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   245篇
  免费   7篇
  国内免费   1篇
安全科学   15篇
废物处理   8篇
环保管理   63篇
综合类   15篇
基础理论   74篇
污染及防治   52篇
评价与监测   15篇
社会与环境   11篇
  2023年   1篇
  2021年   2篇
  2020年   1篇
  2019年   4篇
  2018年   4篇
  2017年   6篇
  2016年   8篇
  2015年   4篇
  2014年   9篇
  2013年   20篇
  2012年   13篇
  2011年   9篇
  2010年   6篇
  2009年   11篇
  2008年   20篇
  2007年   4篇
  2006年   16篇
  2005年   5篇
  2004年   4篇
  2003年   4篇
  2002年   17篇
  2001年   6篇
  2000年   15篇
  1999年   7篇
  1998年   3篇
  1997年   2篇
  1996年   3篇
  1995年   2篇
  1994年   5篇
  1993年   6篇
  1992年   2篇
  1991年   5篇
  1990年   1篇
  1989年   1篇
  1986年   3篇
  1984年   1篇
  1983年   1篇
  1982年   4篇
  1981年   2篇
  1979年   3篇
  1978年   2篇
  1977年   1篇
  1975年   1篇
  1974年   2篇
  1973年   1篇
  1972年   1篇
  1971年   2篇
  1970年   1篇
  1969年   1篇
  1968年   1篇
排序方式: 共有253条查询结果,搜索用时 15 毫秒
91.
This study uses California data to compare redevelopment for properties subject to mandatory and voluntary cleanup. CalSites are subject to the CERCLA liability approach, while properties in the Voluntary Cleanup Program (VCP) are subject to a risk-based approach (RBA) that allows some contamination to remain for non-residential redevelopment. The expectation is that VCPs will show a greater proportion of industrial redevelopment, which has the least stringent standard, and a smaller proportion of residential redevelopment. The results show an overall trend toward more residential redevelopment of contaminated properties, but consistent with expectations, the trend is weaker for VCP properties than CalSites.  相似文献   
92.
Oxytetracycline (2-(amino-hydroxy-methylidene)-4-dimethylamino-5,6,10,11,12a-pentahydroxy-6-methyl-4,4a,5,5a-tetrahydrotetracene-1,3,12-trione) is a major member of the tetracycline antibiotics family of which are widely administered to animals in concentrated animal feeding operations for purposes of therapeutical treatment and health protection. With the disposal of animal manure as fertilizer into agricultural land, tetracyclines enter the environment. However, tetracyclines chelate with multivalent cations and proteins, resulting in low extraction efficiencies from animal manure for tetracycline residue analysis. In this study an efficient extraction method for oxytetracycline from steer manure using methanol/water solution amended with chelating organic acid was developed for the analysis of high performance liquid chromatography. The effect of species and amount of amendment acids, shaking time, methanol/water ratio, manure weight, and repeated times of extraction was investigated. It was optimized to amend 2.5 g citric acid and 1.1 g oxalic acid with 10.0 g manure sample in a 50-ml centrifuge tube and extract with 15 ml methanol/water (9:1 in volume) by vigorously shaking for 30 min in a reciprocating shaker. After centrifugation at 11,000 rpm, supernatant is collected. Sample was extracted for a total of 3 times. The developed extraction method was further applied to extract oxytetracycline from fresh and aged cow manure, swine and poultry manure, and soil. Satisfactory recoveries ranging from (84.1 ± 2.4) % to (102.0 ± 3.1) % were obtained, demonstrating that the optimized extraction method is robust for oxytetracycline from different manure sample matrixes.  相似文献   
93.
Abstract

A high‐intensity short‐wavelength UV light system was studied for its ability to degrade the pesticides carbofuran, fenamiphos sulfoxide (nemacur sulfoxide), and propazine in aqueous solutions. Half‐lives, rate constants, and breakdown products were determined for all chemicals. The presence of hydrogen peroxide, an oxidant and potential source of hydroxyl radicals, had no effect on the rate of breakdown of any of the chemicals investigated. Short‐wavelength UV light appears to be solely responsible for the observed pesticide breakdown. The breakdown of all three pesticides followed first order kinetics. Carbofuran, nemacur sulfoxide, and propazine had half lives of 3.9, 1.1, and 3.9 minutes, respectively. Breakdown product analysis was performed using capillary gas chromatography/mass spectrometry.  相似文献   
94.
The fate and transport of antibiotics in natural water systems is controlled in part by interactions with nanometer (10−9 m) metal oxide particles. Experiments were performed by mixing solutions of ampicillin (AMP), a common, penicillin-class human and veterinary antibiotic, with 25 nm-TiO2 (anatase) nanoparticles at different pH conditions. Both sorption and degradation of AMP were observed in the AMP-nanoparticle solutions. For AMP concentrations from ∼3 μM to 2.9 mM the overall AMP removal from solution can be described by linear isotherms with removal coefficients (Kr) of 3028 (±267) L kg−1 at pH 2, 11,533 (±823) L kg−1 at pH 4, 12,712 (±672) L kg−1 at pH 6, and 1941 (±342) L kg−1 at pH 8. Mass spectral analysis of AMP solutions after removal of the solid nanoparticles yielded ions that indicate the presence of peniclloic acid, penilloic acid and related de-ammoniated by-products as possible compounds resulting from the degradation of AMP at the TiO2 surface.  相似文献   
95.
