全文获取类型
收费全文 | 8301篇 |
免费 | 1444篇 |
国内免费 | 1953篇 |
专业分类
测绘学 | 215篇 |
大气科学 | 1142篇 |
地球物理 | 2732篇 |
地质学 | 3464篇 |
海洋学 | 2130篇 |
天文学 | 66篇 |
综合类 | 537篇 |
自然地理 | 1412篇 |
出版年
2024年 | 44篇 |
2023年 | 109篇 |
2022年 | 279篇 |
2021年 | 291篇 |
2020年 | 403篇 |
2019年 | 459篇 |
2018年 | 354篇 |
2017年 | 391篇 |
2016年 | 405篇 |
2015年 | 411篇 |
2014年 | 524篇 |
2013年 | 607篇 |
2012年 | 503篇 |
2011年 | 561篇 |
2010年 | 459篇 |
2009年 | 550篇 |
2008年 | 548篇 |
2007年 | 553篇 |
2006年 | 500篇 |
2005年 | 457篇 |
2004年 | 413篇 |
2003年 | 388篇 |
2002年 | 290篇 |
2001年 | 284篇 |
2000年 | 284篇 |
1999年 | 277篇 |
1998年 | 179篇 |
1997年 | 212篇 |
1996年 | 170篇 |
1995年 | 153篇 |
1994年 | 132篇 |
1993年 | 114篇 |
1992年 | 92篇 |
1991年 | 46篇 |
1990年 | 51篇 |
1989年 | 45篇 |
1988年 | 37篇 |
1987年 | 13篇 |
1986年 | 22篇 |
1985年 | 14篇 |
1984年 | 19篇 |
1983年 | 15篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
81.
82.
83.
84.
闽江口水动力和污染扩散数值模拟 总被引:3,自引:0,他引:3
本文建立了闽江口二维水动力、污染扩散数值模型,模型采用ADI双向隐式求解。在水动力模拟中,对岸界的丁坝有用线性边界进行拟合,并考虑到河口区侧向摩擦作用;在污染扩散模拟中,用动态拟合的方法对浓度水边界进行了较为合理的改进。计算结果表明,本模型是成功的。 相似文献
85.
The intertidal erosion rate of cohesive sediment: a case study from Long Island Sound 总被引:2,自引:0,他引:2
Over the past decades, many attempts have been made to generate useful bottom erosion models for the study of cohesive sediment movement. This study addresses some of the key questions involved in determining the functional relationship between erosion rate and bottom shear stress. Current, wave, and turbidity data were collected from a bottom mounted instrument array in a moderately energetic estuarine environment. The bottom shear stress was calculated from a wave–current interaction model. The erosion rate was derived from the observed sediment concentration using a vertical mixing model. Examination of the relationship between erosion rate and bottom stress showed that the erosion rate varied at intertidal frequency. When averaged over the tidal fluctuation, the erosion rate remained approximately constant at low stress, but increased sharply when the shear stress rose above a critical value. This suggests two-stage erosion. The bed has a layered structure, in which a thin layer of loose, high water content material overlies a more consolidated bed. The top layer of high water content material (fluff) was easily disturbed and re-suspended by tidal currents, but the consolidated bottom layer was eroded only under conditions of high shear stress. 相似文献
86.
Benthic photosynthesis in submerged Wadden Sea intertidal flats 总被引:3,自引:1,他引:3
Markus Billerbeck Hans Ry Katja Bosselmann Markus Huettel 《Estuarine, Coastal and Shelf Science》2007,71(3-4):704-716
In this study we compare benthic photosynthesis during inundation in coarse sand, fine sand, and mixed sediment (sand/mud) intertidal flats in the German Wadden Sea. In situ determinations of oxygen-, DIC- and nutrient fluxes in stirred benthic chamber incubations were combined with measurements of sedimentary chlorophyll, incident light intensity at the sediment surface and scalar irradiance within the sediment. During submergence, microphytobenthos was light limited at all study sites as indicated by rapid response of gross photosynthesis to increasing incident light at the sea floor. However, depth integrated scalar irradiance was 2 to 3 times higher in the sands than in the mud. Consequently, gross photosynthesis in the net autotrophic fine sand and coarse sand flats during inundation was on average 4 and 11 times higher than in the net heterotrophic mud flat, despite higher total chlorophyll concentration in mud. Benthic photosynthesis may be enhanced in intertidal sands during inundation due to: (1) higher light availability to the microphytobenthos in the sands compared to muds, (2) more efficient transport of photosynthesis-limiting solutes to the microalgae with pore water flows in the permeable sands, and (3) more active metabolic state and different life strategies of microphytobenthos inhabiting sands. 相似文献
87.
88.
89.
浙江省海塘塘顶高程的确定 总被引:10,自引:1,他引:10
介绍了浙江省海塘塘顶高程确定时所涉及的波浪爬高,越浪量等的计量,同时分析了1997年后浙江省海塘塘顶高程确定的方法,由已建海塘的塘顶高程分析可见,在背水坡和塘顶有保护措施的情况下,采用允许最大越波流量来控制海塘塘顶高程,可适当降低塘身高度。 相似文献
90.
珠江口伶仃洋锋的类别及其对沉积的影响 总被引:1,自引:0,他引:1
根据近年在珠江口伶仃洋的观测资料,对比国外有关河口锋的定义,归纳了伶仃洋内几种锋的现象,计有潮侵锋、岬角锋及湖水退急时的浅滩锋等。解释了锋生的原因与潮汐进退,特别与随潮入侵的咸水关系。文中也探讨了这些锋对沉积环境的影响,认为它是陆架水入侵河口地区的一种不容忽视的沉积动力过程。 相似文献