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   633篇
  免费   52篇
  国内免费   139篇
安全科学   45篇
废物处理   27篇
环保管理   131篇
综合类   381篇
基础理论   81篇
污染及防治   67篇
评价与监测   29篇
社会与环境   51篇
灾害及防治   12篇
  2024年   2篇
  2023年   11篇
  2022年   18篇
  2021年   25篇
  2020年   30篇
  2019年   23篇
  2018年   30篇
  2017年   27篇
  2016年   31篇
  2015年   19篇
  2014年   27篇
  2013年   51篇
  2012年   34篇
  2011年   55篇
  2010年   31篇
  2009年   40篇
  2008年   28篇
  2007年   43篇
  2006年   34篇
  2005年   32篇
  2004年   31篇
  2003年   24篇
  2002年   26篇
  2001年   20篇
  2000年   14篇
  1999年   15篇
  1998年   15篇
  1997年   11篇
  1996年   10篇
  1995年   16篇
  1994年   5篇
  1993年   7篇
  1992年   7篇
  1991年   5篇
  1990年   3篇
  1989年   4篇
  1988年   4篇
  1987年   3篇
  1985年   1篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1980年   2篇
  1979年   2篇
  1975年   2篇
  1972年   1篇
  1971年   1篇
排序方式: 共有824条查询结果,搜索用时 296 毫秒
191.
A model is described for generating hierarchically scaled spatial pattern as represented in a thematic raster map. The model involves a series of Markov transition matrices, one for each level in the scaling hierarchy. In full generality, the model allows the transition matrices to be different at each level, potentially making available a large number of parameters for landscape characterization. The model is self-similar when the transition matrices are all equal. A method is presented for fitting the model to data that take the form of a single-resolution thematic raster map. Explicit analytic solutions are obtained for the fitted parameters. The fitting method is based on a relationship between the hierarchical transitions in the model and spatial transitions at varying distance scales in the data map, a categorical analogy of the geostatistical variogram.  相似文献   
192.
用田间长期定位试验法研究了施肥与地膜覆盖条件下玉米连作在壤质棕壤中有机质的矿化、积累和平衡。结果表明,土壤有机质矿化率在0.0107~0.0438/a之间,施肥与地膜覆盖有利于土壤有机质的积累与平衡,并加快有机质矿化;在本试验各施肥处理中土壤有机质均有所积累;在连年稳定施肥条件下,有机肥的施用会明显提高土壤有机质平衡值  相似文献   
193.
Several attempts for evaluating environmental impact of active agents allowed in organic olive farming against Bactrocera oleae have been made, but very few studies were performed contemporaneously on more than one of them. Insects were chosen as indicators because they are known to react very quickly to environmental perturbations, mainly at the community level. In fact, the coenosis is the functional unit interacting with biotic and abiotic environmental parameters. Seven taxa, known for their sensitivity to habitat alterations, were sampled and grouped in functional groups: predators and parasitoids, phytophagouses and pollinators. The coenotic balance between these two functional groups was analyzed. The study was carried out in an organic olive orchard in the municipality of Terranova da Sibari, Cosenza, Southern Italy. The tested active agents (Azadirachtin, Rotenone, Copper Oxychloride) were sprayed twice (end of September and middle October). During the treatments the population dynamics of all the taxa were knocked-down. No one tested compound seems to be harmless to the entomocoenosis, particularly on phytophagouses and pollinators. In truly organic farming it is necessary to provide natural refuge areas to beneficial insects (i.e. pest antagonists) in which no active agents are sprayed and alternative preys could be found.  相似文献   
194.
