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   458篇
  免费   2篇
  国内免费   6篇
安全科学   16篇
废物处理   29篇
环保管理   62篇
综合类   41篇
基础理论   70篇
环境理论   1篇
污染及防治   159篇
评价与监测   69篇
社会与环境   18篇
灾害及防治   1篇
  2023年   9篇
  2022年   36篇
  2021年   20篇
  2020年   4篇
  2019年   8篇
  2018年   10篇
  2017年   12篇
  2016年   11篇
  2015年   9篇
  2014年   25篇
  2013年   58篇
  2012年   26篇
  2011年   19篇
  2010年   18篇
  2009年   15篇
  2008年   20篇
  2007年   22篇
  2006年   19篇
  2005年   23篇
  2004年   14篇
  2003年   8篇
  2002年   9篇
  2001年   4篇
  2000年   2篇
  1999年   4篇
  1998年   5篇
  1997年   3篇
  1996年   3篇
  1994年   3篇
  1992年   2篇
  1988年   2篇
  1987年   2篇
  1984年   2篇
  1982年   4篇
  1981年   2篇
  1980年   2篇
  1979年   3篇
  1973年   1篇
  1972年   2篇
  1968年   1篇
  1967年   2篇
  1966年   1篇
  1965年   1篇
  1964年   2篇
  1963年   1篇
  1962年   2篇
  1959年   2篇
  1958年   1篇
  1956年   2篇
  1955年   2篇
排序方式: 共有466条查询结果,搜索用时 250 毫秒
191.
The pultruded jute/phenolic composites were aged under various humidity, hydrothermal and weathering conditions. Aging-induced effect of these conditions on the jute profiles was studied in terms of their physico-mechanical properties. It is observed that dimensional change of the profiles was only upto 4% even in an accelerated water aging condition. The effect of absorbed moisture/water on the jute profile was more pronounced in an accelerated water aging than the samples are being exposed to high humidity and alternate wetting and drying cycles. The changes in the values of internal bond strength of the profiles could be used as an indicator because of its sensitivity towards aging. Accentuation of fibres on the weathered samples along with severe resin erosion has suggested to layer the surface of the profiles with rich resin prior to use in the outdoor. The properties of jute profile door frame were satisfactory when compared with the requirements mentioned in IS: 4021–83 – Indian standard specification for timber door, window and ventilator frames. Performance of the installed door frame has shown no sign of dimensional instability in terms of warping and bulging after 3 years. It is suggested that jute door frames could be used as an alternative to the wooden door frames in buildings.  相似文献   
192.
Twenty-six-day-old black turtle bean cv. 'Domino' plants were exposed to nitrogen dioxide (0.0, 0.025, 0.05 and 0.10 microl liter(-1)), 7 h per day for 5 days per week for 3 weeks, under controlled environment. Data were collected on net photosynthesis rate (PN), stomatal resistance (SR), and dark respiration rate (DR), immediately after exposure, 24 h after the termination of exposure and at maturity (when the leaves had just started turning yellow), using a LICOR 6000 Portable Photosynthesis System. Chlorophyll-a (Ch-a), chlorophyll-b (Ch-b), total chlorophyll (tot-Ch) and leaf nitrogen were measured immediately after exposure and at maturity. Growth characteristics-relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR) and root: shoot ratio (RSR)-were computed for treated plants. Net photosynthesis rate increased by 53% in 0.10 microl liter(-1) NO2 treated plants immediately after exposure compared to control plants. Dark respiration rates were also higher in treated plants. Ch-a, Ch-b and tot-Ch showed significant increases with 0.1 microl liter(-1) NO2 treatment immediately after exposure. Foliar nitrogen content showed an increase in treated plants both immediately after exposure and at maturity. Increases were also seen in RGR and NAR. Plant yield increased by 86% (number of pods), 29% (number of seeds) and 46% (weight of seeds), respectively. Nitrogen dioxide stimulated the overall plant growth and crop yield.  相似文献   
193.
