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   67536篇
  免费   1133篇
  国内免费   646篇
测绘学   2010篇
大气科学   4922篇
地球物理   13281篇
地质学   23676篇
海洋学   5842篇
天文学   15632篇
综合类   203篇
自然地理   3749篇
  2021年   626篇
  2020年   624篇
  2019年   727篇
  2018年   1601篇
  2017年   1475篇
  2016年   1950篇
  2015年   1103篇
  2014年   1800篇
  2013年   3468篇
  2012年   1978篇
  2011年   2661篇
  2010年   2338篇
  2009年   3056篇
  2008年   2602篇
  2007年   2632篇
  2006年   2529篇
  2005年   2065篇
  2004年   1970篇
  2003年   1949篇
  2002年   1856篇
  2001年   1646篇
  2000年   1589篇
  1999年   1364篇
  1998年   1330篇
  1997年   1326篇
  1996年   1143篇
  1995年   1096篇
  1994年   1035篇
  1993年   931篇
  1992年   847篇
  1991年   842篇
  1990年   848篇
  1989年   819篇
  1988年   769篇
  1987年   904篇
  1986年   798篇
  1985年   987篇
  1984年   1044篇
  1983年   988篇
  1982年   907篇
  1981年   882篇
  1980年   785篇
  1979年   724篇
  1978年   693篇
  1977年   694篇
  1976年   612篇
  1975年   593篇
  1974年   621篇
  1973年   657篇
  1972年   384篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The riverine mud that escapes retention in the estuaries and enters the Gulf of Papua appears to be transported southeastward, across depth contours, by the prevailing currents in a series of wind-driven events. The mud deposits to the southeast of the rivers, at the mid-shelf region within a depth range of 40–60 m. Mud transported farther eastward is carried down the continental rise. Coarser riverine sediment (silt and sand) is deposited closer inshore. On the outer shelf (depth >60 m) relict carbonate debris dominates. The area of mud has maximum rates of pelagic and benthic productivity in the gulf.  相似文献   
942.
943.
We report the results of petrological, geochemical and rock magnetic studies of basalt dredged from the eastern end of the west Sheba Ridge during cruise 11/1979 of R. R. S. Shackleton to the Western Gulf of Aden. The ridge is part of the Red Sea-Gulf of Aden spreading axis and the basalts are olivine tholeiites. The abundances of some elements are characteristic of normal MORB (mid-ocean ridge basalt) but other elemental abundances suggest affinites with transitional-type MORB.The observed magnetic properties are interpreted in terms of the composition, concentration and microstructure of the magnetic mineral fraction by recourse to the available data on synthetic analogues. The analysis has been carried out in greater detail than has been attempted in previous magneto-petrological studies. It appears that submarine weathering of the magnetic minerals (maghemitization) brings about not only the expected change in composition but also a fall in concentration of the magnetic fraction. This could result from the removal-of-iron oxidation mechanism operating in the submarine environment. It is also found that the fall in remanence with increasing degree of maghemitization is not explicable in terms of the change in composition and concentration of the magnetic minerals. A further influence—probably microstructural change—significantly reduces the remanence intensity.  相似文献   
944.
945.
Water surface profiles and horizontal and vertical water particle velocity components have been measured to investigate the properties of intermediate depth waves generated in the laboratory. The data has been compared with linear wave theory. It was found that linear theory predicted the attenuation of velocity field with depth successfully and that it overestimates both components of velocity slightly.  相似文献   
946.
947.
The average corrected heat flow in the Wilmington Canyon region, an area of inferred slope instability, is 35 ± 10 mW/m2. This average heat flow is marginally consistent with the 46 ± 9 mW/m2 measured at other North Atlantic sites over 160 m.y. old. High topographic relief causes most of the variability in surface heat flow and may lower the mean surface heat flow. There is no significant difference between the average corrected heat flow of 35 ± 10 mW/m2 in sediment slide areas and the average corrected heat flow of 34 ± 10 mW/m2 in undisturbed sediments.  相似文献   
948.
Abstract. Survival and behaviour of the hermatypic coral Diploria strigosa was studied during 6–24 h doses with water-accomodated fractions of chemically dispersed crude oil, and for a subsequent recovery period of 1 month. Experiments utilized a flow-through laboratory dosing procedure and incorporated petroleum hydrocarbon measurements in order to simulate a major but short-term oil spill in shallow subtidal benthic reef environments. Chemically dispersed oil treatments consisted of Arabian Light Crude oil with Corexit 9527 or BP1100WD at 1–20 ppm concentrations of oil.
In general, effects observed were sub-lethal, temporary, and associated with the highest concentrations tested. Responses to the presence of dispersed oil at 20ppm for 24 h included mesenterial filament extrusion, extreme tissue contraction, tentacle retraction and localized tissue rupture. The nature and severity of reactions during the dosing phase varied between colonies and treatments, but colonies typically resumed normal behaviour within 2 h to 4 d of the recovery period. It therefore seems unlikely that observed biological effects would impair long-term viability.  相似文献   
949.
950.
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