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排序方式: 共有204条查询结果,搜索用时 15 毫秒
1.
Daniel Lane Colin P.R. McCarter Murray Richardson Chris McConnell Tim Field Huaxia Yao George Arhonditsis Carl P.J. Mitchell 《水文研究》2020,34(3):598-614
The estimation of hydrologic transit times in a catchment provides insights into the integrated effects of water storage, mixing dynamics, and runoff generation processes. There has been limited effort to estimate transit times in southern boreal Precambrian Shield landscapes, which are characteristically heterogeneous with surface cover including till, thin soils, bedrock outcrops, and depressional wetland features that play contrasting hydrologic roles. This study presents approximately 3.5 years of precipitation and streamflow water isotope data and estimates mean transit times (MTTs) and the young water fraction (py) across six small catchments in the Muskoka-Haliburton region of south-central Ontario. The main objectives were to define a typical range of MTTs for headwater catchments in this region and to identify landscape variables that best explain differences in MTTs/py using airborne light detection and ranging and digital terrain analysis. Of the transit time distributions, the two parallel linear reservoir and gamma distributions best describe the hydrology of these catchments, particularly because of their ability to capture more extreme changes related to events such as snowmelt. The estimated MTTs, regardless of the modelling approach or distribution used, are positively associated with the percent wetland area and negatively with mean slope in the catchments. In this landscape, low-gradient features such as wetlands increase catchment scale water storage when antecedent conditions are dryer and decrease transit times when there is a moisture surplus, which plausibly explains the increases in MTTs and mean annual runoff from catchments with significant coverage of these landscape features. 相似文献
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J.R.McConnell 《海洋地质前沿》2001,17(1)
地面冰盖对气候变化的反应可能会对未 来的海平面变化产生重大的影响.近年来格 陵兰南部的卫星调查显示,较大高度的冰盖 总体高度变化甚小,但空间变化很大.当然 仅仅依靠卫星数据难以测定是什么地球物理 过程引起了这种高度变化以及近年的变化速 率是否超过了正常变化速率.我们利用雪粒 密度增大的物理模型和根据高海拔12个冰 心再造的年雪堆积记录,获取了1978~1988 年格陵兰南部冰盖高度的变化. 地中海的干涸及其产生的后果 К.Н. Несис 很久以来就知道,地史最后阶段最具戏 剧性的事件之一就是大约在6Ma前的中新 世末期地中海的被隔离和完全干涸.据西西 里岛墨西拿城附近该时期著名的沉积剖面, 这个事件被称之为墨西拿盐量转变. 马建华摘译自 , 2000, Vol.406,No.24 周立君校 相似文献
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Regional variation in maturation of sandeels in the North Sea 总被引:1,自引:0,他引:1
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The nature of the solubility of water as [4H]Si defects in quartz, and their role in providing a source of molecular water on heating, is investigated. Existing ab inito energy calculations on the incorporation of water in quartz are used to show that energetically 4H for Si substitution is likely to constitute the most prevalent mode of water uptake on the atomic scale in quartz under equilibrium conditions, and that the planar defects previously observed by a number of different authors by electron microscopy in wet quartz are likely to be planar rafts of aggregated [4H]Si defects which are formed on supersaturation. These new conclusions call into question the previous identification of the planar defects as high pressure water clusters and require that their role in the production of molecular water in the context of recent theories of hydrolytic weakening be re-assessed. Accordingly the existing ab initio results have been used to establish the characteristics of the phase diagram for the system quartz-water in the temperature and pressure range of interest in hydrolytic weakening. Additional electron-optical experiments on wet quartz show that, on annealing at temperature in the electron microscope, similar planar defects develop in wet quartz by a diffusion process. In the context of existing theories of hydrolytic weakening it is now proposed that the conversion of [4H]Si defects to molecular water, where this is dictated by the equilibrium phase diagram, leads to a relatively large increase in volume and to the appearance of the bubbles of free water and the nucleation of associated prismatic dislocation loops of Burgers vector b=1/3 a $\langle 11\bar 20\rangle $ as previously observed. Ultimately the development of these loops leads to dislocation-induced plasticity. 相似文献
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R. M. Kippen J. Ryan A. Connors M. McConnell C. Winkler L. O. Hanlon V. Schönfelder J. Greiner M. Varendorff W. Collmar W. Hermsen L. Kuiper 《Astrophysics and Space Science》1995,231(1-2):231-234
In its first three years of operation, the COMPTEL instrument on theCompton Gamma-Ray Observatory has measured the locations (mean accuracy 1°) and spectra (0.75-30 MeV) of 18 gamma-ray bursts and continues to observe new events at a rate of 1/month. With good angular resolution and sensitivity at MeV energies, the growing COMPTEL burst catalog is an important new piece of evidence in the on-going GRB mystery. The COMPTEL burst locations are consistent with an isotropic distribution of sources, yet the spatial coincidence of two of the bursts indicates the possibility of repetition. The COMPTEL burst spectra are in most cases consistent with a single power law model with spectral index in the range 2–3. However, two bursts show evidence of a spectral break in the MeV range. Measurement of rapid variability at MeV energies in the stronger bursts provides evidence that either the sources are nearby (within the Galaxy) or the gamma-ray emission is relativistically beamed. We present an overview of analysis results obtained from the COMPTEL burst catalog concentrating on the search for burst repetition and the implications of highly variable MeV emission. 相似文献
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Climate Suitability: For Stable Malaria Transmission in Zimbabwe Under Different Climate Change Scenarios 总被引:1,自引:0,他引:1
Jessica Hartman Kristie Ebi K. John McConnell Nathan Chan John Weyant 《Global Change & Human Health》2002,3(1):42-54
As climate is one factor determining the potential range of malaria, climate change may work with or against efforts to bring
malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission is based on the MARA/ARMA model
of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using sixteen projections of climate in
2100. The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature
and precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense
human population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission,
while the lowveld and areas currently limited by precipitation show varying degrees of change, depending on climate sensitivity
and greenhouse gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed
can be used within or across other African countries.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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