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   94篇
  免费   3篇
  国内免费   4篇
大气科学   5篇
地球物理   10篇
地质学   50篇
海洋学   7篇
天文学   21篇
自然地理   8篇
  2022年   2篇
  2021年   4篇
  2020年   2篇
  2019年   7篇
  2018年   5篇
  2017年   10篇
  2016年   7篇
  2015年   4篇
  2014年   3篇
  2013年   5篇
  2012年   7篇
  2011年   4篇
  2010年   6篇
  2009年   3篇
  2008年   2篇
  2007年   3篇
  2006年   2篇
  2005年   4篇
  2004年   1篇
  2003年   8篇
  2002年   2篇
  1999年   4篇
  1998年   2篇
  1995年   1篇
  1988年   1篇
  1982年   1篇
  1977年   1篇
排序方式: 共有101条查询结果,搜索用时 15 毫秒
31.
We consider the evolution of the ionization zone around Population III stars with M * ?? 25?C200M ?? in protogalaxies with M ?? 107 M ?? at redshifts z = 12, assuming that the dark-energy profile is a modified isothermal sphere. We study the conditions for the growth of instabilities in the ionization zones. The Rayleigh-Taylor and thermal instabilities develop efficiently in the ionization zones around 25?C40M ?? stars, while this efficiency is lower for stars withM * ?? 120M ??. For more massive stars (??200M ??), the flux of ionizing photons is strong enough to considerably reduce the gas density in the ionization zone, and the typical lifetimes of stars (??2 Myr) are insufficient for the growth of instabilities. The gas in a protogalaxy with M ?? 107 M ?? with a 200M ?? central star is completely ionized by the end of the star??s lifetime; in the case of a 120M ?? central star, only one-third of the total mass of gas is ionized. Thus, ionizing photons from stars with M * ? 120M ?? cannot leave protogalaxies with M ? 107 M ??. If the masses of the central stars are 25 and 40M ??, the gas in protogalaxies of this mass remains essentially neutral. We discuss the consequences of the evolution of the ionization zones for the propagation of the envelope after the supernova explosions of the strs and the efficiency of enrichment of the intergalactic medium in heavy elements.  相似文献   
32.
Recent studies have shown that, in addition to the role of solar variability, past climate changes may have been connected with variations in the Earth??s magnetic field elements at various timescales. An analysis of variations in geomagnetic field elements, such as field intensity, reversals, and excursions, allowed us to establish a link between climate changes at various timescales over the last millennia. Of particular interest are sharp changes in the geomagnetic field intensity and short reversals of the magnetic poles (excursions). The beginning and termination of the examined geomagnetic excursions can be attributed to periods of climate change. In this study, we analyzed the possible link between short-term geomagnetic variability (jerks) and climate change, as well as the accelerated drift of the north magnetic pole and surface temperature variations. The results do not rule out the possibility that geomagnetic field variations which modulate the cosmic ray flux could have played a major role in climate change in addition to previously induced by solar radiation.  相似文献   
33.
Doklady Earth Sciences - Methane concentration in dominant landscapes of typical tundra of Western Yamal has been measured. The highest methane content in the active layer was measured in tundra...  相似文献   
34.
Doklady Earth Sciences - The results of study of primary melt inclusions in accessory Cr–spinelides from dunite have revealed features of the chemical compositions of high-magnesium...  相似文献   
35.
Doklady Earth Sciences - It was established that along with permafrost degradation, the processes of permafrost aggradation occur in the modern low accumulative surfaces of Kara Sea. The cycle of...  相似文献   
36.
Doklady Earth Sciences - The paper presents the results from the first 40Ar/39Ar isotope dating of eleven mafic sills recovered by deep boreholes in the eastern Siberian Platform. Most of the dates...  相似文献   
37.
The problem of computation of elliptic Hansen coefficients and their derivatives is considered for constructing a motion theory of an artificial Earth satellite with large eccentricity. An algorithm for analytical and numerical computation of these coefficients and their derivatives is described. The recurrence relations for derivatives of the first and second order and initial values for recurrences are obtained. As an example, numerical values of some elliptic Hansen coefficients are given for the orbit with eccentricityk=0.74.  相似文献   
38.
39.
The results of permafrost and coastal dynamics investigations at four key sites on the shores of the Kara and Barents Seas are discussed. Three ACD key sites, Marre-Sale, Shpindler, and Kolguev, characterize areas with active thermal erosion; key site Cape Bolvansky is found on a relatively stable coast. It is found that the coastal retreat rate has spatial and temporal variability, which is typical of the entire Arctic coast. Coastal deposits on the Kara and Barents Seas have a low organic carbon content. Annual input of material into the Kara Sea resulting from coastal degradation reaches 35–40 million t, including about 7.5 million t of ice, 0.35 million t of organic carbon, and 0.3 million t of soluble salts.This revised version was published online January 2005 with corrections to the title of the article.  相似文献   
40.
We consider the problem of year-round cooling of water-saturated soil to freezing temperatures in order to convert it into a state of permafrost.A new soil-cooling apparatus is proposed.The apparatus is to be made in modular form and connected to passive-active thermal piles (thermosyphons).The estimated capacity of one apparatus allows simultaneous use of up to 1,000 thermal piles for ground freezing.The apparatus is based on natural sources of energy:solar radiation and wind;and it can be used for soil freezing.This approach can prevent thawing of soft soils under railways and roads,as well as under buildings or structures,in an area of more than tens of hectares.The apparatus has no mechanical moving parts and can operate for a long time in stand-alone mode without staff involvement.  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