全文获取类型
收费全文 | 6895篇 |
免费 | 962篇 |
国内免费 | 1127篇 |
专业分类
测绘学 | 862篇 |
大气科学 | 808篇 |
地球物理 | 1280篇 |
地质学 | 3272篇 |
海洋学 | 958篇 |
天文学 | 10篇 |
综合类 | 495篇 |
自然地理 | 1299篇 |
出版年
2024年 | 53篇 |
2023年 | 146篇 |
2022年 | 247篇 |
2021年 | 320篇 |
2020年 | 283篇 |
2019年 | 319篇 |
2018年 | 244篇 |
2017年 | 309篇 |
2016年 | 341篇 |
2015年 | 314篇 |
2014年 | 466篇 |
2013年 | 486篇 |
2012年 | 441篇 |
2011年 | 472篇 |
2010年 | 428篇 |
2009年 | 419篇 |
2008年 | 441篇 |
2007年 | 432篇 |
2006年 | 475篇 |
2005年 | 350篇 |
2004年 | 293篇 |
2003年 | 247篇 |
2002年 | 250篇 |
2001年 | 188篇 |
2000年 | 159篇 |
1999年 | 129篇 |
1998年 | 149篇 |
1997年 | 87篇 |
1996年 | 90篇 |
1995年 | 72篇 |
1994年 | 72篇 |
1993年 | 79篇 |
1992年 | 67篇 |
1991年 | 24篇 |
1990年 | 19篇 |
1989年 | 27篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有8984条查询结果,搜索用时 15 毫秒
21.
22.
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
23.
Fuzzy Optimum Model of Semi-Structural Decision for Lectotype Optimization of Offshore Platforms 总被引:8,自引:0,他引:8
In the process of concept design of offshore platforms, it is necessary to select the best from feasible alternatives through comparison and filter. The criterion set, used to evaluate and select the satisfying alternative, consists of many qualitative and quantitative factors. Therefore, the selection is a problem of multicriteria and semi- structural decision- making. Different from traditional methods in semi- structural decision- making, a new framework and methodology is presented in this paper for evaluation of offshore platform alternatives. First, the criterion set is established for the evaluation of alternatives. Next, the approach is studied to construct the relative membership degree matrix, in which both qualitative and quantitative factors are consistent with the uniform calculating standard. And then a new weight-assessing method is developed for calculation of the weights based on the relative membership degree matrix. Finally, a multi-hierarchy fuzzy optimum model is adopted to select t 相似文献
24.
I\rnooUcrIoxThe drpdric fish species cor-npositlon is an imPOrtant element 1n the study of fish ecologyand plays an important guiding role ln fishery preduction and roouLrces rnanagement. Lin(l988) and Zhang (1994 and l995) have studied the simi1drities of mpulation COtwsition ofame s1ngle species of different yea-rs including hairtail Trichuras haumee and yellDw cndertwinena cmi. But no rePOrt is available on the discridrination of the sidrildrities amongmuLlt1ple sPecies composition of… 相似文献
25.
刘文斌 《中国海洋大学学报(自然科学版)》1991,(1)
作者曾给出了模糊代数系的统一定义和一个代数系上的模糊子集是模糊子代数的充要条件。本文是以上结果的继续,给出了一个模糊子代数系是模糊理想的统一定义和充要条件,是诸文献上模糊正规子群,环的模糊理想等概念的统一和推广。 相似文献
26.
依据模糊集合理论,提出了反求水文地质参数的一种新方法,即用模糊模式识别评价计算水位与观测水位的拟合程度,依模糊ISODATA聚类法的原理建立目标函数,以相应的聚类中心作为要求的水文地质参数。 相似文献
27.
应用模糊综合评价方法对大连臭水套海域疏浚物预选倾倒区的水质状况进行了评价,得到了有益的结论。 相似文献
28.
A bottom longline fishery operated in the EEZ of New Caledonia from 1988 to 1991. Fishing focused on five seamounts with summits at depths ranging from 500 to 750 m. The target species was alfonsino, Beryx splendens. As the soundings available from marine charts were not detailed enough, the fishing masters had to make their own charts in order to set the gear in the right location. A series of 11 scientific cruises devoted to a research program on alfonsino was launched in late 1991. During the first scientific cruises, several days were spent mapping the seabed to improve the existing knowledge of the topography of three seamounts by coupling the EDO echosounder depth measurements to the GPS positions. As this procedure is slow, it is applicable to limited areas or, if a wider grid is used, to large zones to locate major structures such as ridges and seamounts. The emergence of the multibeam echosounder has greatly improved seabed mapping performance. This tool seems to fit the requirement of exploratory deep-bottom fishing particularly well, as it covers large areas while providing details of the bottom. The EM 12 was used to obtain bathymetry and imagery of the SE portion of the EEZ of New Caledonia, covering an approximate area of 70,000 km2 in two weeks. For depths ranging from 500 to 4,500 m, the results were impressive. They confirmed the known major features and provided greater topographical detail, revealing fine unknown structures. They also provided information on the type of substratum, information which might influence the fishing strategy. Finally, they made it possible to obtain an accurate estimate of the exploitable area which in turn led to new stock estimates. 相似文献
29.
30.