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   337篇
  免费   3篇
  国内免费   4篇
安全科学   15篇
废物处理   10篇
环保管理   38篇
综合类   94篇
基础理论   66篇
污染及防治   92篇
评价与监测   18篇
社会与环境   9篇
灾害及防治   2篇
  2023年   3篇
  2022年   3篇
  2021年   18篇
  2020年   4篇
  2019年   5篇
  2018年   7篇
  2017年   10篇
  2016年   9篇
  2015年   11篇
  2014年   14篇
  2013年   17篇
  2012年   15篇
  2011年   28篇
  2010年   16篇
  2009年   15篇
  2008年   18篇
  2007年   17篇
  2006年   17篇
  2005年   17篇
  2004年   12篇
  2003年   12篇
  2002年   11篇
  2001年   3篇
  2000年   6篇
  1999年   7篇
  1998年   5篇
  1997年   3篇
  1996年   2篇
  1995年   4篇
  1993年   2篇
  1992年   3篇
  1991年   3篇
  1989年   2篇
  1988年   1篇
  1987年   3篇
  1986年   2篇
  1984年   1篇
  1982年   1篇
  1981年   3篇
  1980年   3篇
  1979年   3篇
  1978年   1篇
  1977年   1篇
  1976年   2篇
  1966年   1篇
  1965年   1篇
  1964年   1篇
  1924年   1篇
排序方式: 共有344条查询结果,搜索用时 15 毫秒
101.
102.
ABSTRACT: Valley Creek watershed is a small stream system that feeds the Schuylkill River near Philadelphia, Pennsylvania. The watershed is highly urbanized, including over 17 percent impervious surface cover (ISC) by area. Imperviousness in a watershed has been linked to fish community structure and integrity. Generally, above 10 to 12 percent ISC there is marked decline in fish assemblages with fish being absent above 25 percent ISC. This study quantifies the importance of ground water in maintaining fish species diversity in subbasins with over 30 percent ISC. Valley Creek contains an atypical fish assemblage in that the majority of the fish are warm‐water species, and the stream supports naturally reproducing brown trout, which were introduced and stocked from the early 1900s to 1985. Fish communities were quantified at 13 stations throughout the watershed, and Simpson's species diversity index was calculated. One hundred and nine springs were located, and their flow rates measured. A cross covariance analysis between Simpson's species diversity index and spring flow rates upstream of fish stations was performed to quantify the spatial correlation between these two variables. The correlation was found to be highest at lag distances up to about 400 m and drop off significantly beyond lag distances of about 800 m.  相似文献   
103.
In a commitment to zero ozone depletion, the United Nations and the U.S. Environmental Protection Agency (EPA) have called for the phase-out of the manufacture and import of hydrochlorofluorocarbons (HCFCs), used as auxiliary blowing agents (ABAs) in the manufacture of polyurethane foams. As a result, more environmentally benign alternative ABAs are being sought by the foam-blowing industry. This study examined the life cycle of HCFC-22, hydrofluorocarbon-134a (HFC-134a), and cyclopentane, which are currently used or considered as potential alternative ABAs in the manufacture of rigid polyurethane foams that serve as insulation in a model North American refrigerator. The raw material extraction/refining, manufacturing, use, and disposal stages of the life cycle of each ABA were considered, and their resulting relative impacts on ozone depletion and global warming were compared. The manufacturing, use, and disposal stages were determined to affect ozone depletion and global warming to the largest extent, emphasizing the need for a greater focus on pollution prevention opportunities in these stages. The HFC-134a life cycle yields no impact on ozone depletion and a significantly decreased global warming impact compared with its predecessor, HCFC-22, and a tradeoff of slightly higher global warming impact and fewer added safety concerns compared with its more flammable counterpart, cyclopentane.  相似文献   
104.
Ecological interactions of conifers and coniferophagous bark beetles are determined in part by terpenoids (isoprenoids), which are major defense metabolites of conifer oleoresin. Curiously, similar compounds are important aggregation pheromones of conifer-attacking bark beetles. Terpene synthases are responsible for generating the enormous variety of terpenoid carbon skeletons found in nature. These catalysts convert short-chain prenyl diphosphates to a diverse assortment of hemiterpene, monoterpene, sesquiterpene, and diterpene natural products. While terpene synthases have frequently been characterized from plant and microbial sources, they have not yet been described in animals. Here we report the discovery of a monoterpene synthase activity in an insect, the pine engraver, Ips pini (Say) (Coleoptera: Scolytidae). Cell-free assays of I. pini revealed that geranyl diphosphate (GDP) is converted to the acyclic monoterpene myrcene in whole-body extracts from males, but not females. Furthermore, the monoterpene synthase activity in males can be induced by prior treatment with juvenile hormone III (JH III) or by feeding on phloem from the host trees, Jeffrey pine (Pinus jeffreyi Grev. &; Balf.) or red pine (Pinus resinosa Ait.). The sex-specificity and endocrine induction of this activity argue for its involvement in the biosynthesis of monoterpenoid pheromones mediated by enzymes from insect tissue. This discovery is the first example of a monoterpene synthase in the Metazoa and evokes exciting new questions about the origin, evolution, and occurrence of terpene synthases.  相似文献   
105.
A bench-scale pilot plant has been developed for the treatment of olive-mill water. The plant is fed in a continuous mode and implements a primary treatment (sand filtering and irradiation with UV-rays) and a secondary treatment (anoxic and aerobic biological treatment). Satisfactory results were obtained and the treated green water falls under the limits of the Italian legislation. Veratric and ferulic acid biodegradation were studied under anoxic conditions in order to verify the requirements for optimal biodegradation. Electronic Publication  相似文献   
106.
107.
108.
Although no precise figures are available, many congenital brain lesions arise from intrauterine disruption, frequently due to obstetric complications. The most common entities include intracranial hemorrhage, ischemic lesions, thrombosis of venous vessels and infections. Accurate prenatal diagnosis is possible in many of these cases. However, the findings may be subtle, particularly in the early stage of the disruptive process. Identification of these conditions requires therefore specific expertise, the combination of fetal neurosonography and magnetic resonance, and frequently there is a need for serial examinations. Targeted diagnostic imaging should be offered to obstetric patients with conditions predisposing to prenatal cerebral insults. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
109.
110.
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