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   30962篇
  免费   295篇
  国内免费   265篇
安全科学   805篇
废物处理   1278篇
环保管理   4065篇
综合类   5568篇
基础理论   7742篇
环境理论   10篇
污染及防治   8243篇
评价与监测   1963篇
社会与环境   1687篇
灾害及防治   161篇
  2022年   216篇
  2021年   242篇
  2019年   228篇
  2018年   400篇
  2017年   403篇
  2016年   654篇
  2015年   528篇
  2014年   788篇
  2013年   2385篇
  2012年   917篇
  2011年   1257篇
  2010年   985篇
  2009年   1160篇
  2008年   1303篇
  2007年   1397篇
  2006年   1239篇
  2005年   1020篇
  2004年   1061篇
  2003年   1022篇
  2002年   983篇
  2001年   1229篇
  2000年   847篇
  1999年   544篇
  1998年   390篇
  1997年   390篇
  1996年   442篇
  1995年   450篇
  1994年   443篇
  1993年   406篇
  1992年   368篇
  1991年   360篇
  1990年   366篇
  1989年   327篇
  1988年   325篇
  1987年   299篇
  1986年   274篇
  1985年   279篇
  1984年   318篇
  1983年   315篇
  1982年   308篇
  1981年   294篇
  1980年   256篇
  1979年   266篇
  1978年   223篇
  1977年   199篇
  1976年   179篇
  1975年   185篇
  1974年   175篇
  1973年   174篇
  1972年   174篇
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
961.
In this study, we investigated whether bird feathers can be used as a non-destructive biomonitor for organic pollutants. We analysed the outermost tail feathers of 8 terrestrial and aquatic bird species from Belgium (8 species, n=108) for polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and organochlorine pesticides (OCPs). Every compound class could be quantified in one single tail feather of the birds under study (sum PCBs ranging from 5.5 to 510 ng/g feather, sum PBDEs from 0.33 to 53 ng/g feather, sum DDTs from 1.5 to 730 ng/g feather), except for PBDEs in feathers of the common moorhen (Gallinula chloropus). Further, we calculated Pearson correlations between concentrations of organic pollutants in feathers and concentrations in corresponding muscle or liver tissue from the birds. Correlations were found significant in half of the cases of the terrestrial species, but were found not significant for the aquatic species, with the exception of a significant correlation of sum PCBs in the common moorhen. Only for the common buzzard (Buteo buteo) (n=43) all correlations were found significant (0.32相似文献   
962.
Fluorinated organic compounds (FOCs) are a group of chemicals widely used as surfactants, lubricants, polymers, and fire-fighting foams. Recent studies have shown the ubiquitous distribution of FOCs in the environment, wildlife, and humans. We here report the results of a pilot study conducted to provide preliminary data on the levels of 13 FOCs in the blood of 48 residents in Catalonia, Spain, in relation to gender and age (25+/-5 and 55+/-5 years). The highest mean concentration was obtained for perfluorooctane sulfonate (PFOS, 7.64 ng/ml), followed by perfluorohexane sulfonate (PFHxS, 3.56 ng/ml) and perfluorooctanoic acid (PFOA, 1.80 ng/ml). Four other FOCs showed mean levels between 0.30 and 0.44 ng/ml, whereas those of the remaining 6 compounds were below the detection limit. Regarding gender, the blood levels of PFHxS and PFOA were significantly higher (p<0.05) in men than in women, while differences according to age were only noted for PFHxS (p<0.05) and perfluorooctane sulfonamide (PFOSA) (p<0.001), for which the levels were higher in the younger (25+/-5 years) group of subjects. A significant correlation between PFOS levels and those of the remaining detected FOCs (except PFDA) was found. In general terms, the current FOC concentrations were lower than those found in recent studies concerning levels of these chemicals in human blood and serum of subjects from different countries.  相似文献   
963.
