首页 | 官方网站   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   561篇
  免费   3篇
  国内免费   17篇
环境安全   581篇
  2023年   11篇
  2022年   17篇
  2021年   28篇
  2020年   10篇
  2019年   6篇
  2018年   14篇
  2017年   22篇
  2016年   14篇
  2015年   11篇
  2014年   19篇
  2013年   63篇
  2012年   21篇
  2011年   33篇
  2010年   31篇
  2009年   29篇
  2008年   24篇
  2007年   26篇
  2006年   32篇
  2005年   23篇
  2004年   19篇
  2003年   16篇
  2002年   10篇
  2001年   15篇
  2000年   8篇
  1999年   8篇
  1998年   5篇
  1997年   3篇
  1996年   7篇
  1995年   3篇
  1994年   7篇
  1993年   3篇
  1992年   4篇
  1991年   3篇
  1990年   4篇
  1989年   4篇
  1988年   2篇
  1986年   5篇
  1985年   1篇
  1983年   1篇
  1982年   3篇
  1981年   2篇
  1978年   1篇
  1973年   3篇
  1956年   2篇
  1955年   1篇
  1938年   1篇
  1933年   1篇
  1931年   2篇
  1926年   1篇
  1920年   1篇
排序方式: 共有581条查询结果,搜索用时 15 毫秒
1.
A case of Meckel—Gruber syndrome was diagnosed by embryoscopy at 10 menstrual weeks, allowing for early termination of pregnancy. Post-mortem examination confirmed the presence of polydactyly and bilateral cystic lesions of the mesonephros and metanephros. Both the forming nephrons and the collecting ducts were involved in the formation of renal cysts.  相似文献   
2.
引言 人类活动导致了水资源的过度开发和污染.<水框架指令>(WFD,2000/60/EG)就是为确保水资源的可持续利用、确保水资源的效果而拟定的.为达到WFD所概括的目标,一项明显的内容是:水资源的管理中要有各利益方的参与.把各利益方吸纳进来是一个重要步骤,可确保流域管理计划的发展考虑当地的经验,并且考虑这些计划对当地利益的影响.  相似文献   
3.
This paper presents an economic study of a novel thermal fry-drying technology which transforms sewage sludge and recycled cooking oil (RCO) into a solid fuel. The process is shown to have significant potential advantage in terms of capital costs (by factors of several times) and comparable operating costs. Three potential variants of the process have been simulated and costed in terms of both capital and operating requirements for a commercial scale of operation. The differences are in the energy recovery systems, which include a simple condensation of the evaporated water and two different heat pump configurations. Simple condensation provides the simplest process, but the energy efficiency gain of an open heat pump offset this, making it economically somewhat more attractive. In terms of operating costs, current sludge dryers are dominated by maintenance and energy requirements, while for fry-drying these are comparatively small. Fry-drying running costs are dominated by provision of makeup waste oil. Cost reduction could focus on cheaper waste oil, e.g. from grease trap waste.  相似文献   
4.
The removal of heavy metals from wastewater has become a global challenge, which demands the continuous study of efficient and low-cost treatment alternatives such as adsorption. In this research, the removal of zinc was evaluated using batch adsorption processes with nonconventional materials such as graphene oxide (GO), magnetite (MG), and their composites (GO:MG), formulated with three weight ratios (2:1, 1:1, and 1:2). Graphene was synthesized by the modified Marcano method, using pencil lead graphite as a precursor. MG and the composites were synthesized by chemical coprecipitation of ferrous sulfate and ferric chloride. The materials were characterized by Raman and Fourier transform infrared spectroscopies, scanning electron microscopy, X-ray diffraction, and the Brunauer–Emmett–Teller method to determine the functional groups, microstructural and morphological characteristics, and specific surface area. Batch adsorption tests were carried out to optimize the adsorbent dose and contact time with zinc solutions of 10 ppm. Zinc adsorption reached equilibrium at 2 h, with an optimal dose between 0.25 and 1.0 g/L. The maximum zinc removal efficiencies/adsorption capacities were 98.6%/165.6, 83.4%/47.6, 83.5%/21.9, 72.8%/19.9, and 82.2%/9.25 mg/g using GO, 2GO:1MG, 1GO:1MG, 1GO:2MG, and MG, respectively. Furthermore, the analysis of the isotherm and adsorption kinetics models determined that the adsorption processes using MG and the composites fit the Sips and pseudo-second-order models.  相似文献   
5.
Environmental Science and Pollution Research - The rice husk ash (RHA) was used as an alternative source of silica for the synthesis of the functionalized mesoporous material, which was used in the...  相似文献   
6.
