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   74047篇
  免费   1492篇
  国内免费   677篇
测绘学   1799篇
大气科学   5268篇
地球物理   14801篇
地质学   26218篇
海洋学   6458篇
天文学   17007篇
综合类   223篇
自然地理   4442篇
  2022年   409篇
  2021年   708篇
  2020年   805篇
  2019年   867篇
  2018年   1943篇
  2017年   1801篇
  2016年   2298篇
  2015年   1363篇
  2014年   2243篇
  2013年   3929篇
  2012年   2357篇
  2011年   3242篇
  2010年   2728篇
  2009年   3659篇
  2008年   3388篇
  2007年   3161篇
  2006年   2980篇
  2005年   2442篇
  2004年   2347篇
  2003年   2209篇
  2002年   2009篇
  2001年   1862篇
  2000年   1800篇
  1999年   1434篇
  1998年   1529篇
  1997年   1427篇
  1996年   1139篇
  1995年   1186篇
  1994年   1012篇
  1993年   920篇
  1992年   890篇
  1991年   786篇
  1990年   889篇
  1989年   768篇
  1988年   687篇
  1987年   858篇
  1986年   696篇
  1985年   916篇
  1984年   989篇
  1983年   928篇
  1982年   884篇
  1981年   773篇
  1980年   716篇
  1979年   643篇
  1978年   640篇
  1977年   599篇
  1976年   576篇
  1975年   536篇
  1974年   531篇
  1973年   500篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
This paper describes the process of launching and joining of two sections of a product carrier of 30,500 DWT built at Dianca shipyard at Puerto Cabello, Venezuela. The specifications and characteristics of this ship are in line with the market requirements. This paper deals with the problems encountered during the decision of dividing the ship in two halves, use of syncrolift for launching and subsequent joining of two halves in the dry dock.  相似文献   
993.
Abstract. New data on the planktonic diatoms from the Gulf of Naples are presented together with those from the literature. Information is given on abundances, seasonal cycles and distributions of 183 taxa, including species, varieties and forms.  相似文献   
994.
995.
In this paper we examine the use of bathymetric sidescan sonar for automatic classification of seabed sediments. Bathymetric sidescan sonar, here implemented through a small receiver array, retains the advantage of sidescan in speed through illuminating large swaths, but also enables the data gathered to be located spatially. The spatial location allows the image intensity to be corrected for depth and insonification angle, thus improving the use of the sonar for identifying changes in seafloor sediment. In this paper we investigate automatic tools for seabed recognition, using wavelets to analyse the image of Hopvågen Bay in Norway. We use the back-propagation elimination algorithm to determine the most significant wavelet features for discrimination. We show that the features selected present good agreement with the grab sample results in the survey under study and can be used in a classifier to discriminate between different seabed sediments.  相似文献   
996.
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   
997.
998.
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   
999.
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   
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