For testing the potential use of stable iodine as a countermeasure to reduce radioiodine transfer to milk, concentrations of stable iodine and radioiodine in the milk of dairy cows fed different amounts of stable iodine were measured. The results indicated that, compared to a normal average stable iodine intake of about 20 mg d(-1) for cows, low iodine dietary intake (<1.5 mg d(-1)) resulted in a reduced transfer of radioiodine to milk by 25%, varying stable iodine intakes in the range of 10-500 mg d(-1) did have no significant effect; at stable iodine intake rates above 1000 mg I d(-1), a reduction by a factor of approximately two was achieved. The high dietary iodine intakes--being about 100 times the normal iodine supply--required to reduce the radioiodine transfer significantly, will result in stable iodine concentrations in milk in excess of advised or legal limits for human consumption. Nevertheless, the provision of stable iodine via the milk pathway might be considered for emergency situations when stable iodine is used as a preventative measure for dose reduction to humans.  相似文献   
964.
Radiological assessment of the impact of nuclear weapons testing on the local population in the Semipalatinsk Test Site (STS) requires comprehensive site-specific information on radionuclide behaviour in the environment. However, information on radionuclide behaviour in the conditions of the STS is rather sparse and, in particular, there are no data in the literature on parameters of radionuclide transfer from feed to rabbit products which have been identified as contributors to internal dose to the inhabitants. The transfer of (137)Cs and (90)Sr to rabbit meat was studied under laboratory conditions in a controlled experiment with 32 locally bred rabbits maintained in the Kazakh Agricultural Research Institute. The equilibrium transfer coefficients for (137)Cs and (90)Sr from feed to rabbit meat were estimated to be 0.4 d kg(-1) and 0.15 d kg(-1), respectively. The biological half-lives were estimated to be 0.1 d for (137)Cs and 0.14 d for (90)Sr. Whereas for (137)Cs the distribution in the body is relatively homogeneous, there are large differences between the organs and tissues for (90)Sr for which, as expected, the highest concentrations were found in bone.  相似文献   
965.
In summer 1993 we measured the transfer of (239/240)Pu to milk from herbage from a pasture located 5 km from the Chernobyl nuclear power plant. In one treatment cows were allowed to graze freely on the pasture. In a second treatment, cows were fed herbage collected from the pasture in stalls. The milk transfer coefficient; F(m) did not vary significantly between treatments and the mean value of 7.5x10(-6)d l(-1) was higher than previously reported values. Despite many values of F(m) for Pu in the literature we identified few relevant original data sets. Transfer coefficient values for Pu are only appropriate when used in conjunction with a specified time period or an appropriate model which allows for the biological half-life. We recommend for screening purposes an F(m) value of 1x10(-5)d l(-1) for Pu, with an order of magnitude lower value being appropriate for cows which are only exposed for one grazing season.  相似文献   
966.
Following an intensive survey of domestic radon levels in the United Kingdom (UK), the former National Radiological Protection Board (NRPB), now the Radiation Protection Division of the Health Protection Agency (HPA-RPD), established a measurement protocol and promulgated Seasonal Correction Factors applicable to the country as a whole. Radon levels in the domestic built environment are assumed to vary systematically and repeatably during the year, being generally higher in winter. The Seasonal Correction Factors therefore comprise a series of numerical multipliers, which convert a 1-month or 3-month radon concentration measurement, commencing in any month of the year, to an effective annual mean radon concentration. In a recent project undertaken to assess the utility of short-term exposures in quantifying domestic radon levels, a comparative assessment of a number of integrating detector types was undertaken, with radon levels in 34 houses on common geology monitored over a 12-month period using dose-integrating track-etch detectors exposed in pairs (one upstairs, one downstairs) at 1-month and 3-month resolution. Seasonal variability of radon concentrations departed significantly from that expected on the basis of the HPA-RPD Seasonal Correction Factor set, with year-end discontinuities at both 1-month and 3-month measurement resolutions. Following this study, monitoring with electrets was continued in four properties, with weekly radon concentration data now available for a total duration in excess of three and a half years. Analysis of this data has permitted the derivation of reliable local Seasonal Correction Factors. Overall, these are significantly lower than those recommended by HPA-RPD, but are comparable with other results from the UK and from abroad, particularly those that recognise geological diversity and are consequently prepared on a regional rather than a national basis. This finding calls into question the validity of using nationally aggregated Seasonal Correction Factors, especially for shorter exposures, and the universal applicability of these corrections is discussed in detail.  相似文献   
967.
