全文获取类型
收费全文 | 3507篇 |
免费 | 2110篇 |
国内免费 | 831篇 |
专业分类
测绘学 | 494篇 |
大气科学 | 138篇 |
地球物理 | 370篇 |
地质学 | 3866篇 |
海洋学 | 1247篇 |
天文学 | 6篇 |
综合类 | 232篇 |
自然地理 | 95篇 |
出版年
2024年 | 43篇 |
2023年 | 103篇 |
2022年 | 210篇 |
2021年 | 283篇 |
2020年 | 271篇 |
2019年 | 310篇 |
2018年 | 237篇 |
2017年 | 292篇 |
2016年 | 306篇 |
2015年 | 298篇 |
2014年 | 374篇 |
2013年 | 332篇 |
2012年 | 371篇 |
2011年 | 356篇 |
2010年 | 257篇 |
2009年 | 269篇 |
2008年 | 260篇 |
2007年 | 231篇 |
2006年 | 186篇 |
2005年 | 169篇 |
2004年 | 151篇 |
2003年 | 135篇 |
2002年 | 132篇 |
2001年 | 131篇 |
2000年 | 104篇 |
1999年 | 112篇 |
1998年 | 94篇 |
1997年 | 73篇 |
1996年 | 87篇 |
1995年 | 46篇 |
1994年 | 63篇 |
1993年 | 41篇 |
1992年 | 39篇 |
1991年 | 27篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1972年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有6448条查询结果,搜索用时 15 毫秒
31.
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
32.
珠江口东南近海海区污损生物研究 总被引:4,自引:2,他引:4
为研究珠江口东南近海海区污损生物状况,于1986年5月至1987年6月,在香港东南约114和160km,水深为95和113m处布设了两个生物浮标站,并对距香港约172km,水深为115m处的Marex水文气象浮标上的污损生物群落进行调查.此次调查共采集和鉴定出污损生物78种,其中在浸海只有3个月的试板上,主要有柄蔓足类、水螅和藻类,优势种是细板条茗荷、茗荷和直杯螅.至于浸海时间达6~12个月的浮标(包括沉标)及锚链系统,其上还有相当数量的多种双壳类软体动物、无柄蔓足类和苔藓动物等硬性污损生物附着.在种类垂直分布方面,污损生物群落组成随深度发生明显变化. 相似文献
33.
34.
1 .IntroductionThe structural design method has evolvedfromthe workingstress method,damage stage methodtolimit state method.The more recent probabilisticlimit state design method,whichis based onreliabili-tytheory,has beengenerallyacceptedinthe designcode… 相似文献
35.
AbstractHelical piles have emerged as an attractive foundation system for offshore applications with renewed interest from the offshore community. Significant research gap currently exists in transferring this technology offshore and this paper discusses how existing and emerging knowledge can be successfully used to bridge some of the gaps. We focus on the Coupled Eulerian Lagrangian (CEL) large deformation finite element (LDFE) modelling technique that is commercially available and can be used to model the three-dimensional installation process with consideration of strain rate and softening effects in soft offshore clays. A helical pile of L?=?7.5?m long is modelled with one or two large-diameter helices (D?=?2?m) attached to a central shaft of d?=?0.5?m in diameter.The net effect of strain rate and softening is to increase the installation torque. The measured torque is within the range of 200–400?kN.m for the offshore clay and the pile geometry studied. Additional helices increase the uplift force but to a lesser degree than that of the measured torque. Remoulding induced strength reduction is found to be within the range of 25–33% of the intact clay strength. Issues of extracting and reusing offshore helical pile foundations are discussed. 相似文献
36.
在连云港近岸海域计算潮流场基础上建立拉格朗日余流模型,并对连云港市两大堤建成前后的拉格朗日余流变化进行了分析,且选择有代表性的排污口进行了数值跟踪。 相似文献
37.
LI Hongwei TAN Jiahua Ph. D. Candidate School of Naval Architecture Ocean Engineering Shanghai Jiaotong University 《中国海洋工程》1998,(4)
This paper analyzes the pipe network system of oil-gas collection and transportation foroffshore oilfield development.A"0-1"integer linear programming model is constructed to optimize theinvestment of seabed pipe network.The mathematical model is solved by the spanning tree method ofgraph theory and network analysis.All spanning trees of a network graph compose all the feasible solu-tions of the mathematical model.The optimal solution of the model is the spanning tree with the minimumcost among all spanning trees.This method can be used to optimize the seabed pipe network system andgive a minimum cost plan for the development of offshore marginal oilfield groups. 相似文献
38.
39.
Lectotype optimization of offshore platforms is of particular importance in the concept design process. Lectotype optimization involves multiple objectives with uncertainty and so is a problem of multiple attribute decision making. To date, there have been few published works on this topic in the context of offshore engineering. This paper develops a framework and methodology for evaluation of offshore platform alternatives, where a fuzzy optimum model is proposed to integrate the influence of each objective in the criteria set, and a new weight-assessing method is developed to mimic the decision maker’s experience and preference based on complementary pairwise comparisons. A case study shows that the new framework and methodology is scientific, reasonable and easy to use in practice. 相似文献
40.
中国近海的天然气勘探 总被引:1,自引:0,他引:1
据最新勘探资料,在综合分析中国近海海域天然气勘探现状、资源潜力及其区域分布规律的基础上,分析了我国近海海域天然气勘探的有利区带及目前比较现实的勘探目标,展示了我国近海海域天然气勘探的良好前景。 相似文献