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   20026篇
  免费   193篇
  国内免费   145篇
安全科学   473篇
废物处理   878篇
环保管理   2135篇
综合类   3248篇
基础理论   5382篇
环境理论   9篇
污染及防治   5504篇
评价与监测   1412篇
社会与环境   1214篇
灾害及防治   109篇
  2023年   105篇
  2022年   240篇
  2021年   238篇
  2020年   163篇
  2019年   182篇
  2018年   358篇
  2017年   418篇
  2016年   558篇
  2015年   433篇
  2014年   684篇
  2013年   1558篇
  2012年   745篇
  2011年   991篇
  2010年   800篇
  2009年   750篇
  2008年   942篇
  2007年   962篇
  2006年   800篇
  2005年   680篇
  2004年   678篇
  2003年   630篇
  2002年   592篇
  2001年   706篇
  2000年   507篇
  1999年   290篇
  1998年   192篇
  1997年   224篇
  1996年   222篇
  1995年   264篇
  1994年   257篇
  1993年   189篇
  1992年   212篇
  1991年   198篇
  1990年   215篇
  1989年   199篇
  1988年   164篇
  1987年   170篇
  1986年   170篇
  1985年   166篇
  1984年   155篇
  1983年   151篇
  1982年   141篇
  1981年   128篇
  1980年   124篇
  1979年   130篇
  1978年   107篇
  1977年   116篇
  1975年   93篇
  1973年   98篇
  1972年   90篇
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
961.
A set of biochemical and histological responses was measured in wild gudgeon collected upstream and downstream of urban and pharmaceutical manufacture effluents. These individual end-points were associated to fish assemblage characterisation. Responses of biotransformation enzymes, neurotoxicity and endocrine disruption biomarkers revealed contamination of investigated stream by a mixture of pollutants. Fish from sampled sites downstream of the industrial effluent exhibited also strong signs of endocrine disruption including vitellogenin induction, intersex and male-biased sex-ratio. These individual effects were associated to a decrease of density and a lack of sensitive fish species. This evidence supports the hypothesis that pharmaceutical compounds discharged in stream are involved in recorded endocrine disruption effects and fish population disturbances and threaten disappearance of resident fish species. Overall, this study gives argument for the utilisation of an effect-based monitoring approach to assess impacts of pharmaceutical manufacture discharges on wild fish populations.  相似文献   
962.
Novel catalytic nano-sized materials based on LaCoO(x) perovskite nanoparticles incapsulated in the mesoporous matrix of zirconia were prepared, characterized by physicochemical methods and tested in complete methanol oxidation. LaCoO(x) nanoparticles were prepared inside the mesopores of ZrO(2) by decomposition of bimetallic La-Co glycine precursor complexes. The catalysts have been studied by diffuse-reflectance FTIR-spectroscopy using such probe molecules as CO, CD(3)CN and CDCl(3) to test low-coordinated metal ions. At low temperatures of decomposition of complexes (up to 400°C), low-coordinated Co(3+) ions predominate in the LaCoO(x) nanoparticles, whereas basically Co(2+) ions are found upon increasing the decomposition temperature to 600°C. The novel nano-sized perovskite catalysts exhibit a very high catalytic activity in the abatement of volatile organic compounds present in air, like methanol and light hydrocarbons.  相似文献   
963.
