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   3122篇
  免费   386篇
  国内免费   520篇
测绘学   325篇
大气科学   340篇
地球物理   734篇
地质学   1510篇
海洋学   341篇
天文学   315篇
综合类   174篇
自然地理   289篇
  2024年   9篇
  2023年   50篇
  2022年   149篇
  2021年   152篇
  2020年   143篇
  2019年   135篇
  2018年   162篇
  2017年   123篇
  2016年   177篇
  2015年   150篇
  2014年   169篇
  2013年   176篇
  2012年   157篇
  2011年   199篇
  2010年   199篇
  2009年   179篇
  2008年   158篇
  2007年   152篇
  2006年   142篇
  2005年   105篇
  2004年   93篇
  2003年   79篇
  2002年   94篇
  2001年   75篇
  2000年   86篇
  1999年   88篇
  1998年   75篇
  1997年   60篇
  1996年   50篇
  1995年   53篇
  1994年   62篇
  1993年   45篇
  1992年   34篇
  1991年   22篇
  1990年   22篇
  1989年   12篇
  1988年   8篇
  1987年   24篇
  1986年   17篇
  1985年   12篇
  1984年   14篇
  1983年   11篇
  1982年   21篇
  1981年   14篇
  1980年   15篇
  1979年   8篇
  1978年   7篇
  1976年   9篇
  1974年   3篇
  1973年   6篇
排序方式: 共有4028条查询结果,搜索用时 31 毫秒
21.
Deep towed side-scan sonar vehicles such as TOBI acquire high quality imagery of the seafloor with very high spatial resolution but poor locational accuracy. Fusion of the side-scan sonar data with bathymetry data from an independent source is often desirable to reduce ambiguity in geological interpretations, to aid in slant-range correction and to enhance seafloor representation. The main obstacle to fusion is accurate registration of the two datasets.The application of hierarchical chamfer matching to the registration of TOBI side-scan sonar images and multi-beam swath bathymetry is described. This matches low level features such as edges in the TOBI image, with corresponding features in a synthetic TOBI image created by simulating the flight of the TOBI vehicle through the bathymetry. The method is completely automatic, relatively fast and robust, and much easier than manual registration. It allows accurate positioning of the TOBI vehicle, enhancing its usefulness as a research tool. The method is illustrated by automatic registration of TOBI and multi-beam bathymetry data from the Mid-Atlantic Ridge.  相似文献   
22.
The transfer of liquid bulk through flexible transfer lines can be accomplished despite relatively large ship motions. For this reason, open sea berth terminals have replaced conventional harbors in many places. The thorough understanding of moored ships dynamics when subjected to waves, wind and currents, combined with the use of flexible dolphins, flexible fenders, asymmetric constant-tension winches and nylon tails permit us to design open sea berth terminals for relatively exposed areas. The design of an integrated system of marine sensors to continuously monitor all the critical elements-ship motion and mooring and fender forces-will enhance the operational procedure whilst insuring safe operations. A berth code can then be established for insuring the maximum efficiency of the terminal on the basis of the measurement of these critical elements.  相似文献   
23.
东海黑潮及琉球群岛以东海流研究进展   总被引:4,自引:0,他引:4  
东海是西太平洋的一个边缘海,它西部有广阔的大陆架,东面以九州岛、琉球群岛(由奄美诸岛、冲绳诸岛、先岛诸岛组成)和台湾岛连线为界,具有较深的海槽。黑潮是一支高温、高盐、高流速的西边界流,它起源于菲律宾以东海域、流经台湾东岸进入东海,沿东海大陆架外缘向东北向流动,穿越吐噶喇海峡返回太平洋。通常的把自台湾东北端起至吐噶喇海峡一段称为东海黑潮。此外,在琉球群岛以东海域也常年存在一支稳定的西边界流,称为琉球海流。 对于东海黑潮和琉球海流的硏究,主要起步于20世纪80年代,通过进行中日联合调查研究、中日副热带环流调查研究等,取得了许多重要成果,苏纪兰(1994)、袁耀初(2000,Yuan,2006)、管秉贤(2002)等人都做过评述。本文基于以上研究评述,主要叙述200年以来对东海黑潮及琉球海流的硏究新进展。  相似文献   
24.
立足样品测试数据,利用空间分析、空间插值、地质统计以及景观生态学方法,深入分析了深圳大鹏湾表层沉积物碎屑矿物的空间分布特征,并使用球状模型对相应半变异函数进行理论建模。结果表明,碎屑矿物分布的Hurst分维数为0.28~0.97,空间几何分维数为1.03~1.72;Moran Ⅰ型空间自相关系数-0.15~0.53。在此基础上,以等值线分布所包围范围作为划分尺度,以Shannon-Wiener信息指数作为度量,得到的矿物分布所反映出的信息量或者富集程度指数为0.88~1.85。  相似文献   
25.
本文介绍了一种数字测深仪的接收机的具体设计,其特点是低噪声、增益程序控制,可以输出高质量的回波信号。稍加调整,即可用作其它声纳的接收机。  相似文献   
26.
27.
The objective in this experimental work is to evaluate the capability of several cylindrical buoys to follow and measure waves. Eleven configurations have been studied, eight among which were furnished with disks of different diameters at the waterline. The experiments took place in the test basin at ISITV. On the one hand, we have obtained a set of transfer coefficients for each frequency and each configuration in regular waves. On the other hand, we have determined the corresponding transfer functions, then we have used the latter to measure irregular waves. The time signals as measured by the buoys with and without corrections have been compared with wave gage measurements and subjected to a wave-by-wave analysis. The results allow the conclusion that the buoy with a medium size disk constitutes the best compromise. In fact, it permits the buoy to follow the free surface while minimizing parasitic motions.  相似文献   
28.
29.
The use of diving animals as autonomous vectors of oceanographic instruments is rapidly increasing, because this approach yields cost-efficient new information and can be used in previously poorly sampled areas. However, methods for analyzing the collected data are still under development. In particular, difficulties may arise from the heterogeneous data distribution linked to animals’ behavior. Here we show how raw temperature data collected by penguin-borne loggers were transformed to a regular gridded dataset that provided new information on the local circulation off Kerguelen. A total of 16 king penguins (Aptenodytes patagonicus) were equipped with satellite-positioning transmitters and with temperature–time–depth recorders (TTDRs) to record dive depth and sea temperature. The penguins’ foraging trips recorded during five summers ranged from 140 to 600 km from the colony and 11,000 dives >100 m were recorded. Temperature measurements recorded during diving were used to produce detailed 3D temperature fields of the area (0–200 m). The data treatment included dive location, determination of the vertical profile for each dive, averaging and gridding of those profiles onto 0.1°×0.1° cells, and optimal interpolation in both the horizontal and vertical using an objective analysis. Horizontal fields of temperature at the surface and 100 m are presented, as well as a vertical section along the main foraging direction of the penguins. Compared to conventional temperature databases (Levitus World Ocean Atlas and historical stations available in the area), the 3D temperature fields collected from penguins are extremely finely resolved, by one order finer. Although TTDRs were less accurate than conventional instruments, such a high spatial resolution of penguin-derived data provided unprecedented detailed information on the upper level circulation pattern east of Kerguelen, as well as the iron-enrichment mechanism leading to a high primary production over the Kerguelen Plateau.  相似文献   
30.
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