全文获取类型
收费全文 | 1484篇 |
免费 | 302篇 |
国内免费 | 466篇 |
专业分类
测绘学 | 363篇 |
大气科学 | 254篇 |
地球物理 | 221篇 |
地质学 | 773篇 |
海洋学 | 193篇 |
天文学 | 36篇 |
综合类 | 148篇 |
自然地理 | 264篇 |
出版年
2024年 | 8篇 |
2023年 | 27篇 |
2022年 | 74篇 |
2021年 | 132篇 |
2020年 | 75篇 |
2019年 | 99篇 |
2018年 | 106篇 |
2017年 | 102篇 |
2016年 | 96篇 |
2015年 | 120篇 |
2014年 | 115篇 |
2013年 | 96篇 |
2012年 | 107篇 |
2011年 | 115篇 |
2010年 | 91篇 |
2009年 | 97篇 |
2008年 | 97篇 |
2007年 | 73篇 |
2006年 | 82篇 |
2005年 | 87篇 |
2004年 | 56篇 |
2003年 | 47篇 |
2002年 | 33篇 |
2001年 | 44篇 |
2000年 | 40篇 |
1999年 | 40篇 |
1998年 | 29篇 |
1997年 | 31篇 |
1996年 | 24篇 |
1995年 | 21篇 |
1994年 | 27篇 |
1993年 | 16篇 |
1992年 | 16篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1979年 | 1篇 |
1957年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2252条查询结果,搜索用时 31 毫秒
661.
662.
Graham J. Pierce Jianjun Wang Xiaohong Zheng Jose M. Bellido Peter R. Boyle Vencent Denis 《International journal of geographical information science》2013,27(8):763-784
Cephalopod stocks are of increasing economic importance. Cephalopod fisheries show marked inter-annual fluctuations unrelated to fishery landings and effort. Their population dynamics, particularly recruitment, are thought to be strongly susceptible to changes in environmental conditions. This arises in part from the short life cycle, resulting in poor buffering of the population against changing conditions. These characteristics make traditional approaches to stock assessment and fishery management inappropriate. GIS offers a tool to improve understanding of spatio-temporal trends in abundance and facilitate rational management. A cephalopod fishery geographical information system for Northeast Atlantic waters (CFGIS-NEA) was developed. The system covers the area from 28.0° W to 11.0° E, and 34.5° N to 65.5° N. It was designed for investigating cephalopod resource dynamics in relation to environmental variation. It is based on Unix Arc/Info, and PC ArcView, combined with the statistical software package S-PLUS and supported by a database in Microsoft Access. Environmental data (e.g. sea surface temperature and salinity, sea bottom temperature and salinity, and bathymetric data), cephalopod fishery, survey and biological data, from a variety of sources, were integrated in the GIS as coverages, grids, shapefiles, and tables. Special functions were developed for data integration, data conversion, query, visualisation, analysis and management. User-friendly interfaces were developed allowing relatively inexperienced users to operate the system. The spatial and temporal distribution patterns of cephalopod abundance by species, the spatial and temporal relationships between cephalopod abundance and environmental factors, and the spatial and temporal patterns of cephalopod fishing activity were analysed using a combination of visual (qualitative) and quantitative methods. Predictive empirical models, such as GAMs (generalized additive models), were developed for modelling cephalopod abundance using environmental variables. 相似文献
663.
历史街区游客意象空间是游客对区域感知的具象化描述方式.本研究借助城市意象理论,探讨三坊七巷历史街区游客意象空间构成情况.首先采用深入访谈法,基于游客自身的游览体验描述,总结出游客意象空间因子,由坊巷道路、边界、名人文化景点、地标物以及非物质文化5个因子构成;其次借鉴相关文献资料,总结出每种意象空间因子包含的最具代表性的意象空间元素;最后采用问卷调查法,详细了解游客对意象空间因子及元素的感知情况,借以描绘出三坊七巷历史街区游客意象空间地图.研究发现,三坊七巷历史街区具有较强的“可意象性”,“历史街区游客意象空间”是游客对历史街区的一种逻辑思维结构,呈现出“街道突出,街区微弱”的特征. 相似文献
664.
湘西黔东地区铅锌矿床与古油藏关系初探 总被引:3,自引:0,他引:3
本文以湖南花垣铅锌矿床和贵州牛角塘铅锌矿床为例,探讨了湘西黔东地区铅锌矿与古油藏的关系。二者在空间分布上关系密切,存在"共生"和"上油下矿"两种关系,下寒武统清虚洞组既是铅锌矿重要的赋矿层位也是古油藏储集层之一;铅锌矿源层可能为新元古代基底岩系或下寒武统石牌组碎屑岩,古油藏烃源岩主要为下寒武统牛蹄塘组。古油藏中的油田卤水萃取了石牌组碎屑岩中的铅锌等成矿物质,形成成矿流体并运移,在古油藏形成后,由于加里东末期的构造运动的影响,古油藏和成矿流体的平衡被打破导致铅锌矿质沉淀,在这个过程中古油藏中的油田卤水可能为铅锌矿的沉淀提供了部分硫源。铅锌矿成矿时代与加里东期形成或破坏的古油藏时间上较为一致。 相似文献
665.
