全文获取类型
收费全文 | 6378篇 |
免费 | 1186篇 |
国内免费 | 1419篇 |
专业分类
测绘学 | 759篇 |
大气科学 | 971篇 |
地球物理 | 1943篇 |
地质学 | 3400篇 |
海洋学 | 951篇 |
天文学 | 85篇 |
综合类 | 311篇 |
自然地理 | 563篇 |
出版年
2024年 | 33篇 |
2023年 | 127篇 |
2022年 | 199篇 |
2021年 | 218篇 |
2020年 | 246篇 |
2019年 | 275篇 |
2018年 | 237篇 |
2017年 | 314篇 |
2016年 | 314篇 |
2015年 | 320篇 |
2014年 | 407篇 |
2013年 | 428篇 |
2012年 | 380篇 |
2011年 | 444篇 |
2010年 | 310篇 |
2009年 | 489篇 |
2008年 | 498篇 |
2007年 | 478篇 |
2006年 | 445篇 |
2005年 | 358篇 |
2004年 | 359篇 |
2003年 | 269篇 |
2002年 | 273篇 |
2001年 | 198篇 |
2000年 | 229篇 |
1999年 | 192篇 |
1998年 | 173篇 |
1997年 | 153篇 |
1996年 | 120篇 |
1995年 | 116篇 |
1994年 | 76篇 |
1993年 | 86篇 |
1992年 | 47篇 |
1991年 | 36篇 |
1990年 | 32篇 |
1989年 | 23篇 |
1988年 | 20篇 |
1987年 | 20篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有8983条查询结果,搜索用时 31 毫秒
181.
182.
渤海悬浮颗粒物的三维输运模式 I.模式 总被引:14,自引:4,他引:14
为了长时间,大范围研究渤海中悬浮物的输运规律,研究应用并改造了备国汉堡大学的粒子追踪悬浮物输运的三维模式,模式中考虑了风、气压等气象要素以外海传入的潮波作用下的三维正压海流对悬浮颗粒物的输运.同时考虑了悬浮颗粒物的学降及再悬浮机制和底质中的细颗粒物的运动,将风浪的作用引入了悬浮物输运的计算,数值模式应用的粒五追踪方法,能较好地反映悬浮物浓度的迅速变化。 相似文献
183.
184.
185.
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
186.
We develop techniques of numerical wave generation in the time-dependent extended mild-slope equations of Suh et al. [1997. Time-dependent equations for wave propagation on rapidly varying topography. Coastal Engineering 32, 91–117] and Lee et al. [2003. Extended mild-slope equation for random waves. Coastal Engineering 48, 277–287] for random waves using a source function method. Numerical results for both regular and irregular waves in one and two horizontal dimensions show that the wave heights and the frequency spectra are properly reproduced. The waves that pass through the wave generation region do not cause any numerical disturbances, showing usefulness of the source function method in avoiding re-reflection problems at the offshore boundary. 相似文献
187.
The Eastern Venezuelan Basin (EVB) contains one of the largest hydrocarbon accumulations in the world. Main petroleum targets are buried structures of the Monagas Fold-Thrust Belt (MFTB) which forms the northeastern edge of the EVB. The objective of this study is to integrate the seismic and well data that has been acquired over the last 10 years across the MFTB and EVB, to create an updated structural model. Three regional cross sections 60-75 km long are presented across an area of 4000 km2.Five structural domains are described: Amarilis, Furrial, Jusepín, Cotoperí and Pirital. They are characterized by thrusts and high-angle reverse faults. Structural style changes along strike are related to variations in depth of detachment levels and to the strike-slip component of the deformation. We have estimated a shortening between 43 and 59 km that increases eastward over a distance of 40 km.The evolution of the MFTB is divided in four episodes based on stratigraphic, structural and thermal maturity evidences: (1) Oligocene-early Miocene initial movement of Pirital thrust. (2) Early Miocene simultaneous movement on Pirital, Furrial and Cotoperí thrusts. (3) Middle Miocene increases in velocity and change in geometry of Pirital thrust, during an out of sequence period of thrusting. (4) Late Miocene to Holocene minor thrust activity. This evolution is consistent with the oblique convergence between the Caribbean and South American plates and the convergence between North and South America that affected Eastern Venezuela during the Cenozoic.By analyzing the along-strike variations in structural style, new exploratory opportunities have been identified. Under the Orocual and Santa Bárbara fields two untested duplex structures are proposed; they were developed during the middle Miocene. Other prospective hydrocarbon traps are associated to oblique transpressive faults that create anticline structures. 相似文献
188.
