全文获取类型
收费全文 | 18570篇 |
免费 | 1518篇 |
国内免费 | 3752篇 |
专业分类
安全科学 | 1819篇 |
废物处理 | 431篇 |
环保管理 | 4556篇 |
综合类 | 10620篇 |
基础理论 | 1815篇 |
环境理论 | 2篇 |
污染及防治 | 1464篇 |
评价与监测 | 1663篇 |
社会与环境 | 1008篇 |
灾害及防治 | 462篇 |
出版年
2024年 | 59篇 |
2023年 | 256篇 |
2022年 | 448篇 |
2021年 | 531篇 |
2020年 | 573篇 |
2019年 | 465篇 |
2018年 | 468篇 |
2017年 | 647篇 |
2016年 | 801篇 |
2015年 | 894篇 |
2014年 | 926篇 |
2013年 | 1263篇 |
2012年 | 1410篇 |
2011年 | 1505篇 |
2010年 | 1044篇 |
2009年 | 1073篇 |
2008年 | 798篇 |
2007年 | 1305篇 |
2006年 | 1223篇 |
2005年 | 1002篇 |
2004年 | 854篇 |
2003年 | 854篇 |
2002年 | 720篇 |
2001年 | 596篇 |
2000年 | 557篇 |
1999年 | 485篇 |
1998年 | 358篇 |
1997年 | 357篇 |
1996年 | 298篇 |
1995年 | 254篇 |
1994年 | 211篇 |
1993年 | 202篇 |
1992年 | 148篇 |
1991年 | 118篇 |
1990年 | 87篇 |
1989年 | 89篇 |
1988年 | 77篇 |
1987年 | 72篇 |
1986年 | 46篇 |
1984年 | 48篇 |
1983年 | 58篇 |
1982年 | 58篇 |
1981年 | 72篇 |
1980年 | 82篇 |
1979年 | 72篇 |
1978年 | 51篇 |
1977年 | 47篇 |
1973年 | 46篇 |
1972年 | 39篇 |
1971年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
511.
本文对GB17323—1998《瓶装饮用纯净水》标准中电导率、氯化物、pH、高锰酸钾消耗量等指标的标准值的测定方法提出了不同看法,并建议了更为有效的测定方法。 相似文献
512.
测定环境空气中微量氟的方法一般采用滤膜法,但此法工作量大,针对这种情况,本文作两点改进:一是将采集的两张滤膜同时测定;二是将测定过程中的搅拌时间缩短,这样不影响测定结果的准确性,而且降低了工作量。 相似文献
513.
514.
515.
Bernard Barraqué 《Natural resources forum》2003,27(3):200-211
The article contributes to a discussion on two global issues on water: water resources management, and water supply and sanitation. Focusing on Europe, it traces the legal roots of current systems in history: as a resource, water is considered as a common property, rather than a market good; while as a public service it is usually a commodity. Public water supply and sanitation technologies and engineering have developed under three main paradigms: quantitative and civil engineering; qualitative and chemical/sanitary engineering (both on the supply side); and the most recent one, environmental engineering and integrated management (on the demand side). The cost of public drinking water is due to rise sharply in view of the two‐fold financial challenge of replacing an ageing infrastructure and keeping up with ever‐rising environmental and sanitary quality standards. Who will pay? Government subsidies, or water users? The author suggests that apparent successes with privatisation may have relied heavily on hidden government subsidies and/or the healthy state of previously installed water infrastructure: past government subsidies are still felt for as long as the lifetime of the infrastructure. The article stresses the importance of public participation and decentralized local management of water and sanitation services. Informing and involving users in water management decisions is seen as an integral part of the ‘ethics’ side of the crucial three E's (economics, environment, ethics). The article strongly argues for municipal provision of water services, and hopes that lessons learnt and solutions found in the European experience may serve water services management efforts in other regions of the world. 相似文献
516.
517.
