全文获取类型
收费全文 | 398篇 |
免费 | 62篇 |
国内免费 | 8篇 |
专业分类
安全科学 | 11篇 |
废物处理 | 14篇 |
环保管理 | 250篇 |
综合类 | 114篇 |
基础理论 | 29篇 |
污染及防治 | 10篇 |
评价与监测 | 23篇 |
社会与环境 | 11篇 |
灾害及防治 | 6篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 9篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 17篇 |
2018年 | 7篇 |
2017年 | 14篇 |
2016年 | 17篇 |
2015年 | 18篇 |
2014年 | 17篇 |
2013年 | 13篇 |
2012年 | 14篇 |
2011年 | 16篇 |
2010年 | 7篇 |
2009年 | 16篇 |
2008年 | 13篇 |
2007年 | 15篇 |
2006年 | 29篇 |
2005年 | 12篇 |
2004年 | 18篇 |
2003年 | 28篇 |
2002年 | 25篇 |
2001年 | 16篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有468条查询结果,搜索用时 15 毫秒
181.
岩溶水体中溶解无机碳(DIC)主要以HCO_3~-形式存在,其同位素(δ~(13)CDIC)被广泛用于示踪DIC的不同来源及其影响因素.为了解亚热带典型岩溶溪流溶解无机碳及其稳定同位素的分布规律,本文以广西柳州官村地下河补给的地表溪流为研究对象,对其水化学特征和δ~(13)CDIC进行分析.结果表明,溪流上游和下游的DIC与δ~(13)CDIC都表现出明显的时空变化特征,地下河出口(G1点)HCO_3~-旱季浓度变化范围为(4.73±0.14)mmol·L~(-1),而雨季为(4.23±0.68)mmol·L~(-1).溪流下游(G2点)HCO_3~-旱季浓度变化范围为(4.56±0.23)mmol·L~(-1),而雨季为(4.20±0.59)mmol·L~(-1).溪流上游的旱季δ~(13)CDIC变化范围为-12.22‰±0.49‰,雨季的变化范围为-12.28‰±0.82‰;溪流下游的旱季变化范围为-10.73±0.71‰,雨季的变化范围为-11.10‰±0.90‰.两个点水体DIC含量旱季均高于雨季,且G1点要高于下游G2点.两个点水体δ~(13)CDIC值旱季较雨季偏重,且G2点水体δ~(13)CDIC值显著高于G1点δ~(13)CDIC值.地下河水和溪流DIC主要来源于土壤CO2和碳酸盐岩溶蚀,但是溪流上游与下游DIC和δ~(13)CDIC值差异表明水体的CO2脱气作用,水生植物的光合作用显著影响了水体DIC和δ~(13)CDIC值. 相似文献
182.
天山北麓宁家河阶地上的黄土堆积及其磁学特征 总被引:1,自引:0,他引:1
本文报道了新疆地区天山北麓宁家河阶地上的黄土堆积。研究剖面的两层黄土为河流砾石层所隔开,这在新疆地区较为少见。通过系统的岩石磁学和粒度测量,分析了该剖面两层黄土的磁学特征,并初步探讨磁化率变化机制。结果表明:黄土中的主要磁性矿物为磁铁矿和磁赤铁矿,并含有少量赤铁矿和针铁矿。亚铁磁性矿物主要以多畴(MD)、假单畴(PSD)颗粒为主,反映了这一地区极弱的成土作用。砾石层上下两层黄土磁学性质存在着差异,表现为上层黄土具有较高的磁性矿物含量、较粗的磁颗粒和相对含量较高的软磁性矿物。下层黄土受到后期河水的改造可能是导致这些差异的原因。磁化率与粒度呈现较好的正相关关系,与黄土高原的情况相反,说明干旱地区的黄土磁学性质主要受原生磁性矿物控制。搬运风力和源区变化是磁化率变化的主导因素。 相似文献
183.
Burak Avcioglu Christopher J. Anderson Latif Kalin 《Journal of the American Water Resources Association》2017,53(3):562-575
Estimation of stream channel heads is an important task since ephemeral channels play a significant role in the transport of sediment and materials to perennial streams. The slope‐area method utilizes digital elevation model (DEM) and related information to develop slope‐area threshold relationships used to estimate the position of channel heads in the watershed. A total of 162 stream channel heads were mapped across the three physiographic regions of Alabama, including the Southwestern Appalachians (51), Piedmont/Ridge and Valley (61), and Coastal Plains (51). Using Geographic Information System and DEM, the local slope and drainage area for each mapped channel head was calculated and region‐specific models were developed and evaluated. Results demonstrated the local slope and drainage area had an inverse and strong correlation in the Piedmont/Ridge and Valley region (r2 = 0.71) and the Southwestern Appalachian region (r2 = 0.61). Among three physiographic regions, the weakest correlation was observed in the Coastal Plain region (r2 = 0.45). By comparing the locations of modeled channel heads to those located in the field, calculated reliability and sensitivity indices indicated model accuracy and reliance were weak to moderate. However, the slope‐area method helped define the upstream boundaries of a more detailed channel network than that derived from the 1:24,000‐scale National Hydrography Dataset, which is commonly used for planning and regulatory purposes. 相似文献
184.