One month old soybean (Glycine max (L.) Merrill) cv. 'Williams' plants were exposed to nitrogen dioxide (NO2 at 0.1, 0.2, 0.3, and 0.5 microl liter(-1) and carbon filtered air (control), 7 h per day for five days, under controlled environment. Data were collected on net photosynthetic rate (PN), stomatal resistance (SR), and dark respiration rate (DR), immediately following the fifth day of exposure and 24 h after termination of exposure. Chlorophyll a (Ch a), chlorophyll b (Ch b), total chlorophyll (tot Ch) and foliar nitrogen (N) were measured before and after exposures. Growth characteristics--relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), and root shoot ratio (RSR) -- were computed for treated plants using standard growth equations. Increases of 18% and 23% in PN were observed immediately following exposure to 0.2 microl liter(-1) NO2 and after 24 h recovery period, respectively. With 0.5 microl liter(-1) NO2 treatment, reductions in PN of 23% and 50% were observed, immediately after exposure and following 24 h recovery, respectively. DR rates with 0.2 l liter(-1) treatment were higher than the control. Chlorophyll a and tot Ch showed significant reduction with 0.5 microl liter(-1) NO2 treatment. The percent reduction in Ch a and tot Ch with 0.5 microl liter(-1) NO2 were 45% and 47%, respectively. Increases in foliar nitrogen content after 0.2 and 0.3 microl liter(-1) NO2 treatments were 46% and 69%, respectively. Nitrogen dioxide at 0.5 microl liter(-1) reduced RGR and NAR by 47% and 51%, respectively. Leaf area ratio was 42% higher in 0.5 microl liter(-)1 NO2 treated plants, compared with the control; this increase was insufficient to compensate for the decrease in NAR resulting in a net decline in RGR. Nitrogen dioxide up to 0.2 microl liter(-1) increased PN and foliar-N content of soybean. With 0.5 microl liter(-1) NO2, significant decreases were observed in PN, leaf chlorophyll, foliar-N, NAR and RGR. Nitrogen dioxide up to 0.2 microl liter(-)1 has a favorable influence on overall growth characteristics of soybean; however, inhibitory effects were seen with NO2 treatment at 0.5 microl liter(-1).  相似文献   
194.
Gomti river receives industrial as well as domestic wastes from various drains of Lucknow city. In the process the water and sediment of the river Gomti get contaminated with heavy metals and other pollutants. In the present study, impacts of domestic/industrial wastes on the water and sediment chemistry of river Gomti with special reference to heavy metals have been investigated in different seasons (summer, winter and rainy). For this, seven sampling sites: Gaughat, Mohan Meakin, Martyrs Memorial, Hanuman Setu, Nishatganj bridge, Pipraghat and Malhaur, in the river Gomti in Lucknow region were identified and samples of water and sediments were collected in all the three seasons. In the collected water and sediment samples, six metals (Cd, Cr, Cu, Ni, Pb, and Zn) were analyzed on ICP-AES (Inductively coupled plasma emission spectroscopy) Labtam Plasmalab 8440. High concentrations of all the metals were noticed in water and sediment in rainy season compared to summer and winter. Because in rainy season runoff from open contaminated sites, agricultural field and industries, directly comes into the river without any treatment. In both the cases, the concentration of zinc was maximum (0.091 g/ml in water and 182.13 g/g in sediment) and the concentration of cadmium (0.001 g/ml in water and 17.26 g/g in sediment) was minimum. Higher concentration of metal in water and sediment during rainy season could be due to the industrial/agricultural/domestic runoff coming into the river.  相似文献   
195.
Accumulation of Cu and Cd by Vallisneria spiralis was studied under laboratory conditions. Plants showed ability to reduce 5 µg ml–1 Cu background concentration to below 0.05 µg ml–1 (m.p.l., WHO 1985) within 48 h. The Cd concentration of 1.0 µg ml–1 was reduced to below m.p.l. (0.005 µg ml–1) in 168 h. Cysteine synthesis was more under Cd stress condition. Both the metals were toxic to the plants at higher concentrations; more in the case of Cd.NBRI Rsearch Publication No. 417 (N.S.).  相似文献   
196.
The concentrations of total suspended particulate matter (TSP) and particulate matter less than 10 microns (PM10) were measured at various locations in a Jawaharlal Nehru port and surrounding harbour region. Meteorological data was also collected to establish the correlation with air pollutant concentration. The results are analysed from the standpoint of monthly and seasonal variations, annual trends as well as meteorological effects. The monthly mean concentration of TSP was in the range of 88.2 to 199.3 microg m(-3). The maximum and minimum-recorded value of PM10 was 135.8 and 20.3 microg m(-3), respectively. The annual average concentration of PM10 was 66.1 microg m(-3). There are clear associations between TSP and PM10 data set at all the measured three sites with a correlation coefficient of 0.89, 0.69 and 0.81, respectively. PM10 data appears to be a constant fraction of the TSP data throughout the year, indicating common influences of meteorology and sources. Particle size analysis showed PM10 to be 47% of the total TSP concentration, which is lower than reported for industrial area and traffic junctions in Mumbai. Anthropogenic sources contribute significantly to the PM10 fraction in an industrial region, while contributions from natural sources are more in a port and harbour area. Statistical analysis of air quality data shows that TSP is strongly correlated with wind speed but weakly correlated with temperature. There appears to be a simple inverse relationship between TSP and wind speed data, indicating the dilution and transport by winds.  相似文献   
197.
