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   201篇
  免费   6篇
  国内免费   24篇
测绘学   3篇
大气科学   9篇
地球物理   132篇
地质学   56篇
海洋学   15篇
天文学   7篇
综合类   4篇
自然地理   5篇
  2023年   2篇
  2021年   1篇
  2020年   4篇
  2019年   11篇
  2018年   7篇
  2015年   2篇
  2014年   4篇
  2013年   6篇
  2012年   18篇
  2011年   28篇
  2010年   3篇
  2009年   1篇
  2008年   17篇
  2007年   7篇
  2006年   4篇
  2005年   14篇
  2004年   12篇
  2003年   10篇
  2002年   12篇
  2001年   6篇
  2000年   11篇
  1999年   4篇
  1998年   10篇
  1997年   3篇
  1996年   4篇
  1995年   4篇
  1994年   5篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1990年   6篇
  1988年   3篇
  1983年   1篇
  1978年   2篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
排序方式: 共有231条查询结果,搜索用时 15 毫秒
11.
Sanya Bay encompasses a high diversity of natural habitats, ranging from coral reefs, rocky and sandy shores and mudflats to mangroves. Seasonal physicochemical and biological investigations were conducted from 1998 to 1999 and again in April 2000. Water-related environmental quality in Sanya Bay is in good condition. The levels of dissolved oxygen, nitrogen, phosphorus and heavy metals are within the first class of National Seawater Quality Standards for China. Annual mean values of chlorophyll a of 0.93 mg m(-3) and phytoplankton primary productivity of 440.8 mgC m(-2)d(-1), respectively, were found in the waters, both of which show a significant correlation with inorganic nitrogen. A mean new productivity of 144.6 mgC m(-2) d(-1) was recorded in summer. Sanya Bay is rich in natural resources and biodiversity with 235 species of phytoplankton and 129 species of zooplankton identified in the survey. The annual mean abundance of phytoplankton and zooplankton were 1564 x 10 cells m(-3) and 121 individuals m(-3), respectively, with an annual mean zooplankton biomass of 129 mg m(-3). A total of 243 species of fish were sampled in the survey including many of high economic value. Three hundred and eighty-four species of benthos in 121 families were found by mud sampling and trawling. The average biomass of benthic organisms was 11.55 gm(-2), with a density of 31 individuals m(-2). Molluscs were the dominant group, followed by crustaceans; coelenterates exhibited the lowest biomass. One hundred and twenty-six species from 48 families of intertidal organisms were collected by frame sampling, with a mean annual biomass of 644.7 gm(-2) and average density of 816 individuals m(-2). The highest biomass of 1673.5 gm(-2) was collected in a coral reef region, while the highest density of 1219 individuals m(-2) occurred in a mangrove region. The coastline is characterized by coral reefs that accounts for 30% of the total coastline length in the bay, so coral reefs are a key ecosystem that are important for maintaining the regional marine resources and biodiversity. We need to pay much more attention to such diverse marine resources to maintain the integrity and function of these coastal ecosystems.  相似文献   
12.
It is of major scientific interests to determine the parameters of momentum, heat and vapor exchange in the planetary boundary layer in order to study the effects of ocean-ice-atmosphere interactions and their feedback mechanisms on global climate[1]. Lin…  相似文献   
13.
Peng X  Zhang G  Mai B  Min Y  Wang Z 《Marine pollution bulletin》2002,45(1-12):295-299
Bottom sediments and a 210Pb dated sedimentary core in Macao Estuary were quantitatively analyzed with GC-MS for coprostanol and other sterols. Higher coprostanol concentrations were detected at Port Interior and Lower Qianshan River, indicative of serious sewage pollution from densely populated Macao Island and Zhuhai City. However, very low concentrations of coprostanol were detected around Coloane Island as well as Port Exterior and Maliuzhou River except sites adjacent sewage outlets. Coprostanol pollution in Macao Estuary originates mainly from locally direct discharge of untreated wastewater. The concentrations of coprostanol in ZJ-9 were mainly in range of 150–280 ng/g with an average of 210 ng/g for more than 20 years from early 1970s to early 1990s. However, it increased obviously since 1993, and reached the highest in 1995–1996. However, a sharp decrease of coprostanol concentration from 470 to 31 ng/g after 1996 was observed corresponding to the first wastewater treatment plant in Taipa Island going into action.  相似文献   
14.
