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   22584篇
  免费   195篇
  国内免费   175篇
安全科学   496篇
废物处理   1079篇
环保管理   2393篇
综合类   3579篇
基础理论   6178篇
环境理论   7篇
污染及防治   6092篇
评价与监测   1642篇
社会与环境   1386篇
灾害及防治   102篇
  2023年   103篇
  2022年   263篇
  2021年   230篇
  2020年   154篇
  2019年   171篇
  2018年   469篇
  2017年   449篇
  2016年   705篇
  2015年   437篇
  2014年   702篇
  2013年   1625篇
  2012年   1100篇
  2011年   1176篇
  2010年   855篇
  2009年   792篇
  2008年   966篇
  2007年   1033篇
  2006年   868篇
  2005年   1043篇
  2004年   1134篇
  2003年   992篇
  2002年   635篇
  2001年   756篇
  2000年   543篇
  1999年   318篇
  1998年   200篇
  1997年   233篇
  1996年   217篇
  1995年   274篇
  1994年   261篇
  1993年   194篇
  1992年   217篇
  1991年   201篇
  1990年   217篇
  1989年   200篇
  1988年   157篇
  1987年   167篇
  1986年   156篇
  1985年   163篇
  1984年   149篇
  1983年   146篇
  1982年   128篇
  1981年   120篇
  1980年   117篇
  1979年   129篇
  1978年   101篇
  1977年   115篇
  1975年   94篇
  1973年   97篇
  1972年   90篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
High temperature alkaline chemical liquids have caused injuries and hazardous situations in Finnish pulp manufacturing mills. There are no requirements and/or test method standards concerning protection against high temperature alkaline chemical splashes. This paper describes the test method development process to test and identify materials appropriate for hot liquid chemical hazard protection. In the first phase, the liquid was spilled through a stainless steel funnel and the protection performance was evaluated using a polyvinyl chloride (PVC) film under the test material. After several tentative improvements, a graphite crucible was used for heating and spilling the chemical, and a copper-coated K-type thermometer with 4 independent measuring areas was designed to measure the temperature under the material samples. The thermometer was designed to respond quickly so that peak temperatures could be measured. The main problem was to keep the spilled amount of chemical constant, which unfortunately resulted in significant variability in data.  相似文献   
972.
973.
PROBLEM: This study assesses the impact of crash and casualty numbers in correspondence to the introduction of mobile speed cameras in the rural county of Norfolk, England. METHOD: Road traffic accident casualty and crash data were collected for two years before the introduction of cameras and two years subsequently. The casualties and crashes occurring at 29 camera sites were identified and separated from those occurring in the rest of the county. Trends in crashes and casualties, and their severity, were examined graphically and comparisons were made between before and after periods. The regression to the mean effect at individual sites was estimated. RESULTS: After the introduction of cameras, overall crashes declined by 1% and crashes involving fatalities or serious injuries declined by 9% on the roads without cameras. At the camera sites, crashes decreased by 19% and fatal and serious crashes by 44%. The reduction in total crashes was significantly greater than that expected from the effect of regression to the mean in 12 out of 20 sites tested. SUMMARY: The introduction of cameras appears to have resulted in real and measurable reductions in crash risk in this rural county. IMPACT ON INDUSTRY: Our results suggest the deployment of mobile speed cameras is an effective tool for organizations wishing to reduce road traffic casualties in areas where high crash rates have been associated with excessive vehicle speeds.  相似文献   
974.
In the late 1990s China started to expand its market economic reform to the public sector, such as water services. This reform led to major changes in urban water management, including water tariff management. The reforms in water tariff management relate not only to tariffs, but also to the decision-making on tariffs. Water tariff decision-making seems to move away from China's conventional mode of highly centralized and bureaucratic policy- and decision-making. The legalization, institutionalization and performance of public hearings in water tariff management forms a crucial innovation in this respect. This article analyzes the emergence, development and current functioning of public hearings in water tariff setting, and assesses to what extent public hearings are part of a turning point in China's tradition of centralized bureaucratic decision-making, towards more transparent, decentralized and participative governance.  相似文献   
975.
