全文获取类型
收费全文 | 33719篇 |
免费 | 6071篇 |
国内免费 | 8288篇 |
专业分类
测绘学 | 2711篇 |
大气科学 | 7117篇 |
地球物理 | 8265篇 |
地质学 | 16626篇 |
海洋学 | 4027篇 |
天文学 | 1368篇 |
综合类 | 3668篇 |
自然地理 | 4296篇 |
出版年
2024年 | 183篇 |
2023年 | 597篇 |
2022年 | 1530篇 |
2021年 | 1794篇 |
2020年 | 1445篇 |
2019年 | 1720篇 |
2018年 | 1845篇 |
2017年 | 1696篇 |
2016年 | 1964篇 |
2015年 | 1734篇 |
2014年 | 2109篇 |
2013年 | 1984篇 |
2012年 | 1931篇 |
2011年 | 1996篇 |
2010年 | 2112篇 |
2009年 | 1985篇 |
2008年 | 1828篇 |
2007年 | 1736篇 |
2006年 | 1359篇 |
2005年 | 1267篇 |
2004年 | 990篇 |
2003年 | 1001篇 |
2002年 | 939篇 |
2001年 | 976篇 |
2000年 | 1121篇 |
1999年 | 1513篇 |
1998年 | 1220篇 |
1997年 | 1148篇 |
1996年 | 1073篇 |
1995年 | 928篇 |
1994年 | 810篇 |
1993年 | 734篇 |
1992年 | 581篇 |
1991年 | 460篇 |
1990年 | 334篇 |
1989年 | 319篇 |
1988年 | 273篇 |
1987年 | 152篇 |
1986年 | 144篇 |
1985年 | 96篇 |
1984年 | 99篇 |
1983年 | 75篇 |
1982年 | 65篇 |
1981年 | 58篇 |
1980年 | 41篇 |
1979年 | 34篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1958年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
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
82.
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
83.
84.
黄河三角洲地貌环境体系 总被引:4,自引:0,他引:4
黄河三角洲是由三角洲上部冲积平原一下部冲积海积平原(超潮滩)─周边潮滩三个区带的地貌系列构成.它们之间形成三条地貌环境岸线,是一个复杂而统一的陆上─潮滩堆积地貌体系.该体系研究对三角洲发育.环境及其开发利用有一定理论和实践意义. 相似文献
85.
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
86.
Li Runpei Chen Weigang Gu Yongning
Professor Shanghai Jiao Tong University Shanghai Assistant Shanghai Jiao Tong University Shanghai 《中国海洋工程》1996,(1)
In this paper a numerical analysis method combining FEM incemental technique with limit analysis concept is proposed for the study of the static strength of offshore platform in collision. Large deformation and plasticity are accounted for and the limit yield surface expressed by generalized stress for a tubular section is derived. The modified stiffness matrix of space beam element is formulated by Plastic Node Method. The buckling behavior of beam columns can also be taken into account. It can trace the generation of plastic hinges during loading and finally the ultimate strength of offshore platform against collision is obtained. 相似文献
87.
波浪作用下异重流运动特性研究 总被引:3,自引:0,他引:3
本文通过水槽试验和理论分析手段对波浪作用下异重流运动特性进行了研究,应用流体运动基本方程推导了异重流在水平底面运动时的运动速度、厚度和流量表达式。结果表明,计算结果与水槽试验较一致 相似文献
88.
The interaction of waves and currents is studied by the dynamical coupling of a third generation wave model and a two-dimensional storm surge model. The coupling process of the two models is implemented synchronously. To estimate the effects of waves on the generation of storm surges, the theory of Janssen is used. The effects of the wave radiation stress on surge levels and the effects of storm-induced currents on waves are also investigated.The coupled wave and storm surge models have been tested by hindcasting two storm events in the northern South China Sea. The use of the Simth and Banke stress relation underestimates the surges by 10%. The inclusion of the radiation stress improves the accuracy of the computed results slightly by 2%. The introduction of a wave-dependent surface drag gives a significant improvement. The storm-induced currents clearly affect the wave characteristics at the peak stage. However, as far as the prediction of wave height is concerned, it is better not to consider the wave radiation stress in the storm surge model unless this is accompanied by a wave-dependent surface drag. 相似文献
89.
90.