国土资源已成为社会经济发展的基础和根本支撑,如何科学合理的管理、利用资源,关系到整个社会的发展和未来。通过建立垦利县国土资源管理委员会集体会审系统,对土地出让的前期工作做了数字化、信息化,提出一个基于工作流技术和GIS技术的综合解决方案,利用现有的地理信息服务平台,建立会审系统为国土资源管理委员会的集体会审工作提供技术支撑并对出让地块加以管理。 相似文献
666.
The relationship between land surface temperature and land use/land cover in Guangzhou,China 总被引:1,自引:1,他引:0
The integration of remote sensing, geographic information system, landscape ecology and statistical analysis methods was applied
to study the urban thermal environment in Guangzhou. Normalized Difference Vegetation Index (NDVI), Normalized Difference
Build-up Index (NDBI), Normalized Difference Barren Index (NDBaI) and Modified Normalized Difference Water Index (MNDWI) were
used to analyze the relationships between land surface temperature (LST) and land use/land cover (LULC) qualitatively. The
result revealed that, most urban built-up lands were located in the middle part, and high LST areas mostly and were in the
middle and southern parts. Therefore, the urbanization and thermal environment in the middle and southern parts need to be
determined. Land surface temperature increased with the density of urban built-up and barren land, but decreased with vegetation
cover. The relationship between MNDWI and LST was found to be negative, which implied that pure water would decrease the surface
temperature and the polluted water would increase the surface temperature. A multiple regression between LST and each indices
as well as the elevation was created to elevate the urban thermal environment, which showed that NDVI, NDBI, NDBaI, MNDWI
were effective indicators for quantifying LULC impacts on LST. 相似文献
667.
多氯联苯(PCBs)是环境中一类强致癌性持久性有机污染物,而其在环境中含量极低(10-9~10-8mg/kg级),选择合适的前处理方法,以实现对环境复杂背景中痕量PCBs的分离富集,这对于PCBs的环境毒理学研究具有重要意义。使用绿色环保的前处理技术,减少有机试剂用量,并能简化实验步骤,提高富集和分离效率,且最大程度上减少背景干扰是当前PCBs前处理方法发展的方向。近年来PCBs的前处理方法取得了较快发展,开发新型的萃取材料是发展高效快捷前处理方法的关键因素。文章综述了国内外PCBs的前处理方法,包括液液萃取、超临界流体萃取、微波萃取、加速溶剂萃取、固相萃取。固相萃取已经成为富集PCBs的最佳提取方法之一,固相萃取方法使用的材料(键合硅胶、有机物聚合树脂、活性炭、纳米材料、分子印迹材料)对PCBs富集原理和富集效率、操作过程等各有优缺点。新型的磁性固相纳米萃取材料由于其极高的比表面积和强吸附性能,较常规的固相萃取方法大大缩短了前处理时间;分子印迹萃取纳米材料对PCBs兼具高富集性和高选择性的突出优点,可以大大降低背景干扰,非常适合于痕量PCBs的无干扰萃取。这两种材料是今后主要的发展方向。 相似文献
668.
Preparation of strontium ferrite from strontium residue 总被引:1,自引:0,他引:1
Strontium ferrite was prepared from Strontium Waste Residue (SWR) as a material. Strontium chloride was obtained by leaching SWR with ammonia chloride, and then SrCl2 was converted to SrCO3. Strontium ferrite (SrFe12O19) was formed by roasting the mixture of SrCO3 and FeCl3 in a proper proportion. The structure and magnetic susceptibility of strontium ferrite were investi-gated. The results showed that strontium conversion ratio increased with decreasing SWR grain diameter. The largest ratio was pre-sented when n(NH4Cl/Sr) was 3.6. What is more, the conversion process coincided with the kinetic characteristics of fractal reaction. The magnetic susceptibility of strontium ferrite decreased with increasing Fe3+/Sr2+ mole ratio and pH. SrFe12O19 exhibited face-centered and cubic closely-packed hexagonal structures. There were the strong diffraction peaks of Fe2O3 in the X-ray diffracto-gram of strontium ferrite. Strontium recovery ratio was 87.0%. 相似文献
669.
根据青海多龙恰柔勘查区已有的地质信息,以含辉钼矿化、黄铜矿化的印支期、燕山期花岗岩为主要研究对象,用地球化学土壤(岩屑)测量、地球物理双频激电扫面综合圈定了3个有意义的成矿远景区,用激电测深与EH4大地电磁测深初步固定了2个大的异常带的空间大致分布:均是走向以NNW向为主、倾向以SWW向为主、倾角较陡的大型异常带,总结了此矿区地质一地球物理一地球化学成矿模型,最后在推断出的异常部位布设钻孔并见矿。这次工作表明:因地制宜地结合各种物探方法,利用地质填图资料,综合全局考虑化探异常,扬长避短,发挥各自优势,在西部特殊景观区寻找金属矿科研与实践中具有重要意义。 相似文献
670.