全文获取类型
收费全文 | 15169篇 |
免费 | 1899篇 |
国内免费 | 3297篇 |
专业分类
测绘学 | 1173篇 |
大气科学 | 1864篇 |
地球物理 | 1864篇 |
地质学 | 6204篇 |
海洋学 | 2311篇 |
天文学 | 5193篇 |
综合类 | 747篇 |
自然地理 | 1009篇 |
出版年
2024年 | 46篇 |
2023年 | 122篇 |
2022年 | 368篇 |
2021年 | 407篇 |
2020年 | 491篇 |
2019年 | 520篇 |
2018年 | 466篇 |
2017年 | 467篇 |
2016年 | 511篇 |
2015年 | 588篇 |
2014年 | 885篇 |
2013年 | 968篇 |
2012年 | 971篇 |
2011年 | 1112篇 |
2010年 | 1079篇 |
2009年 | 1407篇 |
2008年 | 1342篇 |
2007年 | 1205篇 |
2006年 | 1167篇 |
2005年 | 1012篇 |
2004年 | 848篇 |
2003年 | 749篇 |
2002年 | 579篇 |
2001年 | 499篇 |
2000年 | 442篇 |
1999年 | 416篇 |
1998年 | 344篇 |
1997年 | 177篇 |
1996年 | 168篇 |
1995年 | 136篇 |
1994年 | 141篇 |
1993年 | 168篇 |
1992年 | 80篇 |
1991年 | 71篇 |
1990年 | 71篇 |
1989年 | 66篇 |
1988年 | 52篇 |
1987年 | 17篇 |
1986年 | 27篇 |
1985年 | 41篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1982年 | 25篇 |
1981年 | 13篇 |
1980年 | 15篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 17篇 |
1877年 | 1篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
171.
Weng Keqin
Associate Professor Hydraulic Hydro-Power Engineering Dept. Tsinghua University Beijing 《中国海洋工程》1995,(2)
This paper reveals that the long-period statistic distribution of the characteristic heights of deep-water waves assumes the lognormal distribution. Thereafter, the largest wave-height which may occur in the service life of coastal structures is derived in this paper. 相似文献
172.
本文以南麂海洋站1983~1990年风、浪的实测资料为依据,建立了南麂海城春、夏、秋、冬季定常波风浪波高与风速的经验关系式。检验结果表明,曲线回归显著,计算值与实测值吻合良好。文中还对偏NNE向和偏SSW向计算波高随风速增大的快慢,同一方向在同一风速作用下计算波高的季节变化及其机理作了初浅的讨论。 相似文献
174.
本文探讨西庄附近海域的波浪状况,分析由于人工挖沙影响,使得登州浅滩的防护作用发生变化,导致近岸波浪作用增强,造成海岸侵蚀.最后讨论设计波要素的确定,为防浪护坡工程提供必要的设计依据. 相似文献
175.
176.
W.R. Geyer 《Estuarine, Coastal and Shelf Science》1997,44(6):713-722
Observations of two small estuaries in Cape Cod, U.S.A. indicate large variations in salinity structure that are forced by variations in along-estuary wind stress. During onshore winds, the estuarine circulation is reduced, and the along-estuary salinity gradient increases as freshwater accumulates. During offshore winds, the surface outflow is enhanced, freshwater is flushed out of the estuary, and the along-estuary salinity gradient becomes weak. Constrictions block the wind-induced flushing, resulting in strong salinity fronts across the constrictions. The residence time of one of the estuaries varies by more than a factor of three in response to variations in wind-induced flushing. The other estuary has little variation of flushing associated with winds, due to a constriction at the mouth that inhibits the wind-induced exchange. The strong influence of winds on the flushing of these estuaries is due in part to their shallow depths, which accentuates the influence of wind stress relative to the effects of the horizontal density gradient. In addition, the residence times of the estuaries are comparable to the time scale of wind forcing, allowing large changes in water properties during wind events. 相似文献
177.
178.
179.
规则波和不规则波作用下消波建筑物前的波高分析 总被引:1,自引:0,他引:1
消波建筑物在国内外已得到广泛应用。本文采用近似方法分析了明基床上直立式消波建筑物前的波高及消波室内的波高,从而确定建筑物的消波效果。并在规则波的基础上将成果推广至不规则波作用下的情况。 相似文献
180.
The Eastern Flank Hydrocarbon Province borders the southeastern edge of the South Oman Salt Basin in the southern part of Oman. An intensive exploration programme by PDO over the past seven years has led to the discovery of almost 2 × 109 m3 of oil with current production of some 15000 m3/d from six fields.In stark contrast to other oil habitats of the Arabian Peninsula, the main play involves rock units and geological events ranging in age from Late Precambrian to Quaternary Times, while trap development and charging are closely related to syn-tectonic salt dissolution.The principal reservoirs and seals are poorly consolidated, Palaeozoic clastics which drape, due to salt dissolution, over residual ‘cores’ principally composed of either Lower Palaeozoic sandstones (Haima Group), or Late Proterozoic carbonates (Huqf Group), or some combination of these. Oils have been geochemically correlated with algal source rocks of the Huqf Eastern Flank. Structures are considered to have been ‘charged’ from Late Mesozoic times onwards in conjunction with progressive subsurface salt removal and the onset of maturation of local source rocks. The effectiveness of ‘charging’ along the retreating salt edge is indicated by the small percentage of dry wells.Major oil zones are found in both anticlinal and truncation traps which are commonly developed around sandstone (Haima Group) cores. Oils show a wide range of characteristics but are typically heavy, early expulsion crudes, high sulphur with little associated gas. Bacterial transformation is not uncommon.Producing reservoirs mainly occur at relatively shallow depths (600–1200 m). Primary recovery factors of around 7% reflect the high density and viscosity of the Eastern Flank crudes and have initiated interest in Enhanced Oil Recovery (EOR) techniques. Two such pilot projects, involving steam and polymer flooding, are due to commence in 1984 and, if successful, will substantially increase the reserve base of these fields. 相似文献