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   18310篇
  免费   245篇
  国内免费   161篇
安全科学   585篇
废物处理   679篇
环保管理   2825篇
综合类   3301篇
基础理论   4552篇
环境理论   12篇
污染及防治   4470篇
评价与监测   1113篇
社会与环境   1037篇
灾害及防治   142篇
  2022年   141篇
  2021年   150篇
  2020年   137篇
  2019年   167篇
  2018年   242篇
  2017年   285篇
  2016年   410篇
  2015年   335篇
  2014年   424篇
  2013年   1584篇
  2012年   568篇
  2011年   767篇
  2010年   604篇
  2009年   685篇
  2008年   754篇
  2007年   774篇
  2006年   720篇
  2005年   575篇
  2004年   585篇
  2003年   578篇
  2002年   512篇
  2001年   589篇
  2000年   456篇
  1999年   282篇
  1998年   233篇
  1997年   228篇
  1996年   245篇
  1995年   262篇
  1994年   241篇
  1993年   237篇
  1992年   233篇
  1991年   229篇
  1990年   230篇
  1989年   193篇
  1988年   176篇
  1987年   153篇
  1986年   188篇
  1985年   178篇
  1984年   191篇
  1983年   183篇
  1982年   183篇
  1981年   188篇
  1980年   166篇
  1979年   160篇
  1978年   119篇
  1977年   129篇
  1974年   117篇
  1973年   95篇
  1972年   114篇
  1971年   93篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
511.
Continued interest in improving air quality in the United States along with renewed interest in the expansion of urban passenger ferry service has created concern about air pollution from ferry vessels. This paper presents a methodology for estimating the air pollution emissions from passenger ferries and the costs of emissions control strategies. The methodology is used to estimate the emissions and costs of retrofitting or re-powering ferries with seven technological options (combinations of propulsion and emission control systems) onto three vessels currently in service in San Francisco Bay. The technologies include improved engine design, cleaner fuels (including natural gas), and exhaust gas cleanup devices. The three vessels span a range of ages and technologies, from a 25-year-old monohull to a modern, high-speed catamaran built only four years ago. By looking at a range of technologies, vessel designs, and service conditions, a sense of the broader implications of controlling emissions from passenger ferries across a range of vessels and service profiles is provided. Tier 2-certified engines are the most cost-effective choice, but all options are cost-effective relative to other emission control strategies already in place in the transportation system.  相似文献   
512.
Sexually mature female tilapia were exposed to sublethal concentrations of waterborne Cu and/or Cd over 6 days, and subsequent body concentrations of these metals were determined in several organs. The results show that the distribution of Cu and Cd was metal and organ specific. This is demonstrated, for example, by the observation that in tilapia, Cu exposure did not result in Cu accumulation in the liver, whereas in the intestinal wall, notably high concentrations of Cu and Cd were measured in metal exposed fish. In addition to single metal exposed fish, we also determined Cu and Cd body distribution in Cu?Cd co-exposed fish. The observed interactions in metal accumulation were most pronounced in the organs of fish exposed to low, environmentally realistic, metal concentrations.  相似文献   
513.
Tissue lead data are presented for populations of feral pigeons (Columba livia) from three locations in Madrid (Spain). The lead present in the lungs and digestive tract of pigeons increased progressively with traffic density and in parallel with atmospheric and ground lead values. The contribution of the respiratory route of Pb intake to the pigeons was about three times greater than the digestive route. The highest Pb values were found in bones. It is suggested that the pigeons gave a greatly magnified picture of lead pollution in cities than indicated by atmospheric lead concentrations.  相似文献   
514.
Grass, and particularly cut grass, recently has been shown to emit significant amounts of volatile organic compounds (VOCs) into the atmosphere. Some components of these emissions are highly reactive and may contribute to photochemical smog in urban areas. A simple model for estimating the VOC emissions from grass and for grass cutting that allows these processes to be included in urban/regional emissions inventories is presented here. Using previous work and recent literature values, estimates are made of these biogenic volatile organic compound (BVOC) emissions for two typical urban airsheds, those including the cities of Sydney and Melbourne in Australia. Grass and cut grass could contribute approximately 2% for Sydney and 3% for Melbourne of the total VOCs emitted into these urban atmospheres annually. These contributions could rise to 4 and 5%, respectively, during the weekends of the summer growing season and, thus, could contribute to weekday/weekend ozone differences. It is recommended that the emissions of BVOCs from grass and cut grass be included in urban and global emissions inventories so that more accurate predictions of smog chemistry can be determined.  相似文献   
515.
