全文获取类型
收费全文 | 34526篇 |
免费 | 6115篇 |
国内免费 | 9608篇 |
专业分类
测绘学 | 5134篇 |
大气科学 | 5273篇 |
地球物理 | 8755篇 |
地质学 | 17640篇 |
海洋学 | 4269篇 |
天文学 | 264篇 |
综合类 | 2663篇 |
自然地理 | 6251篇 |
出版年
2024年 | 136篇 |
2023年 | 394篇 |
2022年 | 1186篇 |
2021年 | 1423篇 |
2020年 | 1707篇 |
2019年 | 1902篇 |
2018年 | 1652篇 |
2017年 | 1704篇 |
2016年 | 1896篇 |
2015年 | 2090篇 |
2014年 | 2308篇 |
2013年 | 2561篇 |
2012年 | 2392篇 |
2011年 | 2552篇 |
2010年 | 2077篇 |
2009年 | 2302篇 |
2008年 | 2284篇 |
2007年 | 2382篇 |
2006年 | 2414篇 |
2005年 | 2038篇 |
2004年 | 1875篇 |
2003年 | 1576篇 |
2002年 | 1420篇 |
2001年 | 1197篇 |
2000年 | 1061篇 |
1999年 | 936篇 |
1998年 | 855篇 |
1997年 | 743篇 |
1996年 | 650篇 |
1995年 | 552篇 |
1994年 | 474篇 |
1993年 | 402篇 |
1992年 | 270篇 |
1991年 | 220篇 |
1990年 | 147篇 |
1989年 | 117篇 |
1988年 | 104篇 |
1987年 | 67篇 |
1986年 | 38篇 |
1985年 | 38篇 |
1984年 | 24篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
201.
Full-range equation covering all the flow regimes in a wave boundary layer is proposed for the boundary layer thickness. The results are compared with the available experimental data and good agreement has been found. In case of wave boundary layers, there are three definitions of boundary layer thickness in use. Therefore, the full-range equation is derived for three of the definitions. The findings of this study may be useful in calculating suspended sediment transport in coastal environments and studying wave–current combined motion. 相似文献
202.
The recent sea-ice reduction in the Arctic Ocean is not spatially uniform, but is disproportionally large around the Northwind
Ridge and Chukchi Plateau compared to elsewhere in the Canada Basin. In the Northwind Ridge region, Pacific Summer Water (PSW)
delivered from the Bering Sea occupies the subsurface layer. The spatial distribution of warm PSW shows a quite similar pattern
to the recent ice retreat, suggesting the influence of PSW on the sea-ice reduction. To understand the regionality of the
recent ice retreat, we examine the dynamics and timing of the delivery of the PSW into this region. Here, we adopt a two-layer
linearized potential vorticity equation to investigate the behavior of Rossby waves in the presence of a topographic discontinuity
in the high latitude ocean. The analytical results show a quite different structure from those of mid-latitude basins due
to the small value of β. Incident barotropic waves excited by the sea-ice motion with large annual variation can be scattered
into both barotropic and baroclinic modes at the discontinuity. Since the scattered baroclinic Rossby wave with annual frequency
cannot propagate freely, a strong baroclinic current near the topographic discontinuity is established. The seasonal variation
of current near the topographic discontinuity would cause a kind of selective switching system for shelf water transport into
the basin. In our simple analytical model, the enhanced northward transport of summer water and reduced northward transport
of winter water are well demonstrated. The present study indicates that these basic dynamics imply that a strengthening of
the surface forcing during winter in the Canada Basin could cause sea-ice reduction in the Western Arctic through the changes
of underlying Pacific Summer Water. 相似文献
203.
204.
辽东湾地区下第三系地震速度—岩性预测模型研究 总被引:9,自引:1,他引:9
地震速度-岩性预测模型由四个子模型组成:即(1)砂泥岩压实模型;(2)地震层速度转换模型;(3)速度校正模型;(4)砂岩指数转换模型。辽东湾地区的实际资料证明,上述四个子模型不但决定了岩性预测的具体方法,而且严格控制岩性预测的精度。 相似文献
205.
