全文获取类型
收费全文 | 3222篇 |
免费 | 636篇 |
国内免费 | 685篇 |
专业分类
测绘学 | 318篇 |
大气科学 | 331篇 |
地球物理 | 962篇 |
地质学 | 1509篇 |
海洋学 | 533篇 |
天文学 | 74篇 |
综合类 | 327篇 |
自然地理 | 489篇 |
出版年
2024年 | 13篇 |
2023年 | 46篇 |
2022年 | 102篇 |
2021年 | 128篇 |
2020年 | 169篇 |
2019年 | 175篇 |
2018年 | 135篇 |
2017年 | 142篇 |
2016年 | 178篇 |
2015年 | 157篇 |
2014年 | 208篇 |
2013年 | 264篇 |
2012年 | 197篇 |
2011年 | 229篇 |
2010年 | 174篇 |
2009年 | 182篇 |
2008年 | 209篇 |
2007年 | 226篇 |
2006年 | 185篇 |
2005年 | 162篇 |
2004年 | 150篇 |
2003年 | 101篇 |
2002年 | 118篇 |
2001年 | 118篇 |
2000年 | 112篇 |
1999年 | 90篇 |
1998年 | 95篇 |
1997年 | 87篇 |
1996年 | 75篇 |
1995年 | 39篇 |
1994年 | 48篇 |
1993年 | 50篇 |
1992年 | 32篇 |
1991年 | 29篇 |
1990年 | 20篇 |
1989年 | 21篇 |
1988年 | 22篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1954年 | 5篇 |
排序方式: 共有4543条查询结果,搜索用时 171 毫秒
21.
Trends in biomass, density and diversity of North Sea macrofauna 总被引:6,自引:2,他引:6
22.
作用于平台桩腿的海冰屈曲破坏冰压力随机过程模型及其参数确定 总被引:2,自引:1,他引:2
冰对结构的作用过程是典型的随机过程。本文在冰压力过程为平稳过程的假设下,从渤海海冰对平台桩腿作用的大量实测冰压力数据中,选取了21条冰屈曲破坏时的冰压力时程曲线,对它们进行谱分析后,得到了单点冰屈曲破坏的压力随机过程的谱密度,并确定了谱参数及其跟环境要素的关系,依据文献[1]中冰压力沿圆柱面的空间分布,建立了绕桩腿的冰压力随机场模型,并得到了作用于桩腿的总冰力随机过程及其谱密度。本文的研究成果为平台结构冰激随机振动和疲劳累积损伤分析提供了荷载基础 相似文献
23.
24.
25.
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
26.
27.
运用扫描电镜(SEM)和X-射线衍射(XRD)技术研究了电化学脱盐处理对钢样-砂浆界面微观结构的影响。试验结果表明,经电化学脱盐处理后,钢样-砂浆界面的微观形貌特征与组成发生了明显的变化。 相似文献
28.
Breaking wave induced nearsurface turbulence has important consequences for many physical and biochemical processes including water column and nutrients mixing,heat and gases exchange across air-sea interface.The energy loss from wave breaking and the bubble plume penetration depth are estimated.As a consequence,the vertical distribution of the turbulent kinetic energy(TKE),the TKE dissipation rate and the eddy viscosity induced by wave breaking are also provided.It is indicated that model results are found to be consistent with the observational evidence that most TKE generated by wave breaking is lost within a depth of a few meters near the sea surface.High turbulence level with intensities of eddy viscosity induced by breaking is nearly four orders larger than υwl(=κuwz),the value predicted for the wall layer scaling close to the surface,where uw is the friction velocity in water,κ with 0.4 is the von Kármán constant,and z is the water depth,and the strength of the eddy viscosity depends both on wind speed and sea state,and decays rapidly through the depth.This leads to the conclusion that the breaking wave induced vertical mixing is mainly limited to the near surface layer,well above the classical values expected from the similarity theory.Deeper down,however,the effects of wave breaking on the vertical mixing become less important. 相似文献
29.
A model for the depth-limited distribution of the highest wave in a sea state is presented. The distribution for the extreme wave height is based on a probability density function (pdf) for depth-limited wave height distribution for individual waves [Méndez, F.J., Losada, I.J., Medina, R. 2004. Transformation model of wave height distribution. Coastal Eng, Vol. 50, 97:115.] and considers the correlation between consecutive waves. The model is validated using field data showing a good representation of the extreme wave heights in the surf zone. Some important statistical wave heights are parameterized obtaining useful expressions that can be used in further calculations. 相似文献
30.
High-resolution underway temperature and conductivity measurements collected by R/V Knorr during winter and spring 2003 are used to characterize errors associated with spatial aliasing in the northern and central Adriatic Sea. During winter, 99th percentile temperature, salinity and density errors were 0.62 °C, 0.25 and 0.12 kg/m3 (0.25 °C, 0.10 and 0.05 kg/m3) for sampling at 10 km (5 km) horizontal resolution, respectively. The corresponding values in spring were 1.31 °C, 0.50 and 0.40 kg/m3 (0.93 °C, 0.25 and 0.22 kg/m3) for the 10 km (5 km) sample spacing, respectively. The largest errors were associated with energetic regions over the shallow, western Adriatic, in front of the Po River mouth and off the tip of the Istrian peninsula. The deeper eastern basin exhibited smaller errors. The variability of errors in time and space reflected the variability of small-scale density features, characterized by wavelengths as small as 2 km in winter and 1 km in spring and being more pronounced in the western and northern parts of the Adriatic. As these results indicate that errors associated with undersampling can be considerable, they should be taken into account while planning future CTD measurements in the region. 相似文献