全文获取类型
收费全文 | 768篇 |
免费 | 81篇 |
国内免费 | 126篇 |
专业分类
测绘学 | 118篇 |
大气科学 | 60篇 |
地球物理 | 92篇 |
地质学 | 183篇 |
海洋学 | 232篇 |
天文学 | 106篇 |
综合类 | 79篇 |
自然地理 | 105篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 37篇 |
2021年 | 51篇 |
2020年 | 43篇 |
2019年 | 54篇 |
2018年 | 30篇 |
2017年 | 33篇 |
2016年 | 32篇 |
2015年 | 42篇 |
2014年 | 32篇 |
2013年 | 49篇 |
2012年 | 38篇 |
2011年 | 29篇 |
2010年 | 27篇 |
2009年 | 34篇 |
2008年 | 35篇 |
2007年 | 40篇 |
2006年 | 46篇 |
2005年 | 46篇 |
2004年 | 33篇 |
2003年 | 28篇 |
2002年 | 18篇 |
2001年 | 20篇 |
2000年 | 27篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1997年 | 13篇 |
1996年 | 20篇 |
1995年 | 5篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有975条查询结果,搜索用时 62 毫秒
41.
John C. Patterson 《Aquatic Sciences - Research Across Boundaries》1991,53(2-3):218-238
A model of the time dependent relationship between productivity and light intensity following changes in light intensity is briefly described. The model incorporates two response timescales simulating initial response and photoinhibition, although additional timescales could easily be incorporated. The model is calibrated against one set of time dependent data, and applied to two simple models of motion in the upper mixed layer of a lake. The two models are: organised motion simulating Langmuir cells, and disorganised motion simulating the turbulent velocity field associated with surface wind stirring. The depth and therefore light histories for a number of photosynthesising particles are calculated by these models, and used by the productivity model to calculate mean productivities. The results show that the influence of the time dependent nature of the productivity relationship depends on the ratio of the mixed layer depth to the euphotic depth, and to a less extent, on the rate at which the particles circulate in the mixed layer. 相似文献
42.
The change in atmospheric relative humidity affects the physical and optical properties of aerosol particles. It would be
interesting to study the effect of an increase in relative humidity on the angular scattering of light by aerosols (by incorporating
the changes due to it as the complex refractive index and the parameters of the size distribution function). In the present
paper we have computed the angular scattering function for rural and urban aerosols, for light of wavelength 0.55 μn. The
results obtained for these two models, representative of different environments, are interesting and show some discriminating
features. 相似文献
43.
该文提出了一种利用积分球原理设计的新型日照传感器。该传感器由限角挡环、积分球体和光电探测器组成。积分球为一有5个针孔的空心正球体。针孔可阻挡散射光进入球内,而射入球内的直射光,经内壁多次漫反射后,其亮度呈均匀分布。与日照阈值下相应的亮度相比较可确定日照之有无。该日照传感器具有无转动部件、结构简单、无需调整及便于操作等优点。 相似文献
44.
“准地籍测量”是在已有的地形图上根据地籍台帐于实地标绘宗地界域线,划分街道、街坊、调查区及编号,调查宗地座落、地名、门牌号码、房屋结构及层数等;基于这种测量模式,其成果以传统的图、表展示已很难适应。实践运用MGE地理信息基础平台开发出的地籍信息管理系统,其准地籍测量约70%的宗地成果与实际确权一致,不失为一种快速、经济有效的地籍测量模式。 相似文献
45.
