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   1710篇
  免费   376篇
  国内免费   226篇
测绘学   12篇
大气科学   95篇
地球物理   401篇
地质学   524篇
海洋学   1155篇
天文学   1篇
综合类   56篇
自然地理   68篇
  2024年   10篇
  2023年   32篇
  2022年   58篇
  2021年   62篇
  2020年   64篇
  2019年   74篇
  2018年   65篇
  2017年   176篇
  2016年   85篇
  2015年   93篇
  2014年   159篇
  2013年   89篇
  2012年   81篇
  2011年   123篇
  2010年   114篇
  2009年   115篇
  2008年   119篇
  2007年   104篇
  2006年   81篇
  2005年   55篇
  2004年   46篇
  2003年   63篇
  2002年   97篇
  2001年   33篇
  2000年   35篇
  1999年   43篇
  1998年   48篇
  1997年   22篇
  1996年   27篇
  1995年   20篇
  1994年   10篇
  1993年   28篇
  1992年   9篇
  1991年   20篇
  1990年   12篇
  1989年   7篇
  1988年   6篇
  1987年   1篇
  1986年   3篇
  1985年   7篇
  1984年   6篇
  1983年   7篇
  1982年   2篇
  1978年   1篇
排序方式: 共有2312条查询结果,搜索用时 15 毫秒
961.
益生菌在水产育苗中的应用研究   总被引:3,自引:0,他引:3  
许章程 《台湾海峡》2006,25(2):279-284
本文报道在室内试验条件下,对枯草芽孢杆菌、硝化菌、乳酸杆菌和酵母菌等4种菌在对虾工厂化育苗中的应用研究结果.将4种菌按不同比例复合在一起,在凡纳滨对虾和日本对虾工厂化育苗中的应用进行实验研究,研究在0.5、1.0、2.0、3.0、4.0g/t、对照组(加药品)和对照组(不加药品)等7组不同微生物密度对凡纳滨对虾和日本对虾幼体存活、生长和变态的影响.实验结果表明在1.0、2.0g/t和3.0g/t这三组微生物密度中生存的幼体,其存活、生长及变态率较好,其次是对照组(加药品),第三是0.5g/t和4.0g/t.最差是对照组(不加药品),0.5g/t实验组,可能是菌量不足,4.0g/t实验组,可能是菌量过多造成对虾幼体存活、生长和变态的不利影响.  相似文献   
962.
Within the UK, the Department for Environment, Food and Rural Affairs (DEFRA) is one of several government departments which undertakes research in support of its policy aims. For example, DEFRA has responsibility for licensing the deposit of materials in the sea in order to protect the environment, public health and prevent interference with other uses of the sea. This includes assessment of pollutant responses in marine organisms. The objectives include assessment of the sub-lethal effect that pollutants have at the cellular, organ and individual level, for example in normal genetic, behavioural and reproductive activity and extrapolation of the potential impact of pollutants to populations. This work helps DEFRA to establish whether individually or in combination, pollutants have an adverse effect on the environment. This paper gives some examples of the research undertaken and demonstrates how biological research can provide cost effective solutions to analytical problems and an opportunity to predict the way in which proposed disposal operations may have an impact on the marine environment. The way such research may influence policy is also discussed.  相似文献   
963.
Ayman B. Mahfouz   《Ocean Engineering》2007,34(8-9):1151-1163
As the capability of polar plots becomes better understood, improved dynamic positioning (DP) systems are possible as the control algorithms greatly depend on the accuracy of the aerodynamic and hydrodynamic models. The measurements and estimation of the environmental disturbances have an important role in the optimal design and selection of a DP system for offshore platforms. The main objective of this work is to present a new method of predicting the Capability-Polar-Plots for offshore platforms using the combination of the artificial neural networks (NNs) and the capability polar plots program (CPPP). The estimated results from a case study for a scientific drilling vessel are presented. A trained artificial NN is designed in this work and is able to predict the maximum wind speed at which the DP thrusters are able to maintain the offshore platform in a station-keeping mode in the field site. This prediction for the maximum wind speed will be a helpful tool for DP operators in managing station-keeping for offshore platforms in an emergency situation where the automation of the DP systems is disabled. It is obvious from the obtained results that the developed technique has potential for the estimation of the capability-polar-plots for offshore platforms. This tool would be suitable for DP operators to predict the maximum wind speed and direction in a very short period of time.  相似文献   
964.
G. Rajasekaran   《Ocean Engineering》2006,33(3-4):517-529
An attempt has been made to investigate the microfabric and mineralogical features of marine sediments collected from the north-east coastal region of Singapore. A limited laboratory studies on shear strength, consolidation and chemical analysis were carried out to examine the geotechnical characteristics of marine sediments. Emphasis has been focussed on the microfabric aspects of microfossils (diatom) and pyrite, and their influence on the soil properties. Test results indicated the predominant presence of microfossils (diatom) and pyrite, and their impact on the marine sediments behaviour has been discussed briefly. The abundant presence of microfossils results in an increase in strength, compressibility and hydraulic conductivity due to the presence of large voids between the skeleton structures.  相似文献   
965.