A systematic approach to optimizing water network has traditionally been utilized to exam and plan water conservation in industrial processes. In the present case study, water-pinch technology was used to analyze and optimize the water network of a steel plant near China's Zhangjiakou city. A system design was developed and a limiting constraint (Cl(-) concentration) was identified based on investigations of water quality then the minimum freshwater and wastewater targets were determined without considering water losses. The analysis was then extended by calculating the additional input of freshwater required to balance the actual water losses. A nearest-neighbor algorithm (NNA) was used to distribute the freshwater and recycled water among each of the plant's operations. The results showed that with some reconstruction of the water network, the flow rates of freshwater and wastewater could be decreased by 57.5% and 81.9%, respectively.  相似文献   
976.
In this study, the Tsunami-caused deterioration of soil and groundwater quality in the agricultural fields of coastal Nagapattinam district of Tamilnadu state in India is presented by analyzing their salinity and sodicity parameters. To accomplish this, three sets of soil samples up to a depth of 30cm from the land surface were collected for the first six months of the year 2005 from 28 locations and the ground water samples were monitored from seven existing dug wells and hand pumps covering the study region at intervals of 3 months. The EC and pH values of both the soil and ground water samples were estimated and the spatial and temporal variability mappings of these parameters were performed using the geostatistical analysis module of ArcGIS((R)). It was observed that the spherical semivariogram fitted well with the data set of both EC and pH and the generated kriged maps explained the spatial and temporal variability under different ranges of EC and pH values. Further, the recorded EC and pH data of soil and ground water during pre-Tsunami periods were compared with the collected data and generated variability soil maps of EC and pH of the post-Tsunami period. It was revealed from this analysis that the soil quality six months after the Tsunami was nearing the pre-Tsunami scenario (EC< 1.5dSm(-1); pH<8), whereas the quality of ground water remained highly saline and unfit for irrigation and drinking. These observations were compared with the ground scenarios of the study region and possible causes for such changes and the remedial measures for taking up regular agricultural practices are also discussed.  相似文献   
977.
Arbuscular mycorrhizal fungi (AMF) may play an important role in phytoremediation of As-contaminated soil. In this study the effects of AMF (Glomus mosseae, Glomus intraradices and Glomus etunicatum) on biomass production and arsenic accumulation in Pityrogramma calomelanos, Tagetes erecta and Melastoma malabathricum were investigated. Soil (243 +/- 13 microg As g(-1)) collected from Ron Phibun District, an As-contaminated area in Thailand, was used in a greenhouse experiment. The results showed different effects of AMF on phytoremediation of As-contaminated soil by different plant species. For P. calomelanos and T. erecta, AMF reduced only arsenic accumulation in plants but had no significant effect on plant growth. In contrast, AMF improved growth and arsenic accumulation in M. malabathricum. These findings show the importance of understanding different interactions between AMF and their host plants for enhancing phytoremediation of As-contaminated soils.  相似文献   
978.
A greenhouse pot experiment was conducted to evaluate the effect of sewage sludge (SS), of sugar beet sludge (SBS), or of a combination of both, in the remediation of a highly acidic (pH 3.6) metal-contaminated soil, affected by mining activities. The SS was applied at 100 and 200 Mg ha(-1) (dry weight basis), and the SBS at 7 Mg ha(-1). All pots were sown with Italian ryegrass (Lolium multiflorum Lam.). After 60 d of growth, shoot biomass was quantified and analysed for Cu, Pb and Zn. The pseudo-total and bioavailable contents of Cu, Pb and Zn and the enzymatic activities of beta-glucosidase, acid phosphatase, cellulase, protease and urease were determined in the soil mixtures. Two indirect acute bioassays with leachates from the soil (luminescent inhibition of Vibrio fischeri and Daphnia magna immobilization) were also used. The SS, in particular when in combination with SBS, corrected soil acidity, while increasing the total organic matter content and the cation exchange capacity. The application of SS led to a decrease in the level of effective bioavailable metals (extracted by 0.01 M CaCl(2), pH 5.7, without buffer), but caused an increase in their potential bioavailability (extracted by a solution of 0.5M NH(4)CH(3)COO, 0.5 M CH(3)COOH and 0.01 M EDTA, pH 4.7). Plant biomass increased more than 10 times in the presence of 100 Mg SS ha(-1), and more than five times with the combined use of 100 Mg SS ha(-1) and SBS, but a considerable phytotoxic effect was observed for the application rate of 200 Mg SS ha(-1). Copper, Pb and Zn concentrations in the shoots of L. multiflorum decreased significantly when using 100 Mg SS ha(-1) or SBS. The activities of beta-glucosidase, urease and protease increased with increasing SS applications rates, but cellulase had a reduced activity when using 200 Mg ha(-1)SS. Both amendments were able to suppress soil toxicity to levels that did not affect D. magna, but increased the soil leachate toxicity towards V. fischeri, especially with the application of 200 Mg SS ha(-1). This study showed that for this type of mine soils, and when using SS of similar composition, the maximum SS application rate should be 100 Mg ha(-1), and that liming the SS amended soil with SBS did not contribute to a further improvement in soil quality.  相似文献   
979.