The ecological risk posed by dioxin-like PCBs and PCDD/Fs congeners mixtures in five organisms representative of the food web of the lagoon of Venice (Italy) was estimated by applying the US-EPA [US-EPA. Guidelines for Ecological Risk Assessment. EPA/630/R-95/002F. Final Report. U.S. Environmental Protection Agency, Washington, DC; 1998.] procedure. Experimental concentrations of dioxin-like PCBs and PCDD/Fs in sediments, water, and organisms in six lagoon zones were used to define the spatial distribution of the pollutant homolog patterns. The Principal Component Analysis of homolog patterns in biota permitted to remark the difference between PCDD/Fs and dioxin-like PCBs bioaccumulation. Dioxin-like PCBs were found almost unaltered in all selected organisms, while PCDD/Fs homologs underwent an enrichment of low chlorinated furans in fish. The ecological risk for the dioxin-like PCBs and PCDD/Fs was estimated in the selected lagoon zones according to the Hazard Quotient approach by comparing the biota experimental concentrations in TEQ with an Internal No Effect Concentration of the 2,3,7,8-TCDD, estimated from both Ambient Quality Criteria and literature toxicity data. A high potential risk was found for benthic biota (i.e. clam and crab) and for mussel, while a negligible risk was estimated for fish. Moreover, the ecological risk resulted higher in the central part of the lagoon, and lower in the northern lagoon. Finally, the comparison between the TEQ concentrations of each homolog in biota and the estimated ecological risk highlighted that the risk was determined essentially by lower chlorinated PCDD/Fs (i.e. pentachloro and hexachloro PCDD/Fs), and by pentachloro-PCBs. These compounds should be regarded as homologs of concern and preferentially investigated in environmental monitoring of sediment, water, and biota.  相似文献   
968.
The presence of linear alkylbenzene sulfonates (LAS) and their degradation intermediates, sulfophenylcarboxylic acids (SPCs), with concentrations up to 100 ppb has been found in surface waters taken from the estuary of the river Guadalete (Cádiz, SW of Spain). Higher concentrations were found at the sampling site located adjacent to the discharge outlet of a wastewater treatment plant (WWTP). The concentrations decreased downstream to a few ppb as a result of dilution, sorption, and degradation processes, which were taking place along the estuary. Once the presence of both xenobiotics was confirmed in the environment, an in vivo assay was conducted to study their biotransformation and effects in the benthic fish Solea senegalensis. A flow-through system was employed, consisting of an exposure phase (120 h) with environmental levels of the surfactant (200, 500 and 800 microg/L of 2?C(10)LAS), followed by a depuration stage (72 h). The generation of SPCs has been quantified during these phases in both water and fish, with LAS biotransformation shown in all cases. The antioxidant enzymes catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR), the phase II enzyme glutathione S-transferase (GST), and the phase III acid and alkaline phosphatases (AcP, ALP) were also estimated and utilized as biomarkers.  相似文献   
969.
The dependence of the annual increment of vegetative organs on air temperature and humidity and the amount of precipitation per phenophase, as well as the period of their growth in Scots pine, were studied in the forest-steppe zone of Cisbaikalia. The multiple effect of variation in environmental conditions on the annual increment of organs increased when precipitation in September of the previous year was taken into account. These factors proved to have a stronger effect on variation in the annual increment of needles (R 2 = 0.59, p = 0.00005) than that in the annual ring width (R 2 = 0.38, p = 0.0002).  相似文献   
970.
Olivine, one of the most abundant minerals existing in nature, is explored as a CO2 carbonation agent for direct carbonation of CO2 in flue gas. Olivine based CO2 capture is thermodynamically favorable and can form a stable carbonate for long-term storage. Experimental results have shown that water vapor plays an important role in improving CO2 carbonation rate and capacities. Other operation conditions including reaction temperature, initial CO2 concentration, residence time corresponding to the flow rate of CO2 gas stream, and water vapor concentration also considerably affect the performance of the technology.  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