全文获取类型
收费全文 | 21487篇 |
免费 | 5578篇 |
国内免费 | 7800篇 |
专业分类
测绘学 | 3940篇 |
大气科学 | 2882篇 |
地球物理 | 4176篇 |
地质学 | 14143篇 |
海洋学 | 4745篇 |
天文学 | 338篇 |
综合类 | 1762篇 |
自然地理 | 2879篇 |
出版年
2024年 | 138篇 |
2023年 | 496篇 |
2022年 | 1238篇 |
2021年 | 1505篇 |
2020年 | 1281篇 |
2019年 | 1360篇 |
2018年 | 1430篇 |
2017年 | 1300篇 |
2016年 | 1254篇 |
2015年 | 1570篇 |
2014年 | 1475篇 |
2013年 | 1833篇 |
2012年 | 2044篇 |
2011年 | 2030篇 |
2010年 | 1946篇 |
2009年 | 1797篇 |
2008年 | 1944篇 |
2007年 | 1714篇 |
2006年 | 1640篇 |
2005年 | 1434篇 |
2004年 | 1040篇 |
2003年 | 845篇 |
2002年 | 923篇 |
2001年 | 845篇 |
2000年 | 639篇 |
1999年 | 326篇 |
1998年 | 156篇 |
1997年 | 125篇 |
1996年 | 87篇 |
1995年 | 65篇 |
1994年 | 55篇 |
1993年 | 46篇 |
1992年 | 42篇 |
1991年 | 22篇 |
1990年 | 33篇 |
1989年 | 18篇 |
1988年 | 24篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 4篇 |
1979年 | 13篇 |
1974年 | 2篇 |
1965年 | 2篇 |
1958年 | 3篇 |
1957年 | 6篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
151.
152.
153.
154.
A method combining boundary and finite element approaches as well as modal analysis to solve the acoustical scattering from elastic obstacle in infinite fluid is described. An elastic cylinder with finite length immersed in water is chosen as an example for numerical demonstration. The computed frequency response and direction pattern of the backscattering target strength of the cylinder are conformable to those measured. 相似文献
155.
156.
We establish the equations of finite element approximation for three-dimensional ocean current and calculate the Kuroshio current in the eastern sea area off Taiwan Province. The interpolation error of finite element approximation is given as Eq. (3. 14). 相似文献
157.
A nutrient dynamic model coupled with a 3D physical model has been developed to study the annual cycle of phytoplankton production in the Yellow Sea. The biological model involves interactions between inorganic nitrogen (nitrate and ammonium), phosphate and phytoplankton biomass. The model successfully reproduces the main features of phytoplankton-nutrient variation and dynamics of production. 1. The well-mixed coastal water is characterized by high primary production, as well as high new production. 2. In summer, the convergence of tidal front is an important hydrodynamic process, which contributes to high biomass at frontal areas. 3. The evolution of phytoplankton blooms and thermocline in the central region demonstrate that mixing is a dominant factor to the production in the Yellow Sea. In this simulation, nitrate- and ammonium-based productions are estimated regionally and temporally. The northern Yellow Sea is one of the highly ranked regions in the Yellow Sea for the capability of fixing carbon and nitrogen. The annual averaged f-ratio of 0.37 indicates that regenerated production prevails over the Yellow Sea. The result also shows that phosphate is the major nutrient, limiting phytoplankton growth throughout the year and it can be an indicator to predict the bloom magnitude. Finally, the relative roles of external nutrient sources have been evaluated, and benthic fluxes might play a significant role in compensating 54.6% of new nitrogen for new production consumption. 相似文献
158.
研究区位于1964~1976年黄河由刁口流路入海时形成的三角洲潮坪.为进行石油开采在潮坪上构筑的交通设施对波浪形成了良好的屏障,水动力条件具有显著差异的屏障两侧潮坪是研究潮坪特征对水动力条件响应的天然实验场所.在屏障两侧各选择一典型区,实测地貌形态,取样品进行粒度成分分析,根据实测资料分析确定潮坪分形特征.发现水动力环境的强弱决定着潮坪的形貌、沉积物粒度分维值的变化规律.水动力环境强的一侧潮坪滩面分维值高,且随着初始计算网格宽度增大迅速降维;表层沉积物粒度分维值小,且离散性大.相反,在另一侧潮坪滩面分维值低,且随着初始计算网格宽度增大分维值无显著变化;表层沉积物粒度分维值高,且具有较好的一致性.当初始计算网格宽度增大到某个值时,两侧潮坪形貌分维值渐趋一致.在屏障两侧各沿一条与屏障大角度相交的测线取样,并各选择一点采取不同深度的样品做分析计算,发现在水动力条件弱的一侧,样品的粒度分维值表现为远离屏障逐步降维、随深度增加分维值增大的规律;相反一侧粒度分维值变化的规律性很不明显.讨论了水动力环境对潮坪分形特征影响机理. 相似文献
159.
西太平洋暖池变异及其对西太平洋次表层海温场的影响 总被引:9,自引:0,他引:9
应用热带太平洋上层XBT温度资料,分析研究了西太平洋暖池区(0°~16°N,125°~145°E)上层海洋的变化特征以及与西太平洋次表层海温场之间的关系.研究表明,西太平洋暖池区的垂向温度存在显著的年际变化,尤其在次表层(120~200m)的变化最为明显.西太平洋暖池区的次表层冷暖信号明显早于西太平洋次表层的海温异常.分析发现,西太平洋暖池区的海温异常是导致整个西太平洋次表层海温场变异的关键区,当西太平洋暖池区的次表层冷暖信号加强时,3~4个月后西太平洋海温场出现大范围的冷暖异常. 相似文献
160.
The probability of fractal determination of coastal types based on GIS is preliminarily discussed with China as an example. Finally, some significant conclusions are drawn: (1) The fractal dimension of coastline of the bedrock coast is larger than that of the plain coast on the same scale map; (2) As far as the bedrock coast is concerned, the larger fractal dimension of coastline of the bedrock coast on the same scale map indicates that the bedrock coast is probably not typical; (3) As far as the plain coast is concerned, the smaller fractal dimension of coastline of the plain coast on the same scale map indicates that it is probably the silt plain coast; (4) The different substantial compositions affect the fractal dimensions of coastlines of different coastal types. In general, the coast which lies in the north of the Hangzhou Bay consists of sand mainly, its surface is flat, and it is connected with the coastal plain, its landform is broad shoal, its total change is comparatively homogenous in the tidal dynamic process, and thus, the relatively smaller fractal dimension of coastline results from this. For the bedrock coast, there is more bedrock, the coastline is comparatively smooth and straight, being affected by the faults and ocean dynamic process, which result in the larger fractal dimension. 相似文献