Polyfluorinated alkyl compounds (PFCs) are a group of chemicals of growing concern that have been detected in biological and abiotic samples worldwide. This study reports the concentrations of a suite of PFCs: perfluorooctyl sulfonate (PFOS), perfluorooctyl sulfonamide (PFOSA) and perfluorinated carboxylic acids (PFCAs) in guillemot (Uria aalge) eggs, collected in North-Western Europe, from Iceland, the Faroe Islands, Sweden and two locations in Norway. The highest concentrations of PFOS were found in samples from Sweden (mean 400 ng g(-1) wet weight (w.w.)), which were almost five times higher than concentrations found in Norwegian samples (mean 85 ng g(-1)w.w. from both sample sites). The concentrations found in Icelandic and Faroe samples were lowest (mean 16 and 15 ng g(-1)w.w., respectively). Only Swedish samples differed significantly from the other locations. In general, PFCAs show a different spatial trend than PFOS. Perfluorooctanoic acid (PFOA) was not detected in any sample and perfluorononanoic acid (PFNA) was only detected in samples from Sweden. The most abundant PFCA was perfluoroundecanoic acid (PFUA) with highest concentrations in samples from Sweden (mean 82 ng g(-1)w.w.), samples from the Faroe Islands had the second highest concentration (mean 57 ng g(-1)w.w.) and samples from Iceland and Norway had concentrations ranging between 18 and 30 ng g(-1)w.w. The original hypothesis was based on the idea that PFC concentrations are the highest close to more densely populated and industrialized areas and lower levels in remote areas. However, the geographic pattern is more complicated than predicted and varies among different PFCs.  相似文献   
980.
Chloramphenicol (CA) is a largely used antibiotic and it is an inhibitor of protein synthesis that also induces ROS production. In this work there were investigated activities and expressions in the Adriatic bivalve Chamelea gallina of some antioxidant and detoxification proteins like superoxide dismutase (Mn-SOD, Cu/Zn-SOD), catalase (CAT) and Cytochrome P450 (CYP1A). Clams exposed to 5mgl(-1) of chloramphenicol were sampled 2, 4 and 8 days after treatment (CA2, CA4 and CA8). SODs, CAT, and CYP1A activity and/or expression were detected in pooled digestive glands by Western blotting and by spectrophotometrical analysis. Enzymes activities increase during the entire antibiotic exposure. With respect to the control Cu/Zn-SOD expression increases, while Mn-SOD expression decreases significantly after 4 days. Two CYP1A immunopositive-proteins (57.7 and 59.8kDa) were detected. The lower band significantly decreases in CA8, the upper one also in CA4 condition. High levels of Mn-SOD, CAT activity and Cu/Zn-SOD expression, indicate intense ROS production while Mn-SOD expression inhibition might be ascribable to mitochondrial alterations due to CA and indirectly to ROS. CYP1A1 action determines H(2)O(2) production that would contribute to a CYP1A1 gene promoter down regulation, a response to oxidative stress with the antioxidant enzymes activation as a final result. This study highlights the close association, in C. gallina, in presence of chloramphenicol, between SOD/CAT and CYP system, and it appear particularly interesting to the lack of similar researches on mollusc species.  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