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   1794篇
  免费   352篇
  国内免费   399篇
测绘学   36篇
大气科学   197篇
地球物理   419篇
地质学   498篇
海洋学   1203篇
天文学   26篇
综合类   93篇
自然地理   73篇
  2024年   5篇
  2023年   25篇
  2022年   45篇
  2021年   68篇
  2020年   53篇
  2019年   68篇
  2018年   52篇
  2017年   66篇
  2016年   73篇
  2015年   74篇
  2014年   110篇
  2013年   94篇
  2012年   105篇
  2011年   97篇
  2010年   101篇
  2009年   123篇
  2008年   119篇
  2007年   139篇
  2006年   110篇
  2005年   90篇
  2004年   104篇
  2003年   83篇
  2002年   95篇
  2001年   76篇
  2000年   68篇
  1999年   79篇
  1998年   65篇
  1997年   58篇
  1996年   36篇
  1995年   35篇
  1994年   47篇
  1993年   39篇
  1992年   32篇
  1991年   27篇
  1990年   16篇
  1989年   18篇
  1988年   12篇
  1987年   6篇
  1986年   2篇
  1985年   9篇
  1984年   3篇
  1983年   4篇
  1982年   7篇
  1981年   2篇
  1980年   2篇
  1979年   3篇
排序方式: 共有2545条查询结果,搜索用时 15 毫秒
41.
在连云港近岸海域计算潮流场基础上建立拉格朗日余流模型,并对连云港市两大堤建成前后的拉格朗日余流变化进行了分析,且选择有代表性的排污口进行了数值跟踪。  相似文献   
42.
43.
水槽造流系统水力计算与泵机选择   总被引:1,自引:0,他引:1  
提供一种完整的用于试验水槽造流系统的水力计算和泵机选择方法 ,可用于其他类似工程设计。  相似文献   
44.
胶州湾三维变动边界的潮流数值模拟   总被引:35,自引:3,他引:35  
基于Blumberg等(1986)的河口、陆架和海洋模式,引入变边界处理技术,建立了胶州湾三维变动边界的潮流模型,模型以σ-正交曲线坐标下三维非线性潮波方程为基本方程,引入2.5阶瑞封闭方程组,采用分裂算子法数值求解方程组,利用湍封闭方程求解垂直紊动粘滞系数,采用干湿网格方法模拟潮流漫滩过程,三维变动边界潮流模型计算结果与实测值吻合良好。  相似文献   
45.
探讨一种基于完全非线性Boussinesq方程的波浪破碎模型在沿岸流计算中的应用问题。针对控制方程中的完全非线性项对沿岸流成长过程的影响进行了深入讨论。数学模型计算结果表明,完全非线性项有使平均流局部化的作用;通过数模实验还发现,垂向高阶涡度项可以有效抑制破波区外回流;运用Visser的实验室沿岸流实测资料从沿岸流速度、波高和平均水位几方面对所提模型进行了验证,并给出了紊动参数的计算结果。  相似文献   
46.
以某25万吨矿石码头工程为例,分别进行了单流、单浪和浪流共同作用下,系泊船舶撞击力和系缆力试验。研究了不同水位、不同船舶载度、不同浪流夹角,单流、单浪和浪流共同作用时对船舶撞击力和系缆力的影响。分析了该码头工程护舷和缆绳的布置情况,为工程设计提供了依据。  相似文献   
47.
本方案采用850、700、500hPa三个层次的环境平均流场作控制点法。综合考虑这些层次上的引导气流在不同时、空域中的相对重要性。试验结果表明,其效果比单一取某层作引导为佳。且对用来预测台风的未来24小时路径是否异常具有一定的参考价值。  相似文献   
48.
