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   1385篇
  免费   155篇
  国内免费   467篇
安全科学   123篇
废物处理   65篇
环保管理   96篇
综合类   938篇
基础理论   249篇
污染及防治   338篇
评价与监测   74篇
社会与环境   73篇
灾害及防治   51篇
  2024年   7篇
  2023年   43篇
  2022年   110篇
  2021年   104篇
  2020年   115篇
  2019年   81篇
  2018年   94篇
  2017年   98篇
  2016年   75篇
  2015年   104篇
  2014年   99篇
  2013年   135篇
  2012年   134篇
  2011年   142篇
  2010年   106篇
  2009年   93篇
  2008年   94篇
  2007年   63篇
  2006年   39篇
  2005年   25篇
  2004年   22篇
  2003年   36篇
  2002年   36篇
  2001年   31篇
  2000年   19篇
  1999年   24篇
  1998年   9篇
  1997年   11篇
  1996年   14篇
  1995年   12篇
  1994年   5篇
  1993年   9篇
  1992年   3篇
  1991年   6篇
  1990年   1篇
  1989年   3篇
  1988年   1篇
  1985年   1篇
  1983年   2篇
  1955年   1篇
排序方式: 共有2007条查询结果,搜索用时 978 毫秒
401.
This paper provides a methodology for generating forest management plans, which explicitly maximize carbon (C) sequestration at the forest-landscape level. This paper takes advantage of concepts first presented in a paper by Meng et al. (2003; Mitigation Adaptation Strategies Global Change 8:371–403) by integrating C-sequestration objective functions in existing wood supply models. Carbon-stock calculations performed in WoodstockTM (RemSoft Inc.) are based on C yields generated from volume table data obtained from local Forest Development Survey plots and a series of wood volume-to-C content conversion factors specified in von Mirbach (2000). The approach is used to investigate the impact of three demonstration forest-management scenarios on the C budget in a 110,000 ha forest in south-central New Brunswick, Canada. Explicit demonstration scenarios addressed include (1) maximizing timber extraction either by clearcut or selection harvesting for greatest revenue generation, (2) maximizing total C storage in the forest landscape and in wood products generated from harvesting, and (3) maximizing C storage together with revenue generation. The level of clearcut harvesting was greatest for scenario 1 (≥15 × 104 m3 of wood and ≥943 ha of land per harvesting period), and least for scenario 2 (=0 m3 per harvesting period) where selection harvesting dominated. Because softwood saw logs were worth more than pulpwood ($60 m−3 vs. $40 m−3) and were strategic to the long-term storage of C, the production of softwood saw logs exceeded the production of pulpwood in all scenarios. Selection harvesting was generally the preferred harvesting method across scenarios. Only in scenario 1 did levels of clearcut harvesting occasionally exceed those of selection harvesting, mainly in the removal of old, dilapidated stands early in the simulation (i.e., during periods 1 through 3). Scenario 2 provided the greatest total C-storage increase over 80 years (i.e., 14 × 106 Mg C, or roughly 264 Mg ha−1) at a cost of $111 per Mg C due to lost revenues. Scenarios 3 and 1 produced reduced storage rates of roughly 9 × 106 Mg C and 3 × 106 Mg C, respectively; about 64% and 22% of the total, 80-year C storage calculated in scenario 2. The bulk of the C in scenario 2 was stored in the forest, amounting to about 76% of the total C sequestered.  相似文献   
402.
利用吸附生物降解法处理啤酒废水,处理后的出水达到国家排放标准(GB8978-19960)。  相似文献   
403.
本文对科尔沁沙地生态环境特点、现状、生态环境恶化的主要原因及对经济、社会和环境产生的影响进行了评价,并提出了科尔沁沙地经济、社会可持续发展的对策及发展战略,为全面落实《全国生态保护纲要》提供依据。  相似文献   
404.
405.
