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   13306篇
  免费   101篇
  国内免费   1346篇
安全科学   209篇
废物处理   960篇
环保管理   1505篇
综合类   2782篇
基础理论   3753篇
环境理论   1篇
污染及防治   3228篇
评价与监测   1141篇
社会与环境   1013篇
灾害及防治   161篇
  2023年   63篇
  2022年   183篇
  2021年   125篇
  2020年   95篇
  2019年   88篇
  2018年   1592篇
  2017年   1501篇
  2016年   1337篇
  2015年   330篇
  2014年   312篇
  2013年   370篇
  2012年   778篇
  2011年   1632篇
  2010年   910篇
  2009年   861篇
  2008年   1138篇
  2007年   1438篇
  2006年   210篇
  2005年   168篇
  2004年   146篇
  2003年   204篇
  2002年   225篇
  2001年   123篇
  2000年   130篇
  1999年   132篇
  1998年   151篇
  1997年   84篇
  1996年   77篇
  1995年   74篇
  1994年   59篇
  1993年   55篇
  1992年   48篇
  1991年   15篇
  1990年   19篇
  1989年   11篇
  1988年   12篇
  1987年   5篇
  1986年   6篇
  1985年   2篇
  1984年   13篇
  1983年   10篇
  1982年   2篇
  1981年   7篇
  1979年   2篇
  1977年   2篇
  1975年   1篇
  1974年   1篇
  1972年   1篇
  1971年   2篇
  1935年   2篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
pH、溶解氧、叶绿素a之间相关性研究Ⅰ:养殖水体   总被引:6,自引:1,他引:5  
利用国内、外近20年的资料和饮用水水源地潘家口水库现场围隔实验结果,分析养殖水体中pH、溶解氧(dissolved oxygen,DO)和叶绿素a之间的相互关系.结果表明,当叶绿素a平均含量低于10μg/L时,水体交换弱的夏季和秋季养殖水域水体中pH、DO与叶绿素a无明显相关甚至无相关;水体交换强的夏季和秋季养殖水域水...  相似文献   
992.
Composting is the biological degradation and transformation of organic materials under controlled conditions to promote aerobic decomposition. To find effective ways to accelerate composting and improve compost quality, numerous methods including additive addition, inoculation of microorganisms, and the use of biosurfactants have been explored. Studies have shown that biosurfactant addition provides more favorable conditions for microorganism growth, thereby accelerating the composting process. However, biosurfactants have limited applications because they are expensive and their use in composting and microbial fertilizers is prohibited. Meanwhile, alkyl polyglycoside (APG) is considered a “green” surfactant. This study aims to determine whether APG addition into a compost reaction vessel during 28-day composting can enhance the organic matter degradation and composting process of dairy manure. Samples were periodically taken from different reactor depths at 0, 3, 5, 7, 14, 21, and 28 days. pH levels, electrical conductivity (EC), ammonium and nitrate nitrogen, seed germination indices, and microbial population were determined. Organic matter and total nitrogen were also measured.Compared with the untreated control, the sample with APG exhibited slightly increased microbial populations, such as bacteria, fungi, and actinomycetes. APG addition increased temperatures without substantially affecting compost pH and EC throughout the process. After 28 days, APG addition increased nitrate nitrogen concentrations, promoted matter degradation, and increased seed germination indices. The results of this study suggest that the addition of APG provides more favorable conditions for microorganism growth, slightly enhancing organic matter decomposition and accelerating the composting process, improving the compost quality to a certain extent.  相似文献   
993.
