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   326篇
  免费   7篇
  国内免费   1篇
测绘学   23篇
大气科学   20篇
地球物理   75篇
地质学   89篇
海洋学   27篇
天文学   47篇
自然地理   53篇
  2022年   4篇
  2021年   4篇
  2020年   6篇
  2019年   3篇
  2018年   6篇
  2017年   6篇
  2016年   10篇
  2015年   6篇
  2014年   8篇
  2013年   12篇
  2012年   6篇
  2011年   7篇
  2010年   7篇
  2009年   10篇
  2008年   10篇
  2007年   6篇
  2006年   14篇
  2005年   17篇
  2004年   9篇
  2003年   9篇
  2002年   12篇
  2001年   12篇
  2000年   6篇
  1999年   9篇
  1998年   11篇
  1997年   3篇
  1996年   5篇
  1995年   4篇
  1993年   8篇
  1991年   4篇
  1990年   3篇
  1989年   3篇
  1987年   5篇
  1986年   6篇
  1985年   6篇
  1984年   5篇
  1982年   3篇
  1981年   7篇
  1980年   2篇
  1979年   8篇
  1978年   6篇
  1977年   3篇
  1976年   8篇
  1975年   7篇
  1974年   3篇
  1973年   3篇
  1968年   2篇
  1967年   3篇
  1966年   2篇
  1940年   2篇
排序方式: 共有334条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
The atmospheric forcing of the Bering Sea over its eastern shelf is estimated using the 40-year record of daily data from the NCEP/NCAR Reanalysis. This data set includes estimates of the processes responsible for the atmospheric forcing, namely the surface fluxes of momentum, sensible and latent heat, and longwave and shortwave radiation, and therefore permits quantifying effects that previously could be inferred only from the large-scale nature of the flow. The forcing in 1995–1999 is described in detail using daily time series; historical context for these results is provided with seasonal averages for the years 1959–1999.The analysis for winter concentrates on aspects related to the formation and advection of sea ice. Results indicate that the presence of sea ice is strongly related to the net surface-heat fluxes as well as the cross-shelf component of the wind. The 40-year record lacks any discernible long-term trend in the winter forcing and response. There was a notably cold period in the early to middle 1970s, and a warm period from the late 1970s into the early 1980s, but conditions during the 1990s are similar to those in the late 1950s and 1960s.The analysis for the warm season focuses on the mechanisms responsible for the variability in SST warming. Much of the intraseasonal and interannual variability in this warming can be attributed to variations in the downward shortwave radiation (solar heating). The 40-year record does indicate a long-term trend toward increased solar heating, and reduced surface latent-heat fluxes (evaporative cooling). These changes have led to August SSTs in the 1990s that are roughly 1°C warmer than in the 1960s.  相似文献   
7.
A mechanically-actuated locking-compass was designed for mounting on corers to record equipment orientation during the sampling process, thereby providing magnetic orientation data on the recovered deep-sea core. Locking occurs upon impact by the corer with the sea-floor; after retrieval, the device is easily unlocked and reset for another station. Compass construction makes use of commercially available parts, requires no welding and little machining, and thus allows inexpensive and easy assembly at sea.  相似文献   
8.
Carbonate-rich sedimentary rocks of the western Anabar region, northern Siberia, preserve an exceptional record of evolutionary and biogeochemical events near the Proterozoic/Cambrian boundary. Sedimentologically, the boundary succession can be divided into three sequences representing successive episodes of late transgressive to early highstand deposition; four parasequences are recognized in the sequence corresponding lithostratigraphically to the Manykal Formation. Small shelly fossils are abundant and include many taxa that also occur in standard sections of southeastern Siberia. Despite this coincidence of faunal elements, biostratigraphic correlations between the two regions have been controversial because numerous species that first appear at or immediately above the basal Tommotian boundary in southeastern sections have first appearances scattered through more than thirty metres of section in the western Anabar. Carbon- and Sr-isotopic data on petrographically and geochemically screened samples collected at one- to two-metre intervals in a section along the Kotuikan River, favour correlation of the Staraya Reckha Formation and most of the overlying Manykai Formation with sub-Tommotian carbonates in southeastern Siberia. In contrast, isotopic data suggest that the uppermost Manykai Formation and the basal 26 m of the unconformably overlying Medvezhya Formation may have no equivalent in the southeast; they appear to provide a sedimentary and palaeontological record of an evolutionarily significant time interval represented in southeastern Siberia only by the sub-Tommotian unconformity. Correlations with radiometrically dated horizons in the Olenek and Kharaulakh regions of northern Siberia suggest that this interval lasted approximately three to six million years, during which essentially all 'basal Tommotian' small shelly fossils evolved.  相似文献   
9.
In a previous paper Adams, Cary and Cohen (1994) presented a model of a supernova. In that paper the equations of General Relativity describing the evolution of a spherically symmetric, radiating star were solved analytically. The evolution of the star was determined by the application of boundary conditions at the center and at the edge. Due to lmitations in the presupernova model, only the very slow inward motion of an unstable, degenerate core could be considered. The solution was also limited by the need to exclude a runaway term, one that increased exponentially with time. Without the exclusion of the runaway, the luminosity would have increased without bound and the mass would have become negative.This paper presents a completely analytic solution to the equations of General Relativity describing the evolution of a Type II supernova. Professor S.E. Woosley kindly gave us data on the physical variables of a 12M 0 presupernova star. In our model the core collapses within 1 s, leaving a 1.3M 0 remnant. Shortly afterward 10.6M 0 is ejected to infinity, and 0.17M 0 is radiated away in the form of neutrinos. The distance of the edge from the center increases proportionally to the two-thirds power of the time. The luminosity decreases proportionally to the inverse four-thirds power.Although the runaway solution was modified by the exploding rather than a static envelope, it must still be excluded by adjusting initial conditions. Its character is changed from an exponential to a very large power (55) of time. The removal of a degree of freedom by this exclusion leads to physically non-sensical results such as negative luminosity. The inclusion of a term describing motion of the mantle due to neutrino interactions provides the additional degree of freedom necessary for physically reasonable results.  相似文献   
10.
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