全文获取类型
收费全文 | 1625篇 |
免费 | 430篇 |
国内免费 | 307篇 |
专业分类
测绘学 | 32篇 |
大气科学 | 72篇 |
地球物理 | 639篇 |
地质学 | 905篇 |
海洋学 | 305篇 |
天文学 | 41篇 |
综合类 | 49篇 |
自然地理 | 319篇 |
出版年
2024年 | 5篇 |
2023年 | 28篇 |
2022年 | 49篇 |
2021年 | 44篇 |
2020年 | 59篇 |
2019年 | 67篇 |
2018年 | 61篇 |
2017年 | 71篇 |
2016年 | 65篇 |
2015年 | 68篇 |
2014年 | 93篇 |
2013年 | 102篇 |
2012年 | 68篇 |
2011年 | 93篇 |
2010年 | 67篇 |
2009年 | 131篇 |
2008年 | 115篇 |
2007年 | 146篇 |
2006年 | 107篇 |
2005年 | 104篇 |
2004年 | 94篇 |
2003年 | 84篇 |
2002年 | 89篇 |
2001年 | 60篇 |
2000年 | 83篇 |
1999年 | 53篇 |
1998年 | 51篇 |
1997年 | 37篇 |
1996年 | 46篇 |
1995年 | 37篇 |
1994年 | 33篇 |
1993年 | 34篇 |
1992年 | 21篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有2362条查询结果,搜索用时 437 毫秒
951.
Because of their profound influence on water movement and nutrient cycling in salt marshes, the two key physical properties of hydraulic conductivity and compressibility were studied in the Great Sippewissett Marsh and in the Ebben Creek Marsh in Massachusetts. Hydraulic conductivity was the most variable property: most frequently observed conductivities were of the order of 10?3 cm s?1 in both marshes, but extremes ranged from about 10?1 to 10?5 cm s?1. Compressibility was much less variable, and contributed of the order of 10?3 cm?1 to the specific storativity of marsh sediment, making compression a major mechanism for changes in water storage in the sediment. Surface sediments frequently exhibited below-average conductivity, in contrast to freshwater bog peats which are usually most conductive at the surface. These measured properties may be applied to estimate the importance of many critical processes, such as the extent of infiltration occurring on the marsh surface, the hydrologic influence of the tidally varying creeks, and the hydrologic response to spring-neap tidal cycles. 相似文献
952.
Masanori Sakamoto Kiyoji Shiono Shinji Masumoto Kiyoshi Wadatsumi 《Natural Resources Research》1993,2(2):140-147
In this article we describe the basic framework of the computerized geologic mapping system cigma. The system, whic is based on a mathematical formulation of geologic concepts, consists of the following six subsystems: (1) input of geologic data set; (2) inference of stratigraphic sequence; (3) construction of logical models of geologic structures; (4) determination of three-dimensional geologic boundary surfaces; (5) construction of three-dimensional solid model of geologic structures; and (6) graphical presentation. Geologic structures are summarized in several tables called logical models of geologic structures. Each model is constructed automatically from input data on structural relations between geologic bodies. The model interprets the data automatically to create data files necessary to determine the shapes of geologic boundaries; it also provides a threedimensional solid model of geologic structures referring to the shapes of boundaries. As a prototype, we introduce two types of contacts corresponding to conformity and unconformity into the logical model and show that it is possible to draw a geologic map automatically. More complex geologic structures can be introduced into the geologic mapping system through further formulation of geologic structures. 相似文献
953.
阿塔卡玛盐湖的综合开发 总被引:4,自引:1,他引:3
近年来,智利阿塔卡玛盐湖的开发进展迅速。本文报道了阿塔卡玛盐湖的形成、资源、开发过程、主要技术路线、氯化钾和碳酸锂产品技术经济指标以及阿塔卡玛盐湖的开发前景。 相似文献
954.
955.
956.
Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of their response to wave loading is a minimum requirement for efficient probabilistic analysis of these structures. Due to nonlinearity of Morison wave loading and also due to intermittency of wave loading on members in the splash zone, the response is often non-Gaussian. Part I of this paper was devoted to the development and validation of a new probability model for drag-only responses (i.e. responses due to the drag component of Morison wave loading). This part is devoted to the development and validation of new probability models for both inertia-only and total responses. 相似文献
957.
958.
Risk Based Optimal Inspection and Repair Planning for Ship Structures Subjected to Corrosion Deterioration 总被引:1,自引:1,他引:1
A framework of risk based inspection and repair planning was presented to optimize for the ship structures subjected to corrosion deterioration. The planning problem was formulated as an optimization problem where the expected lifetime costs were minimized with a eonstraint on the minimum aceeptable rehability index. The safety margins were established for the inspection events, the repair events and the failure events for ship struetures. Moreover, the formulae were derived to calculate failure probabihties and repair probabilities. Based on them, a component subjected to corrosion is investigated for illustration of the process of selecting the optimal inspection and repair strategy. Furthermore, some sensitivity studies were provided. The results show that the optimal inspection instants should take place before the reliability index reaches the minimum acceptable reliability index. The optimal target failure probability is 10^-3. In addition, a balance can be achieved between the risk cost and total expected inspection and repair costs by means of the risk-based optimal inspection and repair method, which is very effective in selecting the optimal inspection and repair strategy. 相似文献
959.
Laboratory observations of green water overtopping a fixed deck 总被引:1,自引:0,他引:1
A small-scale laboratory experiment was conducted to quantify a transient wave overtopping a horizontal, deck fixed above the free surface. Detailed free surface and velocity measurements were made for two cases with and without the deck structure to quantify the effect of the deck on the wave kinematics. The study showed that the structure increased the free surface above the leading edge of the deck by 20%. The velocity profile at the leading edge was fairly uniform, and the maximum horizontal velocity was similar to the maximum crest velocity measured without the deck. Immediately below the deck, the maximum velocity was 2.5 times greater than the corresponding velocity without the deck and 2.1 times greater than the maximum crest velocity without the deck. On the deck, the wave collapsed into a thin bore with velocities that exceeded 2.4 times the maximum crest velocity measured without the deck. 相似文献
960.
受腐蚀钢筋混凝土结构力学性能研究现状 总被引:5,自引:1,他引:5
在总结近年来国内外大量研究成果的基础上,对受腐蚀钢筋混凝土结构的力学性能进行了论述,同时针对海洋环境腐蚀的特点,提出了海洋环境下结构力学性能方面应该研究的课题。为海洋腐蚀环境下钢筋混凝土结构的耐久性设计和使用寿命评估提供参考。 相似文献