全文获取类型
收费全文 | 617篇 |
免费 | 108篇 |
国内免费 | 175篇 |
专业分类
测绘学 | 95篇 |
大气科学 | 203篇 |
地球物理 | 86篇 |
地质学 | 263篇 |
海洋学 | 112篇 |
天文学 | 7篇 |
综合类 | 53篇 |
自然地理 | 81篇 |
出版年
2024年 | 6篇 |
2023年 | 17篇 |
2022年 | 29篇 |
2021年 | 31篇 |
2020年 | 35篇 |
2019年 | 31篇 |
2018年 | 20篇 |
2017年 | 35篇 |
2016年 | 35篇 |
2015年 | 39篇 |
2014年 | 44篇 |
2013年 | 35篇 |
2012年 | 42篇 |
2011年 | 36篇 |
2010年 | 31篇 |
2009年 | 45篇 |
2008年 | 28篇 |
2007年 | 63篇 |
2006年 | 33篇 |
2005年 | 31篇 |
2004年 | 35篇 |
2003年 | 22篇 |
2002年 | 25篇 |
2001年 | 25篇 |
2000年 | 20篇 |
1999年 | 23篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有900条查询结果,搜索用时 615 毫秒
601.
利用在水温垂直剖面无因次自模函数研究海洋垂直热结构方面的经验 ,对含中层冷水垂直热结构海水水温的正、负梯度层 ,提出了 2种无因次温度和深度表达式 ,然后利用实测资料按单站和整个研究海区分别拟合了自模函数θ =f(η)。回算检验结果表明 ,用上述自模函数回算水温的平均均方误差均小于 0 .1 5℃ ,证明了含中层冷水的垂直热结构亦存在自模性 ,所提出的无因次经验表达式具有可靠性 ,纠正了认为自模函数的建立仅适用于单跃层结构的观点 ,并为进一步建立黄海中层冷水垂直热结构数值预报模式奠定了实验基础 相似文献
602.
水产加工技术发展现状及展望 总被引:1,自引:0,他引:1
综述了水产品加工技术研究及其应用现状和展望,并对海洋水产资源的开发利用现状和前景作了论述,许多先进技术,如微波技术,辐照杀菌技术,超高压杀菌技术等,在水产品加工业中应用前景广阔,对海洋低值鱼类资源,水产加工废弃物,以及尚未利用的海洋生物资源的开发利用已引起重视,海洋生物技术在开发海洋食用生物资源方面具有重要意义,现代高新技术的应用将成为21世纪水产加工业发展趋势。 相似文献
603.
Coastal structures may be built on natural sedimentary intermediate grounds, which mainly consist of silty soils and fine sandy soils. In this study, extensive field and laboratory tests were performed on the nattwal marine intermediate deposits to demonstrate the difference in behavior between natural marine clayey soils and natural marine intermediate deposits. The natural intermediate deposits have almost the same miles of natural water content to liquid limit as those of the soft natural marine clays, but the former have much higher in-situ strength and sensitivity than the latter. The research results indicate that grain size distributions of soils affect significantly tip resistance obtained in field cone penetration tests. The mechanical parameters of natural marine intermediate deposits are also significantly affected by sample disturbance due to their high sensitivity and relatively large permeability. Unconfined compression shear tests largely underestimate the strength of natural marine intermediate soils. The triaxial consohdated compression shear tests with simulated insitu confined pressure give results much better than those of uncomfined compression shear tests. 相似文献
604.
Motoyo Itoh 《Journal of Oceanography》2007,63(4):637-641
Okhotsk Sea Intermediate Water (OSIW), the source water for ventilation of North Pacific Intermediate Water, exhibits a multidecadal
warming trend. Historical data show that OSIW temperatures increased by 0.28, 0.57, 0.31 and 0.10°C during 1955 to 2003 at
potential densities of 26.8, 27.0, 27.2 and 27.4σ
θ
, at depths of approximately 250, 500, 700 and 900 m, respectively. This rate of warming is much faster than that of the global
ocean. This OSIW warming is likely linked to the reduced ventilation of cold Dense Shelf Water associated with brine rejection
during sea ice formation. 相似文献
605.
606.
607.
WANG Le GAO Shen QIN Kezhang SONG Guoxue HAN Ri SU Shiqiang GUO Jihai PANG Xuyong LI Guangming 《《地质学报》英文版》2023,97(5):1462-1474
Oxygen fugacity(fO2) is a key intensity variable during the entire magmatic-hydrothermal mineralization courses.The redox state and its variations between different stages of the ore-forming fluids of intermediate sulfidation epithermal deposits are rarely deciphered due to the lack of appropriate approaches to determine fO2 of the fluids.Here,we reported the δ34S of the sulfides from three different stages(stage Ⅰ,Ⅱ,Ⅲ) of Zhengguang,an Early Ordovician Au-rich i... 相似文献
608.
