全文获取类型
收费全文 | 19347篇 |
免费 | 3596篇 |
国内免费 | 3880篇 |
专业分类
测绘学 | 662篇 |
大气科学 | 973篇 |
地球物理 | 5832篇 |
地质学 | 9320篇 |
海洋学 | 4044篇 |
天文学 | 2042篇 |
综合类 | 901篇 |
自然地理 | 3049篇 |
出版年
2024年 | 70篇 |
2023年 | 215篇 |
2022年 | 516篇 |
2021年 | 646篇 |
2020年 | 745篇 |
2019年 | 903篇 |
2018年 | 746篇 |
2017年 | 720篇 |
2016年 | 780篇 |
2015年 | 832篇 |
2014年 | 1003篇 |
2013年 | 1104篇 |
2012年 | 1029篇 |
2011年 | 1186篇 |
2010年 | 974篇 |
2009年 | 1321篇 |
2008年 | 1316篇 |
2007年 | 1345篇 |
2006年 | 1391篇 |
2005年 | 1119篇 |
2004年 | 1140篇 |
2003年 | 1111篇 |
2002年 | 849篇 |
2001年 | 796篇 |
2000年 | 752篇 |
1999年 | 693篇 |
1998年 | 693篇 |
1997年 | 456篇 |
1996年 | 403篇 |
1995年 | 359篇 |
1994年 | 330篇 |
1993年 | 287篇 |
1992年 | 257篇 |
1991年 | 157篇 |
1990年 | 124篇 |
1989年 | 115篇 |
1988年 | 72篇 |
1987年 | 71篇 |
1986年 | 47篇 |
1985年 | 38篇 |
1984年 | 14篇 |
1983年 | 22篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1954年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Mohamed?IsmailEmail author Tadashi?Kimura Yumiko?Suzuki Makoto?Tsuchiya 《Journal of Oceanography》2005,61(3):631-644
Total mass flux, size distribution of sediment particles and some chemical components such as total carbon (TC), total nitrogen (TN) and calcium carbonate (CaCO3) were monitored monthly using a multi-cup sediment traps at seven coral reef sites (6 reef flat and 1 reef slope) of the Marine Protected Areas around Ishigaki, Kohama, Kuroshima and Iriomote Islands in the southern Ryukyus, Japan from September 2000 to September 2001. The size distribution of trapped sediments revealed mostly uni-modal fine sand to mud in the reef flat and gravelly to coarse sand in the reef slope. The total mass flux ranged between 0.54 to 872 gm−2d−1, and showed a pronounced seasonality (high in summer-autumn and low in spring) at each site, which was consistent with the rainfall and typhoon regime. Exceptionally high values were observed on the reef slope (Iriomote) in February–March 2001 (1533 gm−2d−1) owing to a large amount of bottom sediment re-suspension. On the reef flat (Todoroki South and North; Ishigaki), values obtained in July–August 2001 (872 gm−2d−1) and August–September 2001 (800 gm− 2d−1) indicate the high terrestrial discharge from Todoroki River. Trapped sediment particles consist of CaCO3 (1.2–27.1%) and a non-carbonate fraction (98.8–72.9%), which contains total carbon (4.9–26%), carbonate carbon (CO2-C) (0.2–3.1%) and non-carbonate carbon (NC-C) (7.9–25.6%). Total nitrogen content was in the range 0.02–0.48%. TN is contained mainly in the carbonate fraction and NC-C may be contained in the non-carbonate fraction. The low TN/OC ratio of the trapped sediments suggests that they were mostly of terrestrial origin and that both fractions migrated. The high total mass flux derived from Todoroki River exceeded the threshold at which a lethal effect on coral community is caused. The results stress the importance of conducting seasonal studies of sedimentation over more than one year and at more than one location in south Japan coral reef ecosystems to gain an understanding of the processes controlling the total mass fluxes and their nutrients content, also to develop an awareness of how to prevent the damage of coral reef ecosystems and, if it does occur, to allow mitigation measures to be undertaken. 相似文献
122.
厦门港潮汐水流及浑水悬沙整体物理模型于1989年建成后,已进行了不少有意义的试验研究工作,取得较好效果。本文主要介绍模型的设计思想、相似准则、浑水悬沙相似理论的探讨、模型设计方法以及模型沙的选择等。 相似文献
123.
124.
125.
You Yuming Hou Min Senior Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing Assistant Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1992,(3)
- The data of landsat TM of multi-temporal for Lingdingyang Estuary, Pearl River in China is firstly used with suspended sediment concentration of field measurement to establish a correlative model equation. After the ratio processing of TM data and atmospheric correction, the images of suspended sediment concentration of different temporals are exported from the image processing systems AREIS II and III. These images express the characteristics of suspended sediment distribution, the mode of sediment transport and the extent of dispersion under the actions of tidal current and wind condition of different seasons. 相似文献
126.
127.
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
128.
台湾海峡西部柱状沉积物粘土矿物的分析 总被引:4,自引:0,他引:4
根据台湾海峡西部10个柱102个样品的X 射线衍射等分析,鉴定了该区粘土矿物组合与含量变化,分析了其与沉积环境的关系.结果表明,该区粘土矿物组合大多数站位以伊利石含量占首位,绿泥石和高岭石次之,且含少量蒙脱石;伊利石含量随距岸、水深的增加而递增,高岭石则反之;蒙脱石含量与火山活动密切相关,绿泥石含量呈斑块状分布;775和819号站有典型的陆相层,为早玉木冰期的“台湾陆桥”或“东山陆桥”提供有力证据. 相似文献
129.
本文用耗散结构理论推导出南海热带气旋的移动公式,通过实际应用和实例检验,证明它对估计南海热带气旋路径演变有一定的实用价值。 相似文献
130.
Q. J. Huggett A. K. Cooper M. L. Somers A. R. Stubbs 《Marine Geophysical Researches》1992,14(1):47-63
GLORIA side-scan sonographs from the Bering Sea Basin show a complex pattern of interference fringes sub-parallel to the ship's track. Surveys along the same trackline made in 1986 and 1987 show nearly identical patterns. It is concluded from this that the interference patterns are caused by features in the shallow subsurface rather than in the water column. The fringes are interpreted as a thin-layer interference effect that occurs when some of the sound reaching the seafloor passes through it and is reflected off a subsurface layer. The backscattered sound interferes (constructively or desctructively) with the reflected sound. Constructive/destructive interference occurs when the difference in the length of the two soundpaths is a whole/half multiple of GLORIA's 25 cm wavelength. Thus as range from the ship increases, sound moves in and out of phase causing bands of greater and lesser intensity on the GLORIA sonograph. Fluctuations (or wiggles) of the fringes on the GLORIA sonographs relate to changes in layer thickness. In principle, a simple three dimensional image of the subsurface layer may be obtained using GLORIA and bathymetric data from adjacent (parallel) ship's tracks. These patterns have also been identified in images from two other systems; SeaMARC II (12 kHz) long-range sonar, and TOBI (30 kHz) deep-towed sonar. In these, and other cases world-wide, the fringes do not appear with the same persistence as those seen in the Bering Sea. 相似文献