全文获取类型
收费全文 | 15453篇 |
免费 | 2916篇 |
国内免费 | 4880篇 |
专业分类
测绘学 | 920篇 |
大气科学 | 2835篇 |
地球物理 | 4066篇 |
地质学 | 9725篇 |
海洋学 | 1890篇 |
天文学 | 849篇 |
综合类 | 1654篇 |
自然地理 | 1310篇 |
出版年
2024年 | 41篇 |
2023年 | 186篇 |
2022年 | 415篇 |
2021年 | 495篇 |
2020年 | 404篇 |
2019年 | 463篇 |
2018年 | 488篇 |
2017年 | 480篇 |
2016年 | 603篇 |
2015年 | 513篇 |
2014年 | 617篇 |
2013年 | 596篇 |
2012年 | 557篇 |
2011年 | 1027篇 |
2010年 | 940篇 |
2009年 | 981篇 |
2008年 | 677篇 |
2007年 | 794篇 |
2006年 | 899篇 |
2005年 | 990篇 |
2004年 | 1453篇 |
2003年 | 1022篇 |
2002年 | 786篇 |
2001年 | 728篇 |
2000年 | 608篇 |
1999年 | 773篇 |
1998年 | 771篇 |
1997年 | 702篇 |
1996年 | 623篇 |
1995年 | 514篇 |
1994年 | 437篇 |
1993年 | 614篇 |
1992年 | 533篇 |
1991年 | 334篇 |
1990年 | 198篇 |
1989年 | 197篇 |
1988年 | 152篇 |
1987年 | 115篇 |
1986年 | 88篇 |
1985年 | 48篇 |
1984年 | 39篇 |
1983年 | 27篇 |
1982年 | 42篇 |
1981年 | 33篇 |
1980年 | 23篇 |
1979年 | 25篇 |
1977年 | 19篇 |
1976年 | 19篇 |
1958年 | 19篇 |
1937年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
盐藻和β-胡萝卜素研究述评 总被引:11,自引:0,他引:11
养殖盐藻生产β-胡萝卜素是近十几年新兴起的研究领域,因其应用前途广阔,现已成为微藻生物学的研究前沿和热点,预计本世纪末和下世纪初将有更大发展。鉴于我国在这方面文章不系统,不全面,本文从盐藻生物学,养殖学,β-胡萝卜素异构体,β-胡萝卜素形成生理等角度全面概念了该领域研究现状,并提出存在的问题与研究方向。 相似文献
42.
The modified hybrid element method (MHEM) is utilized to predict and analyze wave forces on arbitrarily shaped multiple bodies. This method can be applied to waves of all water depths, i. e. shallow, intermediate, and deep waters, on slowly varying seabed. The MHEM employs the ICCG method to save CPU and storage, thus the computation of wave forces for large multi-body systems can be carried out on microcomputers. Numerical results of the present method are compared with experimental data and other solutions. It is shown that the MHEM provides more accurate solutions of the wave forces than other numerical methods do. Therefore, the methodology presented herein can be used in the design of coastal and ocean structures. 相似文献
43.
44.
-Morphology, reproduction, ecology and isoenzyme electrophoresis of a Capitella complex in Qingdao were examined from 1983 to 1984. We determined that the Capitella complex in Qingdao was composed of at least three sibling species: Capitella cf capitata, Capitella sp. I and Capitella sp. IT. Although these three species are very similar in morphology, they differ in: three kinds of isoenzyme electrophoresis, staining reactions, developmental pattern, larval morphology and dispersal, reproductive strategies, breeding season and population ecology. In addition, they show a series of minor quantitative variations in adult morphology, especially in number and morphology of setae. Such differences can be detected only at the population level. Some ecological data such as density, growth rate, mortality and sex distribution are also provided in this paper. 相似文献
45.
青藏高原东部多年冻土退化对环境的影响 总被引:3,自引:0,他引:3
退化是本区多年冻土变化的基本趋势,不同区段退化幅度有差异,影响退化的因素除了全球气候转暖外,还有局地气候和地下水迳流。在退化敏感的地带,工程建设,牧区生态平衡都有不可忽视的影响。 相似文献
46.
Li Yucheng He Ming Professor Dalian University of Technology Dalian Former master student Dalian University of Technology Dalian 《中国海洋工程》1994,(3)
-Based on the extended Morison Equation and model tests, the in-line forces on small square cylinders caused by waves (regular and irregular) and currents are analyzed in detail in this paper. The hydrodynamic coefficient CD and Cu related to KC number and the effect of direction of wave incidence are also given, which can be used in engineering practice. 相似文献
47.
48.
Li Dashan Shen Ying Ren Rushu Chen Yao
Senior Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing Associate Professor Hohai University Nanjing Master Hohai University Nanjing 《中国海洋工程》1997,(1)
In this paper,the characteristics of density current under the action of waves are describedwith the help of flume experiment and theoretical analysis.The study shows that turbid water under the ac-tion of the waves can present three types of motion,i.e.significant stratification,fragile stratification andstrong mixing.The motion of turbid water presents significant stratification when(H/D)/△ρ/ρ~(1/2)≤4.5,generally this state is known as density current.The formulas of motionvelocity,thickness,and discharge of density current moving on horizontal bottom are derived by use of ba-sic equations such as momemtum equation,equation of energy conservation and continuity equation offluid.The time-average velocity and the thickness of density current under the action of waves have a rela-tionship with such parameters as relative density(△ρ/ρ),wave height(H),and water depth(D).Whenthese parameters are determined,the time-average thickness and motion velocity of density current are al-so determined.The relat 相似文献
49.
Zhang Jianguo Yan Chi Yan Shuwang
Lecturer Dept. of Hydraulic Eng. Tianjin University Tianjin Associate Professor Dept. of Hydraulic Eng. Tianjin University Tianjin Professor Dept. of Hydraulic Eng. Tianjin University Tianjin 《中国海洋工程》1996,(1)
This paper describes the model tests for determining the axial friction and the lateral resistance of sand to pipeline by using fine sand and prototype pipeline, and the calculation method based on limit analysis theory is verified. The effect of cyclic loading is considered in the test. 相似文献
50.
Liu Jiaju Zhang Jingchao Prof. Senior Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing Senior Engineer River Harbour Department Nanjing Hydralulic Research Institute Nanjing 《中国海洋工程》1992,(2)
- This paper, after briefly reviewing the experimental research on sediment transport on muddy beach since the 1950s, improves and perfects the method for forecasting siltation in navigation channels and harbour basins which was first put forward in China by the authors. In consideration of silty sediment and sand, some factors in forecasting methods have been changed and modified. Consequently, the modified methods can be used either to compute siltation in navigation channels and harbour basins on muddy beach or to compute siltation and scouring in navigation channels and harbour basins on both silty beach and sandy beach. The verification of field data from eleven large, medium and small natural harbours shows a good agreement between the forecasting by the modified method and the natural conditions. Finally, the paper deals with the rational utilization of water area after the construction of the West Dyke in Lianyungang, the maintenance of water depth of the navigation channel at the entrance, siltation distribution, siltation in the navigation channel and harbour basin for ships of 100 thousand tonnnage. Results once again prove that the prospect of constructing Lianyungang Harbour into a deepwater harbour is bright. 相似文献