Baxter E. Vieux Fekadu G. Moreda 《Journal of the American Water Resources Association》2003,39(4):757-769
ABSTRACT: A synthetic relationship is developed between nutrient concentrations and discharge rates at two river gauging sites in the Illinois River Basin. Analysis is performed on data collected by the U.S. Geological Survey (USGS) on nutrients in 1990 through 1997 and 1999 and on discharge rates in 1988 through 1997 and 1999. The Illinois River Basin is in western Arkansas and northeastern Oklahoma and is designated as an Oklahoma Scenic River. Consistently high nutrient concentrations in the river and receiving water bodies conflict with recreational water use, leading to intense stakeholder debate on how best to manage water quality. Results show that the majority of annual phosphorus (P) loading is transported by direct runoff, with high concentrations transported by high discharge rates and low concentrations by low discharge rates. A synthetic relationship is derived and used to generate daily phosphorus concentrations, laying the foundation for analysis of annual loading and evaluation of alternative management practices. Total nitrogen (N) concentration does not have as clear a relationship with discharge. Using a simple regression relationship, annual P loadings are estimated as having a root mean squared error (RMSE) of 39.8 t/yr and 31.9 t/yr and mean absolute percentage errors of 19 percent and 28 percent at Watts and Tahlequah, respectively. P is the limiting nutrient over the full range of discharges. Given that the majority of P is derived from Arkansas, management practices that control P would have the most benefit if applied on the Arkansas side of the border. 相似文献
518.
ABSTRACT: The time to hydrograph peak of a watershed basin has been found to correlate with various statistical attributes (e.g., skewness and kurtosis) of its hypsometric curve (treated as probability distribution). This paper presents a theoretical travel time that is conceptually analogous to the time to hydrograph peak and can be calculated directly from the hypsometric curve of a watershed basin based on gravity and acceleration. The theoretical travel times for 23 selected watersheds in the United States are found to correlate significantly with their corresponding hypsometric attributes. In addition, the theoretical travel times are consistent with the times of concentration estimated from the Federal Aviation Administration method. Thus, this paper offers a simple theoretical explanation to the empirically identified linkage between time to hydrograph peak and hypsometric attributes. This theoretical travel time can provide an alternative way of characterizing the effects of basin morphometry on hydrologic response. 相似文献
519.
Keith E. Schilling Robert D. Libra 《Journal of the American Water Resources Association》2003,39(4):851-860
ABSTRACT: Historical trends in annual discharge characteristics were evaluated for 11 gauging stations located throughout Iowa. Discharge records from nine eight‐digit hydrologic unit code (HUC‐8) watersheds were examined for the period 1940 to 2000, whereas data for two larger river systems (Cedar and Des Moines Rivers) were examined for a longer period of record (1903 to 2000). In nearly all watersheds evaluated, annual base flow, annual minimum flow, and the annual base flow percentage significantly increased over time. Some rivers also exhibited increasing trends in total annual discharge, whereas only the Maquoketa River had significantly decreased annual maximum flows. Regression of stream discharge versus precipitation indicated that more precipitation is being routed into streams as base flow than as storm flow in the second half of the 20th Century. Reasons for the observed stream flow trends are hypothesized to include improved conservation practices, greater artificial drainage, increasing row crop production, and channel incision. Each of these reasons is consistent with the observed trends, and all are likely responsible to some degree in most watersheds. 相似文献
520.
James V. Bonta Bruce Cleland 《Journal of the American Water Resources Association》2003,39(6):1481-1496
ABSTRACT: Quantifying natural variability, uncertainty, and risk with minimal data is one of the greatest challenges facing those engaged in water quality evaluations, such as development of total maximum daily loads (TMDL), because of regulatory, natural, and analytical constraints. Quantification of uncertainty and variability in natural systems is illustrated using duration curves (DCs), plots that illustrate the percent of time that a particular flow rate (FDC), concentration (CDC), or load rate (LDC; “TMDL”) is exceeded, and are constructed using simple derived distributions. Duration curves require different construction methods and interpretations, depending on whether there is a statistically significant correlation between concentration (C) and flow (Q), and on the sign of the C‐Q regression slope (positive or negative). Flow DCs computed from annual runoff data vary compared with an FDC developed using all data. Percent exceedance for DCs can correspond to risk; however, DCs are not composed of independent quantities. Confidence intervals of data about a regression line can be used to develop confidence limits for the CDC and LDC. An alternate expression to a fixed TMDL is suggested as the risk of a load rate being exceeded and lying between confidence limits. Averages over partial ranges of DCs are also suggested as an alternative expression of TMDLs. DCs can be used to quantify watershed response in terms of changes in exceedances, concentrations, and load rates after implementation of best management practices. 相似文献