全文获取类型
收费全文 | 2812篇 |
免费 | 440篇 |
国内免费 | 497篇 |
专业分类
测绘学 | 94篇 |
大气科学 | 651篇 |
地球物理 | 596篇 |
地质学 | 1283篇 |
海洋学 | 479篇 |
天文学 | 11篇 |
综合类 | 184篇 |
自然地理 | 451篇 |
出版年
2024年 | 11篇 |
2023年 | 32篇 |
2022年 | 91篇 |
2021年 | 122篇 |
2020年 | 98篇 |
2019年 | 132篇 |
2018年 | 98篇 |
2017年 | 102篇 |
2016年 | 104篇 |
2015年 | 113篇 |
2014年 | 152篇 |
2013年 | 196篇 |
2012年 | 128篇 |
2011年 | 174篇 |
2010年 | 145篇 |
2009年 | 162篇 |
2008年 | 206篇 |
2007年 | 192篇 |
2006年 | 215篇 |
2005年 | 168篇 |
2004年 | 168篇 |
2003年 | 130篇 |
2002年 | 125篇 |
2001年 | 100篇 |
2000年 | 82篇 |
1999年 | 94篇 |
1998年 | 83篇 |
1997年 | 66篇 |
1996年 | 56篇 |
1995年 | 31篇 |
1994年 | 26篇 |
1993年 | 17篇 |
1992年 | 22篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 9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3749条查询结果,搜索用时 31 毫秒
191.
利用2014—2020年河北沧州逐小时气象与环境监测数据,对沧州市臭氧(O3)污染加剧现状及其与气象因子的关系进行分析。结果表明:(1)沧州地区O3污染呈加剧态势,且O3已上升为该地区首要污染物;O3污染集中出现在5—9月,O3质量浓度日变化呈单峰单谷型,最大浓度出现在16:00前后;(2)5—9月O3日最大8 h平均质量浓度(简称“O3-8 h”)所处时段,平均气温、最高气温、相对湿度、总辐射辐照度与O3质量浓度的相关性较好,本站气压、水汽压和平均风速与O3质量浓度的相关性未通过显著性检验;(3)5—9月O3-8 h时段,当同时满足8 h平均气温高于30.9℃、最高气温高于32.7℃、平均相对湿度低于42.1%、平均总辐射辐照度高于505.8 W·m-2时,出现O3污染的概率达84%;(4)气象因子不是O3 相似文献
192.
Naifang BEI Xia LI Qiyuan WANG Suixin LIU Jiarui WU Jiayi LIANG Lang LIU Ruonan WANG Guohui LI 《大气科学进展》2021,38(7):1141-1152
The effects of aerosol–radiation interactions(ARI) are not only important for regional and global climate, but they can also drive particulate matter(PM) pollution. In this study, the ARI contribution to the near-surface fine PM(PM2.5)concentrations in the Guanzhong Basin(GZB) is evaluated under four unfavorable synoptic patterns, including "northlow", "transition", "southeast-trough", and "inland-high", based on WRF-Chem model simulations of a persistent heavy PM pollution episode in January 2019. Simulations show that ARI consistently decreases both solar radiation reaching down to the surface(SWDOWN) and surface temperature(TSFC), which then reduces wind speed, induces sinking motion,and influences cloud formation in the GZB. However, large differences under the four synoptic patterns still exist. The average reductions of SWDOWN and daytime TSFC in the GZB range from 15.2% and 1.04°C in the case of the"transition" pattern to 26.7% and 1.69°C in the case of the "north-low" pattern, respectively. Furthermore, ARI suppresses the development of the planetary boundary layer(PBL), with the decrease of PBL height(PBLH) varying from 18.7% in the case of the "transition" pattern to 32.0% in the case of the "north-low" pattern. The increase of daytime near-surface PM2.5 in the GZB due to ARI is 12.0%, 8.1%, 9.5%, and 9.7% under the four synoptic patterns, respectively. Ensemble analyses also reveal that when near-surface PM2.5 concentrations are low, ARI tends to lower PM2.5 concentrations with decreased PBLH, which is caused by enhanced divergence or a transition from divergence to convergence in an area. ARI contributes 15%–25% toward the near-surface PM2.5 concentrations during the severe PM pollution period under the four synoptic patterns. 相似文献
193.
Shilpa Rao Shonali Pachauri Frank Dentener Patrick Kinney Zbigniew Klimont Keywan Riahi Wolfgang Schoepp 《Global Environmental Change》2013,23(5):1122-1130
Air pollution and its related health impacts are a global concern. This paper addresses how current policies on air pollution, climate change and access to clean cooking fuels can effectively reduce both outdoor and household air pollution and improve human health. A state of the art modeling framework is used that combines an integrated assessment model and an atmospheric model to estimate the spatial extent and distribution of outdoor air pollution exposures. Estimates of household energy access and use are modeled by accounting for heterogeneous household energy choices and affordability constraints for rural and urban populations spanning the entire income distribution. Results are presented for 2030 for a set of policy scenarios on air pollution, climate change and energy access and include spatially explicit emissions of air pollutants; ambient concentrations of PM2.5; and health impacts in terms of disability adjusted life years (DALYs) from both ambient and household air pollution. The results stress the importance of enforcing current worldwide air quality legislation in addressing the impacts of outdoor air pollution. A combination of stringent policies on outdoor air pollution, climate change and access to clean cooking fuels is found to be effective in achieving reductions in average ambient PM2.5 exposures to below World Health Organization recommended levels for a majority of the world's population and results in a significant decline in the global burden of disease from both outdoor and household air pollution. 相似文献
194.
