收费全文 | 33326篇 |
免费 | 322篇 |
国内免费 | 318篇 |
安全科学 | 920篇 |
废物处理 | 1461篇 |
环保管理 | 4314篇 |
综合类 | 4829篇 |
基础理论 | 8855篇 |
环境理论 | 8篇 |
污染及防治 | 8879篇 |
评价与监测 | 2418篇 |
社会与环境 | 2062篇 |
灾害及防治 | 220篇 |
2022年 | 296篇 |
2021年 | 316篇 |
2020年 | 232篇 |
2019年 | 293篇 |
2018年 | 502篇 |
2017年 | 501篇 |
2016年 | 808篇 |
2015年 | 546篇 |
2014年 | 836篇 |
2013年 | 2741篇 |
2012年 | 1024篇 |
2011年 | 1354篇 |
2010年 | 1216篇 |
2009年 | 1172篇 |
2008年 | 1432篇 |
2007年 | 1515篇 |
2006年 | 1391篇 |
2005年 | 1097篇 |
2004年 | 1169篇 |
2003年 | 1086篇 |
2002年 | 1035篇 |
2001年 | 1432篇 |
2000年 | 966篇 |
1999年 | 605篇 |
1998年 | 470篇 |
1997年 | 416篇 |
1996年 | 467篇 |
1995年 | 472篇 |
1994年 | 467篇 |
1993年 | 424篇 |
1992年 | 437篇 |
1991年 | 391篇 |
1990年 | 421篇 |
1989年 | 408篇 |
1988年 | 361篇 |
1987年 | 312篇 |
1986年 | 265篇 |
1985年 | 277篇 |
1984年 | 336篇 |
1983年 | 316篇 |
1982年 | 345篇 |
1981年 | 284篇 |
1980年 | 232篇 |
1979年 | 280篇 |
1978年 | 234篇 |
1977年 | 207篇 |
1975年 | 186篇 |
1974年 | 191篇 |
1973年 | 181篇 |
1972年 | 193篇 |
The consensus in the literature holds that female-headed households (FHHs) are more vulnerable to social and economic exclusion than male-headed households (MHHs). This paper investigates the socioeconomic determinants of household cooking fuel choices across MHHs and FHHs, using the rich Nigerian Demographic Health Survey data. Using the exogenous switching treatment effect regression (ESTER) technique, the study is able to unravel differences in socioeconomic effects of gender inequality on cooking fuel choices in Nigeria. The results validate the energy ladder hypothesis in the Nigerian case and show that the choices of dirty fuel (biomass) is more prevalent among the de-jure FHH when compared with the de-facto FHH and MHHs. Also, the probability of biomass-use among MHHs would have fallen by 1.3% if MHHs had similar socioeconomic attributes as the FHHs. In the same vain for FHHs, the probability of kerosene-use would have increased by 2%. The study observed no gender gap in kerosene-use. Thus, the established gender gap in biomass- and kerosene-use would have reduced to 6.7% and 2.8%, respectively, if the de-facto FHHs had same socioeconomic attributes as the de-jures. Considering the traditional gendered household division of labor within the households, de-jure FHHs’ energy choices may be due to limited economic opportunities that guarantees cleaner energy options.
相似文献The automobile exhausts are one of the major sources of particulate matter in urban areas and these particles are known to influence the atmospheric chemistry in a variety of ways. Because of this, the oxidation of dissolved sulfur dioxide by oxygen was studied in aqueous suspensions of particulates, obtained by scraping the particles deposited inside a diesel truck exhaust pipe (DEP). A variation in pH showed the rate to increase with increase in pH from 5.22 to about ~6.3 and to decrease thereafter becoming very slow at pH?=?8.2. In acetate-buffered medium, the reaction rate was higher than the rate in unbuffered medium at the same pH. Further, the rate was found to be higher in suspension than in the leachate under otherwise identical conditions. And, the reaction rate in the blank reaction was the slowest. This appears to be due to catalysis by leached metal ions in leachate and due to catalysis by leached metal ions and particulate surface both in suspensions. The kinetics of dissolved SO2 oxidation in acetate-buffered medium as well as in unbuffered medium at pH?=?5.22 were defined by rate law: k obs ?=?k 0?+?k cat [DEP], where k obs and k 0 are observed rate constants in the presence and the absence of DEP and k cat is the rate constant for DEP-catalyzed pathway. At pH?=?8.2, the reaction rate was strongly inhibited by DEP in buffered and unbuffered media. Results suggest that the DEP would have an inhibiting effect in those areas where rainwater pH is 7 or more. These results at high pH are of particular significance to the Indian subcontinent, because of high rainwater pH. Conversely, it indicates the DEP to retard the oxidation of dissolved SO2 and control rainwater acidification.
相似文献The land disposal of waste and wastewater is a major source of N2O emission. This is due to the presence of high concentrations of nitrogen (N) and carbon in the waste. Abattoir wastewater contains 186 mg/L of N and 30.4 mg/L of P. The equivalent of 3 kg of abattoir wastewater-irrigated soil was sieved and taken in a 4-L plastic container. Abattoir wastewater was used for irrigating the plants at the rates of 50 and 100 % field capacity (FC). Four crop species were used with no crop serving as a control. Nitrous oxide emission was monitored using a closed chamber technique. The chamber was placed inside the plastic container, and N2O emission was measured for 7 days after the planting. A syringe and pre-evacuated vial were used for collecting the gas samples; a fresh and clean syringe was used each time to avoid cross-contamination. The collected gas samples were injected into a gas chromatography device immediately after each sampling to analyse the concentration of N2O from different treatments. The overall N2O emission was compared for all the crops under two different abattoir wastewater treatment rates (50 and 100 % FC). Under 100 % FC (wastewater irrigation), among the four species grown in the abattoir wastewater-irrigated soil, Medicago sativa (23 mg/pot), Sinapis alba (21 mg/pot), Zea mays (20 mg/pot) and Helianthus annuus (20 mg/pot) showed higher N2O emission compared to the 50 % treatments—M. sativa (17 mg/pot), S. alba (17 mg/pot), Z. mays (18 mg/pot) and H. annuus (18 mg/pot). Similarly, pots with plants have shown 15 % less emission than the pots without plants. Similar trends of N2O emission flux were observed between the irrigation period (4-week period) for 50 % FC and 100 % FC. Under the 100 % FC loading rate treatments, the highest N2O emission was in the following order: week 1 > week 4 > week 3 > week 2. On the other hand, under the 50 % FC loading rate treatments, the highest N2O emission was recorded in the first few weeks and in the following order: week 1 > week 2 > week 3 > week > 4. Since N2O is a greenhouse gas with high global warming potential, its emission from wastewater irrigation is likely to impact global climate change. Therefore, it is important to examine the effects of abattoir wastewater irrigation on soil for N2O emission potential.
相似文献