Soil freeze-thaw cycles have important effects on surface water and energy balance,and then affect vegetation growth,soil water content,carbon cycle and terrestrial ecosystem. Passive microwave plays an important role in monitoring global and regional surface freeze-thaw processes due to its high temporal resolution,abundant data and sensitivity to soil moisture. With the launch of passive microwave sensors at home and abroad,it provides conditions for the study of permafrost interannual variation,seasonal variation,diurnal variation and long time series of near-surface soil freeze-thaw cycle. In recent years,the study of surface freeze-thaw cycle using passive microwave data has gradually increased. Based on previous studies,this paper summarizes the types of passive microwave remote sensing data and the characteristics of the bands contained in them. Expounded the principle of passive microwave monitoring data used for freezing and thawing,focus on passive microwave data in five categories in the study of freezing and thawing monitoring algorithms,including double index algorithm,the decision tree algorithm,freeze-thaw discriminant algorithm,seasonal threshold algorithm and based on the freezing L-band relative factors discriminant algorithm threshold,and analysis of 5 kinds of algorithms are compared;The freeze-thaw products based on different algorithms and passive microwave data were combed. Finally,the problems and future research directions of passive microwave remote sensing in surface freeze-thaw applications are summarized. In the acquisition of passive microwave data,it is found that the passive microwave data is missing due to the physical characteristics of the sensor,the shape and orbit of the earth,and the low resolution of passive microwave data leads to the low precision of freeze-thaw discrimination. For the problem of missing passive microwave data,it is proposed to use the average value of passive microwave data before and after two days to fill the missing brightness temperature data,or establish statistical function to complement the missing data. For the problem of low passive microwave resolution,the current development trend is to scale down based on passive microwave data and combine with multiple data products,such as ground temperature and active microwave data,or perform probability discrimination on surface freezing-thawing state in pixels,so as to better describe surface freeze-thaw state. In terms of the algorithm for discriminating surface freezing-thawing,based on the problem that dual-index algorithm,decision tree algorithm,freezing-thawing discriminant algorithm and seasonal threshold algorithm cannot accurately distinguish snow and frozen soil,this paper proposes to adopt the method of data assimilation or start from the snow radiation and frozen soil dielectric model. Optimization of the algorithm for the snow covered surface can further improve the accuracy of freeze-thaw classification. Based on existing freeze-thaw products,Although SMAP freeze-thaw products continue to be updated,SAMP satellite was launched late,and SAMP freeze-thaw products have a short time series. In the future,the time span of this algorithm for freezing-thawing products can be extended by combining L-band data provided by SMOS satellite. The problems mentioned above and the direction of further research are of great significance for improving the accuracy of freezing and thawing discrimination and improving the understanding of the variation law of freezing and thawing cycles,and also have certain research space. © 2022 Science Press (China). 相似文献
609.
详细介绍了3D产品(DOM、DLG、DEM)在1954北京坐标系、1980西安坐标系、2000国家大地坐标系之间的相互转换。3D源数据包括以Geo TIFF格式为代表DOM数据、以Autodesk公司的DXF文件为代表的DLG数据和以Arc/Info Binary Grid格式为代表的DEM数据。本系统以VB6.0为平台进行开发设计,通过解析各数据文件的文件结构,直接定位、修改数据文件的坐标信息,该系统独立于现有GIS及测绘相关软件产品,数据处理快速,转换效率高,能够比较精确地实现小区域的坐标转换。 相似文献
610.
关键陆表参数遥感产品真实性检验方法研究进展 总被引:1,自引:0,他引:1
遥感产品真实性检验是定量遥感基础研究的重要环节,是客观评价遥感产品精度、稳定性和一致性的重要手段,对于提高遥感定量化水平、推动和扩展遥感产品的深化应用具有重要的意义。本文基于当前陆表参数遥感产品真实性检验研究的相关成果,归纳总结了陆表参数遥感产品真实性检验方法,并就其中的5种真实性检验方法,即基于地面单点测量检验、基于地面多点采样检验、基于高分辨率数据的检验、交叉检验和间接检验,阐述了各方法的特点、局限性、适用条件。文章在最后探讨了陆表关键参数遥感产品真实性检验评价指标和验证中影响精度评价的关键因素。本文对于遥感产品真实性检验工作的开展和真实性检验系统研发具有重要的指导意义。 相似文献