全文获取类型
收费全文 | 4097篇 |
免费 | 648篇 |
国内免费 | 540篇 |
专业分类
测绘学 | 993篇 |
大气科学 | 243篇 |
地球物理 | 1271篇 |
地质学 | 1629篇 |
海洋学 | 564篇 |
天文学 | 47篇 |
综合类 | 272篇 |
自然地理 | 266篇 |
出版年
2024年 | 11篇 |
2023年 | 23篇 |
2022年 | 91篇 |
2021年 | 104篇 |
2020年 | 133篇 |
2019年 | 169篇 |
2018年 | 123篇 |
2017年 | 192篇 |
2016年 | 160篇 |
2015年 | 166篇 |
2014年 | 206篇 |
2013年 | 279篇 |
2012年 | 267篇 |
2011年 | 307篇 |
2010年 | 213篇 |
2009年 | 255篇 |
2008年 | 269篇 |
2007年 | 282篇 |
2006年 | 283篇 |
2005年 | 230篇 |
2004年 | 218篇 |
2003年 | 211篇 |
2002年 | 134篇 |
2001年 | 132篇 |
2000年 | 141篇 |
1999年 | 120篇 |
1998年 | 93篇 |
1997年 | 82篇 |
1996年 | 70篇 |
1995年 | 58篇 |
1994年 | 69篇 |
1993年 | 37篇 |
1992年 | 31篇 |
1991年 | 17篇 |
1990年 | 28篇 |
1989年 | 28篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 14篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有5285条查询结果,搜索用时 343 毫秒
151.
大数据技术中的一个难点是如何统筹多源异构的数据。在多源数据协同定量遥感产品生产系统中,不同传感器数据的协同使用为生产系统的各个环节都带来了许多的问题,例如异构数据文件的统一表示和调度,繁杂生产流程的统一抽象等。领域驱动设计是一种应对软件核心复杂性的设计方式。领域驱动是指在设计过程中经过不断的迭代,逐渐提炼出一套灵活优雅的领域模型。领域模型专注于分析问题领域本身,发掘重要的业务领域概念,并建立业务领域概念之间的关系。本文在不断实践的基础上提出了一组较成熟的领域模型,该模型用一种统一的方式解决了多源数据协同生产系统中各方面的问题,并显著地降低了系统集成的难度和工作量,且为新数据源的加入预留了灵活性。 相似文献
152.
Automation of the cartographic design process is central to the delivery of bespoke maps via the web. In this paper, ontological modeling is used to explicitly represent and articulate the knowledge used in this decision-making process. A use case focuses on the visualization of road traffic accident data as a way of illustrating how ontologies provide a framework by which salient and contextual information can be integrated in a meaningful manner. Such systems are in anticipation of web-based services in which the user knows what they need, but do not have the cartographic ability to get what they want. 相似文献
153.
The bus route map is a diagram that aims to convey necessary information for map readers to find an appropriate way of moving from an origin to a destination. Design of bus route map is a complicated and time-consuming task that requires careful consideration of readability and aesthetics. This paper proposes a new computational method for designing bus route maps. The method helps us to reduce six types of undesirable elements in bus route maps, i.e., gap, shift, crossing, overlap, misalignment, and acute bend. The method consists of two phases: line layout phase determines the relative order of bus routes on each road segment and map layout phase calculates the actual position of bus routes drawn on a map. This paper applies the method to the design of bus route maps of Chiba City, Japan. The result supports the effectiveness of the method as well as reveals open topics for future research. 相似文献
154.
大三江盆地群位于黑龙江省东部,中生代以来经历了多期构造运动,形成现今各自分割的10余个残余盆地。由于缺乏关键性证据,前人对大三江地区早白垩世是否存在统一湖盆存在争议。本次研究通过野外地质调查和钻井岩心观察,认为盆地总体缺乏边缘相沉积,并且主要以三角洲平原亚相和滨浅湖亚相为主。古水流恢复和重矿物特征显示,研究区主要存在西部和西北部、东部以及东南部三大物源体系,并且平面上具有由四周向中心汇聚的特征。地震资料反射特征显示下白垩统具有典型的断陷-坳陷复合结构,坳陷时期地层由各盆地中心至边部未出现明显的地层减薄现象,现今的盆地边界断裂多为后期对盆地进行改造、破坏的逆冲断裂。这些证据都是对大三江地区早白垩世存在统一湖盆的有力支撑。本研究不仅能为大三江盆地群原型盆地的恢复提供重要依据,也将为东北盆地群油气资源远景评价和进一步的勘探部署提供参考。 相似文献
155.
