全文获取类型
收费全文 | 3452篇 |
免费 | 478篇 |
国内免费 | 568篇 |
专业分类
测绘学 | 525篇 |
大气科学 | 300篇 |
地球物理 | 626篇 |
地质学 | 1646篇 |
海洋学 | 489篇 |
天文学 | 215篇 |
综合类 | 238篇 |
自然地理 | 459篇 |
出版年
2024年 | 10篇 |
2023年 | 48篇 |
2022年 | 127篇 |
2021年 | 152篇 |
2020年 | 155篇 |
2019年 | 146篇 |
2018年 | 142篇 |
2017年 | 133篇 |
2016年 | 182篇 |
2015年 | 153篇 |
2014年 | 167篇 |
2013年 | 189篇 |
2012年 | 180篇 |
2011年 | 199篇 |
2010年 | 244篇 |
2009年 | 192篇 |
2008年 | 194篇 |
2007年 | 157篇 |
2006年 | 175篇 |
2005年 | 127篇 |
2004年 | 146篇 |
2003年 | 177篇 |
2002年 | 301篇 |
2001年 | 243篇 |
2000年 | 138篇 |
1999年 | 63篇 |
1998年 | 41篇 |
1997年 | 29篇 |
1996年 | 23篇 |
1995年 | 21篇 |
1994年 | 21篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 23篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 20篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1976年 | 10篇 |
1974年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有4498条查询结果,搜索用时 15 毫秒
21.
利用邻域度给出了1种由fuzzy拓扑产生smooth拓扑的方法;利用smooth拓扑的自身结构给出了smooth拓扑产生fuzzy拓扑的方法,讨论了它们在映射间的联系并引入了强smooth拓扑并获得了一些重要结果. 相似文献
22.
23.
The spectral methods and ice-induced fatigue analysis are discussed based on Miner's linear cumulative fatigue hypothesis and S-N curve data.According to the long-term data of full-scale tests on the platforms in the Bohai Sea,the ice force spectrum of conical structures and the fatigue environmental model are established.Moreover,the finite element model of JZ20-2MSW platform,an example of ice-induced fatigue analysis,is built with ANSYS software.The mode analysis and dynamic analysis in frequency domain under all kinds of ice fatigue work conditions are carried on,and the fatigue life of the structure is estimated in detail.The methods in this paper can be helpful in ice-induced fatigue analysis of ice-resistant platforms. 相似文献
24.
水动力作用下管道稳定性的试验研究 总被引:2,自引:2,他引:2
利用振荡流水槽在以下两种约束条件下,研究波浪作用下直接铺设于砂质海底的管道失稳临界条件:1)管道两端自由;2)管道可水平、垂直自由运动,但流动受到限制。试验结果表明,管重无量纳数G与管道失稳的临界Fr数之间大致呈线性关系,而当G超过一定数值时,管道是侧向稳定的。管道的约束条件、砂床特性和加载速度对管道稳定性均有影响。 相似文献
25.
Automatic Registration of TOBI Side-Scan Sonar and Multi-Beam Bathymetry Images for Improved Data Fusion 总被引:1,自引:0,他引:1
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
26.
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
27.
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
28.
29.
30.
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