Douglas S. Cherkauer 《Journal of the American Water Resources Association》1975,11(5):987-998
ABSTRACT: The impact of various urban land uses on water flow and quality in streams is being studied by monitoring small streams in the Milwaukee urban area. This paper compares the responses of an urban watershed and an agricultural watershed to an autumn rainfall of 2.2 cm. Flow from the urban basin showed a substantially greater response to the rain than that from the rural. Dilution, resulting from the greater quantities of surface runoff in the urban watershed, caused lower concentrations of sodium, chloride, calcium, magnesium, bicarbonate and total dissolved solids in the urban stream. The total quantity of these materials removed per unit drainage area of the urban basin was much greater, however. Road salt was still among the dominant dissolved materials in the urban water chemistry seven months after the last road salting. Sodium was apparently being released from adsorption by clays in the urban basin. Suspended sediment concentrations and total loads were higher in the urban stream. 相似文献
185.
根据塔里木河下游的地下水位、植物调查数据,对比分析了塔里木河下游生态输水后地下水位、生物量、物种多样性变化。结果表明:实施生态输水工程后,地下水位对生态输水的响应显著,地下水位逐渐抬升,下降趋势得以控制。草本植物生物量的变化趋势与每次输水量变化趋势基本一致,即随着输水量的增加草本植物的生物量也相应增加,草本植物生物量对生态输水的响应程度与输水的时间、输水量的多少有密切关系。地下水位埋深上升,物种多样性也呈上升趋势,但二者并不是同步,物种多样性上升趋势滞后于地下水位的上升,这表明地下水位的抬升有利于植物多样性的增加,但是地下水位变化对植物多样性的影响是一个渐变的过程。 相似文献
186.
Alison H. Purcell David W. Bressler Michael J. Paul Michael T. Barbour Ed T. Rankin James L. Carter Vincent H. Resh 《Journal of the American Water Resources Association》2009,45(2):306-319
Abstract: Biological indicators, particularly benthic macroinvertebrates, are widely used and effective measures of the impact of urbanization on stream ecosystems. A multimetric biological index of urbanization was developed using a large benthic macroinvertebrate dataset (n = 1,835) from the Baltimore, Maryland, metropolitan area and then validated with datasets from Cleveland, Ohio (n = 79); San Jose, California (n = 85); and a different subset of the Baltimore data (n = 85). The biological metrics used to develop the multimetric index were selected using several criteria and were required to represent ecological attributes of macroinvertebrate assemblages including taxonomic composition and richness (number of taxa in the insect orders of Ephemeroptera, Plecoptera, and Trichoptera), functional feeding group (number of taxa designated as filterers), and habit (percent of individuals which cling to the substrate). Quantile regression was used to select metrics and characterize the relationship between the final biological index and an urban gradient (composed of population density, road density, and urban land use). Although more complex biological indices exist, this simplified multimetric index showed a consistent relationship between biological indicators and urban conditions (as measured by quantile regression) in three climatic regions of the United States and can serve as an assessment tool for environmental managers to prioritize urban stream sites for restoration and protection. 相似文献
187.
Gustav B. Seixas Timothy J. Beechie Caleb Fogel Peter M. Kiffney 《Journal of the American Water Resources Association》2018,54(4):974-991
Riparian forests attenuate solar radiation, thereby mediating an important component of the thermal budget of streams. Here, we investigate the relationship between riparian degradation, stream temperature, and channel width in the Chehalis River Basin, Washington State. We used lidar data to measure canopy opening angle, the angle formed between the channel center and trees on both banks; we assumed historical tree heights and calculated the change in canopy angle relative to historical conditions. We then developed an empirical relationship between canopy angle and water temperature using existing data, and simulated temperatures between 2002 and 2080 by combining a tree growth model with climate change scenarios from the NorWeST regional prediction. The greatest change between historical and current conditions (~7°C) occurred in developed portions of the river network, with the highest values of change predicted at channel widths less than ~40 m. Tree growth lessened climate change increases in maximum temperature and the length of river exceeding biologically critical thresholds by ~50%–60%. Moreover, the maximum temperature of channels with bankfull widths less than ~50 m remained similar to current conditions, despite climate change increases. Our findings are consistent with a possible role for the riparian landscape in explaining the low sensitivity of stream temperatures to air temperatures observed in some small mountain streams. 相似文献
188.
