全文获取类型
收费全文 | 24808篇 |
免费 | 4424篇 |
国内免费 | 6454篇 |
专业分类
测绘学 | 4567篇 |
大气科学 | 4907篇 |
地球物理 | 5852篇 |
地质学 | 10575篇 |
海洋学 | 3555篇 |
天文学 | 236篇 |
综合类 | 2055篇 |
自然地理 | 3939篇 |
出版年
2024年 | 87篇 |
2023年 | 289篇 |
2022年 | 879篇 |
2021年 | 1031篇 |
2020年 | 1226篇 |
2019年 | 1392篇 |
2018年 | 1161篇 |
2017年 | 1335篇 |
2016年 | 1377篇 |
2015年 | 1533篇 |
2014年 | 1610篇 |
2013年 | 1902篇 |
2012年 | 1721篇 |
2011年 | 1744篇 |
2010年 | 1374篇 |
2009年 | 1570篇 |
2008年 | 1582篇 |
2007年 | 1669篇 |
2006年 | 1573篇 |
2005年 | 1383篇 |
2004年 | 1222篇 |
2003年 | 1041篇 |
2002年 | 980篇 |
2001年 | 817篇 |
2000年 | 748篇 |
1999年 | 680篇 |
1998年 | 627篇 |
1997年 | 548篇 |
1996年 | 479篇 |
1995年 | 441篇 |
1994年 | 393篇 |
1993年 | 343篇 |
1992年 | 213篇 |
1991年 | 183篇 |
1990年 | 125篇 |
1989年 | 98篇 |
1988年 | 89篇 |
1987年 | 58篇 |
1986年 | 29篇 |
1985年 | 35篇 |
1984年 | 17篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1976年 | 4篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
231.
岬间海湾岸线平衡形态神经网络模型 总被引:1,自引:0,他引:1
讨论了目前海湾岸线平衡形态经验模型存在的不足之处。从沿岸输沙公式入手,阐述了平衡岸线的机理模式,重新定义了平衡海湾的“下岬角”,给出了模型参数与主波向的具体计算方法,并以华南典型海湾为学习样本,建立了岸线平衡形态的神经网络模型。通过模拟海湾与实际稳定海湾——乌场湾间的对比分析,表明所建神经网络模型是较抛物模型更为理想的平衡岸线模型。 相似文献
232.
At the circular Babi Island in the Flores tsunami (1992) and pear shaped island in the Okushiri event (1993), unexpectedly large tsunami run‐up heights in the lee of conic islands were observed. The flume and basin physical model studies were conducted in the Coastal Hydraulic Laboratory, Engineering Research and Development Center, U.S. Army Corps of Engineers to provide a better understanding of the physical phenomena and verify numerical models used in predicting tsunami wave run‐up on beaches, islands, and vertical walls. Reasonably accurate comparison of run‐up height of solitary waves on a circular island has been obtained between laboratory experimental results and two‐dimensional computation model results. In this study we apply three‐dimensional RANS model to simulate wave run‐up on conical island. In the run‐up computation we obtain that 3D calculations are in very good comparison with laboratory and 2D numerical results. A close examination of the three‐dimensional velocity distribution around conical island to compare with depth‐integrated model is performed. It is shown that the velocity distribution along the vertical coordinate is not uniform: and velocity field is weaker in the bottom layer and higher on the sea surface. The maximum difference (about 40%) appears at the time when solitary wave reached the circular island. 相似文献
233.
234.
235.
ABSTRACT This study investigated the impact of pastoral land use and nutrient and fine sediment inputs on Microcoleus autumnalis and filamentous algae-dominated mats, and benthic chlorophyll-a in streams (lower North Island, New Zealand). Surveying and sampling was undertaken monthly at 61 sites spanning a wide gradient in catchment cover and environmental conditions. Two boosted regression tree models were built. The first models included pastoral land cover and five environmental variables as predictors. In the second model pastoral land cover was replaced by nutrient/sediment data. The abundance of the two mat types and chlorophyll-a increased when pastoral land cover was between 20% and 70% (model 1). Replacement of pastoral land cover by nutrient/sediment data (model 2) slightly improved the model fit for all three periphyton variables. Microcoleus autumnalis-dominant mats increased with dissolved inorganic nitrogen concentrations up to ca. 0.6?mg?L?1, and in streams with more frequent flushes. In contrast, filamentous algal-dominated mats increased with turbidity, and in streams with less frequent flushes. Chlorophyll-a generally followed the response of the dominant periphyton type. Increased knowledge on responses of specific periphyton types, rather than total biomass, to environmental variables is essential to guide effective management strategies. 相似文献
236.
AbstractWith the large-scale development and utilization of ocean resources and space, it is inevitable to encounter existing submarine facilities in pile driving areas, which necessitates a safety assessment. In this article, by referring to a wharf renovation project as a reference, the surrounding soil response and buried pipe deformation during pile driving in a near-shore submarine environment are investigated by three-dimensional (3D) numerical models that consider the pore water effect. Numerical studies are carried out in two different series: one is a case of a single pile focusing on the effect of the minimum plane distance of the pile–pipe, and the other is a case of double piles focusing on the effect of the pile spacing. 相似文献
237.
B. Gjevik D. Hareide B. K. Lynge A. Ommundsen J. H. Skailand H. B. Urheim 《Marine Geodesy》2006,29(1):1-17
A system for displaying tidal currents in an electronic chart display and information system (ECDIS) has been developed and implemented in compliance with the standards of the International Hydrographic Organization (IHO). The tidal current fields can be displayed in real time on the electronic navigational chart and several options and functions for updating and zooming have been designed. The current fields are calculated from a data base with the harmonic constants for the four major tidal constituents. The harmonic constants are obtained from a high resolution numerical model with horizontal grid resolution of 100 m. The model is validated by comparing with sea level and current measurements. The depth matrix for the central part of the model domain was calculated from data from multibeam bathymetric surveys. An application example of the implementation is given for Trondheimsleia, a part of the main sailing route along the western coast of Norway. 相似文献
238.
I. Brandariz P. Castro M. Montes F. Penedo M.E. Sastre de Vicente 《Marine Chemistry》2006,102(3-4):291-299
Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl2 or CaCl2), with binary mixtures of MgCl2 and CaCl2, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl2, while it is increased by the other electrolytes used in this work. 相似文献
239.
Shigehisa Nakamura 《Marine Geodesy》2005,28(4):305-312
A note is presented on tsunami bore front. This tsunami bore front is an old dynamical problem but also a new problem to be understood. The tsunami event on 2004 December 26 has raised this is an urgent problem. The author introduces here a model in order to see a hydrodynamical specific property of the tsunami bore front. This modeling gives us a new understanding about what mechanics is for the interested tsunami bore front, especially, around a coastal zone. This work adds a new understanding about mechanics of water motions as the tsunamis generated by the earthquake undersea at a distant area from the coast. The model in this work points out a specific transitional pattern as a function of time and space of tsunami bore front. This modeling gives what is essential at considering tsunami bore front. 相似文献
240.