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   11740篇
  免费   919篇
  国内免费   811篇
测绘学   2857篇
大气科学   934篇
地球物理   1048篇
地质学   1663篇
海洋学   851篇
天文学   25篇
综合类   1021篇
自然地理   5071篇
  2024年   41篇
  2023年   105篇
  2022年   550篇
  2021年   608篇
  2020年   566篇
  2019年   657篇
  2018年   482篇
  2017年   659篇
  2016年   613篇
  2015年   625篇
  2014年   652篇
  2013年   944篇
  2012年   744篇
  2011年   718篇
  2010年   510篇
  2009年   542篇
  2008年   536篇
  2007年   610篇
  2006年   574篇
  2005年   465篇
  2004年   460篇
  2003年   337篇
  2002年   311篇
  2001年   205篇
  2000年   191篇
  1999年   130篇
  1998年   105篇
  1997年   96篇
  1996年   77篇
  1995年   53篇
  1994年   56篇
  1993年   40篇
  1992年   58篇
  1991年   18篇
  1990年   21篇
  1989年   18篇
  1988年   14篇
  1987年   13篇
  1986年   16篇
  1985年   21篇
  1984年   11篇
  1983年   6篇
  1982年   2篇
  1981年   4篇
  1980年   4篇
  1978年   1篇
  1971年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
本文主要介绍国家海洋环境预报中心网络与计算机应用的实时通信系统、实时数据处理系统、实时预报发布系统等目前实时运行的十项业务系统.  相似文献   
22.
Abstract. Boonea (= Odostomia) impressa is a common ectoparasite of oysters. In the laboratory, small oysters (Crassostrea virginica) parasitized by natural densities of B. impressa produced 75 % less new shell than unparasitized oysters. Shell deposition rates of previously parasitized oysters increased significantly after all B. impressa were removed. Thus, the decrease in growth rate, although significant, apparently was not permanent. B. impressa preferentially parasitized small, living oysters (≤2.5cm) in the field, even though a higher percentage of large, living oysters (>2.5cm) was available. The snails maintained an aggregated distribution on the oyster reef. The number of B. impressa per oyster clump was positively correlated with the number of living oysters per clump, however some clumps with few or no living oysters had many B. impressa. Thus, food availability only partially explained the pattern of distribution. B. impressa was very mobile. About 50 % of the population moved in one week. Reproduction occurred throughout the year with a peak period in May. Recruitment was greatest in July, however new recruits were observed throughout the year. The reduction in growth rate of parasitized oysters, the snaiľs propensity towards parasitizing small oysters and the snail's tendency to be contagiously distributed suggests that B. impressa potentially exerts a significant influence on the population structure and health of oyster populations.  相似文献   
23.
24.
25.
26.
Seasonal and spatial variations of iceberg drift were studied using continuous satellite scatterometer images off Dronning Maud Land, East Antarctica. Generally, iceberg drift speed showed a westward increase to the Greenwich Meridian. Seasonal variations of the drift speed were high in autumn—early winter and low in spring, and their magnitudes also increased westward. Seasonal variations of the drift speed were significantly correlated with variations of sea levels at Syowa and Mawson Stations, and hence qualitatively consistent with geostrophic current variations. Thus, the scatterometer data are demonstrated to be useful in monitoring iceberg trajectory and oceanic current variations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
27.
遥感与GIS支持下的海洋渔业空间分布研究——以东海为例   总被引:9,自引:1,他引:9  
基于海洋渔业多年来生产实践所表明的海洋渔场与海洋水文要素密切相关性,将研究区的遥感融合信息与生产数据进行GIS空间配准,同时建立了诸多要素数据的空间聚类模式,利用该模式提取了水文信息和中心渔场信息相关联的空间分布规律的隐伏信息,由此阐述了实现海洋渔业现代化,应用空间遥感融合信息和GIS支持下指导海洋渔业生产的渔情预报有着重要意义.  相似文献   
28.
29.
基于“数字海底”系统的理论基础研究和在海底科学应用中的具体实践,提出了“数字海底”的涵义、系统组成和体系结构,对空间数据管理技术、基于XML的WebGIS空间数据表达技术、复杂海底三维建模技术、多源信息的一体化集成显示技术、虚拟现实技术等“数字海底”系统建模中的关键技术进行了探讨,为从事海底资源研究和开发的人员提供各个层次的参考或帮助.  相似文献   
30.
High-resolution underway temperature and conductivity measurements collected by R/V Knorr during winter and spring 2003 are used to characterize errors associated with spatial aliasing in the northern and central Adriatic Sea. During winter, 99th percentile temperature, salinity and density errors were 0.62 °C, 0.25 and 0.12 kg/m3 (0.25 °C, 0.10 and 0.05 kg/m3) for sampling at 10 km (5 km) horizontal resolution, respectively. The corresponding values in spring were 1.31 °C, 0.50 and 0.40 kg/m3 (0.93 °C, 0.25 and 0.22 kg/m3) for the 10 km (5 km) sample spacing, respectively. The largest errors were associated with energetic regions over the shallow, western Adriatic, in front of the Po River mouth and off the tip of the Istrian peninsula. The deeper eastern basin exhibited smaller errors. The variability of errors in time and space reflected the variability of small-scale density features, characterized by wavelengths as small as 2 km in winter and 1 km in spring and being more pronounced in the western and northern parts of the Adriatic. As these results indicate that errors associated with undersampling can be considerable, they should be taken into account while planning future CTD measurements in the region.  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