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   14463篇
  免费   103篇
  国内免费   156篇
安全科学   357篇
废物处理   595篇
环保管理   1586篇
综合类   3263篇
基础理论   3366篇
环境理论   6篇
污染及防治   3592篇
评价与监测   1119篇
社会与环境   765篇
灾害及防治   73篇
  2022年   126篇
  2021年   108篇
  2019年   105篇
  2018年   194篇
  2017年   204篇
  2016年   302篇
  2015年   232篇
  2014年   403篇
  2013年   1037篇
  2012年   453篇
  2011年   598篇
  2010年   471篇
  2009年   534篇
  2008年   569篇
  2007年   595篇
  2006年   540篇
  2005年   494篇
  2004年   456篇
  2003年   459篇
  2002年   434篇
  2001年   595篇
  2000年   373篇
  1999年   261篇
  1998年   151篇
  1997年   169篇
  1996年   172篇
  1995年   188篇
  1994年   182篇
  1993年   132篇
  1992年   164篇
  1991年   176篇
  1990年   169篇
  1989年   141篇
  1988年   157篇
  1987年   97篇
  1986年   130篇
  1985年   127篇
  1984年   123篇
  1983年   115篇
  1982年   121篇
  1981年   120篇
  1980年   87篇
  1979年   99篇
  1978年   101篇
  1976年   92篇
  1974年   104篇
  1972年   87篇
  1971年   85篇
  1967年   100篇
  1964年   92篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
992.
Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an important cause of hereditary stroke. Mutations in the Notch3 gene are clearly causally linked to this progressive vascular disorder. Cerebral ischemic attacks, cognitive decline, strokes, and vascular dementia constitute the major manifestations of this disorder. This report details the prenatal detection of a Notch3 mutation in the fetus of a couple where the father had a known mutation in this gene. This is the first report of a prenatal diagnosis of CADASIL, and another example of a serious, highly penetrant, and relentlessly progressive degenerative genetic disorder presenting decades after birth and for which prenatal diagnosis is an option. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
993.
Development of new economically feasible ecofriendly products from agricultural wastes or byproducts for shrimp farm wastewater treatment is the objective of our continued research. Ammonia is a nitrogenous toxicant, which is commonly found in wastewater from shrimp farms. In the present study, we explored the possibility of the use of simply and inexpensively prepared bagasse products so that this abundant crop byproduct could be used to remove ammonia from shrimp farm wastewater. Bagasse, a natural highly fibrous lignocellulosic byproduct of sugarcane, was converted into five different products. Experimental results have shown that ammonia is efficiently removed from wastewater by four bagasse products with a dose of 1 to 6 g/L within 24 hours. The effect of bagasse products on other water quality parameters and growth kinetics of biofilm bacteria onto bagasse fiber have also been studied. Efficacies of products were compared by using statistical analysis. Products developed from bagasse are useful and economical.  相似文献   
994.
New principles of the assessment of soil cover degradation and desertification, the scale and intensity of destructive processes manifestation are determined.  相似文献   
995.
The effects of the aeration, seeding, and agitation on the composting of vegetable waste were studied in a laboratory-scale reactor. Experimental results showed that the final product at the end of a 4-day composting period met multiple maturity indices suggested by many researchers. The evolution of carbon dioxide during the composting process could be modelled with a modified Gompertz equation that described the bacteria growth successfully. Multivariate regression analysis was used to study the effects of operating parameters on the carbon conversion. The response surface contour plots were constructed using the regression equation for the examination of the dependence of carbon conversion on operating parameters. The maximum carbon conversion of 14.54% was obtained when the percentage of seeding was set at 14.5%, the air suction rate was set at 2.6 L kg(-1) dry-solid min(-1), and the agitator operated half of the time, alternating on and off for every 5 min. Future work will focus on the application of the data and the experience gained in this work to composters of pilot and semi-commercial scales.  相似文献   
996.
997.
Factors effecting Zn+2 uptake by the water hyacinth Eichhonnia cnassipes, were examined. Two phases of zinc uptake were observed throughout the uptake range (1000 – 0.001 ppm). Initially a rapid uptake phase of 4 hours followed by a slower, near linear uptake phase extending past 48 hours. Stirring the solution enhanced uptake, suggesting uptake is partially diffusion limited. Increasing pH from 3 to 5 enhanced zinc uptake. As solution volume was increased, more zinc was removed. With increasing amounts of Hg+2 or Cd+2, the zinc removal rate decreased, suggesting a competition for binding sites on the roots. The presence of complexing agents during the uptake phase reduced zinc uptake. The inability of complexing agents to recover all zinc removed by a plant suggests a translocation to sites within the plant.  相似文献   
998.