This paper reports a study of the field measurements and monitoring of wastewater discharge in sea water at Bari East (Italy). A wastewater sea outfall system is an integral and fundamental part of each wastewater treatment with ultimate sink in the sea water. The design of a water treatment plant and wastewater outfall must take into account the use of the environmental water, the values of physicochemical parameters to be respected in order to safeguard the use itself and the quality of the environmental water where wastewater is issued. In the present study measurements of sea current velocity components were carried out with a VM-ADP (Vessel-Mounted Acoustic Doppler Profiler). Salinity, wind directions and velocities were assessed with, for one survey, the total faecal coliforms and other biochemical parameters. It was emphasized that the measurements necessary for monitoring cannot be concentrated in the wastewater outfall pipe zone only, but should be extended to a neighbouring area of the outfall pipe, with an extension depending on the wastewater discharge, the polluting charge and the magnitude of the sea currents and the winds typical of the zone of interest. The analyses presented in this paper confirm that the sea zones close to the wastewater outfall pipe are particularly sensitive and vulnerable. Such results must be considered in the planning of a wastewater outfall pipe.  相似文献   
49.
Over the past decades, many attempts have been made to generate useful bottom erosion models for the study of cohesive sediment movement. This study addresses some of the key questions involved in determining the functional relationship between erosion rate and bottom shear stress. Current, wave, and turbidity data were collected from a bottom mounted instrument array in a moderately energetic estuarine environment. The bottom shear stress was calculated from a wave–current interaction model. The erosion rate was derived from the observed sediment concentration using a vertical mixing model. Examination of the relationship between erosion rate and bottom stress showed that the erosion rate varied at intertidal frequency. When averaged over the tidal fluctuation, the erosion rate remained approximately constant at low stress, but increased sharply when the shear stress rose above a critical value. This suggests two-stage erosion. The bed has a layered structure, in which a thin layer of loose, high water content material overlies a more consolidated bed. The top layer of high water content material (fluff) was easily disturbed and re-suspended by tidal currents, but the consolidated bottom layer was eroded only under conditions of high shear stress.  相似文献   
50.
Japanese fisheries production in the Japan/East Sea between 1958 and 2003 increased to their peak (1.76 million tons) in the late 1980s and decreased abruptly with the collapse of Japanese sardine. Catch results for 58 fisheries and various environmental time-series data sets and community indices, including mean trophic level (MTL) and Simpson’s diversity index (DI), were used to investigate the impacts of fishing and climate changes on the structure of the fish community in the Tsushima warm current (TWC) region of the Japan/East Sea. The long-term trend in fisheries production was largely dependent on the Japanese sardine that, as a single species, contributed up to 60% of the total production in the Japanese waters of the Japan/East Sea during the late 1980s. Excluding Japanese sardine, production of the small pelagic species was higher during 1960s and 1990s but lower during 1970s and 1980s. This variation pattern generally corresponds with the trend in water temperature, warmer before early 1960s and after 1990s but colder during 1970s and 1980s. The warm-water, large predatory fishes and cold water demersal species show opposite responses to the water temperature in the TWC region, indicating the significant impact of oceanic conditions on fisheries production of the Japan/East Sea. Declines in demersal fishes and invertebrates during 1970s and 1980s suggested some impact of fishing. MTL and DI show a similar variation pattern: higher during 1960s and 1990s but lower during 1970s and 1980s. In particular, the sharp decline during the 1980s resulted from the abundant sardine catches, suggesting that dominant species have a large effect on the structure of the fish community in the Japan/East Sea. Principal component analysis for 58 time-series data sets of fisheries catches suggested that the fish community varied on inter-annual to inter-decadal scales; the abrupt changes that occurred in the mid-1970s and late 1980s seemed to correspond closely with the climatic regime shifts in the North Pacific. These results strongly suggest that the structure of the fish community in the Japan/East Sea was largely affected by climatic and oceanic regime shifts rather than by fishing. There is no evidence showing “fishing down food webs” in the Japan/East Sea. However, in addition to the impacts of abrupt shifts that occurred in the late 1980s, the large predatory and demersal fishes seem to be facing stronger fishing pressure with the collapse of the Japanese sardine.  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