重点介绍了福建马坑矿区ZK8321分支孔受控定向钻进技术。施工中运用了国内先进的螺杆钻造斜技术及光纤陀螺测量定向技术,避开上部复杂孔段(松散破碎层、溶洞地层、采空区等)及对勘探工作的影响,达到了施工目的;总结了施工技术难点与措施,分析了施工技术效果,积累了宝贵的施工经验。 相似文献
156.
For subsea pipeline projects, the costs related to seabed correction and free span intervention are often considerable. Development of reliable methods for fatigue analyses of pipelines in free spans contributes to minimize costs without compromising pipeline integrity. Assessment of wave-induced fatigue damage on multi-span pipelines is investigated, and improved analysis methods are suggested in this paper. A time-domain (TD) algorithm is developed, which accounts for non-linear hydrodynamic loading and dynamic interaction between adjacent spans. The proposed TD approach is employed to evaluate linearized frequency-domain (FD) solutions from recognized design standards and to study the dynamic response of multi-span pipelines to direct wave loading. Differences between multi- and single-span analyses are described for the first time, and the common assumption that the main fatigue damage contribution comes from the fundamental mode is demonstrated not to hold for multi-spans. An improved FD solution capable of predicting multi-mode response is derived and demonstrated to give accurate fatigue life estimates for multi-span pipelines. 相似文献
157.
An industry accepted standard does not currently exist for determination of compression limits in a subsea cable. This has resulted in most manufacturers specifying that subsea cables are not permitted to be axially loaded in compression.Additionally industry guidance does not exist regarding the consequences of inducing compression forces within subsea cables and the resulting effect on cable integrity. Industry recommended practice and guidance also does not have any information regarding experimental test arrangements to determine allowable compression levels within a subsea cable. This lack of modelling/testing guidance along with manufacturer recommendations of zero compressive loads within subsea cables results in overly conservative and restrictive design parameters for subsea cable installation and use.Due to the complex interaction within a subsea cable structure, such as contact interaction and friction between cable strands, theoretical modelling has been unable to provide reliable stress predictions and therefore an experimental testing regime is required if compression limits within the cable are to be appropriately determined. This paper describes combined axial and bending test arrangements that can be used as a guideline for determination of allowable compression limits for subsea cables. 相似文献
158.
基于灵敏度分析的海洋油气资源BP神经网络预测模型的优化 总被引:2,自引:2,他引:0
作者针对BP神经网络结构设计中存在的问题,提出利用灵敏度分析方法对BP神经网络预测模型进行优化。通过BP算法与参数灵敏度分析的结合,寻找网络输入属性与输出属性之间的影响因子;在保证精度的前提下优选网络输入属性,简化网络结构,以增强网络的泛化能力,减少人为主观因素对网络设计的影响。最后以海洋油气资源预测为例,结合实测资料建立BP神经网络预测模型并进行了优化及预测精度评价,表明优化后的模型既能有效提高油气资源预测结果的稳定性,又不损失预测精度。 相似文献
159.
Increasing interest in urban livability demands that geographers and planners more precisely define what constitutes a livable streetscape, a fundamental building block of urban places. Widespread examination of streetscape livability will require precise and efficient measurements of (1) physical characteristics at the spatial scale of individual streetscapes and (2) indicators of experiential quality based on revealed behavior or stated preference. This article reviews approaches to collecting both types of measurements, showing that innovative methods using geographic information systems (GIS), Internet-enabled surveys, and even social media could be useful complements to traditional qualitative methods for collecting streetscape measurements. 相似文献
160.