首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3017篇
  免费   58篇
  国内免费   20篇
安全科学   150篇
废物处理   113篇
环保管理   816篇
综合类   315篇
基础理论   707篇
环境理论   3篇
污染及防治   689篇
评价与监测   174篇
社会与环境   109篇
灾害及防治   19篇
  2023年   24篇
  2022年   24篇
  2021年   37篇
  2020年   40篇
  2019年   48篇
  2018年   57篇
  2017年   57篇
  2016年   101篇
  2015年   66篇
  2014年   69篇
  2013年   307篇
  2012年   112篇
  2011年   170篇
  2010年   125篇
  2009年   137篇
  2008年   146篇
  2007年   152篇
  2006年   135篇
  2005年   80篇
  2004年   110篇
  2003年   108篇
  2002年   90篇
  2001年   58篇
  2000年   44篇
  1999年   50篇
  1998年   43篇
  1997年   42篇
  1996年   45篇
  1995年   57篇
  1994年   45篇
  1993年   42篇
  1992年   29篇
  1991年   34篇
  1990年   36篇
  1989年   24篇
  1988年   30篇
  1987年   25篇
  1986年   37篇
  1985年   21篇
  1984年   35篇
  1983年   28篇
  1982年   30篇
  1981年   30篇
  1980年   18篇
  1979年   18篇
  1978年   12篇
  1977年   10篇
  1976年   9篇
  1974年   8篇
  1972年   10篇
排序方式: 共有3095条查询结果,搜索用时 15 毫秒
671.
A study was established near a former Zn and Pb smelter to test the ability of soil amendments to reduce the availability of Pb, Zn, and Cd in situ. Soil collected from the field was amended in the lab with P added as 1% P-H3PO4, biosolids compost added at 10% (referred to hereafter as "compost"), and a high-Fe by-product (referred to hereafter as "Fe") + P-triple superphosphate (TSP) (2.5% Fe + 1% P-TSP) and incubated under laboratory conditions at a constant soil pH. Changes in Pb bioavailability were measured with an in vitro test and a feeding study with weanling rats. Field-amended and incubated soils using these plus additional treatments were evaluated using the in vitro extraction and tall fescue (Festuca arundinacea Schreb. cv. Kentucky-31) metal concentration. Reductions were observed across all parameters but were not consistent. In the feeding study, the 1% P-H3PO4 and compost treatments resulted in a decrease of 26% in rat tissue Pb concentration compared with the control soil. The 2.5% Fe + 1% P-TSP showed a 39% decrease. The 1% P-H3PO4 treatment caused the greatest reduction in in vitro extractable Pb from field samples (pH 2.2) with a measured reduction of 66%, while the compost treatment had a 39% reduction and the 2.5% Fe + 1% P-TSP treatment a 50% reduction. The in vitro extraction (pH 1.5) run on field samples showed no reduction in the compost or Fe treatments. The 1% P-H3PO4 treatment was the most effective at reducing plant Pb, Zn, and Cd.  相似文献   
672.
    
Groundwater exchanges with most lakes are rarely quantified because there are many technical challenges to quantification. We investigated a lakebed mapping approach to infer the relative areas of groundwater exchange in 12 prairie shallow lakes and five Laurentian mixed forest shallow lakes in Minnesota, USA in 2011. We used a relatively common approach (seepage meters) to provide baseline information on the magnitude and direction of flow at four locations in each lake. To expand from point measurements to the whole‐lake scale, we explored use of specific conductivity as a cheaper and more time efficient proxy for groundwater discharge to lakes. We validated the approach at near shore stations in each lake where seepage meter measurements and specific conductivity surveys overlapped. Specific conductivity surveys provided a similar assessment of groundwater discharge compared to seepage meters for 50% of the lake‐sampling period combinations. The lakebed mapping approach, when validated for a lake with a limited number of seepage meter (or alternative methods) measurements, offers the advantages of being more time and labor efficient over the use of a similar number of seepage meter monitoring locations; seepage meters (or piezometers, for example) are costlier in terms of equipment and labor, even for single‐lake studies. We show the combined approach could provide useful baselines for understanding and mapping groundwater exchange in shallow lakes.  相似文献   
673.
On November 13-14, 2003, a symposium on high-visibility safety belt use enforcement in Raleigh, NC: (a) celebrated the 10th anniversary of North Carolina's Click It or Ticket program; (b) documented current knowledge regarding safety belt use; (c) proposed strategies to increase use further; and (d) discussed research to support these strategies.  相似文献   
674.
Objective: This article investigated and compared frequency domain and time domain characteristics of drivers' behaviors before and after the start of distracted driving.