Soft sediments are often highly polluted as many of the toxic chemicals introduced into surface waters bind to settling particles. The resulting accumulation of pollutants in the sediments poses a risk for benthic communities. However, pollution induced changes in benthic communities have been difficult to determine when using macro-invertebrates as bioindicators, as these organisms are often absent in soft sediment. The present study therefore examined the ability of meiofaunal organisms, specifically, nematodes, to assess the ecological status of soft sediments. Over a 9-year period, nematode communities present in sediments collected from large rivers and lake Constance in Germany were studied. These sediments showed a large range of physico-chemical properties and anthropogenic contamination. After the degree of metal and organic contamination was translated into ecotoxicologically more relevant toxic units (TUs), multivariate methods were used to classify nematode taxa in species at risk (NemaSPEAR) or not at risk (NemaSPE(not)AR). This approach clearly distinguished the influence of sediment texture from that of the toxic potential of the samples and thus allowed classification of the nematode species according to their sensitivity to or tolerance of toxic stress. Two indices, expressing the proportion of species at risk within a sample (NemaSPEAR[%](metal), NemaSPEAR[%](organic)), were calculated from independent data sets obtained in field and experimental studies and showed good correlations with the toxic potential (field data) or chemical concentrations (microcosm data). NemaSPEAR[%] indices for metal and organic pollution were therefore judged to be suitable for assessing the impact of chemical contamination of freshwater soft sediments.  相似文献   
964.
965.
The application of engineered nanomaterials increases strongly. Development of analytical techniques and their application to environmental samples is essential for human and environmental risk assessment of the nanoparticles. The objective of this study was to develop a sensitive analytical method to quantify nC(60) in water, using accurate mass screening liquid chromatography-hybrid linear ion trap Orbitrap mass spectrometry. nC(60) can be transformed by oxidation, reduction and photochemical reaction. Therefore, the formation of some transformation products of nC(60) was studied as well. Finally, the developed analytical method was applied to surface water samples from several locations in the Netherlands. The developed method enabled to detect and quantify aqueous concentrations of the summed nC(60) and its transformation products as low as 5 ng/L. It was observed that nC(60) transformation products exceed quantities of the parent C(60). Despite the high sensitivity of the developed method, no nC(60) or transformation products were detected in an array of Dutch surface waters. This might be due to low emissions, losses in the aqueous phase by sedimentation, sorption or further transformation processes.  相似文献   
966.
Fish advisories for polychlorinated biphenyls (total-PCBs) and mercury are often given on a length-specific basis and fish sex is usually not considered. The relationship between concentration and length is well established for mercury, however its suitability for total-PCBs and the influence of sex over the large scale covered by most monitoring programs is not well known. Here we use what is perhaps the largest consistent sport fish contaminant dataset to evaluate the relationship between total-PCB/mercury and length and sex. We evaluated seven of the most commonly consumed fishes from the Canadian Great Lakes and two Ontario (Canada) inland lakes. For mercury, the relationship between concentration and length was significant (p<0.05) in most fish species and locations. For total-PCB, this relationship was also generally significant in Chinook salmon and lake trout, which are the species with the most advisories for this compound. In contrast, significant relationships were found less often for whitefish, northern pike, smallmouth bass, walleye, and especially yellow perch. However, mercury usually drives fish consumption advisories for these species. Overall, our results support the protocol of issuing contaminant advice on a length-specific basis in fish monitoring programs with reasonable confidence when at least a moderate number of samples over the natural size range of a species are included in the analysis. Sex differences were common for walleye (males>females, p<0.05) but not other species, suggesting that an equal number of male and female walleye should be used in deriving fish advisories for walleye.  相似文献   
967.