Izmir Bay is one of the most polluted estuaries in the whole Mediterranean Sea. The inner part of the Bay (Inner Bay) is heavily
affected by domestic and industrial discharge. As a result of these loads, strong eutrophication occurs in the Inner Bay,
which is temporally anaerobic. The ecologically sensitive approach of the local authorities during the last decade has given
rise to a wide variety of monitoring and research studies on this bay. On the other hand, the municipality of Izmir started
to operate wastewater treatment facilities since January 2000. The Institute of Marine Sciences and Technology — Izmir (IMST)
with its research vessel R/V K Piri Reis has been conducting an intensive monitoring program since 1988 and especially during
the recent few years. These investigations provide an opportunity for the evaluation of the performance of the wastewater
treatment plant in terms of the change in the optical properties of Izmir Bay water in a positive manner. The turbidity values
measured in these monitoring studies indicate that the values have changed drastically after January 2000. Their spatial variation
indicates that the values decrease from the Inner Bay towards the Aegean Sea. The turbidity (light transmission) values are
measured with an automatic CTD (conductivity, temperature and depth) system during each cruise. The seiche disc depth measurement
is carried out only occasionally. The accuracy of the seiche disc depth is dependent on certain daylight conditions and depends
on the operator. The seiche disc depth (D
s) is an important parameter to estimate primary production of organic matter (hereafter called production). A relation between
light transmission (turbidity) value and seiche disc depth (D
s) is found with very good agreement. The correlations are very high (approximately 0.94) with slight seasonal variation. 相似文献
46.
基于结构光和单CCD相机的物体表面三维测量 总被引:1,自引:0,他引:1
非接触式物体表面三维自动测量是计算机视觉领域的中心任务之一 ,围绕这个问题 ,提出了一种利用结构光 ,单 CCD相机和双定向技术实现物体表面三维自动测量的新方法。采用该方法 ,无需测定相机和结构光光截面之间的相对位置 ,在单目序列影像上就可测量出物体表面的三维坐标。 相似文献
47.
48.
目前国内地磁台垂直分量磁变以的灵敏度都普遍偏低,不能适应一些研究工作的需要,必须予以适当的提高,本文在基本不改变仪器固有灵敏度的前提下,采取记录光线二次反射法,以提高仪器的记录灵敏度,利用这种方法既使仪器的灵敏度提高一倍同时又保证了仪器原有的稳定性。 相似文献
49.
Pranab K. Roy Chowdhury Jeanette E. Weaver Eric M. Weber Dalton Lunga St. Thomas M. LeDoux Amy N. Rose 《International Journal of Digital Earth》2020,13(1):119-135
ABSTRACTUrban areas presently consume around 75% of global primary energy supply, which is expected to significantly increase in the future due to urban growth. Having sustainable, universal energy access is a pressing challenge for most parts of the globe. Understanding urban energy consumption patterns may help to address the challenges to urban sustainability and energy security. However, urban energy analyses are severely limited by the lack of urban energy data. Such datasets are virtually non-existent for the developing countries. As per current projections, most of the new urban growth is bound to occur in these data-starved regions. Hence, there is an urgent need of research methods for monitoring and quantifying urban energy utilization patterns. Here, we apply a data-driven approach to characterize urban settlements based on their formality, which is then used to assess intra-urban urban energy consumption in Johannesburg, South Africa; Sana’a, Yemen; and Ndola, Zambia. Electricity is the fastest growing energy fuel. By analyzing the relationship between the settlement types and the corresponding nighttime light emission, a proxy of electricity consumption, we assess the differential electricity consumption patterns. Our study presents a simple and scalable solution to fill the present data void to understand intra-city electricity consumption patterns. 相似文献
50.
Remote sensing technology has been widely recognized for contributing to emergency response efforts after the World Trade
Center attack on September 11th, 2001. The need to coordinate activities in the midst of a dense, yet relatively small area,
made the combination of imagery and mapped data strategically useful. This paper reviews the role played by aerial photography,
satellite imagery, and LIDAR data at Ground Zero. It examines how emergency managers utilized these datasets, and identifies
significant problems that were encountered. It goes on to explore additional ways in which imagery could have been used, while
presenting recommendations for more effective use in future disasters and Homeland Security applications. To plan adequately
for future events, it was important to capture knowledge from individuals who responded to the World Trade Center attack.
In recognition, interviews with key emergency management and geographic information system (GIS) personnel provide the basis
of this paper. Successful techniques should not be forgotten, or serious problems dismissed. Although widely used after September
11th, it is important to recognize that with better planning, remote sensing and GIS could have played an even greater role.
Together with a data acquisition timeline, an expanded discussion of these issues is available in the MCEER/NSF report “Emergency
Response in the Wake of the World Trade Center Attack; The Remote Sensing Perspective” (Huyck and Adams, 2002) 相似文献