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   197篇
  免费   1篇
安全科学   4篇
废物处理   8篇
环保管理   19篇
综合类   95篇
基础理论   19篇
污染及防治   36篇
评价与监测   6篇
社会与环境   10篇
灾害及防治   1篇
  2019年   4篇
  2018年   2篇
  2017年   2篇
  2015年   3篇
  2014年   6篇
  2013年   9篇
  2012年   3篇
  2011年   7篇
  2010年   10篇
  2009年   12篇
  2008年   10篇
  2007年   6篇
  2006年   4篇
  2005年   3篇
  2004年   7篇
  2003年   10篇
  2002年   6篇
  2001年   3篇
  2000年   2篇
  1990年   2篇
  1989年   2篇
  1979年   2篇
  1966年   2篇
  1964年   1篇
  1959年   1篇
  1957年   2篇
  1956年   2篇
  1955年   4篇
  1951年   3篇
  1947年   1篇
  1946年   1篇
  1943年   3篇
  1942年   1篇
  1941年   2篇
  1938年   3篇
  1936年   3篇
  1935年   1篇
  1934年   6篇
  1933年   5篇
  1932年   3篇
  1931年   2篇
  1930年   3篇
  1929年   2篇
  1927年   4篇
  1926年   4篇
  1925年   2篇
  1924年   4篇
  1923年   2篇
  1922年   2篇
  1916年   1篇
排序方式: 共有198条查询结果,搜索用时 31 毫秒
71.
Microarthropods are known as vectors for soil microorganisms, predominantly fungi. This laboratory study uses the widespread unicellular green algae Chlorella vulgaris as model to assess the role of Collembola in algal dispersal and to determine the effects of gut passage on propagation. Living algal cells were observed in 70 % of the faecal pellets of Folsomia candida, Heteromurus nitidus and Protaphorura fimata. Moreover, marker fatty acids for green algae, i.e. 16:2ω6,9 and 16:3ω3,6,9, were consistently detected in the pellets. Compared to the algal diet, the high content of methyl-branched total lipid fatty acid (TLFA) with hydroxyl substitution indicated microbial colonisation during gut passage. The TLFA profile of faeces revealed no species-specific differences but similar changes in microbial communities over the duration of feeding, indicating comparable indigenous bacteria and colonisation mechanisms during gut passage. In sum, faecal pellets of soil microarthropods such as Collembola can act as a vector for both dietary algae and specific gut-associated microorganisms, with the latter likely involved in resource degradation inside and outside the gut habitat.  相似文献   
72.
Despite its successes, the U.S. Endangered Species Act (ESA) has proven challenging to implement due to funding limitations, workload backlog, and other problems. As threats to species survival intensify and as more species come under threat, the need for the ESA and similar conservation laws and policies in other countries to function efficiently has grown. Attempts by the U.S. Fish and Wildlife Service (USFWS) to streamline ESA decisions include multispecies recovery plans and habitat conservation plans. We address species status assessment (SSA), a USFWS process to inform ESA decisions from listing to recovery, within the context of multispecies and ecosystem planning. Although existing SSAs have a single-species focus, ecosystem-based research can efficiently inform multiple SSAs within a region and provide a foundation for transition to multispecies SSAs in the future. We considered at-risk grassland species and ecosystems within the southeastern United States, where a disproportionate number of rare and endemic species are associated with grasslands. To initiate our ecosystem-based approach, we used a combined literature-based and structured World Café workshop format to identify science needs for SSAs. Discussions concentrated on 5 categories of threats to grassland species and ecosystems, consistent with recommendations to make shared threats a focus of planning under the ESA: (1) habitat loss, fragmentation, and disruption of functional connectivity; (2) climate change; (3) altered disturbance regimes; (4) invasive species; and (5) localized impacts. For each threat, workshop participants identified science and information needs, including database availability, research priorities, and modeling and mapping needs. Grouping species by habitat and shared threats can make the SSA process and other planning processes for conservation of at-risk species worldwide more efficient and useful. We found a combination of literature review and structured discussion effective for identifying the scientific information and analysis needed to support the development of multiple SSAs. Article impact statement: Species status assessments can be improved by an ecosystem-based approach that groups imperiled species by shared habitats and threats.  相似文献   
73.
Soil biotic and abiotic factors strongly influence nitrogen (N) availability and increases in nitrification rates associated with the application of manure. In this study, we examine the effects of edaphic properties and a dairy (Bos taurus) slurry amendment on N availability, nitrification rates and nitrifier communities. Soils of variable texture and clay mineralogy were collected from six USDA-ARS research sites and incubated for 28 d with and without dairy slurry applied at a rate of ~300 kg N ha(-1). Periodically, subsamples were removed for analyses of 2 M KCl extractable N and nitrification potential, as well as gene copy numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Spearman coefficients for nitrification potentials and AOB copy number were positively correlated with total soil C, total soil N, cation exchange capacity, and clay mineralogy in treatments with and without slurry application. Our data show that the quantity and type of clay minerals present in a soil affect nitrifier populations, nitrification rates, and the release of inorganic N. Nitrogen mineralization, nitrification potentials, and edaphic properties were positively correlated with AOB gene copy numbers. On average, AOA gene copy numbers were an order of magnitude lower than those of AOB across the six soils and did not increase with slurry application. Our research suggests that the two nitrifier communities overlap but have different optimum environmental conditions for growth and activity that are partly determined by the interaction of manure-derived ammonium with soil properties.  相似文献   
74.
