全文获取类型
收费全文 | 191篇 |
免费 | 13篇 |
国内免费 | 20篇 |
专业分类
测绘学 | 38篇 |
大气科学 | 14篇 |
地球物理 | 41篇 |
地质学 | 31篇 |
海洋学 | 44篇 |
天文学 | 1篇 |
综合类 | 16篇 |
自然地理 | 39篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 14篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 14篇 |
2013年 | 20篇 |
2012年 | 6篇 |
2011年 | 12篇 |
2010年 | 11篇 |
2009年 | 14篇 |
2008年 | 11篇 |
2007年 | 9篇 |
2006年 | 4篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 10篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有224条查询结果,搜索用时 15 毫秒
21.
22.
23.
“Energy” presents a number of complex and interrelated challenges regarding the environment, economy, and politics. In this paper, we argue that cartography should help clarify our understanding of energy issues, but ask whether this has in fact been the case. In a review of over 100 articles pulled from twenty‐three peer‐reviewed geography journals, we qualitatively assess energy maps published since the early 20th century, examining trends in topic and cartographic technique. Energy maps in geography journals have focused on North America and Western Europe while relying on proportional symbols, grayscale production, and the analysis of energy phenomena at the national scale—tendencies that in many instances have limited our understanding of the ways in which energy is actually consumed. Simultaneously, cartographers are limited to the energy data available to them, frequently precluding small‐scale consumption analysis or consideration of diurnal and seasonal trends. We argue that the future of energy cartography relies on access to consumption data coupled with greater user interactivity. 相似文献
24.
25.
A simple, physically based method is developed in this paper to assist in the allocation of areas with high groundwater potential and for the determination of maximum allowed pumping rate to ensure proper groundwater management. This method utilizes the aquifer physical properties as well as GIS technology to accomplish this purpose. The design of this method was considered to be applicable in areas with little data, such as in most arid regions. This technique was applied to a catchment in an arid environment where qualitative as well as quantitative analyses of the results were undertaken. Locations of available groundwater and rates of maximum allowable pumping were compared with observations and experiments in the field and a good agreement was found. It was concluded that the best groundwater location was in the alluvial area, which represents only 16% of the total aquifer, which is a typical case in arid region catchments. The rate of maximum pumping was estimated to be 65 m3/h. However, to benefit 55% of the area, the maximum pumping rate should only be 40 m3/h with an average rate throughout the area (55%) of about 24 m3/h.This revised version was published online in December 2004 with corrections to the category. 相似文献
26.
本文以河北省中南部平原农田表层土壤为研究对象,对表层土壤中7种重金属元素的形态含量进行了统计和分析,对重金属元素的生物有效性进行了评价,并运用相关分析法,对影响重金属元素生物有效性的因素进行了研究。结果表明,研究区表层土壤7种重金属元素的有效态含量以Cd最高,达36.83%,潜在生态危害性较大;其次为Pb,达13.37%,其中碳酸盐结合态达到12.38%,由于土壤呈中性或偏碱性,Pb元素的迁移能力较弱,其潜在危害性较小;Cu、Hg、Cr、As、Zn重金属元素含量均以稳定态的含量存在,之和均在90%以上,表明其潜在危害性较小;研究区土壤重金属元素的活性系数和迁移系数大小顺序为:CdPbHgCuZnAsCr和CdHgAsCuPbZnCr,其中Cd的活性系数和迁移系数平均值分别达到0.330和0.160,展现出较强的生物活性、不稳定性和迁移能力,其他重金属元素在土壤中活性系数(Pb除外)和迁移系数均较小,生物活性较弱,在土壤中稳定存在,由土壤中向植物中的迁移能力弱;研究区不同的重金属的生物有效性与其影响因素的关系不尽相同,其主要因素是土壤重金属元素全量,其次为p H、TOC、CEC、粘粒含量等,二者关系复杂。 相似文献
27.