The Syracuse, NY, AUDIT (Assessment of Urban Dwellings for Indoor Toxics) study was designed to quantify asthma agent levels in the inner-city homes of a birth cohort whose mothers had a diagnosis of asthma. Risk of exposure to particulate matter (PM), particle number and tobacco smoke was assessed in 103 infants' homes. Repeat measurements were made in 44% of the homes. Infants also were examined on a quarterly basis during the first year of life to monitor their respiratory health and urine cotinine levels. Overall geometric mean (GM) values for PM(2.5) of 21.2 μg/m(3) and for PM(10) of 31.8 μg/m(3) were recorded in homes at visit 1. GM values for PM(2.5) and PM(10) in smoking homes were higher at 26.3 and 37.7 μg/m(3), while values in non-smoking homes were 12.7 and 21.2 μg/m(3) respectively. Fifty-four percent of mothers (55/103) smoked at some point in pregnancy (39% smoked throughout pregnancy). Environmental tobacco smoke (ETS) exposure occurred in 68% of homes during the infants' first year. Significant to this study was the size- and time-resolved monitoring of PM at 140 home visits and the classification of PM count data. PM number counts ranged from continuously low levels (little indoor activity) to continuously high counts (constant indoor activity), and recorded apparent instances of prolonged repeated cigarette smoking. Wheezing in the first year of life was recorded for 38% of the infants (39/103). Adjusted logistic regression modeling demonstrated that elevated levels of indoor PM(2.5) (≥ 15 μg/m(3)) were a significant risk factor for infant wheezing after controlling for infant gender, mothers' age and education level, season of home visit and presence of carpeting (OR 4.21; 95% CI 1.36-13.03; p=0.013). An elevated level of the nicotine metabolite cotinine in infant urine also was associated with infant wheezing after adjusting for infant gender, mothers' age and education level (OR 5.10; 95% CI 0.96-27.24; p=0.057). ETS exposure was pervasive in the AUDIT cohort and a risk for developing infants in this urban population.  相似文献   
968.
969.
Adequate radioprotection of the environment requires the identification of biomonitors sensitive to the variation of its radionuclide content. Due to the chemical similarities between calcium and strontium, calcified tissues of mammals are considered to be good 90Sr biomonitors. This work considered Cervus elaphus antlers which, being shed annually, can give information about the importance of radiostrontium contamination in an ecosystem in the time period required for the growth of the antler. The samples were collected at various points of W and SW Spain. The mean value of their 90Sr content was (70 ± 43 (S.D.)) Bq/kg d.w., range (16-218) Bq/kg d.w., and the radionuclide was evenly distributed in the different parts of the antler. There was a good correlation between the antlers’ 90Sr content and the 90Sr deposited in the soil. The antlers’ content of 226Ra (from the natural uranium series) and the contents of some stable elements (Ca, Mg, Sr, and K) were also determined. The values for these stable elements were practically constant in the analyzed samples, and the concentrations measured decreased in the following order:Ca » Mg > K > Sr » 90Sr > 226Ra  相似文献   
970.
The activity of 210Po and 210Pb was determined in mussels of the same size (3.5-4.0 cm shell length) sampled monthly over a 17-month period at the Atlantic coast of Portugal. Average radionuclide concentration values in mussels were 759 ± 277 Bq kg−1 for 210Po (range 460-1470 Bq kg−1 dry weight), and 45 ± 19 Bq kg−1 for 210Pb (range 23-96 Bq kg−1 dry weight). Environmental parameters and mussel biometric parameters were monitored during the same period. Although there was no seasonal variation of radionuclide concentrations in sea water during the study period, the concentration of radionuclide activity in mussels varied seasonally displaying peaks of high concentrations in winter and low concentrations in summer. Analysis of radionuclide data in relation to the physiological Condition Index of mussels revealed that 210Po and 210Pb activities in the mussel (average activity per individual) remained nearly constant during the investigation period, while mussel body weight fluctuated due to fat storage/expenditure in the soft tissues. Similar variation of radionuclide concentrations was observed in mussels transplanted from the sea coast into the Tejo Estuary. However, under estuarine environmental conditions and with higher food availability throughout the year, transplanted mussel Condition Index was higher than in coastal mussels and average radionuclide concentrations were 210 ± 75 Bq kg−1 (dry weight) for 210Po and 10 ± 4 Bq kg−1 (dry weight) for 210Pb, therefore lower than in coastal mussels with similar shell length. It is concluded that the apparent seasonal fluctuation and inter-site difference of radionuclide concentrations were mostly caused by mussel body weight fluctuation and not by radionuclide body burden fluctuation. This interpretation can be extended to the apparent seasonal fluctuation in concentrations of lipophilic and lipophobic contaminants in mussels, and provides an explanation for occasional high concentrations of 210Po and man-made contaminants measured in mussels far from pollution sources.  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