全文获取类型
收费全文 | 4321篇 |
免费 | 875篇 |
国内免费 | 1014篇 |
专业分类
测绘学 | 538篇 |
大气科学 | 336篇 |
地球物理 | 1401篇 |
地质学 | 2443篇 |
海洋学 | 521篇 |
天文学 | 339篇 |
综合类 | 238篇 |
自然地理 | 394篇 |
出版年
2024年 | 13篇 |
2023年 | 52篇 |
2022年 | 105篇 |
2021年 | 124篇 |
2020年 | 151篇 |
2019年 | 202篇 |
2018年 | 140篇 |
2017年 | 196篇 |
2016年 | 214篇 |
2015年 | 225篇 |
2014年 | 221篇 |
2013年 | 276篇 |
2012年 | 305篇 |
2011年 | 250篇 |
2010年 | 261篇 |
2009年 | 310篇 |
2008年 | 299篇 |
2007年 | 328篇 |
2006年 | 336篇 |
2005年 | 282篇 |
2004年 | 258篇 |
2003年 | 193篇 |
2002年 | 210篇 |
2001年 | 152篇 |
2000年 | 171篇 |
1999年 | 180篇 |
1998年 | 113篇 |
1997年 | 112篇 |
1996年 | 96篇 |
1995年 | 92篇 |
1994年 | 68篇 |
1993年 | 67篇 |
1992年 | 42篇 |
1991年 | 34篇 |
1990年 | 21篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1954年 | 5篇 |
排序方式: 共有6210条查询结果,搜索用时 31 毫秒
21.
针对多传感器观测环境下带乘性噪声系统的逆向最优滤波与反褶积融合估计问题 ,本文提出了 1种基于极大似然准则的最优融合算法。该算法中各单传感器间并行计算 ,并且融合中心与单传感器处理中心间无反向通讯 ,因而执行效率较高。仿真表明 ,该融合算法产生的逆向滤波与反褶积比单传感器处理结果有较明显提高 相似文献
22.
23.
24.
A Note on Soil Structure Resistance of Natural Marine Deposits 总被引:1,自引:1,他引:1
It has been well documented that natural normally-consolidated marine soils are generally subjected to the effects of soil structure. The interpretation of the resistance of soil structure is an important issue in the theory study and engineering practice of ocean engineering and geotechnical engineering. It is traditionally considered that the resistance of soil structure gradually disappears with increasing stress level when the applied stress is beyond the consolidation yield stress. In this study, however, it is found that this traditional interpretation of the resistance of soil structure can not explain the strength behavior of natural marine deposits with a normally-consolidated stress history A new interpretation of the resistance of soil structure is proposed based on the strength behavior. In the preyield state, the undrained strength of natural marine deposits is composed of two components: one developed by the applied stress and the other developed by the resistance of soil structure. When the applied stress is beyond the consolidation yield stress, the strength behavior is independent of the resistance of soil structure. 相似文献
25.
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
26.
Michael Riedel 《Marine Geophysical Researches》2007,28(4):355-371
Two single-channel seismic (SCS) data sets collected in 2000 and 2005 were used for a four-dimensional (4D) time-lapse analysis
of an active cold vent (Bullseye Vent). The data set acquired in 2000 serves as a reference in the applied processing sequence.
The 4D processing sequence utilizes time- and phase-matching, gain adjustments and shaping filters to transform the 2005 data
set so that it is most comparable to the conditions under which the 2000 data were acquired. The cold vent is characterized
by seismic blanking, which is a result of the presence of gas hydrate in the subsurface either within coarser-grained turbidite
sands or in fractures, as well as free gas trapped in these fracture systems. The area of blanking was defined using the seismic
attributes instantaneous amplitude and similarity. Several areas were identified where blanking was reduced in 2005 relative
to 2000. But most of the centre of Bullseye Vent and the area around it were seen to be characterized by intensified blanking
in 2005. Tracing these areas of intensified blanking through the three-dimensional (3D) seismic volume defined several apparent
new flow pathways that were not seen in the 2000 data, which are interpreted as newly generated fractures/faults for upward
fluid migration. Intensified blanking is interpreted as a result of new formation of gas hydrate in the subsurface along new
fracture pathways. Areas with reduced blanking may be zones where formerly plugged fractures that had trapped some free gas
may have been opened and free gas was liberated. 相似文献
27.
28.
N,N-二烷基酰胺类物质的膜状态及其在水面溢油集油剂中的应用研究 总被引:1,自引:0,他引:1
合成了 5种 N,N-二烷基酰胺型表面活性剂 ,并对其所成膜的状态进行了测定。表明当N,N-二烷基酰胺类物质单独成膜时获得的集油膜为多层膜 ,而当选用合适的溶剂与其配制成溶液以后 ,所成的集油膜则为转变膜或液态凝聚膜。在 5种 N,N-二烷基酰胺类物质中 ,酰基碳链越长、氮烷基碳链越短则其集油能力越强。应用 N,N-二烷基酰胺类物质配制了 4个配方 ,均具备良好的集油能力 ,并且对原油的集油能力大于对柴油的集油能力 相似文献
29.
天然矿泉水特殊组分的地球化学初步研究 总被引:1,自引:0,他引:1
陈正新 《海洋地质与第四纪地质》1995,15(4):113-120
本文以GB8537-87《饮用天然矿泉水国家标准》为依据,从理论上阐述了天然矿泉水特殊组分(锂、氡、锶、铁、锌、溴、氟、碘、钼、偏硅酸、偏硼酸、硒、二氧化碳)的物理化学性质,分布、岍存形式及迁移规律,以便对我国矿泉水勘察和开发能有所裨益。 相似文献
30.