全文获取类型
收费全文 | 5960篇 |
免费 | 1386篇 |
国内免费 | 1723篇 |
专业分类
测绘学 | 781篇 |
大气科学 | 913篇 |
地球物理 | 1234篇 |
地质学 | 3757篇 |
海洋学 | 924篇 |
天文学 | 153篇 |
综合类 | 581篇 |
自然地理 | 726篇 |
出版年
2024年 | 35篇 |
2023年 | 117篇 |
2022年 | 269篇 |
2021年 | 360篇 |
2020年 | 275篇 |
2019年 | 360篇 |
2018年 | 322篇 |
2017年 | 322篇 |
2016年 | 310篇 |
2015年 | 301篇 |
2014年 | 336篇 |
2013年 | 367篇 |
2012年 | 457篇 |
2011年 | 459篇 |
2010年 | 442篇 |
2009年 | 439篇 |
2008年 | 454篇 |
2007年 | 395篇 |
2006年 | 387篇 |
2005年 | 301篇 |
2004年 | 226篇 |
2003年 | 204篇 |
2002年 | 198篇 |
2001年 | 194篇 |
2000年 | 195篇 |
1999年 | 161篇 |
1998年 | 148篇 |
1997年 | 149篇 |
1996年 | 131篇 |
1995年 | 103篇 |
1994年 | 125篇 |
1993年 | 105篇 |
1992年 | 75篇 |
1991年 | 53篇 |
1990年 | 61篇 |
1989年 | 45篇 |
1988年 | 46篇 |
1987年 | 25篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1973年 | 2篇 |
1957年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有9069条查询结果,搜索用时 609 毫秒
41.
舟山马岙峡道的水文泥沙特性和峡道效应 总被引:6,自引:2,他引:6
根据舟山本岛北部马岙峡道实测水文泥沙资料和沉积物采样分析结果以及对马岙岸段岸滩的现场踏勘结果,分析了马岙峡道的水文泥沙特性及其峡道效应。文章认为,受峡道地形限制,马岙岸段水流呈现显著的往复流特性,潮流流速较强,水体含沙量较低,泥沙淤积较弱,岸滩处于冲淤平衡状态;受峡道内涨落潮流分流和汇流的共同作用,马岙小泥糊礁附近发育水下沙嘴,该沙嘴是以落潮流作用为主形成的浅滩,受涨潮流改造而形成的,并将在涨落潮流作用下逐渐增长,形成连岛沙嘴,使小泥糊礁附近岸线发展成弧形岸线,并达成新的平衡。 相似文献
42.
43.
44.
45.
46.
黄河口及渤海中南部沉积物工程特性及其机理 总被引:3,自引:0,他引:3
采用Kasten取样器从黄河口及渤海湾中南部海底沉积物中取样,对样品通过土工性质、微结构研究以及粘土矿物分析,阐明本研究区三维空间展布的海底沉积物形成机理及其工程地质规律,论证水动力作用和斜坡不稳定性对工程特性和微结构的重要影响. 相似文献
47.
Sea surface temperature variations in the southwestern South China Sea over the past 160 ka 总被引:1,自引:0,他引:1
Sea surface temperatures (SSTs) in the southwestern South China Sea have been reconstructed for the past 160 ka using the Uk37 paleothermometer from the core MD01-2392. The temperature differences between glacial times (MISs 6 and 2) and interglacial times (MISs 5.5 and 1) are 2.2~2.5 ℃. Younger Dryas event during the last deglaciation was documented in both the planktonic foraminiferal δ18O and SST records. After MIS 5.5, SSTs displayed a progressive cooling from 28.6 to 24.5 ℃, culminating at the LGM. During this gradual cooling period, warm events such as MISs 5.3, 5.1 and 3 were also clearly documented. By comparison of SST between the study core and Core 17954, a pattern of low or no meridional SST gradients during the interglacial periods and high meridional SST gradients during the glacial periods was exhibited. This pattern indicates the much stronger East Asian winter monsoon at the glacial than at the interglacial periods. Spectral analysis gives two prominent cycles: 41 and 23 ka, with the former more pronounced, suggesting that SSTs in the southern SCS varied in concert with high-latitude processes through the connection of East Asian winter monsoon. 相似文献
48.
On the radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas 总被引:1,自引:0,他引:1
The radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas of finite depth is investigated. The analytical expressions for the radiated and diffracted potentials are derived as infinite series by use of the method of separation of variables. The unknown coefficients in the series are determined by the eigenfunction expansion matching method. The expressions for wave forces, hydrodynamic coefficients and reflection and transmission coefficients are given and verified by the boundary element method. Using the present analytical solution, the hydrodynamic influences of the angle of incidence, the submergence, the width and the thickness of the structure on the wave forces, hydrodynamic coefficients, and reflection and transmission coefficients are discussed in detail. 相似文献
49.
Shen Yang Xue Shen Hanlong Liu Huayang Ge Xiaoxi Rui 《Marine Georesources & Geotechnology》2020,38(6):706-715
AbstractConstruction of the reefs in the South China Sea is a significant foundation to the secure stability and economic development of China. The construction of an airport runway is necessary for this realization. The calcareous sand is the main primary material in the runway construction. A certain type of calcareous sand near a certain reef of the South China Sea was studied in this paper. To investigate this specific calcareous sand, quartz sand was used as a reference for comparison. Microscopic 3-D imaging, compression and triaxial tests were conducted to test the micro, squeezing and shear properties. The effect mechanism of gradation on the calcareous sand’s compressibility and shear characteristics are discussed from a mesoscopic viewpoint using 3-D morphology. Calcareous sand particles are multiangular and flatter in comparison with quartz sand. The larger the particle sizes are, the more different the two sands’ morphologies are. The compressibility of calcareous sand is greater, and the effect of the coarse fraction (5–1?mm) content in the gradation plays the most significant role in this feature. When the coarse particles’ content is less than 25% and the mass ratio of the middle and fine particles (M) is constant, there is the worst coarse fraction content causing the calcareous sand to be most likely compressed. The worst coarse fraction content decreases with the increase in M, and an empirical formula is proposed. When the gradation, relative density and confining pressure are the same, the peak shear stress and strain of calcareous sand are all at a high level. The effect of confining pressure is manifested in calcareous sand. The shear strength and dilation of calcareous sand are also most affected by the medium coarse fraction (5–0.25?mm) content. 相似文献
50.
Unlike in the open sea, the use of wind information for forecasting waves may encounter more ambiguous uncertainties in the coastal or harbor area due to the influence of complicated geometric configurations. Thus this paper attempts to forecast the waves based on learning the characteristics of observed waves, rather than the use of the wind information. This is reported in this paper by the application of the artificial neural network (ANN), in which the back-propagation algorithm is employed in the learning process for obtaining the desired results. This model evaluated the interconnection weights among multi-stations based on the previous short-term data, from which a time series of waves at a station can be generated for forecasting or data supplement based on using the neighbor stations data. Field data are used for testing the applicability of the ANN model. The results show that the ANN model performs well for both wave forecasting and data supplement when using a short-term observed wave data. 相似文献