Modifications to stream hydrologic regimes can have a profound influence on the dynamics of their fish populations. Using hierarchical linear models, we examined the relations between flow regime and young-of-year fish density using fish sampling and discharge data from three different warmwater streams in Illinois, Alabama, and Georgia. We used an information theoretic approach to evaluate the relative support for models describing hypothesized influences of five flow regime components representing: short-term high and low flows; short-term flow stability; and long-term mean flows and flow stability on fish reproductive success during fish spawning and rearing periods. We also evaluated the influence of ten fish species traits on fish reproductive success. Species traits included spawning duration, reproductive strategy, egg incubation rate, swimming locomotion morphology, general habitat preference, and food habits. Model selection results indicated that young-of-year fish density was positively related to short-term high flows during the spawning period and negatively related to flow variability during the rearing period. However, the effect of the flow regime components varied substantially among species, but was related to species traits. The effect of short-term high flows on the reproductive success was lower for species that broadcast their eggs during spawning. Species with cruiser swimming locomotion morphologies (e.g., Micropterus) also were more vulnerable to variable flows during the rearing period. Our models provide insight into the conditions and timing of flows that influence the reproductive success of warmwater stream fishes and may guide decisions related to stream regulation and management.  相似文献   
96.
According to Snyder's hope theory, high hope individuals possess more goal‐related strategies and are more motivated to achieve their goals than their low hope counterparts. Therefore, we examined the relationship between hope and job performance using three different samples of employees of different job levels and industries. We found that more hopeful sales employees, mortgage brokers, and management executives had higher job performance, as measured a year later, even after controlling for their self‐efficacy and cognitive ability. In a fourth study, we examined if more hopeful employees attempt to solve problems differently than do those with less hope. Higher hope management executives produced more and better quality solutions to a work‐related problem, suggesting that hopefulness may help employees when they are confronted with problems and encounter obstacles at work. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
97.
Habitat valuation methods were implemented to support remedial decisions for aquatic and terrestrial contaminated sites at the East Tennessee Technology Park (ETTP) on the US Department of Energy (DOE) Oak Ridge Reservation in Oak Ridge, TN, USA. The habitat valuation was undertaken for six contaminated sites: Contractor's Spoil Area, K-901-N Disposal Area, K-770 Scrapyard, K-1007-P1 pond, K-901 pond, and the Mitchell Branch stream. Four of these sites are within the industrial use area of ETTP and two are in the Black Oak Ridge Conservation Easement. These sites represent terrestrial and aquatic habitat for vertebrates, terrestrial habitat for plants, and aquatic habitat for benthic invertebrates. Current and potential future, no-action (no remediation) scenarios were evaluated primarily using existing information. Valuation metrics and scoring criteria were developed in a companion paper, this volume. The habitat valuation consists of extensive narratives, as well as scores for aspects of site use value, site rarity, and use value added from spatial context. Metrics for habitat value were expressed with respect to different spatial scales, depending on data availability. There was significant variation in habitat value among the six sites, among measures for different taxa at a single site, between measures of use and rarity at a single site, and among measures for particular taxa at a single site with respect to different spatial scales. Most sites had aspects of low, medium, and high habitat value. Few high scores for current use value were given. These include: wetland plant communities at all aquatic sites, Lepomid sunfish and waterbirds at 1007-P1 pond, and Lepomid sunfish and amphibians at K-901 pond. Aquatic sites create a high-value ecological corridor for waterbirds, and the Contractor's Spoil Area and possibly the K-901-N Disposal Site have areas that are part of a strong terrestrial ecological corridor. The only example of recent observations of rare species at these sites is the gray bat observed at the K-1007-P1 pond. Some aspects of habitat value are expected to improve under no-action scenarios at a few of the sites. Methods are applicable to other contaminated sites where sufficient ecological data are available for the site and region.  相似文献   
98.
99.
100.
An important concern of conservation biologists is determining what conditions most limit the number of individuals in endangered populations. Because time is a constraint, narrowing the search for such factors is beneficial. Toward this end we used broad spatial and temporal data, to test the hypothesis that reproductive success (as measured by juvenile-to-adult ratios) of the endangered Attwater's Prairie Chicken ( Tympanuchus cupido attwateri ) was not equal to that of the nonendangered Greater Prairie Chicken ( T. c. pinnatus ). We then tested the hypotheses that mean clutch size, egg hatchability, nesting success, and number of chicks per brood prior to brood breakup for Attwater's Prairie Chicken were not equal to those of the Greater Prairie Chicken. We found that the mean ratio of juveniles to adults among Attwater's Prairie Chicken was less than that of the Greater Prairie Chicken ( p < 0.011), as would be predicted if reproductive success controls proportional changes in prairie-grouse numbers among years. Mean nesting success (32.2%) and number of chicks per brood prior to brood breakup (4.2) of Attwater's Prairie Chicken were both less than those of the Greater Prairie Chicken (49.5 %, p = 0.0425, and 6.0 p = 0.0001, respectively). We suggest that researchers focus on determining what proportion of Attwater's Prairie Chicken broods survive and why Attwater's Prairie Chicken nesting and brood-rearing success are so poor relative to those of the Greater Prairie Chicken.  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