Method: Data from an existing naturalistic driving study were used. Fast Fourier transform (FFT) was applied for the frequency domain analysis to explore drivers' behavior pattern changes between nondistracted (prestarting of visual–manual task) and distracted (poststarting of visual–manual task) driving periods. Average relative spectral power in a low frequency range (0–0.5 Hz) and the standard deviation in a 10-s time window of vehicle control variables (i.e., lane offset, yaw rate, and acceleration) were calculated and further compared. Sensitivity analyses were also applied to examine the reliability of the time and frequency domain analyses.

Results: Results of the mixed model analyses from the time and frequency domain analyses all showed significant degradation in lateral control performance after engaging in visual–manual tasks while driving. Results of the sensitivity analyses suggested that the frequency domain analysis was less sensitive to the frequency bandwidth, whereas the time domain analysis was more sensitive to the time intervals selected for variation calculations. Different time interval selections can result in significantly different standard deviation values, whereas average spectral power analysis on yaw rate in both low and high frequency bandwidths showed consistent results, that higher variation values were observed during distracted driving when compared to nondistracted driving.

Conclusions: This study suggests that driver state detection needs to consider the behavior changes during the prestarting periods, instead of only focusing on periods with physical presence of distraction, such as cell phone use. Lateral control measures can be a better indicator of distraction detection than longitudinal controls. In addition, frequency domain analyses proved to be a more robust and consistent method in assessing driving performance compared to time domain analyses.  相似文献   

675.
    
ABSTRACT: The quality of the U.S. Army Corps of Engineers' (Corps) total dissolved gas (TDG) data base for the 1995 spring spill season was reviewed to determine the value of this information in real-time management decisions regarding river operations. We concluded that problems in transmitting, archiving, correcting and interpreting the records constitute significant sources of data anomalies that affect the accuracy and reliability of information necessary to manage spill and TDG in the Columbia and Snake rivers. The data base that was reviewed covers 25 selected Columbia and Snake river stations, and includes real-time TDG data needed to regulate spill operations to maintain gas levels within state water quality standards and to monitor effects on fish and aquatic life during the salmon migration season. A wide range of anomalies (daily averages missing or in error or based on incomplete records) was detected in more than one-third (37 percent) of the Corps' gas data base. Extreme anomalies (daily averages including errors and discontinuities for more than eight hours in a day) were found in 16 percent of the data base. The Fish Passage Center, also reviewed the Corps' data and reported an overall 33 percent incidence of anomalous days. Despite arriving at similar findings about the Corps' data base, we detected a 28 percent discrepancy in the type of data anomalies between our analyses. Real. time improvements in the quality of the dissolved gas data base are necessary to provide managers with a reliable product from this monitoring effort.  相似文献   
676.
The primary objective of this paper is to describe the impact of national seat belt enforcement mobilizations in terms of changes in public awareness, perceptions, and opinions as they relate to Operation ABC (Always Buckle Up). In order to monitor changes in public awareness and perceptions, a number of national telephone surveys were conducted. Survey results indicated that the following characteristics were associated with lower self-reported seat belt use rates: (a) males; (b) 18-34 age group; (c) persons with lower income; (d) persons with lower education; (e) persons living in rural areas; (f) residents of the Northeast, Midwest, and Great Lakes; (g) residents of states with secondary enforcement laws; and (h) persons less likely to read a newspaper and more likely to listen to the radio. Telephone surveys also suggested that the following groups are more likely to fail to properly secure a child under 12: (a) persons who say they have problems securing a child in seat belt; (b) farm belt residents; (c) Hispanic and Latinos; (d) persons who indicate that they always wear a seat belt but indicate they have not in the past month; (e) persons with older vehicles; (f) lower income respondents; (g) residents of the Deep South; (h) internet non-users; and (i) urban men. These findings provide support for some basic guidelines and suggestions for conducting seat belt enforcement activities.  相似文献   
677.
本文作者Zeigler博士在防护服研究试验、防护服行业规定及标准、大规模杀伤性武器等方面具有专业知识。作者是美国材料与试验学会(ASTM)防护服F23委员会微粒物质分委员会主任,也是美国防火委员套紧急医疗服务和危险物质防护服厦装备技术委员会成员。为应对恐怖袭击,本文从美国政府拨款、协调机构、信息通报、危机分析、防护服装配备和储存、人员培训等方面进行了论述,有一定参考价值,现予发表,供有关部门、企业和广大读者参阅。  相似文献   
678.
Extensive research has been conducted globally into conceptual frameworks for ecosystem services, the most notable being the Millennium Ecosystem Assessment (Millennium ecosystem assessment: ecosystems and human well-being; a framework for assessment. World Resources Institute, Washington, DC, pp 51, 53–55, 2005). The South East Queensland (SEQ) Ecosystem Services Framework (Australia) aims to provide the tools to enable government, industry, business, researchers, non-government organizations and land managers to apply the concept of ecosystem services in their planning and management practices. This article describes the Framework and the process that has produced matrices and maps that identify and illustrate the linkages between ecosystems, ecosystem functions, ecosystem services and the community’s well-being. The matrices and maps derived can identify areas in the region where the most ecosystem services are generated. This allows areas to be considered as valuable natural assets of the region, deserving appropriate protection measures or significant offsets if they are diminished or degraded in any way. Although the Framework requires further refinement and ongoing development, the process applied and the products produced has enabled decision makers to turn the concept of ecosystem services into practical application in SEQ.  相似文献   
679.
    