Based on the Nansha Islands' closed atoll conception-remote sensing system in Part Ⅰ,through the solution of the information function value and isostatic value of closed and quasi-closed atoll, and by using topological analysis on growth form and the composite remote sensing quantization date as the calculating coefficients, the feature vector system and its mathematical model of two kinds of atoll are built, and the multivariate analysis is made with some examples. 相似文献
206.
The construction of reservoir models is frustrated by the fact that core and well cover only a fraction of the reservoir volume and it is therefore difficult to determine features like facies shape, -size, and -distribution, inter- and intra-facies boundaries and lateral trends from them. These features are, however, critical to fluid flow and they should necessarily be incorporated in the reservoir model and we therefore propose to systematically describe geometry and distribution of facies. To this end we make use of “standard facies models” that a priori contain all elements and boundaries of facies for a number of typical depositional environments. 相似文献
207.
珠江河口西南风强迫下潮流场的数值模拟 总被引:1,自引:0,他引:1
采用Backhaus三维斜压模型模拟了均匀西南风场对珠江口近岸海域的影响,并与无风情况作了对比;通过对珠江河口盐度场及风生环流的分析比较,结果表明,模型较为真实地再现了夏季珠江河口的水动力学特性。 相似文献
208.
JGOFS has revealed the importance of marine biological activity to the global carbon cycle. Ecological models are valuable tools for improving our understanding of biogeochemical cycles. Through a series of workshops, the North Pacific Marine Science Organization (PICES) developed NEMURO (North Pacific Ecosystem Model Understanding Regional Oceanography) a model, specifically designed to simulate the lower trophic ecosystem in the North Pacific Ocean. Its ability to simulate vertical fluxes generated by biological activities has not yet been validated. Here compare NEMURO with several other lower trophic level models of the northern North Pacific. The different ecosystem models are each embedded in a common three-dimensional physical model, and the simulated vertical flux of POM and the biomass of phytoplankton are compared. The models compared are: (1) NEMURO, (2) the Kishi and Nakata Model (Kishi et al., 1981), (3) KKYS (Kawamiya et al., 1995, 2000a, 2000b), and (4) the Denman model (Denman and Peña, 2002). With simple NPZD models, it is difficult to describe the production of POM (Particulate Organic Matter) and hence the simulations of vertical flux are poor. However, if the parameters are properly defined, the primary production can be well reproduced, even though none of models we used here includes iron limitation effects. On the whole, NEMURO gave a satisfactory simulation of the vertical flux of POM in the northern North Pacific. 相似文献
209.
耿贝尔逻辑模型在极值风速和有效波高联合概率分布中的应用 总被引:7,自引:1,他引:7
首先介绍了耿贝尔逻辑模型,采用该模型对南海海域的涠州岛海洋站的风速和有效波高实测数据进行了分析,结果表明耿贝尔逻辑模型较好地描述了年极值风速和有效波高两随机变量的联合分布;采用得到的极值风浪联合概率分布推算了不同重现期的极值风速和波高,表明考虑风速和波高相关性对设计荷载的确定有显著影响。由于耿贝尔逻辑模型具有函数结构简单,参数估计方便,因此有望成为极值风速和波高联合分布的较理想概率模型。 相似文献
210.
V.Hachemi Safai 《Applied Ocean Research》1983,5(4):215-225
The paper presents a theoretical and numerical approach to the dynamical behaviour of risers in deep water which takes into account two types of nonlinearity; that due to viscous drag forces and that due to the large displacements of the riser when submitted to strong axial loads. As the second nonlinearity may have a significant influence upon the behaviour of risers in deep water, a method for automatically updating the structural geometry during the dynamic analysis is given. A computer programme has been written for this purpose. 相似文献