全文获取类型
收费全文 | 5181篇 |
免费 | 1368篇 |
国内免费 | 1171篇 |
专业分类
测绘学 | 378篇 |
大气科学 | 913篇 |
地球物理 | 2458篇 |
地质学 | 1797篇 |
海洋学 | 1136篇 |
天文学 | 79篇 |
综合类 | 501篇 |
自然地理 | 458篇 |
出版年
2024年 | 19篇 |
2023年 | 59篇 |
2022年 | 150篇 |
2021年 | 198篇 |
2020年 | 194篇 |
2019年 | 315篇 |
2018年 | 242篇 |
2017年 | 257篇 |
2016年 | 247篇 |
2015年 | 286篇 |
2014年 | 325篇 |
2013年 | 348篇 |
2012年 | 331篇 |
2011年 | 334篇 |
2010年 | 300篇 |
2009年 | 381篇 |
2008年 | 330篇 |
2007年 | 429篇 |
2006年 | 356篇 |
2005年 | 293篇 |
2004年 | 325篇 |
2003年 | 256篇 |
2002年 | 221篇 |
2001年 | 175篇 |
2000年 | 177篇 |
1999年 | 155篇 |
1998年 | 136篇 |
1997年 | 140篇 |
1996年 | 131篇 |
1995年 | 97篇 |
1994年 | 95篇 |
1993年 | 100篇 |
1992年 | 70篇 |
1991年 | 56篇 |
1990年 | 41篇 |
1989年 | 35篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有7720条查询结果,搜索用时 203 毫秒
71.
72.
研究具有窄谱和Weibull波高分布的波群对非线性桩柱系统作用力的统计性质。求得了桩桩的波浪峰力的各种特征值及其比值。指出这些数值不仅是阻力一惯性力参数bH的函数,也随着波群因子而变化。本文模式更具广泛性。文中给出了一系列计算图表,可从理论计算波群作用于桩柱的波浪峰力。 相似文献
73.
根据中、日合作黑潮调查研究期间(1987-1993年)在九州西侧海域获得的水文资料,计算了129°E断面的地转流速和流量。着重提出129°E断面北侧存在一支较稳定的西向流;分析这支西向流的去向,指出它是向对马暖流输送黑潮水的重要途径;给出了这支西向流及黑潮通过该断面的流速、流轴、流幅及流量的变化特征。 相似文献
74.
A probability density function of surface elevation is obtained through improvement of the method introduced by Cieslikiewicz who employed the maximum entropy principle to investigate the surface elevation distribution. The density function can be easily extended to higher order according to demand and is non-negative everywhere, satisfying the basic behavior of the probability. Moreover because the distribution is derived without any assumption about sea waves, it is found from comparison with several accepted distributions that the new form of distribution can be applied in a wider range of wave conditions. In addition, the density function can be used to fit some observed distributions of surface vertical acceleration although something remains unsolved. 相似文献
75.
Vegetation change and surface elevation dynamics in estuarine wetlands of southeast Australia 总被引:1,自引:1,他引:1
Vertical accretion and surface elevation trends were studied in mangrove and saltmarsh wetlands in southeast Australia. A total of 69 surface elevation tables, each associated with three feldspar marker horizons, was deployed in 10 wetlands across 7 estuaries, and monitored for three years. Saltmarsh and mangrove vegetation distributions were mapped for the same estuaries, and elevation characteristics of the wetlands were modelled. Rates of vertical accretion were found to correlate with tidal range. No relationship was found between rates of vertical accretion and surface elevation increase. A positive relationship was demonstrated between contemporary rates of saltmarsh surface elevation change and longer-term rates of mangrove encroachment into saltmarsh. We conclude that landward mangrove encroachment may be facilitated by local factors contributing to saltmarsh compaction during drought conditions. 相似文献
76.
On the basis of the sound velocity measurements of the coral reef core from Nanyong No.1 well of Yongshu Reef in the Nansha Islands,the paper studies the relations between the vertical sound velocity transition features in the coral reef core and the corresponding stratigraphic depositional facies change as well as stratigraphic gap of erosion,analyses the cause of the sound velocity transition,expounds the concrete process of the sea level change resulting in the stratigraphic gap of erosion and facies change in the coral reef and explains the relations between the vertical sound velocity transition in the coral reef core and the corresponding stratigraphic paleoclimate and the sea level change.This study is of important practical value and theoretical significance to the island and reef engineering construction and the acoustic logging for oil exploration in the reef limestone area as well as the paleoceanographic study of the marginal sea in the westerm Pacific Ocean. 相似文献
77.
78.
C. Svensen D. Vili
i P. Wassmann E. Arashkevich T. Ratkova 《Estuarine, Coastal and Shelf Science》2007,71(3-4):381-390
The aim of this study was to investigate phytoplankton abundance, composition and vertical export in the highly stratified Krka estuary, Croatia. The estuary is stratified throughout the year, and an interface between fresh- and brackish water plays an important role in production and degradation of biogenic matter. Vertical export of particulate organic carbon (POC), phytoplankton carbon (PPC) and faecal pellet carbon (FPC) was studied by deploying sediment traps in the middle and lower reach of the estuary and in the adjacent coastal zone. Zooplankton faecal pellet (FP) production experiments were conducted to provide additional information on the potential contribution of FP to the total carbon flux. High suspended concentrations of POC, chlorophyll a and phytoplankton was found in the lower reaches of the Krka estuary, adjacent to a source of anthropogenic eutrophication. The fraction of organic detritus to the total POC flux was 61–69% inside the estuary but only 7% at the marine station. This indicates that the primary producers in the surface layer of the Krka estuary are decomposed in and below the interface and then settle as detritus to the bottom. Low sedimentation rates in the coastal zone outside the estuary revealed that the eutrophication does not spread out of the estuary. Mesozooplankton played a modest role in vertical flux regulation, due to their low abundance and dominance of smaller forms as well as low faecal pellet production rates. It is concluded that processes taking place at the freshwater-seawater interface are of major importance for the vertical carbon flux in the investigated area. 相似文献
79.
-In previous and this studies it appears that the linear and nonlinear wave theory can notaccurately and easily predict the water particle velocities.Therefore,different from the theoretical consider-ations,in this study we have attempted to determine the transfer function empirically.Laboratory experi-ments were performed under various wave conditions.The empirical formulas of the transfer function ofthe wave height,angular frequency and water particle velocity were obtained on the basis of these test databy dimensional analysis and regression analysis.In intermediate and deep water depth conditions,thetransfer function was only a function of a nondimensional parameter which is composed of the angular fre-quency,the depth of the velocity gauge under the still water level,water depth and the acceleration of grav-ity.Finally,the empirical formulas were compared with experimental data and observational data formpresent and Cavaleri's(1978)studies.The empirical formulas were found to be in sufficient correl 相似文献
80.