全文获取类型
收费全文 | 2026篇 |
免费 | 266篇 |
国内免费 | 970篇 |
专业分类
安全科学 | 191篇 |
废物处理 | 60篇 |
环保管理 | 550篇 |
综合类 | 1552篇 |
基础理论 | 294篇 |
污染及防治 | 348篇 |
评价与监测 | 150篇 |
社会与环境 | 60篇 |
灾害及防治 | 57篇 |
出版年
2024年 | 17篇 |
2023年 | 75篇 |
2022年 | 115篇 |
2021年 | 115篇 |
2020年 | 109篇 |
2019年 | 100篇 |
2018年 | 90篇 |
2017年 | 141篇 |
2016年 | 165篇 |
2015年 | 174篇 |
2014年 | 175篇 |
2013年 | 229篇 |
2012年 | 219篇 |
2011年 | 180篇 |
2010年 | 124篇 |
2009年 | 108篇 |
2008年 | 92篇 |
2007年 | 165篇 |
2006年 | 116篇 |
2005年 | 109篇 |
2004年 | 74篇 |
2003年 | 91篇 |
2002年 | 63篇 |
2001年 | 54篇 |
2000年 | 47篇 |
1999年 | 47篇 |
1998年 | 36篇 |
1997年 | 34篇 |
1996年 | 30篇 |
1995年 | 27篇 |
1994年 | 26篇 |
1993年 | 17篇 |
1992年 | 5篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 15篇 |
1985年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 3篇 |
排序方式: 共有3262条查询结果,搜索用时 9 毫秒
701.
J. Rolf Olsen Jery R. Stedinger Nicholas C. Matalas Eugene Z. Stakhiv 《Journal of the American Water Resources Association》1999,35(6):1509-1523
ABSTRACT: This paper considers the distribution of flood flows in the Upper Mississippi, Lower Missouri, and Illinois Rivers and their relationship to climatic indices. Global climate patterns including El Niño/Southern Oscillation, the Pacific Decadal Oscillation, and the North Atlantic Oscillation explained very little of the variations in flow peaks. However, large and statistically significant upward trends were found in many gauge records along the Upper Mississippi and Missouri Rivers: at Hermann on the Missouri River above the confluence with the Mississippi (p = 2 percent), at Hannibal on the Mississippi River (p < 0.1 percent), at Meredosia on the Illinois River (p = 0.7 percent), and at St. Louis on the Mississippi below the confluence of all three rivers (p = 1 percent). This challenges the traditional assumption that flood series are independent and identically distributed random variables and suggests that flood risk changes over time. 相似文献
702.
703.
Melanie B. Ruhiman Wade L. Nutter 《Journal of the American Water Resources Association》1999,35(2):277-290
ABSTRACT: Historic changes in stream channel morphology were investigated in the Georgia Piedmont to better understand the hydrologic processes and functioning of the region's riverine systems. USGS gaging station data and channel geomorphology data were collected from thirty study sites in the Upper Oconee River Basin for flood frequency analysis. Historic and modern (i.e., present-day) channel capacity discharge (i.e., overbank flow) was calculated using Manning's equation and historic channel cross-section records. The recurrence interval for overbank flow was estimated for each site from flood frequency data. Results indicate that channel expansion has occurred throughout the basin, especially in upper reaches. Recurrence intervals for modern overbank events were variable and generally high ranging from < 2 to > 500 years for first to third order streams. They were less variable and lower for fourth and fifth order streams, ranging from < 2 to 3 years. Potential depositional thresholds were identified that exemplify the complex response of sediment distribution patterns throughout the basin. Results indicate overbank flows occur less frequently now than they once did due to historic accelerated sedimentation and subsequent channel expansion. One application of these findings is that these basin processes are likely applicable across the region and may impact the hydrologic functioning of associated Piedmont riverine wetlands that depend on flooding regimes. 相似文献
704.
Aida Mendez Theo A. Dillaha Saied Mostaghimi 《Journal of the American Water Resources Association》1999,35(4):867-875
ABSTRACT: An 18-month field experiment was conducted to evaluate the effectiveness of grass filter strips in removing sediment and various nitrogen species from runoff. Runoff was collected from six 3.7 m wide experimental plots with 24.7 m long runoff source areas. Two plots had 8.5 m filters, two plots had 4.3 m filters, and two plots had no filters. Runoff was analyzed for total suspended solids (TSS), total Kjeldahl nitrogen (TKN),. filtered TKN (FTKN), NH4+-N, and NO3-N. The Mann-Kendall nonparametric test for trend (changes in filter effectiveness over time) indicated that there were no trends in the yields and concentrations of TSS, NO3--N, NH4-N, TKN, and FTKN for the 8.5 m filter over time. For the shorter 4.3 m filters, there were significant upward trends in TKN yield and downward trends in TSS, NH4-N, and FTKN concentrations, indicating that trapping efficiency may have started changing with time. The Kruskal-Wallis test indicated that the 8.5 m filters reduced median yields and concentrations of TSS and all N species, but the 4.3 m filters only reduced the median yields and concentrations of TSS, NH4+-N, TKN, and the median concentration of FTKN. The 8.5 and 4.3 m filters reduced contaminate yields and concentrations from 42 to 90 percent and from 20 to 83 percent, respectively. 相似文献
705.