Brent Johnson Elizabeth Smith Jerry W. Ackerman Susan Dye Robyn Polinsky Eric Somerville Chris Decker Derek Little Gregory J. Pond Ellen D'Amico 《Journal of the American Water Resources Association》2019,55(1):247-258
Spatial patterns in major dissolved solute concentrations were examined to better understand impact of surface coal mining in headwaters on downstream water chemistry. Sixty sites were sampled seasonally from 2012 to 2014 in an eastern Kentucky watershed. Watershed areas (WA) ranged from 1.6 to 400.5 km2 and were mostly forested (58%–95%), but some drained as much as 31% surface mining. Measures of total dissolved solutes and most component ions were positively correlated with mining. Analytes showed strong convergent spatial patterns with high variability in headwaters (<15 km2 WA) that stabilized downstream (WA > 75 km2), indicating hydrologic mixing primarily controls downstream values. Mean headwater solute concentrations were a good predictor of downstream values, with % differences ranging from 0.55% (Na+) to 28.78% (Mg2+). In a mined scenario where all headwaters had impacts, downstream solute concentrations roughly doubled. Alternatively, if mining impacts to headwaters were minimized, downstream solute concentrations better approximated the 300 μS/cm conductivity criterion deemed protective of aquatic life. Temporal variability also had convergent spatial patterns and mined streams were less variable due to unnaturally stable hydrology. The highly conserved nature of dissolved solutes from mining activities and lack of viable treatment options suggest forested, unmined watersheds would provide dilution that would be protective of downstream aquatic life. 相似文献
189.
Dennis M. Mullen John R. Moring 《Journal of the American Water Resources Association》1988,24(6):1273-1279
ABSTRACT: Autochthonous energy input, in the form of periphyton production and growth, was studied before and after partial logging of the watershed surrounding School Brook, a small tributary of the Aroostook River, Maine. Due to infection by the spruce budworm (Chiristoneura fumiferana), the buffer strip on one bank of the stream was logged and only limited riparian vegetation was left. Though impacts in subsequent years are unknown, the effect of the logging on the periphyton community was insignificant during the nine months following cutting, seemingly due to several factors. Because only 5 percent of the canopy was actually removed, the intensity of available light changed little. Small springs in the area helped maintain a stable thermal regime, and only a small portion of the low gradient watershed was actually logged. Consequently, the nutrients reaching the stream did not change. The relatively low concentrations of nitrates (< 0.3 mg/l) and phosphates (< 10 μg/l), both before and in the first nine months after logging, reflect the limited autochthonous input, thereby reducing the effect of this limited cutting on the stream community. 相似文献
190.
Lawrence S. Feinson Jacob Gibs Thomas E. Imbrigiotta Jessica D. Garrett 《Journal of the American Water Resources Association》2016,52(6):1493-1508
The U.S. Geological Survey's New Jersey and Iowa Water Science Centers deployed ultraviolet‐visible spectrophotometric sensors at water‐quality monitoring sites on the Passaic and Pompton Rivers at Two Bridges, New Jersey, on Toms River at Toms River, New Jersey, and on the North Raccoon River near Jefferson, Iowa to continuously measure in‐stream nitrate plus nitrite as nitrogen (NO3 + NO2) concentrations in conjunction with continuous stream flow measurements. Statistical analysis of NO3 + NO2 vs. stream discharge during storm events found statistically significant links between land use types and sampling site with the normalized area and rotational direction of NO3 + NO2‐stream discharge (N‐Q) hysteresis patterns. Statistically significant relations were also found between the normalized area of a hysteresis pattern and several flow parameters as well as the normalized area adjusted for rotational direction and minimum NO3 + NO2 concentrations. The mean normalized hysteresis area for forested land use was smaller than that of urban and agricultural land uses. The hysteresis rotational direction of the agricultural land use was opposite of that of the urban and undeveloped land uses. An r2 of 0.81 for the relation between the minimum normalized NO3 + NO2 concentration during a storm vs. the normalized NO3 + NO2 concentration at peak flow suggested that dilution was the dominant process controlling NO3 + NO2 concentrations over the course of most storm events. 相似文献