全文获取类型
收费全文 | 41325篇 |
免费 | 514篇 |
国内免费 | 537篇 |
专业分类
安全科学 | 1320篇 |
废物处理 | 1584篇 |
环保管理 | 6066篇 |
综合类 | 7424篇 |
基础理论 | 10620篇 |
环境理论 | 16篇 |
污染及防治 | 10846篇 |
评价与监测 | 2316篇 |
社会与环境 | 1898篇 |
灾害及防治 | 286篇 |
出版年
2022年 | 294篇 |
2021年 | 335篇 |
2020年 | 291篇 |
2019年 | 304篇 |
2018年 | 555篇 |
2017年 | 530篇 |
2016年 | 849篇 |
2015年 | 686篇 |
2014年 | 1001篇 |
2013年 | 3342篇 |
2012年 | 1278篇 |
2011年 | 1797篇 |
2010年 | 1376篇 |
2009年 | 1578篇 |
2008年 | 1780篇 |
2007年 | 1860篇 |
2006年 | 1619篇 |
2005年 | 1346篇 |
2004年 | 1334篇 |
2003年 | 1284篇 |
2002年 | 1237篇 |
2001年 | 1512篇 |
2000年 | 1120篇 |
1999年 | 718篇 |
1998年 | 505篇 |
1997年 | 516篇 |
1996年 | 566篇 |
1995年 | 610篇 |
1994年 | 567篇 |
1993年 | 515篇 |
1992年 | 478篇 |
1991年 | 478篇 |
1990年 | 497篇 |
1989年 | 470篇 |
1988年 | 436篇 |
1987年 | 397篇 |
1986年 | 378篇 |
1985年 | 403篇 |
1984年 | 430篇 |
1983年 | 405篇 |
1982年 | 433篇 |
1981年 | 427篇 |
1980年 | 366篇 |
1979年 | 388篇 |
1978年 | 295篇 |
1977年 | 270篇 |
1976年 | 257篇 |
1974年 | 262篇 |
1973年 | 254篇 |
1972年 | 264篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
Michelle L. Soupir Saied Mostaghimi Amanda Masters Katherine A. Flahive David H. Vaughan Aida Mendez Phillip W. McClellan 《Journal of the American Water Resources Association》2004,40(1):53-66
ABSTRACT: Erosion from construction sites significantly affects water quality in receiving streams. A rainfall simulator was used to evaluate the effectiveness of different methods for controlling erosion from construction sites. Erosion control methods investigated included dry and liquid applications of polyacrylamide (PAM), hydroseed, and straw mulch. Fertilizer was also applied to each plot to examine the effectiveness of the methods in reducing nutrient losses in runoff. Runoff samples were analyzed for total suspended solids (TSS), nitrate, total Kjeldahl nitrogen (TKN), ammonium, total phosphorus (TP), and orthophosphate. Among all treatments investigated, straw mulch was the most effective treatment for controlling TSS and nutrient losses during short term and long term simulations. The low liquid PAM (half the recommended PAM) treatment resulted in the highest reduction in runoff, TSS bound nitrogen, and total nitrogen (TN) concentrations and loadings. The study results indicate that a high application rate (twice the recommended rate) of PAM could actually increase runoff and TSS losses. At a low application rate, both liquid and dry PAM were effective in reducing TSS and nutrient losses in runoff. However, application of the liquid form of PAM to construction sites is more practical and perhaps more economical than applying the PAM in the dry form. 相似文献
983.
Vicente L. Lopes H. Evan Canfield 《Journal of the American Water Resources Association》2004,40(2):311-319
ABSTRACT: This paper evaluates the effects of watershed geometric representation (i.e., plane and channel representation) on runoff and sediment yield simulations in a semiarid rangeland watershed. A process based, spatially distributed runoff erosion model (KINEROS2) was used to explore four spatial representations of a 4.4 ha experimental watershed. The most complex representation included all 96 channel elements identifiable in the field. The least complex representation contained only five channel elements. It was concluded that oversimplified watershed representations greatly influence runoff and sediment yield simulations by inducing excessive infiltration on hillslopes and distorting runoff patterns and sediment fluxes. Runoff and sediment yield decrease systematically with decreasing complexity in watershed representation. However, less complex representations had less impact on runoff and sediment‐yield simulations for small rainfall events. This study concludes that the selection of the appropriate level of watershed representation can have important theoretical and practical implications on runoff and sediment yield modeling in semiarid environments. 相似文献
984.