微波诱导氧化法处理染料废水工艺技术研究   总被引:1,自引:0,他引:1  
文章以雅格素蓝BF-BR染料为处理对象,研究在负载亚铁改性活性炭存在条件下利用微波诱导氧化工艺(MIOP)处理染料雅格素蓝BF-BR模拟废水的可行性,考查并优化了处理工艺条件,研究探讨了MIOP反应机理及雅格素蓝BF-BR的脱色反应动力学.  相似文献   
406.
观音阁水库水体中氮、磷污染现状及其防治对策   总被引:1,自引:0,他引:1  
本文通过对观音阁水库的水质进行监测和调查分析,了解观音阁水库水体中氮、磷污染状况及来源。根据监测和调查结果可以判断,磷是观音阁水库中限制性营养盐。通过采取必要的防治对策和措施,控制氮、磷的浓度,不仅可以控制观音阁水库水体富营养化程度,而且还能产生一定的经济效益。  相似文献   
407.
Artificially contaminated (spiked) natural soils were solidified/stabilized using various combinations of commonly used additives, such as lime, cement, fly ash, activated carbon, and silica fume. The effectiveness of the solidification/stabilization (S/S) processes was evaluated based on experimental findings from compaction testing, unconfined compressive shear strength, and X-ray diffraction (XRD). Correlations of limited reliability between unconfined compressive strength and penetrometer and torvane measurements were derived. Results from XRD experiments indicated that certain organic contaminants (i.e., naphthalene and pyrene) might impact the S/S processes for a given combination of additives. The type and amount of organic contaminants also affected the pozzolanic reactions. Specifically, the absence or small peak intensity of pozzolanic product XRD patterns for a given combination of additives was a good indication that the type and the amount of organic contaminant present inhibited pozzolanic reactions. This phenomenon was tested and confirmed for actual field-contaminated samples.  相似文献   
408.
To demonstrate conformity of transportation projects to National Ambient Air Quality Standards in accordance with State Implementation Plans, the U.S. Environmental Protection Agency (EPA) uses intersection level of service (LOS) as one of its major criteria for screening for potential carbon monoxide (CO) hotspots. Although intersection LOS is a measure of traffic volume, signal timing, and related congestion and delay, the assigned level reflects only the computed averaged stopped delay (ASD) per vehicle at the intersection. Thus, intersections can often operate at the same LOS but produce vastly different levels of predicted CO concentrations. For example, a two-lane approach operating at LOS D will produce very different levels of CO than a five-lane approach also operating at LOS D. This study explores the effectiveness of the LOS D criterion as a screen for identifying potential CO hotspots. The study results indicate that LOS is a poor predictor of potential CO hotspots when compared to results generated with the EPA-recommended micro-scale model CAL3QHCr. To more consistently screen out those intersections that will not be identified as CO hotspots using the micro-scale models, a new criterion, equivalent red-time vehicles (ERTV), is introduced. The modeling results using ERTV suggest that it is a more robust measure for identifying potential CO hotspots, and conversely, screening out those intersections that are not likely to be identified as hotspots using micro-scale simulation results.  相似文献   
409.
采用正交实验研究了微波、超声波条件对废触媒解吸效果的影响,对比实验结果表明,1次微波2次超声波联用技术锌的洗脱率较高,回收的活性炭超过了林业局粉状活性炭二级品指标.用洗脱的醋酸锌溶液制备的磷酸锌符合防锈颜料要求.最终的废液采用电石废渣中和后达到国家废水处理三级排放标准.实现了废触媒的综合回收利用.  相似文献   
410.
绿色化学研究与生态环境保护   总被引:2,自引:0,他引:2  
赵文岩  戴树桂  韩萌 《生态环境》2004,13(3):425-428
绿色化学是指利用一系列原理来降低或消除在化工产品的设计、生产及应用中有害物质的使用和产生的科学。它致力于从源头上制止污染物的生成。文章从非传统的绿色原材料、溶剂、试剂、催化剂、安全化学品及合成方法方面综述了绿色化学的研究进展。绿色化学从材料和能源的内在性质上面对生态环境问题的挑战,在分子水平上设计结构及其相关的性质,通过减少内在的危害而使生态系统的发展具有可持续性。发展绿色化学是实现生态环境保护的途径。  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