全文获取类型
收费全文 | 1649篇 |
免费 | 99篇 |
国内免费 | 117篇 |
专业分类
测绘学 | 428篇 |
大气科学 | 133篇 |
地球物理 | 220篇 |
地质学 | 374篇 |
海洋学 | 102篇 |
天文学 | 304篇 |
综合类 | 96篇 |
自然地理 | 208篇 |
出版年
2023年 | 15篇 |
2022年 | 26篇 |
2021年 | 28篇 |
2020年 | 39篇 |
2019年 | 57篇 |
2018年 | 41篇 |
2017年 | 59篇 |
2016年 | 63篇 |
2015年 | 56篇 |
2014年 | 77篇 |
2013年 | 128篇 |
2012年 | 78篇 |
2011年 | 75篇 |
2010年 | 48篇 |
2009年 | 86篇 |
2008年 | 80篇 |
2007年 | 114篇 |
2006年 | 87篇 |
2005年 | 83篇 |
2004年 | 85篇 |
2003年 | 74篇 |
2002年 | 52篇 |
2001年 | 51篇 |
2000年 | 60篇 |
1999年 | 33篇 |
1998年 | 41篇 |
1997年 | 26篇 |
1996年 | 25篇 |
1995年 | 18篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 16篇 |
1988年 | 5篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1972年 | 10篇 |
1971年 | 7篇 |
排序方式: 共有1865条查询结果,搜索用时 15 毫秒
31.
Open source, spatial analysis, and activity-travel behaviour research: capabilities of the aspace package 总被引:2,自引:0,他引:2
This paper reports on recent experience with the development of aspace, an Open Source (OS) library for the geographic visualization and analysis of activity-travel behaviour. The paper begins
with an overview of recent progress with respect to the convergence of Open Source technology, spatial analysis, and travel
behaviour research. The remainder of the paper focuses on aspace; a collection of functions that, when combined with data describing the geographical location of daily activities, can be
used to visualize and describe spatial properties of individual and household activity spaces. These properties include: size,
orientation, shape, and the geographical dispersion of activity locations contained within the activity space. Several planar
geometries are used to transform measurable spatial properties into intuitive objects for visualizing spatial patterns of
activity participation. Experiments are conducted, using data from the first wave of the 2003 Toronto Travel Activity Panel
Survey, to demonstrate the potential application of aspace for basic and applied policy-based research into activity-travel behaviour. The toolkit is distributed as a downloadable
‘package’ from the Open Source R Project for Statistical Computing.
相似文献
32.
33.
34.
本文在解放军土地管理局研制的“军用土地管理信息系统”的基础上,从系统设计和应用的角度出发,明确了系统应包括的基本功能,提出了改进和完善系统的方法。 相似文献
35.
A geochemical evaluation of the Szc-Halimba-Kisld area, Hungary, covering an area of more than 200 km2 is presented using different statistical and geostatistical methods. The study area is a representative example of allochtonous karst bauxite accumulation. The three groups of deposits studied here have been explored and mined since 1950. Several thousand boreholes have been drilled, and bauxite cores were analyzed for the five main chemical components. A total of 80,000 pleces of analytical data were processed, followed by a geological examination of borehole logs and of mining excavations.The quantitative geochemical evaluation of the data set led to both geochemical and practical results: The geochemical behavior of the allochtonous, clastic karst bauxite deposits differs essentially from that of the autochtonous and parautochtonous ones, as well as that of the lateritic bauxite deposits. The deposits of the study area can be split into several subsequent geochemical-sedimentological units, each representing an event of bauxite transport and accumulation. Clear regional patterns can be revealed in the composition of these units. The geostatistically measured chemical variability of the geochemical units is rather different, the lowest units showing the smallest variability. The interrelations of the main chemical components are weaker and more irregular in the studied deposits than in the autochtonous lateritic bauxite deposits. Additional local genetic features, such as transport routes, can be delineated by the methods applied. Within each deposit, local changes of chemical composition and of its variability can be determined more precisely. These results can be used in bauxite prospecting and exploration, because areas of high or low bauxite quality can be predicted. 相似文献
36.
Limin REN Bing QIN Wenchun TANG Zhendong MA Yikeng HU 《中国地球化学学报》2006,25(B08):10-10
Mercury is a pollutant of concern due to its toxic and bioaccumulative properties. Studies on the distribution and hazard of mercury in the environment are mainly focused on its forms, toxicity and the environment standard, and progresses and results have been achieved. But these studies in the past were concentrated on the scales of laboratory or smaller districts merely, such as a small unit of mineral area, vegetable base, paddy field, lake, etc. Multi-target regional geochemical survey carried out by China Geological Survey from the 1990s to now is a fundamental and commonweal geological survey, large-scale and systematical inquisition and research were conducted in 19 provinces (or municipalities directly under the Central Government) in the eastern overlay region of China, and the purpose is to provide the basic geochemical data for national economic construction, adjustment of industrial and agricultural structures and sustainable social development. Geochemical studies aim at investigating soils in these regions and 52 elements have been tested, producing a great amount of data at the same time. Methods: based on the data from 3061 samples of surface soil and 832 samples of deep soil from the project of multi-purpose geochemical survey in the Chengdu Basin, Sichuan, China, this paper describes the correlation relationship between Hg and other 48 elements and their spatial distribution in surface and deep soils of these areas by applying the method of linear regression and factor analysis. 相似文献
37.
Relations between climatic variability and hydrologic time series from four alluvial basins across the southwestern United States 总被引:1,自引:3,他引:1
Hydrologic time series of groundwater levels, streamflow, precipitation, and tree-ring indices from four alluvial basins in the southwestern United States were spectrally analyzed, and then frequency components were reconstructed to isolate variability due to climatic variations on four time scales. Reconstructed components (RCs), from each time series, were compared to climatic indices like the Pacific Decadal Oscillation (PDO), North American Monsoon (NAM), and El Niño-Southern Oscillation (ENSO), to reveal that as much as 80% of RC variation can be correlated with climate variations on corresponding time scales. In most cases, the hydrologic RCs lag behind the climate indices by 1–36 months. In all four basins, PDO-like components were the largest contributors to cyclic hydrologic variability. Generally, California time series have more variation associated with PDO and ENSO than the Arizona series, and Arizona basins have more variation associated with NAM. ENSO cycles were present in all four basins but were the largest relative contributors in southeastern Arizona. Groundwater levels show a wide range of climate responses that can be correlated from well to well in the various basins, with climate responses found in unconfined and confined aquifers from pumping centers to mountain fronts. 相似文献
38.
本文采用流量级频率分析和统计分析方法,对黄河下游流量及泥沙含量对水环境容量的影响进行了研究分析.分析结果:河流在平滩流量时不仅输沙能力最大[8],而且输运污染物能力也最大,黄河下游水环境容量萎缩是平滩流量降低的必然结果. 相似文献
39.
新疆塔里木河流域平原区土地利用覆盖变化及其对生态环境影响分析 总被引:1,自引:0,他引:1
分析了塔里木河流域平原区近十余年土地利用覆盖变化和用水量的变化情况,对两者间的关系进行了研究,提出了为防止生态环境进一步恶化应采取的对策. 相似文献
40.
克拉玛依夏季日最高气温与08时 850hPa温度的关系 总被引:2,自引:0,他引:2
冀新琪 《沙漠与绿洲气象(新疆气象)》2005,28(4):12-13
根据克拉玛依40年气温观测资料,分析克拉玛依夏季日最高气温与08时850hPa温度的关系,寻找预报夏季日最高气温关键因子. 相似文献