The present study was undertaken to determine the persistence and mobility of 2,4-dichlorophenoxy acetic acid (2,4-D) in unsaturated soil zone under real field conditions for the wheat crop in Roorkee, India. Three experimental plots were chosen in the agricultural field itself to represent the real field conditions in the study area and the potential movement and persistence of herbicide 2,4-D was investigated under three different irrigation treatments. The presence of herbicide along with soil water content was determined in soil at different depths at a temporal scale. The movement of the herbicide was also simulated numerically by solving the coupled soil water content movement and mass transport equations using HYDRUS-1D. The measured soil water content trends and the 2,4-D concentration profiles showed a good agreement with the numerically simulated results. The maximum effect of the herbicide was primarily retained up to 15 cm of the soil profile. The current existing dosage of 0.5 kg ha−1 of pesticide was found to be safe to avoid soil contamination as no residue of 2,4-D was traced at the end of the wheat crop season in any of the plots. Higher concentrations of 2,4-D were also simulated numerically and the simulated results showed that the safe dosage of pesticide application would depend on irrigation treatments.  相似文献   
999.
Improving the efficacy of phytoextraction is critical for its successful application in metal contaminated soils. Mineral nutrition affects plant growth and metal absorption and subsequently the accumulation of heavy metal through hyper-accumulator plants. This study assessed the effects of di-hydrogen phosphates (KH2PO4, Ca(H2PO4)2, NaH2PO4 and NH4H2PO4) application at three levels (22, 88 and 352 mg P/kg soil) on Sedum alfredii growth and metal uptake by three consecutive harvests on aged and Zn/Cd combined contaminated paddy soil. The addition of phosphates (P) significantly increased the amount of Zn taken up by S. alfredii due to increased shoot Zn concentration and dry matter yield (DMY) (P<0.05). The highest phytoextraction of Zn and Cd was observed in KH2PO4 and NH4H2PO4 treatment at 352 mg P/kg soil. The amount of Zn removed by phytoextraction increased in the order of 1st clipping<2nd clipping<3rd clipping, and for Cd extraction the order was 2nd clipping<1st clipping<3rd clipping. These results indicate that the application of P fertilizers coupled with multiple cuttings can enhance the removal of Zn and Cd from contaminated soils by S. alfredii, thus shortening the time needed for accomplishing remediation goals.  相似文献   
1000.
Darwin's Fox: A Distinct Endangered Species in a Vanishing Habitat   总被引:2,自引:0,他引:2  
The temperate rain forest of Chiloé Island, Chile, is inhabited by an endemic fox ( Dusicyon fulvipes ) first described by Charles Darwin and now designated Darwin's fox. Despite morphological differences, Darwin's fox has been considered only an insular subspecies of the mainland chilla fox ( D. griseus ). This follows the assumption that the island population, with an estimated population of less than 500, has been separated from the mainland chilla fox for only about 15,000 years and may have received occasional immigrants from the mainland. Consequently, this island population has not been protected as endangered or bred in captivity. Recently, a population of Darwin's fox was discovered on the Chilean mainland 600 km north of Chiloé Island. This population exists in sympatry with chilla and possibly culpeo ( D. culpaeus ) foxes, which suggests that Darwin's fox may be reproductively isolated. To clarify the phylogenetic position of Darwin's fox, we analyzed 344 bp of mitochondrial DNA control-region sequence of the three species of Chilean foxes. Darwin's foxes from the island and mainland populations compose a monophyletic group distinct from the two other Chilean fox species. This indicates that Darwin's fox was probably an early inhabitant of central Chile, and that its present distribution on the mainland may be a relict of a once much wider distribution. Our results highlight the ability of molecular genetic techniques to uncover historical relationships masked by recent events, such as local extinctions. The "rediscovery" of Darwin's fox as a distinct species implies that greater significance should be given to the protection of this species and its unique habitat and to documenting the extent of its mainland distribution.  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