As an economically developing country, Turkey has very well operated integrated solid waste management applications structured on modern facilities, besides over 2,000 scattered open dump areas in the country. Integrated waste management applications seem eligible for the metropolitan cities like Istanbul and Izmit (Kocaeli). Attempts have not been encouraging for the scattered regional settlements using central storage sites due to financial shortages and received rejections from nearby settlements. Small-scale compact solid waste management systems with materials recycling and composting can be more suitable alternatives in the small-scale regional settlements. The major constituents of municipal solid waste are organic in nature and approximately a quarter of municipal solid waste is recyclable. Although paper, including cardboard, is the main constituent, the composition of recyclable waste varies strongly by the source or the type of collection point. Solid wastes need primary treatment in order to be suitable for incineration and composting. Turkey needs to give more emphasis on the usage of modern solid waste removal technologies to overcome the overgrowing solid waste disposal problems.  相似文献   
994.
The circular economy has been developing rapidly in recent years in China. A legislative system has been created to provide legal protection for the development of a circular economy, including a series of price and tax measures in the waste management area. These measures form the basic foundation for promoting better waste management under the circular economic model. Many challenges, however, remain. For instance, the legal system needs to incorporate more sophisticated science, and China lacks key waste treatment technology that could support the further development of a circular economy. There is also a need to educate the public about the concept of the circular economy and its benefits. Specific suggestions are made for the development and implementation of the circular economic model.  相似文献   
995.
Since hydrogen is a renewable energy source, biohydrogen has been researched in recent years. However, data on hydrogen fermentation by a leachate from a waste landfill as inoculum are scarce. We investigated hydrogen production using a leachate from an industrial waste landfill in Kanagawa Prefecture. The results showed no methane gas production, and the leachate was a suitable inoculum for hydrogen fermentation. The maximum H2 yield was 2.67 mol of H2 per mol of carbohydrate added, obtained at 30°C and an initial pH of 7. The acetate and butyrate production was significant when the H2 yield was higher. Oxidation–reduction potential analysis of the culture suggested that hydrogen-producing bacteria in the leachate were facultative anaerobic. Scanning electron microscope observations revealed that the hydrogen-producing bacteria comprised bacilli about 2 μm in length.  相似文献   
996.
For an effective decomposition and removal of organic halogenated compounds, a packed-bed non-thermal plasma reactor with in situ absorption of the resulting halogenated products by alkaline sorbent incorporated was proposed. In the plasma reactor, α-Al2O3 particles of 1 and 3 mm (mean particle diameter) were packed as solid dielectric medium to enhance the plasma power density in the reactor. Further, alkaline sorbent of Ca(OH)2 was doped onto the surface of α-Al2O3 particles, in order to remove halogenated products by in situ absorption with Ca(OH)2. A high-voltage and high-frequency pulsed power of −15 to 15 kV and 1 kHz was applied to the wire electrode of the plasma reactor by means of a DC power source. In the present study, as the sample of an organic halogenated compound that is most popularly used, we selected dichloromethane (CH2Cl2), and 500 ppm of the initial concentration of CH2Cl2 was fed into the reactor accompanied by air at a fixed flow rate of 500 × 10−6 m3 min−1 at room temperature. As a result, it was recognized that the amount of CH2Cl2 decomposed by non-thermal plasma in an α-Al2O3 particle bed increased with an increase in plasma input power. The ratio of decomposition of CH2Cl2 was almost 100% at 13 kV of electric power and 1 kHz frequency, and CO2, CH3Cl, COCl2, HCl, and Cl2 were observed as the major reaction products. On the other hand, when CH2Cl2 was introduced into the plasma reactor where α-Al2O3 particles doped with Ca(OH)2 were packed, the ratio of decomposition of CH2Cl2 became higher, compared to the case that α-Al2O3 particles were not doped with Ca(OH)2. Moreover, there were no halogenated by-product gases detected in the outlet gas from the reactor. As the solid reaction products, CaClOH and Ca(ClO)2·4H2O were detected on Ca(OH)2 by X-ray diffraction. From these findings, it was recognized that CH2Cl2 was decomposed more effectively without producing unwanted harmful halogenated by-products in the proposed non-thermal plasma reactor where α-Al2O3 particles doped with Ca(OH)2 sorbent were packed.  相似文献   
997.