Contemporary reports on the energy and environmental benefits of bioethanol have suggested that the cellulosic ethanol is significantly more efficient. To understand the development potential of energy crops in Taiwan, the present study has assessed the resources and cost inputs for the planning, harvesting, transporting, and storing procedures of the first generation energy crops during 2007–2010 with the perspective of LCA. In addition, a field investigation focusing on rice straw, the largest agricultural waste in Taiwan, has been conducted since 2010 to obtain fundamental data.This study further analyzes the first and second-generation feedstocks from the perspective of LCA based on field investigated data. Taiwan has not yet established an ethanol plant; therefore, this study established production data by simulating the production efficiency of an economical scale using parameters obtained through production trials, and proposed an evaluation model for the energy input, GHG, and production costs of bioethanol in Taiwan. The results of this study were cross-compared with foreign literature to explore the development potential of bioethanol in Taiwan. The results indicate that based on the current cellulosic ethanol technology in Taiwan, regarding the energy balance, GHG, and production costs, is less efficient than that of the first generation bioethanol.  相似文献   
195.
多层采空区流场局部动态平衡数学建模分析   总被引:1,自引:0,他引:1  
针对大同矿区浅埋深、多煤层群、近距离、两硬条件下开采形成的多层采空区极易发生自燃的问题,进行风流流场调压分析,以达到控制采空区遗煤自燃及防止有害气体流人工作面的目标.建立了多层采空区流场调压数学模型,得出工作面风压调节的最优参数,结合工程实际分析,确定了多层采空区流场调压需要达到的预期效果.提出多层采空区流场局部动态平衡的调压方法,结合达西线性渗流定律,确定了多层采空区流场达到局部动态平衡的调压允许范围,并提出调压自动控制方法.  相似文献   
196.
碳酸盐-硫酸盐矿物强化垃圾渗滤液厌氧处理研究   总被引:1,自引:0,他引:1  
厌氧消化通常是垃圾渗滤液生物处理的首要环节,但处理效率不高.本研究尝试通过添加碳酸盐、硫酸盐等矿物来提高垃圾渗滤液的厌氧转化效率.研究共设置5组厌氧生物反应器,包括投加硬石膏、方解石、石膏、白云石的反应器及空白对照,考察添加矿物对垃圾渗滤液厌氧消化的影响.从实验结果可以看出,添加矿物的反应器中COD的去除率可以达到75%左右,而空白对照组去除率尚不足60%,添加矿物反应器甲烷产量显著高于对照.从反应器中的p H变化可以看出,矿物的添加可以提高溶液中的p H.研究结果表明,添加碳酸盐/硫酸盐矿物对垃圾渗滤液中的有机物厌氧消化过程具有重要的促进作用.  相似文献   
197.
湖北四湖流域的洪涝灾害与景观生态建设   总被引:3,自引:0,他引:3  
金卫斌  雷慰慈 《灾害学》2000,15(4):38-42
对湖北四湖流域洪涝灾害的灾变趋势进行了分析,讨论了流域的景观生态特征及其对洪涝灾害的影响,提出了若干景观生态建设的对策。  相似文献   
198.
第一届亚太区安全健成海报、录像带创作比赛即将在港举行我国有关职业安全卫生单位积极报名参赛第十三届亚太区职业安全健康组织大会及展览会将于1997年4月21日至4月26日在香港举行,这是香港职业安全健康局首次主办的大型国际性会议,预计将有二千多人参加,此...  相似文献   
199.
This article presents a method to determine the carbon content of biomass, which is formed when degrading biodegradable polymers in an aerobic aqueous test system. Existing methods for determining the carbon content of biomass (e.g., fumigazation, protein assays, dry solids) have several disadvantages when applied for polymer degradation tests. In this work a protein assay based on the Lowry method was used. It was shown that the ratio between protein and carbon content is not constant but depends on the composition of the microbial population, the growth phase, and the substrate supply. This effect was used for the method presented in this article. For determining the carbon content of biomass the absorbance obtained by the Lowry test is correlated directly with the carbon content of biomass in dependence on the duration of the degradation test. The calibration curves are obtained by a mixed population of microorganisms during the course of a degradation test.  相似文献   
200.
本文研究了我国重酸雨地区四川,贵州省湖塘溪流的水化学组成及离子平衡关系,结果表明:城郊之间水化学组成存在差异;同时,进行离子平衡衡算时,须对溶解态钙,镁进行校正,否则,会出现阴离子短缺现象,仅由钙,镁及硫酸根和弱酸根组成的简单离子平衡也是大致符合的,但其应用有一定的局限性。  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