ABSTRACT: In southern Alberta, as elsewhere, pressures on limited water supplies are increasing. Not surprisingly, a great deal of attention has been focused on irrigated agriculture, which accounts for the largest share of water consumed in the region. In order to meet broadly accepted water conservation goals, some commentators have suggested that irrigation water use should be metered and that irrigators should be charged based on the amount of water used. An alternative proposal would have water management authorities rely upon the perceived adaptability of irrigators. This paper offers a perspective on the willingness of irrigators to conserve water. Based on a survey of 183 irrigation farmers conducted over the summer and early fall of 1998, we found that irrigators are generally aware of the need to conserve water and soil moisture, and that a variety of water conserving strategies were being employed. Water saving technologies specific to irrigation agriculture were less widely adopted. The findings suggest that there is considerable potential to reduce the amount of water consumed by the irrigation sector through increased efficiency, but that change will be limited if current economic circumstances and institutional arrangements persist.  相似文献   
680.
The 4-year drawdown of Horsetooth Reservoir, Colorado, for dam maintenance, provides a case study analog of vegetation response on sediment that might be exposed from removal of a tall dam. Early vegetation recovery on the exposed reservoir bottom was a combination of (1) vegetation colonization on bare, moist substrates typical of riparian zones and reservoir sediment of shallow dams and (2) a shift in moisture status from mesic to the xeric conditions associated with the pre-impoundment upland position of most of the drawdown zone. Plant communities changed rapidly during the first four years of exposure, but were still substantially different from the background upland plant community. Predictions from the recruitment box model about the locations of Populus deltoides subsp. monilifera (plains cottonwood) seedlings relative to the water surface were qualitatively confirmed with respect to optimum locations. However, the extreme vertical range of water surface elevations produced cottonwood seed regeneration well outside the predicted limits of drawdown rate and height above late summer stage. The establishment and survival of cottonwood at high elevations and the differences between the upland plant community and the community that had developed after four years of exposure suggest that vegetation recovery following tall dam removal will follow a trajectory very different from a simple reversal of the response to dam construction, involving not only long time scales of establishment and growth of upland vegetation, but also possibly decades of persistence of legacy vegetation established during the reservoir to upland transition.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号