Remotely sensed imageries were used to analyze the response of desert vegetation to physiographic factors and accumulated precipitation in drier and wetter years within a region of >16,500 km2 sampled with 5,000 random pixels of 30 m. Vegetation development was indexed by the annual maximum values for greenness (SAVI) and canopy water content (NDII). Precipitation was interpolated from the 0.25° grid of the Tropical Rainfall Measurement Mission satellite-based estimates, showing a regional average of ~55 mm in the wetter year. The vegetation indices were only weakly related to total precipitation, often in a negative sense. Terrain factors that most often affected the vegetation indices, in multiple regression models, were Topographic Wetness Index, elevation, and slope gradient; these often had different signs for SAVI and for NDII. Models for NDII on intrusive igneous rocks gave better results than on extrusive igneous rocks. The strongest patterns in vegetation development were the contrast among Pacific coast, Cordillera, and Gulf coast subregions and the generally stronger results for NDII than SAVI.  相似文献   
7.
A study of trace metal (TM) contamination was conducted at Lake Tonga (Algeria), a site surrounded by several indirect contamination point sources such as an abandoned mine and steelworks. Studying two sampling sites over four seasons, we were able to depict the spatial and temporal variability of TM contamination in the lake. Among the seven TM examined (Pb, Cd, Fe, Zn, Ni, Cu, and Cr), only Fe, Pb, and Cd showed concentrations significantly higher than the site’s geological background. The contamination index (sediment concentration/background concentration) calculated for these three TM (Cd = 1.9?±?1.6, Fe = 6.8?±?1.8, and Pb = 3.3?±?2.6) clearly indicated anthropogenic contamination. Sediment TM contamination differed both between sampling sites and seasons despite environmental variables (e.g., oxygen and pH) being similar, thus suggesting different TM contamination sources. Fe contamination was high at the two sampling sites and over all studied seasons, possibly indicating general lake-scale Fe contamination, probably related to atmospheric deposition of steelworks emissions both on the lake and within the watershed. Lake tributaries were further suspected of channeling Fe contamination from the watershed into the lake. On the other hand, the sampling site close to the outlet was especially rich in Cd and Pb typically reflecting contamination by mine wastes. The indirect connection between the abandoned mine and the lake indicates that runoff of mine leachates through groundwater was likely a candidate in explaining the specificity of the TM contamination in this part of the lake. This study provides insights for management of TM contamination by addressing both spatial and temporal variability within the lake as well as differences in contamination sources.  相似文献   
8.
The aim of this work is to study the colour and chemical modifications of the surfaces in chestnut wood samples as a consequence of irradiating in a controlled environment. The changes were investigated by a new analytical approach by combining traditional techniques such as reflectance spectrophotometry in the visible range and Fourier transform infrared spectroscopy with new hyperspectral imaging, in order to obtain forecast models to describe the phenomenon. The statistical elaboration of the experimental data allowed to validate the measurements and to obtain models enabling to relate the investigated parameters; the elaboration of the hyperspectral images by chemometric methods allowed for studying the changes in the reflectance spectra. A result of great importance is the possibility to correlate the oxidation of wood chemical components with the colour change in a totally non-invasive modality. This result is particularly relevant in the field of cultural heritage and in general in the control processes of wooden materials.  相似文献   
9.
A full-scale sequencing batch reactor (SBR) system was evaluated for its ability to remove carbon and nitrogen from swine wastewater. The SBR was operated on four, six-hour cycles each day, with each cycle consisting of 4.5 hours of “React,” 0.75 hours of “Settling”, 0.75 hours for “Draw” and “Fill.” Within each cycle, an amount of wastewater equivalent to about 5% of the reactor volume (5,500 litres) was removed and added. The SBR system was able to remove 82% of biochemical oxygen demand (BOD) and more than 75% of nitrogen. Even though the SBR effluent, with an average effluent BOD5 of about 588 mg L? 1, did not meet the discharge criteria, it enabled a reduction of the land base required for land application of swine wastewater by about 75%. Results indicated that the SBR system was a viable method for the treatment of swine wastewater.  相似文献   
10.
The microwave enhanced advanced oxidation process (MW/H2O2-AOP) was used to treat separated solid dairy manure for nutrient release and solids reduction. The MW/H2O2-AOP was conducted at a microwave temperature of 120°C for 10 minutes, and at three pH conditions of 3.5, 7.3 and 12. The hydrogen peroxide dosage at approximately 2 mL per 1% TS for a 30 mL sample was used in this study, reflecting a range of 0.53–0.75 g H2O2/g dry sludge. The results indicated that substantial quantities of nutrients could be released into the solution at pH of 3.5. However, at neutral and basic conditions only volatile fatty acids and soluble chemical oxygen demand could be released. The analyses on orthophosphate, soluble chemical oxygen demands and volatile fatty acids were re-examined for dairy manure. It was found that the orthophosphate concentration for untreated samples at a higher % total solids (TS) was suppressed and lesser than actual. To overcome this difficulty, the initial orthophosphate concentration had to be measured at 0.5% TS.  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-23

京公网安备 11010802026262号