全文获取类型
收费全文 | 3005篇 |
免费 | 432篇 |
国内免费 | 517篇 |
专业分类
测绘学 | 141篇 |
大气科学 | 585篇 |
地球物理 | 598篇 |
地质学 | 1530篇 |
海洋学 | 459篇 |
天文学 | 9篇 |
综合类 | 200篇 |
自然地理 | 432篇 |
出版年
2024年 | 13篇 |
2023年 | 47篇 |
2022年 | 102篇 |
2021年 | 121篇 |
2020年 | 104篇 |
2019年 | 125篇 |
2018年 | 86篇 |
2017年 | 102篇 |
2016年 | 109篇 |
2015年 | 119篇 |
2014年 | 174篇 |
2013年 | 185篇 |
2012年 | 134篇 |
2011年 | 186篇 |
2010年 | 157篇 |
2009年 | 175篇 |
2008年 | 216篇 |
2007年 | 199篇 |
2006年 | 227篇 |
2005年 | 173篇 |
2004年 | 181篇 |
2003年 | 140篇 |
2002年 | 128篇 |
2001年 | 98篇 |
2000年 | 92篇 |
1999年 | 100篇 |
1998年 | 94篇 |
1997年 | 69篇 |
1996年 | 66篇 |
1995年 | 37篇 |
1994年 | 34篇 |
1993年 | 22篇 |
1992年 | 28篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有3954条查询结果,搜索用时 15 毫秒
991.
玉苏甫·阿布都拉 热依汗古丽 买买提阿布都拉 米吉提·依明 Yusup·ABDULLA Reyhanguli Maimaitiabudula Mijit·IMIN 《沙漠与绿洲气象(新疆气象)》2006,29(1):24-25,29
对1963~2004年和田市各级别大气能见度进行统计分析,揭示了大气能见度的年际变化和季节变化特征。近20a来和田市大气环境质量趋于好转,造成能见度恶化的重要原因是大气中悬浮颗粒的增多,因此大气能见度是评价大气环境质量的重要指标。 相似文献
992.
993.
辽河流域铁岭段水质现状分析 总被引:2,自引:0,他引:2
本文依据辽河流域铁岭段的水质监测数据,对辽河流域铁岭段水质现状进行了分析评价,并对辽河铁岭段的地表水水资源保护提出了建议. 相似文献
994.
995.
FY 3A三个通道资料反演水云有效粒子半径的研究 总被引:1,自引:0,他引:1
基于水汽吸收波段云的反射率主要依赖于云粒子大小的原理,利用SBDART辐射传输模式和FY-3A极轨气象卫星可见光红外扫描辐射计(VIRR)的通道3(3.7μm)、中分辨率光谱成像仪(MERSI)的通道6(1.64μm)和通道7(2.13μm)所提供的探测数据进行了水云有效粒子半径的反演和比较。发现,1.64、2.13和3.7μm三个通道均能定最反演有效粒子半径的大小,其中1.64和2.13μm通道对大粒子的敏感性较高,3.7μm通道在光学厚度较小时敏感性好。三个通道的有效粒子半径反演产品与MODIS有效粒子半径产品具有较好的相关性。 相似文献
996.
Many organisms have been used as bioindicators of atmospheric contamination, with moss and lichen species being the most common. However, studies using epiphytic vascular species of Tillandsia have shown a good correlation between the presence of pollutants and the bioindicator's response. Therefore, the aim of our investigation was to calibrate and compare the response of four Tillandsia species of Argentina to ascertain whether they could be used as atmospheric contamination biomonitors. For this, we analysed the correlation between the levels of heavy metals in total atmospheric deposition samples and: a) their rate of enrichment; b) the physiological response of the plant samples.
Tillandsia samples collected from a non contaminated area in the province of Córdoba were transplanted to four areas in the capital city with different sources of pollution (industrial or traffic emissions). They were exposed for a period of 3 to 6 months after which the concentrations of Pb, Ni, Fe, Zn, Cu and S as well as the physiological parameters of foliar damage were determined. Simultaneously samples of total atmospheric deposition were also taken.The highest level of metal enrichment was found in T. capillaris followed by T. tricholepis, T. permutata and T. retorta. Also, the use of a foliar damage index proved to be effective and could be a useful tool to evaluate different levels of atmospheric quality in these species. The rate of heavy metal deposition was higher in the industrial area for all metals except for Zn whose values were higher in areas with high levels of traffic. 相似文献
997.
