全文获取类型
收费全文 | 15167篇 |
免费 | 3793篇 |
国内免费 | 2208篇 |
专业分类
测绘学 | 171篇 |
大气科学 | 1068篇 |
地球物理 | 10099篇 |
地质学 | 4397篇 |
海洋学 | 3380篇 |
天文学 | 123篇 |
综合类 | 708篇 |
自然地理 | 1222篇 |
出版年
2024年 | 43篇 |
2023年 | 145篇 |
2022年 | 362篇 |
2021年 | 477篇 |
2020年 | 572篇 |
2019年 | 744篇 |
2018年 | 570篇 |
2017年 | 544篇 |
2016年 | 517篇 |
2015年 | 645篇 |
2014年 | 760篇 |
2013年 | 822篇 |
2012年 | 894篇 |
2011年 | 934篇 |
2010年 | 770篇 |
2009年 | 911篇 |
2008年 | 898篇 |
2007年 | 1149篇 |
2006年 | 1094篇 |
2005年 | 917篇 |
2004年 | 928篇 |
2003年 | 824篇 |
2002年 | 704篇 |
2001年 | 544篇 |
2000年 | 590篇 |
1999年 | 523篇 |
1998年 | 515篇 |
1997年 | 418篇 |
1996年 | 461篇 |
1995年 | 392篇 |
1994年 | 362篇 |
1993年 | 314篇 |
1992年 | 216篇 |
1991年 | 162篇 |
1990年 | 97篇 |
1989年 | 97篇 |
1988年 | 83篇 |
1987年 | 52篇 |
1986年 | 33篇 |
1985年 | 17篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 18篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1973年 | 2篇 |
1954年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
191.
Numerical analyses for the Bragg resonant reflection of carrier waves associated long waves due to sinusoidally varying seabeds are performed by using a set of coupled ordinary differential equations derived from the Boussinesq equations. The Boussinesq equations are firstly approximated with the Fourier decomposition. The coupled governing equations are then derived and used to simulate evolution of both short and long wave components. It is also found that wave groups are generated by two carrier waves with slightly different frequencies. The wave energy of the initial wave components is transferred to other harmonic components during propagation over a long distance. Evolution and reflection of both short and long waves were largely affected by nonlinearity. 相似文献
192.
Wind and waves are major forces affecting the geomorphology and biota in coastal areas. We present a generally applicable method for measuring and calculating fetch length, fetch direction and wave exposure. Fetch length and direction, measured by geographic information system-based methods, are used along with wind direction and wind speed data to estimate wave height and period by applying forecasting curves. The apparent power of waves approaching the shore, used as a proxy for wave exposure, is then calculated by a linear wave model. We demonstrate our method by calculating fetch lengths and wave exposure indices for five areas with varying exposure levels and types of meteorological conditions in the Finnish Archipelago Sea, situated in the northern Baltic Sea. This method is a rapid and accurate means of estimating exposure, and is especially applicable in areas with geomorphologically varying and complicated shorelines. We expect that our method will be useful in several fields, such as basic biogeographical and biodiversity research, as well as coastal land-use planning and management. 相似文献
193.
- The dynamic response behaviors of upright breakwaters under broken wave impact are analysed based on the mass-damper-spring dynamic system model. The effects of the mass, damping, stiffness, natural period, and impulse duration (or oscillation period) on the translation, rotation, sliding force, overturning moment, and corresponding dynamic amplifying factors are studied. It is concluded that the ampli-ying factors only depend on the ratio of the system natural period to impulse duration (or oscillation period) under a certain damping ratio. Moreover, the equivalent static approach to breakwater design is also discussed. 相似文献
194.
本文在作者另文数值模拟得到的三维海浪基础上 ,进一步分析给出了三维波峰长度、高度及方向角度等特征量的统计分布。发现考虑海浪的方向性质后波峰分布不再是均匀连续的 ;波峰的长度分布受方向函数影响 ,方向分布越宽 ,波峰的平均长度越短 ,波峰的方向角分布越宽 ;波峰高度和长度在波峰高度较小时有很大的相关性 ,而在波峰高度很大时无关 相似文献
195.
1 .IntroductionTheglobalairtemperatureroseabout 0 .5~ 0 .6°Coverthepast 2 0thcentury ,andtheglobalmeansealevelincreasedbyabout2 0cmduringtheperiod .Theregionalmeansealevelriseswiththerisingglobalmeansealevel.Zuoetal.( 1 997)indicatedthatthemeanrisingrateofabsolutemeansealevelalongtheChinacoastontheassumptionofunifiedisostaticdatumis 2mm a .Woodworth( 1 999)analyzedsealevelspanning 1 76 8tothepresentinLiverpool,andobtainedaseculartrendforheperiodupto 1 880of0 .39± 0 .1 7mm a ,andatrendfort… 相似文献
196.
CHANG Hsien-Kuo 《中国海洋工程》2002,16(4):499-511
This study presents a three-point method for separating incident and reflected waves to explain normally incident waves' propagating over a sloping bed. Linear wave shoaling is used to determine changes in wave amplitude and phase in response to variations of bathymetry. The wave reflection coefficient and incident amplitude are estimated from wave heights measured at three fixed wave gauges with unequal spacing. Sensitivity analysis demonstrates that the proposed method can predict the reflection and amplitude of waves over a sloping bed more accurately than the two-point method. 相似文献
197.
198.
199.
The Sardinia Channel dataset was collected as part of the European Geotraverse (EGT)—a 4000 km seismic refraction line running from Northern Norway to the Sahara, designed to investigate the structure of the lithosphere beneath Europe. Wideangle seismic data recorded by ocean bottom seismometers deployed in the Sardinia Channel as part of the Southern Segment of the EGT, together with gravity data, were used to constrain the final crustal model. In the centre of the Channel the crust is identified as thinned continental in nature, with a crystalline thickness of 10 km overlain by 4 km of sediments and 2.5 km of water in the most extended region. High velocities in the lower crust in the central region are thought to represent an area of underplating or intrusion by igneous material caused by extension related to the opening of the Tyrrhenian Sea. The crust overlies an anomalously low velocity upper mantle. 相似文献
200.
青岛地区的台风暴潮与潮灾 总被引:3,自引:0,他引:3
本文分析了青岛沿海地区的台风暴潮灾害状况,给出了潮位与海浪的联合作用对灾的影响关系式,提出了今后风暴潮预报的思路。 相似文献