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   6145篇
  免费   789篇
  国内免费   890篇
测绘学   1069篇
大气科学   763篇
地球物理   1159篇
地质学   2215篇
海洋学   1081篇
天文学   52篇
综合类   444篇
自然地理   1041篇
  2024年   38篇
  2023年   97篇
  2022年   177篇
  2021年   251篇
  2020年   249篇
  2019年   305篇
  2018年   199篇
  2017年   311篇
  2016年   301篇
  2015年   302篇
  2014年   465篇
  2013年   455篇
  2012年   446篇
  2011年   434篇
  2010年   362篇
  2009年   363篇
  2008年   388篇
  2007年   403篇
  2006年   390篇
  2005年   303篇
  2004年   248篇
  2003年   210篇
  2002年   227篇
  2001年   134篇
  2000年   138篇
  1999年   113篇
  1998年   111篇
  1997年   61篇
  1996年   57篇
  1995年   53篇
  1994年   59篇
  1993年   48篇
  1992年   49篇
  1991年   16篇
  1990年   14篇
  1989年   6篇
  1988年   10篇
  1987年   7篇
  1986年   8篇
  1985年   6篇
  1984年   3篇
  1983年   1篇
  1982年   1篇
  1978年   4篇
  1977年   1篇
排序方式: 共有7824条查询结果,搜索用时 15 毫秒
21.
22.
High resolution SeaWiFS data was used to detect red tide events that occurred in the Ariake Sound, Japan, a small embayment known as one of the most productive areas in Japan. SeaWiFS chlorophyll data clearly showed that a large red tide event, which damaged seaweed (Nori) cultures, started early in December 2000 in Isahaya Bay, expanded to the whole sound and persisted to the end of February 2001. The monthly average of SeaWiFS data from May 1998 to December 2001 indicated that the chlorophyll peaks appeared twice a year, in early summer and in fall, after the peaks of rain and river discharge. The SeaWiFS data showed that the red tide event during 2000–2001 winter was part of the fall bloom; however, it started later and continued significantly longer than other years. Satellite ocean color data is useful to detect the red tide; however the algorithms require improvement to accurately estimate chlorophyll in highly turbid water and in red tide areas.  相似文献   
23.
富钴结壳分布的分形特征   总被引:8,自引:0,他引:8  
利用我国在西太平洋国际海底两个海山获得的富钴结壳资料进行分形研究后发现,富钴结壳的分布具有变维分形分布的特点,结壳丰度呈二阶累计和分形分布,结壳厚度呈多阶不定累计和分形分布,通过计算得到了它们各自的分维数,进而对两个海山的结壳资源进行了初步评价。  相似文献   
24.
Stable carbon isotope ratios have been used to study the sources of particulate organic carbon (POC) and total dissolved inorganic carbon in the Orinoco Basin. The isotopic composition of total dissolved inorganic carbon shows a range of from -8·1 to -23·0 ppt, an indication of dominance of biological processes. The isotopic composition of POC exhibits a range of from -24·1 to -34·6 ppt with little seasonal variation. The isotopic evidence indicates that the POC is predominantly of terrestrial origin rather than a result of in situ planktonic production. The similarity of isotopic composition of POC and coastal sediments suggests that riverine organic detritus has been transported 30-50 km offshore in a direction parallel to the Orinoco river channel.  相似文献   
25.
叙述了目前海水现场水色测量的弊端 ,指出数字化海洋水色的潜在应用价值 ;根据色度学及色度学的三原色基本理论 ,确定海洋现场水色的色度要素 ,使海洋现场水色标号统一为物理学中严格的颜色物理量。结合 1 996年渤海水域光谱反射测量 ,对渤海水域 4个典型站位的反射光谱做了水色色度分析 ,并进行了 2种测量方法的比较  相似文献   
26.
黄河利津水文站不同粒径悬浮颗粒物中有机碳含量的研究   总被引:1,自引:0,他引:1  
估算不同粒径TSS中POC的入海日通量,对黄河利津水文站悬浮颗粒物(total suspended solid,TSS)样品,采用基于stokes原理的沉降法分为Ⅴ级,对分级后的样品测其有机碳(particulate organic carbon,POC)含量和粒度组成。在此基础上,用多元线性回归法对数据进一步处理,准确得到样品中不同粒径TSS中POC的含量。研究表明,黄河口淡水端水体TSS,<8μm的粘土和极细粉砂、8~16μm的细粉砂中,POC的含量为0.600%和0.400%左右;16~32μm的中粉砂中,POC的含量不足0.200%;而32~63μm的粗粉砂和>63μm砂中POC含量仅为0.050%和0.004%左右,80%以上的POC主要集中在<16μm的TSS中,而<32μm的TSS承载了95%以上的POC。  相似文献   
27.
We present a new approach that incorporates two models to estimate the underwater light field from remote sensing of ocean color. The first employs a series of analytical, semi-analytical, and empirical algorithms to retrieve the spectrum of inherent optical properties (IOPs), including the absorption and the backscatter coefficients, from the spectrum of remote sensing reflectance. The second model computes the profile of photosynthetically available radiation E 0,PAR (z) for a vertically homogeneous water column using the information of the retrieved IOPs and the ambient optical environment. This computation is based on an improved look-up table technology that possesses high accuracy, comparable with the full solution of the radiative transfer equation, and meets the computational requirement of remote sensing application. This new approach was validated by in situ measurements and an extensive model-to-model comparison with a wide range of IOPs. We successfully mapped the compensation depth by applying this new approach to process the SeaWiFS imagery. This research suggests that E 0,PAR (z) can be obtained routinely from ocean-color data and may have significant implications for the estimation of global heat and carbon budget.  相似文献   
28.
On the basis of the data of oceanographic survey in the East China Sea in four seasons during 1997-2000 (23°30'~33°00'N, 118°30'-128°E), the variation of total biomass and diet biomass of zooplankton and their spatial-temporal distribution and relationship with the fishing ground of Engraulis japonicus are approached and analyzed. The results show that the average biomass is 65.32 mg/m3 in four seasons, autumn (86.18 mg/m3) being greater than summer (69.18 mg/m3) greater than spring (55.67 mg/m3) greater than winter (50.33 mg/m3). The average value of diet zooplankton biomass is 40.9 mg/m3. The trends of horizontal distribution both in the total biomass and the diet biomass of zooplankton are similar. The high biomass region (250-500 mg/m3) is very limited, only accounting for 1% of the investigation area. Seasonal variation of the biomass is very remarkable in the west and north parts of East China Sea coastal waters ( 29°30'N,125°E). The horizontal distribution of diet zooplankton depends on the  相似文献   
29.
YANG  Shu-qing 《中国海洋工程》2003,17(4):527-540
Following Bagnold's approach, a relationship between sediment transport and energy dissipation is developed. The major assumption made in the study is that the near bed velocity plays a dominant role in the process of sediment transport. A general relationship between energy dissipation and sediment transport is first proposed. Then the equations for total sediment transport are derived by introducing the appropriate expression of energy dissipation rate under different conditions, such as open channel flows, combination of wave and current, as well as longshore sediment transport. Within the flows investigated, the derived relationships are fairly consistent with the available data over a wide range of conditions.  相似文献   
30.
应用模糊综合评价方法对大连臭水套海域疏浚物预选倾倒区的水质状况进行了评价,得到了有益的结论。  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