The leachability of lindane from different biosolid amended soils was determined and compared to its bioavailability. Sand, soil, and a mixture of soil-sand (1:1 w/w) were spiked with lindane, blended with different amounts of biosolids, and subjected to a leaching process with water that lasted for 1-28 d. This procedure is in accordance with ISO/TS 21268-1: 2007. After these batch tests, lindane was extracted from the leachates using three different solvent-free microextraction techniques, including solid phase microextraction (SPME), stir-bar sorptive extraction (SBSE), and silicone rod extraction (SRE). The amount of lindane was determined with thermal desorption and gas chromatography coupled to mass spectrometry (GC-MS). The efficiencies of the three microextraction techniques were statistically different, and the efficiency could be related to the amount of polydimethylsiloxane (PDMS) in each extraction device. However, all of the techniques provide data that shows that the leachability of lindane is dependent on the amount of organic matter contained in the matrix.The results of the lindane leachability assay were compared to the bioavailability of lindane, which was determined by measuring the amount of lindane that accumulated in the roots of wheat plants grown in similar soil-biosolid systems.It was confirmed that the amount of organic matter in the matrix is a determining factor for lindane immobilization. The presence of biosolids decreases the mobility of lindane in all of the systems under study. Similarly, increasing biosolid concentrations in the soil significantly decreased the bioavailability of lindane and, consequently, plant absorption.The good correlation (R2 = 0.997) between the leachability of lindane from the matrix and plant absorption of lindane indicates that the proposed biomimetic methodology can predict the bioavailability of lindane in a time period as short as 7 d.The results of this work confirm that amending contaminated soils with biosolids is beneficial for immobilizing lindane and helps prevent the percolation of lindane through the soil profile and into groundwater.  相似文献   
75.
We examined acute (2 h exposure of 5-day-old larvae) and subchronic (exposure from fertilization up to an age of 11 days) effects of NiCl(2).6H2O on embryos and larvae of zebrafish (Danio rerio), both alone and in combination with oxygen depletion. The following endpoints were recorded: acute exposure: locomotory activity and survival; subchronic exposure: hatching rate, deformations, locomotory activity (at 5, 8 and 11 days) and mortality. In acute exposures nickel chloride (7.5-15 mg Ni/L) caused decreasing locomotory activity. Oxygen depletion (or=10 mg Ni/L resulted in delayed hatching at an age of 96 h, in decreased locomotory activity at an age of 5 days, and increased mortality at an age of 11 days (LC20=9.5 mg Ni/L). The observed LOEC for locomotory activity (7.5 mg Ni/L) is in the range of environmentally relevant concentrations. Since locomotory activity was already affected by acute exposure, this parameter is recommended to supplement commonly recorded endpoints of toxicity.  相似文献   
76.
77.
This work has been supported by the Centre National de la Recherche Scientifique (C.N.R.S.) through the Action Thématique Programmée Matières Organiques des sols. We thank Dr. B. Guillet and Prof. B. Souchier, Centre de Pédologie Biologique du C.N.R.S., Nancy, for helpful discussions and advice in collecting the samples; we further thank E. Krempp and P. Wehrung for technical assistance in NMR and MS measurements.  相似文献   
78.
79.
Rhizosphere bacteria influence plant growth through several mechanisms. Beneficial interactions are often difficult to identify and isolate for study, and therefore favorable effects on plant productivity are not easily described in quantitative terms. Major beneficial activities of soil bacteria include solubilization of minerals, fixation of nitrogen, production of growth-promoting hormones and competitive suppression of pathogens. Most recent research to improve crop responses has emphasized the study of nitrogen-fixing bacteria indigenous to rhizospheres of cereal crops and other grasses. The amount of nitrogen available to crops from fixation by these organisms is significant under some circumstances, but efforts to control and increase fixation activity have not been consistently successful. Despite considerable research, inoculation experiments frequently fail to improve rates of nitrogen fixation. However, substantial progress has been achieved in understanding mechanisms involved in plant—bacterial interactions, and in defining conditions which control them. Also, recent studies show clearly that bacterial inoculation can be highly beneficial even when nitrogen fixation is not affected. Further research is needed to develop new and effective methods for suppressing growth of competing microorganisms, and promoting dominance of those most useful to plants. Environmental manipulation may not be sufficient to achieve this objective. Genetic development of both plant and bacterial lines which enhance desired interactions is likely to be the most productive research effort for the future.  相似文献   
80.
Karl H  Ruoff U  Blüthgen A 《Chemosphere》2002,49(7):765-773
In 1995-1998 the contents of polychlorinated dibenzodioxins and dibenzofurans of 184 pooled fish samples were analysed. Sampling focused on fish and fishery products with a market share of more than 1% and covered all fishing grounds important for the supply of the German market. Investigation included 15 different fish species, shrimp, mussel and squid samples and various fishery products, typically on the German market. Generally lean fish species like cod, saithe or Alaska pollock were less contaminated on fresh weight basis than fat fish species like herring, Greenland halibut and sardine. In herring the dioxin content is related to the fishing ground. Low concentrations were found in North Sea herring, high concentrations measured in samples from the Baltic Sea. Dioxin contents in fishery products did not differ significantly from the raw fish samples. Results allow an estimation of the daily intake of dioxins and furans via fish consumption in Germany. Based on a daily fish consumption of 20 g the average intake of dioxins via fish is 6.2 pg WHO-PCDD/F-TEQs per person and day.  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