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   137篇
  免费   1篇
测绘学   6篇
大气科学   5篇
地球物理   24篇
地质学   31篇
海洋学   5篇
天文学   53篇
自然地理   14篇
  2022年   1篇
  2021年   2篇
  2020年   3篇
  2019年   2篇
  2018年   1篇
  2017年   6篇
  2014年   3篇
  2013年   7篇
  2012年   2篇
  2011年   7篇
  2010年   2篇
  2009年   3篇
  2008年   6篇
  2007年   7篇
  2006年   6篇
  2005年   2篇
  2004年   4篇
  2003年   7篇
  2002年   1篇
  2001年   3篇
  2000年   6篇
  1999年   1篇
  1998年   2篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   4篇
  1993年   2篇
  1992年   1篇
  1991年   3篇
  1990年   2篇
  1989年   3篇
  1988年   3篇
  1986年   2篇
  1985年   2篇
  1984年   3篇
  1983年   5篇
  1982年   1篇
  1979年   2篇
  1978年   1篇
  1977年   2篇
  1976年   2篇
  1975年   3篇
  1974年   1篇
  1973年   4篇
  1972年   3篇
  1971年   2篇
排序方式: 共有138条查询结果,搜索用时 46 毫秒
1.
2.
3.
The Lynch’s Crater peat deposit in NE-Australia is a sensitive environmental archive located in the tropical Southern Hemisphere. This unique deposit illustrates that local and regional changes had a profound effect on the local Australian ecosystem over the past 55 kyr. To obtain a proxy of past climate changes, trace and major element geochemistry analyses were applied to a 13 m peat core from the crater. Principle component analysis (PCA) was used to identify the main factors that control elemental distribution in the peat and to add interpretative strength to the geochemical behavior of selected major and trace elements. For example, Sc, Al, Cu, and Pb were found to be related to increased erosion of the basin soils, and from this, several periods of significant flux from atmospheric input and/or terrigenous run-off were identified. Geochemically mobile elements during rock weathering and pedogenesis, such as Mg, Ca, and Sr helped to identify the peat ombrotrophic-minerotrophic boundary at ∼1.5 m depth and offered important information about fluxes of these nutrients to the mire and their dynamics within the deposit. Arsenic and V comparisons between the peat record (high concentrations in some peat sections) and in local basin rocks (very low concentrations), suggested the presence of a long range, atmospheric dust source early in the formation of the mire. The Lynch’s Crater peat record presents a continuous record of environmental change in tropical Australia and contributes new understanding to geochemical processes in peatlands.  相似文献   
4.
A microflare or a group of Ellerman bombs was found to be associated with several points of white-light enhancements. These points had similar sizes as facular points (d 0.3 arc sec). Temporal evolution of these activities is described. Origins of these activities are discussed to be deeply seated excess heating in chromospheric and photospheric levels.  相似文献   
5.
The tendency of network bright points (NBPs) to form in their surface distribution non-random, small-scale clusters is studied by a 2-D nearest-neighbours test, based on observational data for the distance between separate NBPs. High-resolution photographs taken from long time series obtained at4308 with the 50-cm refractor of Pic du Midi Observatory are used. Three different epochs of the solar cycle were chosen. The results obtained suggest that the degree of clustering depends on the solar cycle phase. Supposing that the NBPs are good tracers of the kilogauss small-scale magnetic field, we use them to obtain information about the subphotospheric small-scale magnetic field organisation and its dependence on the solar cycle phase.  相似文献   
6.
 Ni-saturated montmorillonite from Camp-Bertaux heated at different temperatures has been studied by X-ray powder diffraction, X-ray absorption (EXAFS) and vibration IR spectroscopy. Analysis of the experimental data has shown that heating of samples at temperatures higher than 150° C was accompanied by migration of Ni cations into vacant cis-octahedra of 2:1 layers. In the octahedral sheet the Ni cation has two “heavy” (Fe) and four “light” (Al and Mg) nearest octahedral cations. A model for the octahedral cation distribution in Camp-Bertaux montmorillonite was proposed in which Fe and Mg octahedral cations are segregated in small clusters. Received July 7, 1996 / Revised, accepted August 23, 1996  相似文献   
7.
The President of the Photogrammetric Society, Mr. I Newton, chaired a panel discussion concerned with those developments in photogrammetry which may take place during the 1990s.  相似文献   
8.
9.
The depth-related content of polycyclic aromatic hydrocarbons (PAH) and heavy metals was determined for two soil profiles (i.e. one Fluvisol and one Gleyic Cambisol) which developed in sediments from floodplains located at an old meander of the Rhine river. The meander had been cut off from the main river in 1829. The separation of the meander from the main river caused a change in sediment deposition (i.e. from sand to silt) which is clearly visible in the soil-profiles. Since that time, approximately 100 cm of sediments have accumulated due to temporary flooding of the area. Each soil profile was separated into 18 samples. The samples were analysed for their content of PAH after solvent extraction. Additionally, several trace elements (Co, Ni, Cd, Pb, Zn, Cr and Cu) were determined in the same sample set, and depth-related concentration profiles for both PAH and trace elements were developed. The distribution patterns of PAH with more than 3 condensed rings did not provide any evidence for PAH biodegradation or vertical transport after deposition of the sediments. Thus, in the case of PAH, the historical record can be derived not only from subhydric sediments but also from floodplain sediments. It was not possible to distinguish between atmospheric and fluvial input of PAH into the sediments from the observed distribution patterns due to the same origin of PAH from pyrolytic processes. A source determination of the PAH was not possible except for perylene, for which biogenic formation can be assumed. A comparison of the results shows that the depth-related PAH and trace element concentrations display similar trends over most of the total profiles. In the uppermost section of the profiles, the concentration of most trace elements declines whereas the PAH concentration remains high. This indicates the presence of different sources for PAH and trace elements in the last decades.  相似文献   
10.
Ackerman  M.  Muller  C. 《Pure and Applied Geophysics》1973,106(1):1325-1335
Values of the mixing ratio by volume of stratospheric NO2 and CH4 deduced from infrared spectra taken by means of balloon-borne spectrometers are presented. Possible evidence for the presence of formaldehyde in the stratosphere is also given.  相似文献   
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