Abstract Groundwater development potential in northern Ghana (108 671 km2) has been assessed by combining spatial layers for five critical factors—recharge rate, regolith thickness, transmissivity, borehole success rate and static water level—through a multi-criteria analysis approach to rank development potential from the viewpoint of groundwater availability and accessibility at a resolution of 1 km2. The results indicate a high potential for development in the study area, as about 70% of the area was found to have high to moderate groundwater availability, while 83% has high to medium groundwater accessibility. Comparing the two main hydrogeological environments, the Precambrian Basement rocks (PCB) area was found to generally have a higher groundwater development potential than the Voltaian Sedimentary rocks (VSB). More detailed investigation revealed that the VSB can produce a small proportion of exceptionally high-yielding boreholes that can support large-scale irrigation. A test of the reliability of results showed that generally, the majority of high- and low-yielding boreholes fall in areas predicted by the model as having high and low groundwater availability, respectively. Editor D. Koutsoyiannis; Associate editor D. Hughes Citation Forkuor, G., Pavelic, P., Asare, E., and Obuobie, E., 2013. Modelling potential areas of groundwater development for agriculture in northern Ghana using GIS/RS. Hydrological Sciences Journal, 58 (2), 437–451. 相似文献
28.
长江中下游典型浅水湖泊沉积物水界面磷与铁的耦合关系 总被引:6,自引:3,他引:6
目前普遍认为磷铁耦合关系是P迁移的主要机制,但大部分研究结果并未提供直接的原位证据.为了探索沉积物剖面磷(P)与铁(Fe)的耦合关系,利用Zr O-Chelex薄膜扩散梯度技术(ZrO-Chelex DGT),分别对太湖、巢湖、鄱阳湖和洞庭湖4个浅水湖泊沉积物有效态Fe和P进行高分辨采样和分析.结果表明,不同湖区有效态Fe和P浓度在沉积物-水界面处开始增加,之后波动变化,垂向异质性较强,但两者浓度变化同步.有效态P和Fe浓度的相关分析结果证明两者浓度具有显著的线性相关.室内厌氧培养实验进一步表明,Fe~(3+)的还原性促使Fe~(2+)与铁结合态磷的释放,促使DGT有效态P与Fe同步变化.该结果表明沉积物P的二次迁移和释放受Fe氧化还原过程的控制,为铁磷耦合关系提供了直接证据. 相似文献
29.
Manuel Castillo‐Rivera Rocío Zárate‐Hernández Selene Ortiz‐Burgos José Zavala‐Hurtado 《Marine Ecology》2010,31(4):633-642
We hypothesized that temporal variation in fish species composition and community structure in a low complexity habitat in the Pueblo Viejo Lagoon, Mexico, is influenced by diel light/dark cycles and tidal stage, and by seasonal changes in salinity and temperature. We collected a total of 17,661 individuals during 2‐h interval sampling over six bi‐monthly 24‐h sampling cycles representing 53 species, of which 11 (~20%) were previously unknown in the system. Diel variation indicated that significantly higher numbers of individuals and species were caught at night, whereas diversity and evenness were higher during the day. Species richness was significantly higher in July and January, whereas diversity and evenness peaked around May; both were correlated with temperature. Diel variation in species composition was influenced primarily by the light/dark cycle. Cluster analyses of each diel cycle separated fish assemblages from midday samples from those of nocturnal samples, separated by an extended wide transition period as fish moved at dawn and during the late afternoon/dusk. Significant shifts (as determined by MANOVA) in assemblage structure occurred between months. Canonical correspondence analysis showed that temperature and day/night effects were the most important environmental variables structuring the fish community. This constrained ordination also defined species with specific habitat preferences as follows: (i) diurnal, warm temperature species (mainly planktivores) (Brevoortia gunteri, Cetengraulis edentulus, Diapterus auratus, and Membras martinica); (ii) nocturnal, warm temperature species (mainly predators) (Citharichthys spilopterus, Cathorops melanopus, and Bairdiella spp.); and (iii) low temperature, diurnal species (Brevoortia patronus and Mugil curema) or those with twilight and nocturnal distributions (Anchoa mitchilli, the most numerically abundant species). Our results indicate that diel and seasonal changes in fish community structure were mainly related to day/night cycles and temperature regimes. 相似文献
30.
对伊犁河谷地区初冬降水条件下风廓线雷达资料评估其数据获取率并与探空资料进行对比分析,定义两者风向偏差在10°以内或风速偏差在1 m/s范围的样本为有效样本,分别用E_v和E_d表示风速有效样本比率(风速有效样本数/总样本数)和风向有效样本比率(风向有效样本数/总样本数)。结果显示:超过80%数据获取率的高度,降雨时为3000 m,降雪时达到预设2000 m;降雪时E_v和E_d均比无降水时高,且降雪量大小与风廓线的探测高度呈正相关,降雪量大小对E_d有明显影响,对E_v无明显影响;比较不同高度数据,降雪时0~3 km范围的E_v和E_d值均比无降水时高30%左右,无降水时3~5 km范围的E_d接近100%。 相似文献