: (1)
terrigenous aluminosilicates (2) organic matter, (3) biogenic carbonates, (4) mineral quartz-aluminosilicates, and (5) Mn-oxides.
Enrichment factors estimated for V, Cr, Mn, Co, Ni, Cu, Zn, and Pb using local pre-industrial sediment showed that all metals
exhibit almost natural background levels, except for Pb, which was found to be slightly elevated (legacy of leaded fuel).
Estimation of contamination factors concluded in similar results, whereas the overall modified degree of contamination was
at the lowest level, therefore suggesting that this transitional water body has not been affected by anthropogenic activities.
The data set may be considered as a baseline for future monitoring projects according to EU policy. 相似文献
418.
Identification of a karst system’s intrinsic hydrodynamic parameters: upscaling from single springs to the whole aquifer 总被引:1,自引:1,他引:0
Andreas Hartmann Martin Kralik Franko Humer Jens Lange Markus Weiler 《Environmental Earth Sciences》2012,65(8):2377-2389
For water management purposes, information about an entire aquifer system is generally more important than information about
a specific spring. Since a karstic aquifer system might drain to several outlets, conclusions derived from a single spring
can be misleading for characterization and modeling. In this study we apply a conceptual model to an Alpine dolomite karst
system in Austria. The particular challenge was that several small springs with strongly varying hydrological behavior and
diffuse flow into surrounding streams drain this system. Instead of applying the model to a single spring, it was calibrated
simultaneously to several observations within the system aiming to identify the karst system’s intrinsic hydrodynamic parameters.
Parameter identification is supported by modeling the transport of water isotopes (δ18O). The parameters were transferred to the whole system with a simple upscaling procedure and a sensitivity analysis was performed
to unfold influence of isotopic information on parameter sensitivity and simulation uncertainty. The results show that it
is possible to identify system intrinsic parameters. But the sensitivity analysis revealed that some are hardly identifiable.
Only by considering uncertainty reasonable predictions can be provided for the whole system. Including isotopic information
increases the sensitivity of some intrinsic parameters, but it goes along with a sensitivity decrease for others. However,
a possible reduction of prediction uncertainty by isotopic information is compensated by deficiencies in the transport modeling
routines. 相似文献
419.
Nadine Hoffmann Klaus Reicherter Christoph Grützner Jochen Hürtgen Andreas Rudersdorf Finn A. Viehberg Martin Wessels 《Central European Journal of Geosciences》2012,4(1):94-110
Lake Ohrid (between FYR of Macedonia and Albania), situated in an active tectonic region of the Balkanides, is characterized by N ?? S trending active faults. To reconstruct the Holocene shoreline evolution we investigated the coastline using sediment cores and geophysical methods to image sedimentary and tectonic structures. We revealed areas of differing sedimentation regimes. The plains north and south of the lake are dominated by clastic input related to climate variations and uplift/erosion, whereas the steep western and eastern margins are controlled by recent tectonics. Furthermore, no evidence for a much higher lake-level during the Holocene was found in the plains north and south of the lake, except rare temporary floodings. This is supported by mappings of the limestone cliffs around Lake Ohrid, which yielded no evidence for abrasional platforms or notches as indicators for past highstands. 相似文献
420.
Markus Reuter Andrea K. Kern Mathias Harzhauser Andreas Kroh Werner E. Piller 《Gondwana Research》2013,23(3):1172-1177
Precipitation over India is driven by the Indian monsoon. Although changes in this atmospheric circulation are caused by the differential seasonal diabatic heating of Asia and the Indo-Pacific Ocean, it is so far unknown how global warming influences the monsoon rainfalls regionally. Herein, we present a Miocene pollen flora as the first direct proxy for monsoon over southern India during the Middle Miocene Climate Optimum. To identify climatic key parameters, such as mean annual temperature, warmest month temperature, coldest month temperature, mean annual precipitation, mean precipitation during the driest month, mean precipitation during the wettest month and mean precipitation during the warmest month the Coexistence Approach is applied. Irrespective of a ~ 3–4 °C higher global temperature during the Middle Miocene Climate Optimum, the results indicate a modern-like monsoonal precipitation pattern contrasting marine proxies which point to a strong decline of Indian monsoon in the Himalaya at this time. Therefore, the strength of monsoon rainfall in tropical India appears neither to be related to global warming nor to be linked with the atmospheric conditions over the Tibetan Plateau. For the future it implies that increased global warming does not necessarily entail changes in the South Indian monsoon rainfall. 相似文献