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   9788篇
  免费   1097篇
  国内免费   3600篇
测绘学   502篇
大气科学   1712篇
地球物理   3281篇
地质学   5712篇
海洋学   997篇
天文学   376篇
综合类   776篇
自然地理   1129篇
  2024年   69篇
  2023年   178篇
  2022年   118篇
  2021年   210篇
  2020年   132篇
  2019年   133篇
  2018年   193篇
  2017年   70篇
  2016年   151篇
  2015年   154篇
  2014年   269篇
  2013年   262篇
  2012年   303篇
  2011年   346篇
  2010年   243篇
  2009年   314篇
  2008年   303篇
  2007年   428篇
  2006年   473篇
  2005年   536篇
  2004年   538篇
  2003年   375篇
  2002年   466篇
  2001年   489篇
  2000年   509篇
  1999年   255篇
  1998年   191篇
  1997年   211篇
  1996年   198篇
  1995年   224篇
  1994年   198篇
  1993年   406篇
  1992年   347篇
  1991年   452篇
  1990年   410篇
  1989年   426篇
  1988年   458篇
  1987年   384篇
  1986年   264篇
  1985年   366篇
  1984年   300篇
  1983年   228篇
  1982年   176篇
  1981年   131篇
  1980年   185篇
  1964年   93篇
  1960年   57篇
  1959年   125篇
  1958年   127篇
  1957年   135篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
1 IntroductionIt is well known that interaction between the trop-ical ocean and atmosphere produces the largest inter-annual climate signal, El Nino-Southern Oscillation(ENSO). In past decades many efforts have been madein understanding and predicting ENSO: such as the hy-pothesis of Bjerknes (1969) that ENSO arises as aself-sustained cycle in which SSTA in the Pacific O-cean causes the trade winds to strengthen or slackenand that this in turn drives the ocean circulation changesthat …  相似文献   
43.
亚得里亚海沉积有机质的来源J.Faganeli等海洋沉积物是大多数浮游植物在海洋透光带产生的下沉有机质的最终归宿。海洋沉积物中有机质的堆积速率与深海初始生产力和沉积速率有关。控制沉积有机质保存的因素复杂,目前还没有完全了解。然而,在成岩作用早期,海洋...  相似文献   
44.
制图学教育在俄罗斯高等综合大学已有65年的历史(1929~1994),早在1929年制图专业就已在莫斯科大学地理系创建。当今在俄罗斯培养高技能制图员的综合大学有莫斯科大学、圣彼得堡大学、伊尔库茨克大学、伊热夫斯克大学、萨兰斯克大学、特维尔大学以及最近(1994年)刚刚获得工程技术综合大学地位的老牌国家测量制图高等学校——莫斯科测绘学院。  相似文献   
45.
1955年11月,苏联科学院海洋研究所考察船“勇士号”在其第二十二航次从太平洋返航途中,曾穿过中国东海的北部,航向由琉球群岛的吐噶喇海峡指向济州岛,然后穿过日本海的朝鲜海峡。在此航程中设了十二个海洋观测站,在这些站上,除了其他的观测外,还获得了底部沉积物和底栖动物区系的资料。  相似文献   
46.
The method developed by Wen et al. (1988 a) for deriving theoretical wind wave frequency spectrum in deep water is extended to the case of water of finite depth, in which a parameter η=H/d is introduced, where H and d represent the average wave height and water depth respectively. The derived spectra reduce to those in deep water when η=0. The case of η=1/2 corresponds to waves impending to break because of the effect of the bottom. Simplified forms of spectra are given. The theoretical results agree with the observed spectra well.  相似文献   
47.
A computer analysis was performed on experimental results obtained when mine tailings were added to seawater. The Mixed Upper-Layer Ecotrophie Simulation (MULES) model was tested by changing the extinction coefficient and the abundance of heterotrophic zooflagellates. Increasing the extinction coefficient resulted in a delay of phytoplankton growth, an increase in zooplankton standing stock and better growth of autotrophic flagellates compared with diatoms. Zooflagellates in the ecosystem influence the growth of zooplankton; secondary production by zooplankton was markedly depressed at low levels of zooflagellates. These results are believed to be of general significance for the diagnosis of suspended sediment effects on planktonic ecosystems.  相似文献   
48.
Nowadays there are some chronic serious environmental problems, such as eutrophication, blue tide and so on, in a complicated coastal zone or a semi-enclosed bay, because the water exchanges between an inner bay and an outer sea is weak compared with the supply of contaminant. Under this situation, a method to improve the water quality by 3-dimensional small unsymmetrical structures has been proposed by Komatsu et al. In this paper, several numerical simulations of the tidal current and concentration for various arrangements of bottom roughness in a semi-enclosed model bay are carfled out with a depth-averaged 2-D numerical model. The model is solved by the hybrid finite analytic method with nonstaggered grid. And the SIMPLES algorithm with Rhie and Chow' s momentum interpolation technique is used for the simulation. The effect of Komatsu' s method for water purification is examined by numerical simulation. The result of numerical experiment indicates that it is possible to generate a new tidal residual current and to activate a tidal exchange by bottom roughness arrangement only.  相似文献   
49.
Hydrophobic contaminants, such as polycyclic aromatic hydrocarbons (PAHs) readily adsorb to organic matter. The aim of this study was to determine the importance of the quality of sedimentary organic matter for the uptake, biotransformation and toxicity of the PAH, fluoranthene (Flu), in the infaunal brittle star Amphiura filiformis. Brittle stars were exposed to a base sediment covered by a 2 cm Flu-spiked top layer (30 microg Flu/g dry wt. sed.), enriched to the same total organic carbon content with either refractory or labile organic matter. The labile carbon source was concentrated green flagellate: Tetraselmis spp. The refractory carbon source was lignin from a paper mill. Tissue concentrations of Flu both in disk and arm-fractions were determined as total Flu, parent Flu (i.e. untransformed), aqueous Flu-metabolites, polar Flu-metabolites and tissue residue Flu (i.e. unextractable). Our results showed that sediment particle ingestion is a pathway by which Flu can enter benthic food webs. Flu toxicity (measured as arm-regeneration), but not net accumulation, was dependent on the nutritional quality of the ingested sediment particles. Flu bioaccumulation could not be attributed solely to equilibrium partitioning between organism lipid content and organic content of the sediment. Biotransformation of Flu by brittle stars was very limited and unaffected by organic matter quality. A. filiformis contributed to the downward transport of Flu from the surface sediment to the burrow lining. The limited breakdown of parent Flu by brittle stars and/or microorganisms was relatively higher in burrows compared to surface sediment, and highest in the presence of labile organic matter. Tissue concentrations were higher in disk than in arms, but the proportion of metabolic products relative to parent Flu was higher in arms than in the disk fraction. We estimate that the yearly mobilization of sediment-associated Flu by arm-regeneration in A. filiformis is in the range of 3.8-29.4 microg total Flu eq. m(-2) year(-1) at a sediment concentration of 30 microg Flu/g dry wt. sed.  相似文献   
50.
1984年海洋学工程的主要措施是在空间建立海洋观察站。新的海军遥控海洋测向系统卫星(NROSS)和欧洲空间站的地球资源卫星(ERS—Ⅰ)已得到政府的批准,列入了预算项目,开展了利用卫星调查内容的计划和操作运行的计划。NROSS 的传感器有用于风的 NASA(国家航空和航天局)的传播计量器;用于水面温度,冰的性质和海冰边端的微波无线  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