The Annualized Agricultural Non‐point Source (AnnAGNPS) pollution model has been widely used to assess and predict runoff, soil erosion, sediment and nutrient loading with a geographic information system. This article presents a case study of the effect of land‐use changes on nonpoint source (NPS) pollution using the AnnAGNPS model in the Xizhi River watershed, eastern Pearl River Delta of Guangdong province, China. The land‐use changes in the Xizhi River watershed between 1998 and 2003 were examined using the multitemporal remote sensing data. The runoff, soil erosion, sediment transport and nutrient loading 1998 and 2003 were assessed using AnnAGNPS. The effects of land‐use changes on NPS were studied by comparing the simulation results of each year. Our results showed that (i) the NPS loadings increased when forest and grass land converted into paddy, orchard and farmland land, and population size and gross domestic product size as well as the usage amounts of fertilizer and pesticide in the entire watershed were firmly correlated with the NPS loadings; (ii) the land‐use change during fast urbanization in particular when other land types were converted into the development land and buildup land led to increasing of NPS pollution; and (iii) urban land expansion showed more important effects on total organic carbon (TOC) loading compared with nitrogen and phosphorus loadings. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
195.
Application of a Bayesian model to infer the contribution of coalbed natural gas produced water to the Powder River,Wyoming and Montana 下载免费PDF全文
The Powder River Basin (PRB) of Wyoming and Montana contains significant coal and coal bed natural gas (CBNG) resources. CBNG extraction requires the production of large volumes of water, much of which is discharged into existing drainages. Compared to surface waters, the CBNG produced water is high in sodium relative to calcium and magnesium, elevating the sodium adsorption ratio (SAR). To mitigate the possible impact this produced water may have on the quality of surface water used for irrigation, the State of Montana passed water anti‐degradation legislation, which could affect CBNG production in Wyoming. In this study, we sought to determine the proportion of CBNG produced water discharged to tributaries that reaches the Powder River by implementing a four end‐member mixing model within a Bayesian statistical framework. The model accounts for the 87Sr/86Sr, δ13CDIC, [Sr] and [DIC] of CBNG produced water and surface water interacting with the three primary lithologies exposed in the PRB. The model estimates the relative contribution of the end members to the river water, while incorporating uncertainty associated with measurement and process error. Model results confirm that both of the tributaries associated with high CBNG activity are mostly composed of CBNG produced water (70–100%). The model indicates that up to 50% of the Powder River is composed of CBNG produced water downstream from the CBNG tributaries, decreasing with distance by dilution from non‐CBNG impacted tributaries from the point sources to ~10–20% at the Montana border. This amount of CBNG produced water does not significantly affect the SAR or electrical conductivity of the Powder River in Montana. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
196.
G. R. Dargahi-Noubary 《Natural Hazards》1988,1(3):227-233
A new threshold method is explained in a manner suitable for workers in the general scientific area. Its application to the prediction of extreme pollutant concentrations is described and the results are compared with those of a conventional procedure, using a set of published data. A discussion concerning the difficulties of the presently used statistical technique is also included. 相似文献
197.
Simultaneous ozone measurements were made at a rural site, 25 km SSW of the city of Jerusalem, and in the center of the city during a period of 28 months. The ozone data were supplemented by SO2, NO/NO
x
,and meteorological measurements at both sites. Elevated ozone concentrations were recorded at the rural site, mostly during the spring months (May and June) during which the monthly averages and the monthly averages of the daily 30 min maximum levels equalled those measured in the city. During the summer months, both average and peak levels were lower at the rural site by 20 and 35 ppb. The increased ozone levels at the rural site were accompanied by a parallel increase of SO2 and NO
x
,suggesting hat the excess ozone at the rural site is a result of a transformation during transport of air pollutants from coastal sources. 相似文献
198.
本文对1987—1993年间,山西50个矿泉水点101份饮用天然矿泉水细菌总数和总大肠菌群进行了检验,其中64份合格,合格率为63;37%。表明山西饮用天然矿泉水源受微生物的污染较为严重,污染程度与水源出露形式和季节变化关系不明显,而主要与矿泉水出露环境的防护措施有密切关系。 相似文献
199.
200.
通过白城市地下水环境地质调查和多年地下水动态监测工作,对白城市1993年地下水污染,地下水质量作出评价。并对多年资料作趋势分析。结果表明:白城市地下水受到不同程度污染、地下水质量濒临恶化,化学组分中Cl ̄-、SO、NO、总硬度、矿化度呈上升趋势。针对上述问题,提出防治措施。 相似文献