全文获取类型
收费全文 | 1502篇 |
免费 | 181篇 |
国内免费 | 226篇 |
专业分类
测绘学 | 342篇 |
大气科学 | 132篇 |
地球物理 | 226篇 |
地质学 | 683篇 |
海洋学 | 185篇 |
天文学 | 4篇 |
综合类 | 155篇 |
自然地理 | 182篇 |
出版年
2024年 | 3篇 |
2023年 | 12篇 |
2022年 | 21篇 |
2021年 | 34篇 |
2020年 | 34篇 |
2019年 | 38篇 |
2018年 | 36篇 |
2017年 | 30篇 |
2016年 | 55篇 |
2015年 | 49篇 |
2014年 | 79篇 |
2013年 | 109篇 |
2012年 | 79篇 |
2011年 | 93篇 |
2010年 | 98篇 |
2009年 | 93篇 |
2008年 | 105篇 |
2007年 | 109篇 |
2006年 | 132篇 |
2005年 | 94篇 |
2004年 | 77篇 |
2003年 | 55篇 |
2002年 | 64篇 |
2001年 | 48篇 |
2000年 | 41篇 |
1999年 | 41篇 |
1998年 | 43篇 |
1997年 | 28篇 |
1996年 | 27篇 |
1995年 | 27篇 |
1994年 | 20篇 |
1993年 | 30篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 10篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1976年 | 4篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1909条查询结果,搜索用时 15 毫秒
1.
This study aims at evaluating the global geoid model for a regional shoreline fitting using advanced soft computing techniques and global navigation satellite system/leveling measurements. Artificial neural networks, fuzzy logic, and least square support vector machine models are developed and used to fit the global geoid model for the north coastal Egyptian line. In addition, a novel estimation geoid model is designed and evaluated based on the latest global geoid models. The results of the three estimation models show that they can be used to correct the shoreline geoid model, in terms of root mean square error that ranges from 1.7 to 8.5?cm. Moreover, it is found that the least square vector machine model is a competitive approach with certain advantage in solving complex problems represented by missing data. 相似文献
2.
3.
4.
FUZZY COMPREHENSIVE EVALUATION OF CONTAINER TRANSPORTATION MODES ALONG THE CHANGJIANG RIVER MAIN LINE AND ITS DELTA AREA 总被引:1,自引:0,他引:1
ZHANGShi-yu XIAOHan-liang 《中国地理科学(英文版)》2003,13(3):259-261
The Changjiang River (Yangtze) is one of the fastest growth areas of container transportation in Chi-na. Rail, road and water transportation have competed against each other for container transportation in the Chang-jiang River main line and its delta area. It is of significance to assess these different transportation modes scientifi-cally in order to organize container transportation efficiently in this area and make decision for integral plan and construction of transportation system in this area. This paper outlines application of fuzzy comprehensive evaluation to appraise different modes of typical direction of containers. Twelve assessment indexes were decided. Membership functions were formulated. Evaluation results indicated that road transportation was optimal mode in the Changjiang River delta area, however water transportation was the primary way in the Changjiang River main line. 相似文献
5.
介绍了模糊控制中的设计思想及方法,并采用模糊控制的方法来改进实际生产中PID控制的一些控制难点。将改进方法应用在一大型水压机控制系统中并在实际生产中取得了理想效果。 相似文献
6.
L. I. Chetverikov 《Mathematical Geology》1991,23(1):33-40
This paper considers the present state of mathematical geology. Three directions are recognized: applied, theoretical, and mathematical. Applied mathematical geology includes formal use of mathematics to solve problems and computer processing of data. Success is achieved by a correspondence of mathematical methods used to the nature of geological data. This correspondence can be demonstrated by purely mathematical means. Theoretical mathematical geology uses mathematics as a language of geology; however, a number of methodological problems must be solved: formalization of initial geological concepts and creation of a strict conceptual basis, substantiation of initial principles of mathematical simulation, creation of theoretical geological models, problems of elementary and coincidence in geology, and methodological substantiations of possibilities of any mathematical model to approximate geological models. The essense and significance of these problems are considered. The main task of mathematical geology is to prove its correspondence to the nature of the geological objects studied, geological data obtained, and geological problems solvable. Finally, the main problems of mathematical geology are not so much mathematical as geological and methodological. 相似文献
7.
1 .IntroductionAshiptravelingatseaundergoesundesirablewave inducedmotions ,namely ,surge ,sway ,heav ing ,rolling ,pitchingandyaw .Thesemotionsoftencauseproblemstothecrew ,theonboardequip mentand ,intheworstcase ,thesafetyofthevessel.Tominimizethewave inducedshipmotions ,controlsystemsmaybeapplied .Theaccuratemodelingofshipmotionsisthereforeveryimportantforshipdesignanddesignofmotioncontrolsystems .Manyresearchershavedevelopedshipmotionpredictionmethodsbasedonthepotentialflowtheo ries (Dong ,… 相似文献
8.
1 .IntroductionTheBohaiGulfisinfestedbyiceinthewholewinter,andoffshorestructuresthereexperiencenotonlywind ,waves ,currentsandearthquake ,butalsoiceloadswhicharecomplicatedbecauseofthedynamicinteractionbetweenicesheetsandstructures.Duanetal.( 2 0 0 0 )hadacomprehensivere viewofthelatestadvancesonice inducedvibration ,fatigueandfractureofoffshorestructures ,payingmuchattentiontothedifferencesinicebreakingmodeanddynamicsofstructuresindifferentice in festedwaters .Theypresentedcriticallythelates… 相似文献
9.
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
10.
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