生活垃圾对环境的污染评价方法探讨 总被引:5,自引:0,他引:5
生活垃圾对环境的污染,主要表现为垃圾渗滤液对地面水、地下水、土壤等的污染 .其污染评价涉及污染物指标、污染物标准值的确定和计算模式的建立等内容.本文在总结现行环境指数评价法的基础上,探讨性地提出一套将基于生活垃圾填埋场环境监测技术标准 (CJJ/T3037-95)中涉及地面水、地下水、土壤等的相关监测项和垃圾中的其他常见重要污染物,一并确定出的污染评价指标,再根据相关有毒物急性毒性分级,结合阈限值和部分浸出毒性鉴别标准值等分为 5类污染指标.并在污染物的标准值确定后,进行对应于5类污染物的不同数学模式计算 ,得到5个分类污染指数,再比较判别这5个分类污染指数,选出最大者作为总污染指数的组合型评价垃圾污染的方法.经实例应用分析,该方法对各种污染物数据分布情况的适宜性优于现行其他常用方法. 相似文献
998.
A. El Mandour F. El Yaouti Y. Fakir Y. Zarhloule J. Benavente 《Environmental Geology》2008,54(3):491-503
The Bou-Areg plain in the Mediterranean coast at the North-eastern of Morocco is characterized by a semi-arid climate. The
aquifer consists of two sedimentary formations of Plio-quaternary age: the upper formation of fine silts and the lower one
of coarse silts with sand and gravels. The aquifer is underlain by marly bedrock of Miocene age that dips toward the coastal
lagoon of Bou-Areg. The hydrodynamic characteristics vary between 10−4 and 10−3 m/s; and transmissivities range between 10−4 and 10−1 m2/s. The general direction of flow is SW to NE, toward the lagoon. The aquifer is crossed by the river Selouane, which also
ends in the lagoon. The groundwater is characterized by a high salinity that can reach 7.5 g/l. The highest values are observed
in the upstream and in the downstream sectors of the aquifer. The temporal evolution of the physico-chemical parameters depends
on the climatic conditions and piezometric variations. The analysis of the spatio-temporal distribution of the physico-chemical
parameters suggests different sources of groundwater salinization: the seawater intrusion, the influence of marly gypsum-bearing
terrains, and the influence of anthropogenic products as the agricultural fertilizers, which cause great nitrate concentrations
that vary between 80 and 140 mg/l. 相似文献
999.
桂林市东区为一较完整的水文地质单元,为桂林市区主要的地下水供水水源地和未来城市中心区,漓江是该区域的排泄基准面。在简述桂林东区地下水硝酸盐整体含量的基础上,以东区白竹干村为例,对这一地段的岩溶地下水硝酸盐污染概况及成因进行分析,结果表明:由于桂林市城市化趋势向东发展,导致东区浅层地下水硝酸盐含量增加,含量介于4.47~41.36 mg/L,均值为16.7 mg/L,受硝酸盐污染程度较高,应通过加强水质监测,对生活污水、垃圾以及禽畜粪便进行妥善处理,村民应合理施肥,控制氮肥和农药的用量,改善当地饮用水卫生状况。 相似文献
1000.
Surface solar radiation (SSR) can affect climate, the hydrological cycle, plant photosynthesis, and solar power. The values of solar radiation at the surface reflect the influence of human activity on radiative climate and environmental effects, so it is a key parameter in the evaluation of climate change and air pollution due to anthropogenic disturbances. This study presents the characteristics of the SSR variation in Nanjing, China, from March 2016 to June 2017, using a combined set of pyranometer and pyrheliometer observations. The SSR seasonal variation and statistical properties are investigated and characterized under different air pollution levels and visibilities. We discuss seasonal variations in visibility, air quality index (AQI), particulate matter (PM10 and PM2.5), and their correlations with SSR. The scattering of solar radiation by particulate matter varies significantly with particle size. Compared with the particulate matter with aerodynamic diameter between 2.5 μm and 10 μm (PM2.5?10), we found that the PM2.5 dominates the variation of scattered radiation due to the differences of single-scattering albedo and phase function. Because of the correlation between PM2.5 and SSR, it is an effective and direct method to estimate PM2.5 by the value of SSR, or vice versa to obtain the SSR by the value of PM2.5. Under clear-sky conditions (clearness index ≥0.5), the visibility is negatively correlated with the diffuse fraction, AQI, PM10, and PM2.5, and their correlation coefficients are ?0.50, ?0.60, ?0.76, and ?0.92, respectively. The results indicate the linkage between scattered radiation and air quality through the value of visibility. 相似文献