全文获取类型
收费全文 | 4931篇 |
免费 | 1025篇 |
国内免费 | 1544篇 |
专业分类
测绘学 | 227篇 |
大气科学 | 952篇 |
地球物理 | 700篇 |
地质学 | 1747篇 |
海洋学 | 3037篇 |
天文学 | 27篇 |
综合类 | 387篇 |
自然地理 | 423篇 |
出版年
2024年 | 34篇 |
2023年 | 123篇 |
2022年 | 178篇 |
2021年 | 237篇 |
2020年 | 242篇 |
2019年 | 287篇 |
2018年 | 245篇 |
2017年 | 207篇 |
2016年 | 242篇 |
2015年 | 293篇 |
2014年 | 284篇 |
2013年 | 365篇 |
2012年 | 279篇 |
2011年 | 299篇 |
2010年 | 241篇 |
2009年 | 327篇 |
2008年 | 290篇 |
2007年 | 315篇 |
2006年 | 314篇 |
2005年 | 294篇 |
2004年 | 278篇 |
2003年 | 249篇 |
2002年 | 239篇 |
2001年 | 233篇 |
2000年 | 204篇 |
1999年 | 199篇 |
1998年 | 164篇 |
1997年 | 145篇 |
1996年 | 121篇 |
1995年 | 111篇 |
1994年 | 111篇 |
1993年 | 88篇 |
1992年 | 59篇 |
1991年 | 47篇 |
1990年 | 43篇 |
1989年 | 23篇 |
1988年 | 25篇 |
1987年 | 12篇 |
1986年 | 3篇 |
1985年 | 16篇 |
1984年 | 4篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有7500条查询结果,搜索用时 15 毫秒
11.
Khalid Maskaoui Tianling Zheng Huasheng Hong Zhiming Yu Zhong Hu Yun Tian Lizhe Cai 《海洋学报(英文版)》2003,22(3):443-451
The surface and bottom waters samples were collected from six locations in Xiamen western sea. The quantified estimation of bacterial production (3H-thymidine method) and observation of bacterial heterotrophic activity (14C-glucose method) have been made in order to have a better understanding of the role of marine bacteria and their activities. The results showed that the mean value of bacterial heterotrophic activity was 9×108 cells/(L.h) in the surface waters and 2.6×108 cells/(L.h) in the bottom waters. The mean value of bacterial production was 38×108 cells/(L.h) in the surface waters and 7.1×108 cells/(L.h) in the bottom waters. The relationship between bacterial production, heterotrophic activity, POC and DOC measured during this survey were discussed. The good understanding of the relationship between bacteria activity and total coliform was addressed. 相似文献
12.
A Computational Model for Velocity Separation in Shallow Sea 总被引:1,自引:0,他引:1
Based on the hydrodynamical feature and the theoretical velocity profiles of tidal flow and vvind-induced flow in shal-low sea, a computational model is established for the first time, which can separate observed velocity into tidal velocity and wind-induced velocity by use of the least square method. With the model, not only the surface velocities of tidal flow and vvind-induced flow are obtained, but also the bed roughness height is determined and the wind velocity above the wa-ter surface is estimated. For verification of the model, the observed velocity in the Yellow River Estuary and the laborato-ry test is separated, then it is applied to the Yangtze River Estuary. All the results are satisfactory. The research results show that the model is simple in method, feasible in process and reasonable in result. The model is a valid approach to analysis and computation of field dala, and can be applied to separate the observed velocity in shallow sea; at the same time, reasonable boundary conditions of th 相似文献
13.
14.
通过分析1980年以后的海冰资料和卫星云图照片,对黄、渤海沿岸11个海冰测点的历史变迁进行了评述,浅析了测点的优劣及使用资料时应注意的事项。 相似文献
15.
The North Pacific has the world's largest groundfish fisheries, with a value in excess of $1 billion annually. The North Pacific also is home to the largest population of Steller sea lions (SSL), an ancient species that is now endangered. Decline of the western stock of SSL in the 1970–1990s coincided with the US nationalization and exponential growth in the Gulf of Alaska and Bering Sea/Aleutian Islands groundfish fishery.The article treats five aspects of the competition between the fishery and protection of the endangered species. First, we analyze competition of interests in the use, management, and preservation of the North Pacific commons, including offshore and near-shore fisheries, environmental organizations, governments (federal, state, and local), and the scientific community. Second, the article compares and contrasts provisions of the National Environmental Policy Act, the Marine Mammal Protection Act, the Endangered Species Act, and the Magnuson–Stevens Act (as amended in 1996 by the Sustainable Fisheries Act).Third, we examine the regulatory environment with a focus on the National Marine Fisheries Service (NMFS) and its relationship to the North Pacific Fishery Management Council. We illustrate how NMFS establishes fishery management plans and the methods, such as crafting biological opinions and environmental-impact-statements, it uses to resolve conflicts. Fourth, we investigate how the dual pressures on the agency—to increase fisheries production for the benefit of the industry and to preserve endangered marine species—have affected its culture (behavioral norms and operational codes). Then, the article explains agency changes in terms of crises, competition among affected interests, and development of new scientific knowledge.The article concludes by drawing lessons from the SSL controversy in the North Pacific which may pertain to national and global biodiversity conflicts. These concern the role of law in biodiversity protection, the role of science, and agency capacity for change. 相似文献
16.
17.
该文对目前工业上生产纳米碳酸钙的方法作了较为详细的综述。对一步碳化法、两步碳化法、多段喷雾碳化法、旋转填充床碳化反应器碳化技术制备链形、纺锤形、球形、立方形等不同形状的纳米碳酸钙材料的方法进行了比较和总结 相似文献
18.
提出了海上浮动软管的三维静态分析模型。在四级海情下,对输送柴油的软管求得了解析解,得出了软管在侧向和垂直方向的偏移及其所受的拉力,认为此时的软管是不安全的。 相似文献
19.
20.
真鲷Pagrosomus major Temminck et Schlegel早期发育阶段游泳行为的发育可以分为:(1)旋转式运动;(2)阶梯型运动;(3)间断式水平运动和滑翔;(4)巡游以及(5)疾游五种类型。前期仔鱼的摄食方式主要是伴有甩头动作的前冲摄食;后期仔鱼的摄食主要有两种类型:一种是身体弯成S形的“S攻击型”;另一种为不作摄食姿势的“咬食攻击型”。摄食方式随着发育水平和饵料种类的不同而异。文中对发育过程中出现的攻击行为、护食行为、互食行为、猝死现象亦进行了描述。并对游泳、摄食以及各种行为的生态意义和实际意义进行了讨论。 相似文献