Waste incineration is becoming increasingly necessary to tackle the rapidly rising amounts of municipal solid waste (MSW); in China many large cities are already surrounded by a girdle of landfills. Still, the not-in-my-backyard (nimby) syndrome holds strong. This attitude stems from fear of dioxins. These have been associated with incineration (‘dioxin factories’) and at times also with polyvinylchloride. In this paper this issue is analysed. China should build additional trust in MSW incineration, following promulgation of stricter emission standards, enforced by stringent controls.  相似文献   
998.
Effective handling of municipal digested sludge requires that the product cake have low water content. To this end, we investigated the change in sludge dewaterability after the addition of fly ash to municipal digested sludge, dewatering of which is difficult because of its high organic content. The performance of the dewatering is compared with that of electroosmotic dewatering (EDW) and conventional mechanical dewatering (CMD). Fly ash classified by sieving to the size of 25–75 μm and >75 μm is added to the municipal digested sludge by 10, 20, and 50 wt% by wet base. When adding fly ash particles to municipal digested sludge, dewatering efficiency improved with smaller fly ash particle size and with increase in the amount. When sludge was dewatered using an electroosmotic dewatering method, the dewatering efficiency is improved about 40% by adding fly ash of 25–75 μm particle size with 20 wt% when compared with conventional mechanical dewatering method without adding the fly ash. It is concluded that fly ash particles rich in inorganic material are helpful in the dewatering process when added to municipal digested sludge and EDW is more effective than CDW.  相似文献   
999.
Different synthesis methods were applied to determine optimal conditions for polymerization of (3S)-cis-3,6-dimethyl-1,4-dioxane-2,5-dione (l-lactide), in order to obtain poly(l-lactide) (PLLA). Bulk polymerizations (in vacuum sealed vessel, high pressure reactor and in microwave field) were performed with tin(II) 2-ethylhexanoate as the initiator. Synthesis in the vacuum sealed vessel was carried out at the temperature of 150 °C. To reduce the reaction time second polymerization process was carried out in the high pressure reactor at 100 °C and at the pressure of 138 kPa. The third type of rapid synthesis was done in the microwave reactor at 100 °C, using frequency of 2.45 GHz and power of 150 W at the temperature of 100 °C. The temperature in this method was controlled via infrared system for in-bulk measuring. The solution polymerization (with trifluoromethanesulfonic acid as initiator) was possible even at the temperature of 40 °C, yielding PLLA with narrow molecular weight distribution in a very short period of time (less than 6 h). The obtained polymers had the number-average molecular weights ranging from 43,000 to 178,000 g mol−1 (polydispersity index ranging from 1 to 3) according to the gel permeation chromatography measurements. The polymer structure was characterized by Fourier transform infrared and NMR spectroscopy. Thermal properties of the obtained polymers were investigated using thermogravimetry and differential scanning calorimetry.  相似文献   
1000.
Plasticized starch (PLS) is a renewable, degradable, and inexpensive polymer, but it suffers from poor mechanical properties. The mechanical properties can be improved by blending PLS with polyolefins, nonetheless, at high PLS content, the mechanical properties remain poor. Here we show that addition of clay can greatly improve the mechanical properties of PLS/polypropylene blends at high starch content. Unmodified and organically modified montmorillonite clays, MMT and Cloisite 30B respectively, were added to blends of glycerol-plasticized starch and polypropylene, compatibilized using maleated polypropylene. TEM indicates that MMT is well dispersed in the PLS phase of the blends, while Cloisite 30B is located both within the PLS phase as well as at the interface between PLS and PP. At high PLS content, the addition of clay increased the tensile strength and tensile modulus by an order of magnitude, while reducing the ultimate elongation only slightly. Such improvements are attributable to both the addition of clay as a reinforcing component, as well as to the change in the two phase morphology due to addition of clay.  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