5种海水鱼同工酶表达的组织特性及其电泳的初步分析   总被引:13,自引:2,他引:13  
于1994年7-12月,山东,福建省沿海采集真鲷、黑鲷、牙鲆、鲈和小黄鱼等5种黄692个生化样品,应用水平淀粉胶和垂直聚丙烯酰胺凝胶电泳方法,对5种鱼的肌肉,眼睛、心脏、鳍,鳃、肾脏共7种组织的23种同工酶进行了初步分析。  相似文献   
966.
-Six cruises were carried out off the south bank of Fujian - Taiwan during the period of December 21, 1987 to November 15, 1988 to estimate the contribution of bacterial biomass carbon (BBC) to the totai particulate organic pools using epifluorescent microscopic technique. The results show that the standing crop of bacteria fluctuated from 0. 95 to 66. 60 mg /m3 (dry weight). Upwelling phenomena appeared in the region around Nanpeng Island in summer while in the region of Waixie in all seasons. The average value of BBC was 27. 60(±6. 08)mg/m3and 21. 32 (±2. 34) mg/m3 respectively. The seasonal and spatial distribution is discussed in relation to environmental factors as well as upwelling phenomena. The role of bacteria in the flow of material and energy in the upwelling ecosystem is emphasized.  相似文献   
967.
The Patos–Mirim Lagoon system along the southern coast of Brazil is linked to the coastal ocean by a narrow mouth and by groundwater transport through a Holocene barrier. Although other groundwater systems are apparently active in this region, the hydraulic head of the lagoon, the largest in South America, drives groundwater transport to the coast. Water levels in wells placed in the barrier respond to changing water level in the lagoon. The wells also provide a measure of the nutrient concentrations of groundwater flowing toward the ocean. Additionally, temporary well points were used to obtain nutrient samples in groundwater on the beach face of the barrier. These samples revealed a subterranean freshwater–seawater mixing zone over a ca. 240 km shoreline. Previously published results of radium isotopic analyses of groundwater and of surface water from cross-shelf transects were used to estimate a water flux of submarine groundwater discharge (SGD) to nearshore surface waters of 8.5 × 107 m3/day. Using this SGD and the nutrient concentrations in different compartments, nutrient fluxes between groundwater and surface water were estimated. Fluxes were computed using both average and median reservoir (i.e. groundwater and surface water) nutrient concentrations. The SGD total dissolved inorganic nitrogen, phosphate and silicate fluxes (2.42, 0.52, 5.92 × 106 mol day− 1, respectively) may represent as much as 55% (total N) to 10% (Si) of the nutrient fluxes to the adjacent shelf environment. Assuming nitrogen limitation, SGD may be capable of supporting a production rate of ca. 3000 g C m2 year− 1in the nearshore surf zone in this region.  相似文献   
968.
古海洋、古气候研究的新工具   总被引:1,自引:1,他引:1  
“分子温度计”是通过有机地球化学方法获得的沉积物中烯酮化合物的相对丰度来估算古海水表面温度的。烯酮化合物的不饱和度(Uk37)与其生物母源Emilianiahuxleyi的生长温度密切相关,同时这种信息不受有机质溶解与成岩作用影响,而能较完整地保存于海洋沉积物中,因而通过它能很好地反映古海洋与古气候的演变。这种方法不受盐度、上升流与极地冰盖变化等因素影响,尤其适用于碳酸盐贫乏海区的古海洋与古气候研究  相似文献   
969.
海洋生态系统动力学研究与海洋生物资源可持续利用   总被引:22,自引:5,他引:22  
围绕国家重点基础研究发展规划(973)项目“东、黄海生态系统动力学与生物资源可持续利用”,介绍了海洋生态系统动力学研究对我国社会与科技发展的意义、研究现状和发展趋势、拟解决的关键科学问题以及实施计划。该项研究的最终目标是弄清我国近海海洋生态系统的结构、功能及其服务与产出,量化其动态变化及生态容纳量,预测生物资源的补充量,寻求可持续开发利用海洋生态系统的途径。使集中多种机制于一体并具陆架特色的我国近海生态系统力学理论体系和研究队伍进行国际先进行列。  相似文献   
970.
海洋二氧化碳的研究进展   总被引:20,自引:1,他引:20  
海洋是一个巨大的碳库,具有潜在的缓冲大气CO2增加的能力,研究CO2在海洋中的转移和归宿,对于预测未来大气CO2含量乃至全球气候变化具有重要意义。综述了海洋CO2的研究现状,着重介绍海洋CO2的源与汇、海—气CO2通量的估算以及海洋环流、生物泵和海洋生态在海洋碳循环中的作用,并对该研究领域的发展趋势进行了总结。  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