Tatiana F. Maria André M. EstevesJan Vanaverbeke Ann Vanreusel 《Estuarine, Coastal and Shelf Science》2011,94(3):272-280
The effect of an abundant sandy beach polychaete, Scolelepis squamata, on the colonisation of defaunated sediments by marine nematodes indicates that sandy beach fauna can be partially controlled by biological interactions within and across size groups. Experimental cores, equipped with windows allowing infaunal colonisation, were filled with defaunated sandy beach sediment containing two different treatments with and without S. squamata. These cores were inserted into microcosms filled with sediment with indigenous meiofauna collected from the field. The treatments were incubated in the laboratory at ambient temperature and salinity for 2, 7, 14 and 21 days, in order to follow the colonisation process of the defaunated sediments by the indigenous nematode fauna over time. Nematodes initially colonised both treatments, with abundances of up to 10% of the densities in the control; after 2 weeks, nematode densities in the cores without S. squamata surpassed the control densities. Nematode assemblages in both treatments were not species rich, and also differed in composition from the natural assemblages. The most successful colonising species, Enoplolaimus litoralis, was rare in the surrounding sediment, suggesting that colonisation was determined by species-specific characteristics such as body size, motility and feeding strategy. Initially the presence of macrofauna did not affect the nematode community composition, but after 2 weeks of the experiment, the presence of the polychaete seemed to facilitate the earlier establishment of non-opportunistic species. 相似文献
189.
Numerical simulation of groundwater flowing to horizontal seepage wells under a river 总被引:6,自引:0,他引:6
A horizontal seepage well, consisting of an interconnected vertical well, galleries, chambers and small-diameter radiating
bores, is used to acquire relatively clean water that has been filtered through natural alluvial deposits in a riverbed. It
has wide application, especially in arid and semi-arid areas. The lack of calculation formulae or models for horizontal seepage
wells, up until now, has resulted in several false applications. Based on the analysis of groundwater flow characteristics,
it has been concluded that several flow regimes coexist and hydraulic head loss exists in the horizontal seepage well. To
avoid the difficulty of confirming the flux or head distribution in such a complex system, the model boundary of the whole
horizontal seepage well has been moved to that of just the vertical well, and the well-aquifer system was treated as a heterogeneous
medium, where the horizontal seepage well itself is a highly permeability medium. A mathematical model has been developed,
based on the coupled seepage-pipe flow, by the introduction of equivalent hydraulic conductivity according to different flow
regimes. Then a three-dimensional finite difference numerical model, based on the mathematical model, was developed and applied
to a horizontal seepage well in China. The numerical model verified the groundwater flow characteristics of the horizontal
seepage well.
An erratum to this article can be found at 相似文献
190.
Monopod caisson foundation is a viable alternative for supporting offshore wind turbines located at shallow water depths. This foundation system has to resist overturning moment generated due to resultant lateral load, arising from wind and water wave action, that can act at any loading height above the seabed. This paper presents results of a numerical investigation performed to determine the influence of loading height, caisson geometry and superstructure load on the ultimate lateral capacity, initial stiffness, and soil failure zone of the foundation, when installed in very dense sand. Both the ultimate and serviceable states of the caisson foundation obtained from the analyses are represented in terms of envelopes plotted between lateral load and overturning moment. Simplified expressions, which take into account the influence of caisson geometry, loading height, and soil properties, are also presented to serve as a preliminary base for design of the monopod caisson foundation. 相似文献