Cadmium, copper, manganese, lead and zinc concentrations were determined in water, periphytonic algae, detritus, and larvae of three aquatic insects, viz. Baetis sp. (Ephemeroptera: Baetidae), Hydropsyche sp. (Trichoptera: Hydropsychiidae), and Chironomus ramosus Choudhury and Das (Diptera: Chironomidae), during two surveys from an unpolluted and a polluted stream in Shillong, Meghalaya State, Northeastern India. Metal concentrations were higher in all the samples from the polluted stream, possibly reflecting the contributions from various non-point sources of metal contamination present in its catchment. Among the three insects, Baetis sp. was found to accumulate cadmium, copper, and zinc, and Hydropsyche sp. manganese, to concentrations significantly higher than those found in the other taxa. The concentrations of all the metals were higher in fine detritus than in C. ramosus, although Cd and Zn concentrations were elevated in Baetis as compared to those in periphytonic algae and fine detritus, indicating possible bioconcentration of these metals by this animal.  相似文献   
198.
A long-term study of temperature, pH, turbidity, suspended solid, salinity, dissolved oxygen, biochemical oxygen demand and ammonia nitrogen has been performed in a port and harbour region in India for four years from December 1996 to November 2000. Marine water quality results showed no regular trend. The mean monthly values of temperature, pH, turbidity, suspended solid, salinity, dissolved oxygen, biochemical oxygen demand and ammonia nitrogen were in the range of 22.64 ± 0.4 to 29.05 ± 1.37 °C; 7.65 ± 0.04 to 7.81 ± 0.13; 28.8 ± 14.7 to 64.2 ± 32.0 NTU; 283.5 ± 81.8 to 356.0 ± 159.7 mg/L; 29.78 ± 7.18 to 29.78 ± 1.04 ppt; 4.67 ± 0.50 to 6.01 ± 1.02 mg/L; 5.41 ± 1.92 to 7.56 ± 2.1 mg/L; and 0.25 ± 0.07 to 0.63 ± 0.49 mg/L, respectively. The results of correlation analysis showed that biochemical oxygen demand (BOD) was inversely correlated dissolved oxygen (DO) and poorly correlated with all other parameters. Turbidity and suspended solid were moderately correlated with each other while salinity was moderately correlated with other water quality parameters. In factor analysis, four factors were drawn out of the eight variables, which represented 74% of the variance of the original data. Factor I was related to suspended solid and turbidity. Factor II represented mainly temperature and DO showing inverse relation between these two. Factor III implied the degree of pollution at any monitoring station. Factor IV included pH and salinity. It could be concluded that the factor model represented almost all the variables.  相似文献   
199.

This article investigates the suitability of utilizing end of life rubber tyre particles in concrete as fine aggregate. Rubber ash and rubber fibers were used to develop two series of rubber ash concrete (series I) and hybrid concrete (series II) mixes. The natural fine aggregate was replaced by rubber ash (by volume of 5%, 10%, 15% and 20%) in series I; whereas in series II, the amount of rubber ash was kept constant at 10% and rubber fiber was introduced as replacement of fine aggregate (by volume of 5%, 10%, 15%, 20% and 25%). The concrete mixes were evaluated for compressive strength, flexural strength, resistance to impact loading, fatigue loading, water penetration and shrinkage strain was evaluated. It was observed that inclusion of rubber ash resulted in the improvement of impact resistance of concrete. The results also show that up to 10% rubber ash and rubber fibers can be utilized as fine aggregate to develop feasible and durable rubberized concrete pavements, crash barriers and paver blocks.

  相似文献   
200.
A waste product generated in the sugar industry in India has been converted into a cheap potential adsorbent. This has been characterised and utilized for the removal of chromium (VI) from synthetic and actual wastewater. The sorption efficiency decreases with increase in pH. Adsorption of Cr (VI) on bagasse fly ash follows the Freundlich and Langmuir isotherms and these have been used to obtain the thermodynamic parameters of the process. The sorption capacity of this adsorbent for chromium removal is found to be comparable to other low cost adsorbents.  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