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   254953篇
  免费   4303篇
  国内免费   3354篇
测绘学   6805篇
大气科学   18871篇
地球物理   53270篇
地质学   88013篇
海洋学   21055篇
天文学   55809篇
综合类   992篇
自然地理   17795篇
  2021年   2224篇
  2020年   2583篇
  2019年   2845篇
  2018年   3149篇
  2017年   2823篇
  2016年   5499篇
  2015年   4178篇
  2014年   6884篇
  2013年   14187篇
  2012年   6307篇
  2011年   7493篇
  2010年   6524篇
  2009年   9220篇
  2008年   8061篇
  2007年   7408篇
  2006年   9586篇
  2005年   7628篇
  2004年   7514篇
  2003年   7015篇
  2002年   6662篇
  2001年   5954篇
  2000年   5914篇
  1999年   5187篇
  1998年   5215篇
  1997年   5016篇
  1996年   4665篇
  1995年   4412篇
  1994年   4093篇
  1993年   3831篇
  1992年   3618篇
  1991年   3589篇
  1990年   3754篇
  1989年   3509篇
  1988年   3296篇
  1987年   3840篇
  1986年   3404篇
  1985年   4218篇
  1984年   4728篇
  1983年   4406篇
  1982年   4314篇
  1981年   3920篇
  1980年   3644篇
  1979年   3509篇
  1978年   3483篇
  1977年   3280篇
  1976年   3043篇
  1975年   2956篇
  1974年   2926篇
  1973年   3079篇
  1972年   2024篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
After examination of the baroclinic structure below 3000 db, recent data were used to map the geopotential topography at 1000, 1500, and 2000 db (referred to 3000 db) in the Pacific Ocean. In the high-latitude regions and in the western boundary currents, considerable relief is present at 1000 and 1500 db, and the Circumpolar Current is still well-developed at 2000 db. The geostrophic circulation inferred is very similar to the surface circulation in these areas. Neglect of the structure below 1000 db results in appreciable errors in estimates of the transport of these currents; direction of near-surface flow is properly shown, however, and computed speeds are not greatly in error. In the equatorial Pacific and central North Pacific, little relief is present, and the trends are generally unlike the surface flow.  相似文献   
995.
A general method for the dynamic analysis of multi-body offshore structures is presented, being based on a constraint matrix approach. A method of deriving the constraint matrix for a general structure is given, and this is then used to derive the equations of motion of a whole system from those of it's component parts. The response of the system to both first and second order random wave forces is found and then used to calculate the forces and moments in the connecting mechanisms. The structure is assumed to have rigid component parts and a linearised frequency domain analysis method is used, although other methods are discussed. To illustrate it's use, the method is applied to both the SBS and Yoke-CALM design of offshore mooring terminal.  相似文献   
996.
First an historical outline of the West African Holocene stratigraphy is briefly presented showing that the present scheme is situated halfway between litho- and climatostratigraphy. Then, on the basis of comparisons between previous hypotheses and published palynostratigraphical results, a tentative climatic zonation is proposed whose congruence with deltaic and continental succession is emphasised. Finally, in the Senegal river, a correlation based on purely lithostratigraphical system clear of all climatic interpretation, provides interesting information on the hydrodynamics of the sea-level change at the very base of the Holocene from the delta to 250km upstream.  相似文献   
997.
998.
Environmental concern for the deep-sea ecosystem is increasing as contaminants, originating from anthropogenic activities, have been detected in deep-sea biota. However, little is known on the xenobiotics metabolising capability of deep-sea fauna. In this study, the deep-sea amphipod Eurythenes gryllus was selected as sentinel species to measure the total oxyradical scavenging capacity (TOSC). Individuals of E. gryllus were sampled at 2000 m depth in the Arctic Ocean. The TOSC assay was measured on the cytosolic fraction and the soluble fraction (3 kDa) of the digestive gland and on the cell-free haemolymph toward peroxyl, hydroxyl and peroxynitrite radicals according to the method of Winston et al. [Free Radical Biology and Medicine 24 (3) (1998) 480] and Regoli and Winston [Toxicology and Applied Pharmacology 156 (1999) 96]. These results provide the first baseline data set for total antioxidant capacity in a deep-sea amphipod.  相似文献   
999.
Numerical experiments on double-diffusive intrusions are reviewed briefly. Though the number of studies is very limited at present, they have undoubtedly an advantage that a heat–salt system can be studied without undesired heat loss from the boundaries.Several possibilities for future numerical experiments are summarized.  相似文献   
1000.
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