Benjamin Felzer Preston Heard 《Journal of the American Water Resources Association》1999,35(6):1327-1339
ABSTRACT: Two general circulation models (GCMs) used in the U.S. national assessment of the potential consequences of climate variability and change (CGCM1 and HadCM2) show a large increase in precipitation in the future over the southwestern U.S., particularly during winter. This precipitation increase is an extension of a larger region of increased precipitation in the Pacific Ocean off the west coast of North America that is associated with a deepened and southward-shifted Aleutian Low, a weaker subtropical high, and warmer sea surface temperatures (SSTs). The models differ in their simulation of precipitation anomalies over the southeastern U.S., with CGCM1 showing drier conditions and HadCM2 showing wetter conditions in the future. While both models show decreased frequency of Atlantic storms, consistent with decreased meridional and land/sea temperature gradients, the more coastal position of the storm track in CGCM1 results in less precipitation than modern along the eastern seaboard of the U.S. During summer, differences in land surface models within the two GCMs sometimes lead to differences in soil moisture that feed back to the precipitation over land due to available moisture. 相似文献
706.
本文系统地介绍了有关水环境主要的形态模型、表面络合模型、点源和非点源污染模型及其计算机模型软件,并着重阐述了生态模型的发展及应用等 相似文献
707.
Rafik Absi 《Environmental Fluid Mechanics》2008,8(4):389-394
In a recent paper published in this journal, Bonakdari et al. (Environ Fluid Mech 8:1–17, 2008) presented a new formulation
of the vertical velocity profile in the central portion of steady fully developed turbulent open-channel flows which is based
on an analysis of the Navier–Stokes equations. The predicted mean streamwise velocity profiles presented by the authors represent
dip phenomenon (maximum velocity below the free surface). The discusser would like to point out some contradictions and an
error in the main demonstration. This error appears in the right-hand side term of the main Eq. 22 (Environ Fluid Mech 8:1–17,
2008) in the parameter α. Our corrected demonstration shows that α is equal to and not to as obtained by the authors (Environ Fluid Mech 8:1–17, 2008). The values of α used by the authors are under-estimated by 1, this difference has a significant effect on velocities and therefore will involve
a difference between measured and predicted velocity profiles. Finally, the assumption of at the free surface is in contradiction with predicted velocity profiles. 相似文献
708.
渤海湾海岸带开发对近岸沉积物重金属的影响 总被引:6,自引:2,他引:6
为了解渤海湾围填海造成的生境变化趋势及重金属污染状况,对2003年和2011年渤海湾表层沉积物4种重金属(Cd、Pb、Cu、Zn)的含量及空间分布分别进行了研究,并采用BCR三步分级提取法分析了2011年渤海湾表层沉积物中这4种重金属不同赋存形态的含量,评估了这4种重金属的生物有效性,最后分别采用富集系数法和潜在生态危害指数法对2011年重金属污染程度及潜在生态危害进行了评价.结果表明,2011年渤海湾沉积物中Cu、Cd、Pb的含量均比2003年偏高,重金属污染形势趋于严峻.Cu、Zn、Cd的空间分布趋势基本相似,其高值区均集中在渤海湾的中部海域.Pb的高值区主要集中在近岸河口和渤海湾中部及南部.4种重金属相互之间相关性显著,说明它们之间可能具有一定的同源性.形态分析表明Cu、Zn、Cd主要以残渣态存在,Pb主要以可还原态存在,各元素生物有效性排序为:Cd>Pb>Cu>Zn.Cd为渤海湾表层沉积物中最主要的污染元素,且具有较强的生态危害.Cu、Zn、Pb污染程度较低,生态危害轻微. 相似文献
709.
我国东北典型河流冰封期细菌多样性的研究——以松花江为例 总被引:4,自引:1,他引:4
在我国东北松花江冰封期时采集了该河流域5个监测断面的河水样本,并分别构建16S rDNA克隆文库,通过16S rDNA序列的系统发育分析,对水样中细菌群落结构和种群多样性进行了研究.试验结果表明,5个采样点的水样pH都呈弱酸性,并且都有不同程度的多环芳烃(PAHs)污染,其中,B(九站)采样点污染最为严重.5个样品中检测到的共同细菌种类有5个:β-变形菌纲(Betaproteobacteria)、γ-变形菌纲(Gammaproteobacteria)、放线菌门(Actinobacteria)、蓝细菌门(Cyanobacteria)和拟杆菌门(Bacteroidetes).5个河水样品中的细菌与许多已知降解菌的亲缘关系较近,并以能降解多环芳烃类有机污染物的微生物种类居多,且在5个样品中均发现了指示河流富营养化的菌种,表明该河流存在普遍的富营养化趋势,特别是D、E段(佳木斯上和佳木斯下)比较严重. 相似文献
710.
应用荷兰Skalar公司的SAN”连续流动注射分析仪测定地表水中的总氮,建立测定地表水中总氮的流动注射分析法.结果显示该方法分析速度快,分析速率可达32个/小时,仪器测定浓度与峰高响应值相关性很高,相关系数为0.9996,线性范围0.0 mg/L ~5.00 mg/L,方法检出限为0.03 mg/L,精密度RSD小于4%,均满足国家实验质量标准要求.紫外消解流动注射分光光度法测定地表水总氮具有分析速度快、准确度高、干扰少,适合大批量的地表水分析. 相似文献