Chen X  Shu L 《Ground water》2002,40(3):284-290
Numerical modeling techniques were used to simulate stream-aquifer interactions from seasonal ground water pumping. We used stream-aquifer models in which a shallow stream penetrates the top of an aquifer that discharges ground water to the stream as base flow. Because of the pumping, the volume of base flow discharged to the stream was reduced, and as the pumping continued, infiltration from the stream to the aquifer was induced. Both base-flow reduction and stream infiltration contributed to total stream depletion. We analyzed the depletion rates and volumes of the reduced base flow and induced stream infiltration during pumping and postpumping periods. Our results suggested that for a shallow penetrating stream with a low streambed conductance, base-flow reduction accounts for a significant percentage of the total stream depletion. Its residual effects in postpumping can last very long and may continue into the next pumping season for areas where recharge is nominal. In contrast, the contribution of the induced stream infiltration to the total stream depletion is much smaller, and its effects often become negligible shortly after pumping was stopped. For areas where surface recharge replenishes the aquifer, the residual effects of base-flow reduction and thus its depletion volume will be significantly reduced. A stream of large conductance has a high hydraulic connection to the aquifer, but the relationship between stream conductance and stream depletion is not linear.  相似文献   
15.
We compared total mercury (THg) concentrations in the fur of northern fur seals (Callorhinus ursinus) from the depleted Pribilof Islands population with those of both declining and thriving populations of Steller sea lions (Eumetopias jubatus) from Prince William Sound (PWS) and Southeast Alaska (SEA), respectively. Relatively low wet weight concentrations (ranges) of THg were detected in the fur of Steller sea lion (SSL) pups (0.90-3.14 microg/g) and juveniles (0.56-6.75 microg/g) from both areas in 1998 and 2000 compared to northern fur seal (NFS) pups (3.15-8.14 microg/g) in 2000. The mean concentration +/- SD for SSLs sampled were 1.46 +/- 0.64 microg/g for pups (n = 22) and 2.74 +/- 2.89 microg/g for juveniles (n = 6). Analyses indicated higher THg concentrations from SSL pups from PWS compared to the SEA. Mean +/- SD. THg in the NFS pups was 4.90 +/- 1.42 microg/g (n = 34) and for post-partum dams was 7.84 +/- 1.78 microg/g (n = 12).  相似文献   
16.
EVOLUTION OF ORE-FORMING FLUIDS AND Ag-Cu POLYMETAL MINERALIZATION IN THE LANPING BASIN, YUNNAN“KeyProjectforResourcesandEconomics” (95 0 2 0 0 1 0 1)oftheMinistryofLandResources  相似文献   
17.
引言在我国及国外进行的实地及室验室研究证明了在地震破裂前的阶段形变场内存在异常变化〔1,2〕。但预报地震的现状离最终达到的目标还很遥远。从经常在震后回顾性分析中识别出前兆异常过渡到震前依据观测到的异常变化实施真实的地震预报是存在许多困难的。原因是对解题计算法的研究很薄弱,并缺乏可以判断某种预报计算法效能的准则。因此,为了客观评价前兆效应的信息量、揭示最稳定的证明地震孕育的标志、研究在各种观测条件下前兆的时空特征并编制预报计算法,就需要加工处理多年的动态观测资料,这已成为当前用形变方法预报地震的迫…  相似文献   
18.
森林冠层上下湍流谱结构和耗散率   总被引:3,自引:1,他引:2  
利用新型三维超声风速 /温度仪 ,根据在长白山原始森林冠层上下两个高度上测量的湍流资料 ,采用涡动相关法计算和分析了森林冠层上下湍流谱的结构、局地各向同性和耗散率 .结果表明 ,在惯性副区 ,归一化湍流谱遵从 - 23的指数规律 ;在森林冠层上 ,尽管谱的形状与均匀表面的一致 ,但是 ,大气湍流是非各向同性的 ;而在森林冠层内则是近似各向同性的 ;森林冠层上下湍流能量和热量耗散率比典型草原和牧场的结果大 ,揭示了森林粗糙表面在湍流输送过程中的动力扰动和对大涡的破碎作用  相似文献   
19.
黄金开采和勘探发展的世界趋势   总被引:1,自引:0,他引:1  
X.  BB 刘连登 《世界地质》1998,17(3):36-38,40
  相似文献   
20.
索伦石的晶体结构   总被引:1,自引:0,他引:1       下载免费PDF全文
索伦石是1961年在我国发现的一种新矿物。成分为CaO·SiO2·H2O,是人工和天然的含水硅酸钙矿物中CaO∶SiO2∶H2O=1:1:1的唯一一种矿物,因此索伦石结构的测定对了解这一类矿物的晶体化学当有助益。  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