Kenneth E. Hyer Douglas L. Mayer 《Journal of the American Water Resources Association》2004,40(6):1511-1526
ABSTRACT: Surface water impairment by fecal coliform bacteria is a water quality issue of national scope and importance. In Virginia, more than 400 stream and river segments are on the Commonwealth's 2002 303(d) list because of fecal coliform impairment. Total maximum daily loads (TMDLs) will be developed for most of these listed streams and rivers. Information regarding the major fecal coliform sources that impair surface water quality would enhance the development of effective watershed models and improve TMDLs. Bacterial source tracking (BST) is a recently developed technology for identifying the sources of fecal coliform bacteria and it may be helpful in generating improved TMDLs. Bacterial source tracking was performed, watershed models were developed, and TMDLs were prepared for three streams (Accotink Creek, Christians Creek, and Blacks Run) on Virginia's 303(d) list of impaired waters. Quality assurance of the BST work suggests that these data adequately describe the bacteria sources that are impairing these streams. Initial comparison of simulated bacterial sources with the observed BST data indicated that the fecal coliform sources were represented inaccurately in the initial model simulation. Revised model simulations (based on BST data) appeared to provide a better representation of the sources of fecal coliform bacteria in these three streams. The coupled approach of incorporating BST data into the fecal coliform transport model appears to reduce model uncertainty and should result in an improved TMDL. 相似文献
985.
Ryan C. Schwartz Peter J. Deadman Daniel J. Scott Linda D. Mortsch 《Journal of the American Water Resources Association》2004,40(3):647-662
ABSTRACT: Recent research that couples climate change scenarios based on general circulation models (GCM) with Great Lakes hydrologic models has indicated that average water levels are projected to decline in the future. This paper outlines a methodology to assess the potential impact of declining water levels on Great Lakes waterfront communities, using the Lake Huron shoreline at Goderich, Ontario, as an example. The methodology utilizes a geographic information system (GIS) to combine topographic and bathymetric datasets. A digital elevation surface is used to model projected shoreline change for 2050 using water level scenarios. An arbitrary scenario, based on a 1 m decline from February 2001 lake levels, is also modeled. By creating a series of shoreline scenarios, a range of impact and cost scenarios are generated for the Goderich Harbor and adjacent marinas. Additional harbor and marina dredging could cost as much as CDN $7.6 million. Lake freighters may experience a 30 percent loss in vessel capacity. The methodology is used to provide initial estimates of the potential impacts of climate change that can be readily updated as more robust climate change scenarios become available and is adaptable for use in other Great Lakes coastal communities. 相似文献
986.
Naomi E. Detenbeck Colleen M. Elonen Debra L. Taylor Leroy E. Anderson Terri M. Jicha Sharon L. Batterman 《Journal of the American Water Resources Association》2004,40(3):705-720
ABSTRACT: In 1998 and 1999, third‐order watersheds in high mature forest (HMF) and low mature forest (LMF) classes were selected along gradients of watershed storage within each of two hydrogeomorphic regions in the Lake Superior Basin to evaluate threshold effects of storage on hydrologic regimes and watershed exports. Differences were detected between regions (North and South Shore) for particulates, nutrients, and pH, with all but silica values higher for South Shore streams (p < 0.05). Mature forest effects were detected for turbidity, nutrients, color, and alkalinity, with higher values in the LMF watersheds, that is, watersheds with less that 50 percent mature forest cover. Dissolved N, ammonium, N:P, organic carbon, and color increased, while suspended solids, turbidity, and dissolved P decreased as a function of storage. Few two‐way interactions were detected between region and mature forest or watershed storage, thus threshold based classification schemes could be used to extrapolate effects across regions. Both regional differences in water quality and those associated with watershed attributes were more common for third‐order streams in the western Lake Superior drainage basin as compared with second‐order streams examined in an earlier study. Use of ecoregions alone as a basis for setting regional water quality criteria would have led to misinterpretation of reference condition and assessment of impacts in the Northern Lakes and Forest Ecoregion. 相似文献
987.
细水雾阻隔火焰热辐射的模拟研究 总被引:1,自引:2,他引:1
从热辐射传递方程出发,根据Mie散射理论,考虑雾滴对热辐射的散射和吸收特性,建立细水雾阻隔火焰热辐射的两通量模型,并给出简化算法;同时建立小尺度模拟实验系统,对理论模型进行验证。结果表明,两通量模型较为合理地预测了细水雾对火焰热辐射的衰减作用。在此基础上,应用上述理论模型进一步探讨火焰温度、细水雾特性参数、雾场厚度对阻隔热辐射效率的影响,为细水雾系统的实际工程应用提供了理论和依据。 相似文献
988.
989.
990.