In irrigated maize areas of an important Portuguese agricultural area, Ribatejo and Oeste Region, alachlor, atrazine and metolachlor were detected in ground water.

During the study performed from 1996 to 1998 atrazine was the herbicide that showed the highest frequency of detection. In the 177 ground water samples collected 62% were contaminated with atrazine, 30% with alachlor and 12% with metolachlor. All these herbicides were detected both in ground water for human consumption and for irrigation, in some cases above 0.1 ug/L. The maximum levels quantified were 13μg/L for alachlor, 30μg/L for atrazine and 56 μg/L for metolachlor.

Seasonal variation of residues in ground water it is also presented through several examples of studies performed during the period 1991–1999.  相似文献   
516.
The impact of salinity and water exchange rate on the accumulation of heavy metals in the benthic fish Zosterissesor ophiocephalus, collected from the shallow sublagoons Tholi and Paleopotamos, was studied. Both sublagoons are influenced by the intensive agricultural activity of the surrounding area in terms of the chemical substances’ drainage, and by the untreated sewage discharges of an urbanized area with Paleopotamos being affected in lesser extent. Paleopotamos is characterised by restricted water renovation, resulting to much higher salinity than Tholi. The bioaccumulation of the heavy metals studied (Manganese, Zinc and Copper), reveals differences among the metals with females showing higher values. Specimens from Paleopotamos showed statistically significant higher bioaccumulation of the heavy metals in both sexes, which is attributed to the extremely high salinity of this sublagoon.  相似文献   
517.
Over the last years, great progress in the research on speciation of butyltins has been made. Many coupling techniques have been successfully developed, with better applications to sediments samples in the environment. Sediments were collected from 1999 to 2000 to elucidate butyltin pollution in Theoule harbour. Most of the analysed samples showed evidence of butyltin compounds. The results show that the concentration of Tributyltin (TBT) was in the range 20–200?µg/kg in March 1999, 20–340?µg/kg in June 1999, 180–1280?µg/kg in July 2000, and 55–820?µg/kg in October 2000. A comparison of the MBT, DBT, and TBT results show that in 1999 the concentrations were in the order TBT?DBT?>?MBT, with some exceptions. The patterns observed in many sediment cores show a great disparity of organotin input concentration among the cores collected during one month and also during two different months, and from one season to the other. This paper provides information on the use of the acetic acid leaching system in the determination of butyltin. The method is applied to evaluate the occurrence of these species in sediments from the Theoule harbour, between 1999 and 2000. In this study, a GC/AES was applied, complemented with acetic acid leaching and monitored using two certified reference materials: PACS-2 reference sediment and BCR 462 (Report EUR 18406 EN, 1998).  相似文献   
518.
The fatty acid (FA) composition was determined in 14 species of marine macroalgae belonging to the Chlorophyta, Phaeophyta and Rhodophyta, which were collected from ?ile in the Black Sea and Kepez in the Dardanelles. Generally, polyunsaturated FAs and monounsaturated FAs were major components (50–77%). Total saturated FAs ranged from 22% to 50%, with 16?:?0 as the most abundant saturate (32–38%). Two samples of Cystoseira barbata collected from a different station had some differences from each other in their contents of 18?:?2n-6 and 18?:?3n-3 and in the 18?:?2n-6/20?:?4n-6 ratios. Green algal species had a significantly higher proportion of unsaturated FAs and a significantly lower proportion of saturated FAs than the red and brown algae. The amount of n-3 FAs was significantly higher in Ulva rigita, Chaetomorpha linum, Enteromorpha linza and Gracilaria verrucosa (8.88, 6.44, 5.31 and 5.24, respectively).  相似文献   
519.
With the present contribution an evaluation of the toxicity of the pure herbicide glyphosate and its commercial formulation Faena® is reported using the cladoceran Daphnia magna Strauss and the rotifer Lecane quadridentata Ehrenberg. LC50, EC50, NOEC, and LOEC values for each toxicant and for both test organisms are obtained. Regarding acute toxicity, Faena was 11-fold more toxic to L. quadridentata than pure glyphosate and slightly more toxic to D. magna (1.7-fold). Inhibition of esterase activity in L. quadridentata by glyphosate was the most sensitive end-point; the EC50 was 1500-fold smaller than the LC50. The implications of these results and their comparison with established international and national limit values for glyphosate are discussed.  相似文献   
520.
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