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   2451篇
  免费   70篇
  国内免费   431篇
安全科学   90篇
废物处理   145篇
环保管理   222篇
综合类   730篇
基础理论   457篇
环境理论   3篇
污染及防治   927篇
评价与监测   193篇
社会与环境   142篇
灾害及防治   43篇
  2024年   3篇
  2023年   24篇
  2022年   82篇
  2021年   75篇
  2020年   46篇
  2019年   68篇
  2018年   53篇
  2017年   76篇
  2016年   102篇
  2015年   133篇
  2014年   181篇
  2013年   264篇
  2012年   201篇
  2011年   188篇
  2010年   139篇
  2009年   132篇
  2008年   188篇
  2007年   150篇
  2006年   136篇
  2005年   98篇
  2004年   92篇
  2003年   81篇
  2002年   87篇
  2001年   53篇
  2000年   34篇
  1999年   40篇
  1998年   35篇
  1997年   27篇
  1996年   32篇
  1995年   22篇
  1994年   21篇
  1993年   19篇
  1992年   15篇
  1991年   13篇
  1990年   8篇
  1989年   4篇
  1988年   5篇
  1986年   3篇
  1985年   3篇
  1983年   3篇
  1982年   3篇
  1981年   2篇
  1977年   2篇
  1975年   1篇
  1973年   1篇
  1966年   1篇
  1965年   1篇
  1964年   1篇
  1958年   1篇
  1956年   1篇
排序方式: 共有2952条查询结果,搜索用时 343 毫秒
991.
羰基硫(COS)紫外光解动力学的研究   总被引:6,自引:0,他引:6  
在185nm紫外光照射下,研究了COS体系、COS-O2体系以及COS-空气体系中COS的转化反应,并考察了光照时间、O2分压和水气对COS光解的影响.推导了COS光解速率方程,并计算了其表观量子产率,据此提出了185nm紫外光作用下COS在不同体系中的反应机理.实验表明,平流层紫外光解是COS的重要汇,也是平流层含硫气溶胶的主要来源之一.  相似文献   
992.
以小风和静风状态下连续点源的大气扩散模式为基础,采用与体源烟团的初始分布尺度相当的初始时间修正其扩散参数公式中的运行时间,从理论上导出了小风和静风状态下连续体源的大气扩散模式。该模式与现有的大气扩散模式体系完全相容,可以方便地应用于小风和静风状态下连续体源引起的地面浓度的预测计算。  相似文献   
993.
苏州市环境污染事故应急监测系统的建立与实施   总被引:4,自引:2,他引:4       下载免费PDF全文
介绍了苏州市环境污染事故应急监测系统的适用范围和基本特点,明确了领导小组、各监测小组及网络成员单位在系统中的职责,提出了系统的工作程序,建议开展应急监测能力培训,建立应急监测信息交流系统,实施例行监督检查,研制并定期更新应急监测信息管理系统,配置必要的应急监测仪器装备,加强与网络成员单位的合作,定期评审和改进应急监测系统,以保证系统的有效运行。环境污染事故应急监测实例表明,该系统在应急监测过程中发挥了良好的作用。  相似文献   
994.
基于加速度研究过山车立环轨道曲线的设计方法.分别研究向心加速度恒定的立环曲线,加速度恒定的立环曲线和以欧拉螺线为基础的立环曲线.建立三种立环曲线的方程,通过数值方法进行求解,借助Matlab计算在给定初始条件和边界条件下的轨道曲线.以加速度为评判标准来分析三种曲线的优点和缺点,最终得到以加速度为基础的立环轨道曲线设计方...  相似文献   
995.
通过对辽河油田公司有关企业开展清洁生产审核,总结出了燃料锅炉量化管理的方法。在自然对流烘干室改造、碱液浓缩炉改造、燃煤锅炉设计效率核准等实例中,该方法可昭示能耗大的"瓶颈"部位,进而为企业制定节能方案、提出具体的节能改造措施提供了科学依据。实践证明:实施锅炉量化管理是企业挖掘节能潜力的重要途径。  相似文献   
996.
Abstract: Nitrate‐nitrogen (NO3‐N) concentrations in stream water often respond uniquely to changes in inter‐annual conditions (e.g., biological N uptake and precipitation) in individual catchments. In this paper, we assess (1) how the spatial distribution of NO3‐N concentrations varies across a dense network of nonnested catchments and (2) how relationships between multiple landscape factors [within whole catchments and hydrologically sensitive areas (HSAs) of the catchments] and stream NO3‐N are expressed under a variety of annual conditions. Stream NO3‐N data were collected during two synoptic sampling events across >55 tributaries and two synoptic sampling periods with >11 tributaries during summer low flow periods. Sample tributaries drain mixed land cover watersheds ranging in size from 0.150 to 312 km2 and outlet directly to Cayuga Lake, New York. Changes in NO3‐N concentration ratios between each sampling event suggest a high degree of spatial heterogeneity in catchment response across the Cayuga Lake Watershed, ranging from 0.230 to 61.4. Variations in NO3‐N concentrations within each of the large synoptic sampling events were also high, ranging from 0.040 to 8.7 mg NO3‐N/l (March) and 0.090 to 15.5 mg NO3‐N/l (October). Although Pearson correlation coefficients suggest that this variability is related to multiple landscape factors during all four sampling events, partial correlations suggest percentage of row crops in the catchments as the only similar factor in March and October and catchment area as the only factor during summer low flows. Further, the strength of the relationships is typically lower in the HSAs of catchment. Advancing current understanding of such variations and relationships to landscape factors across multiple catchments – and under a variety of biogeochemical and hydrological conditions – is important, as (1) nitrate continues to be employed as an indicator of regional aquatic ecosystem health and services and (2) a unified framework approach for understanding individual catchment processes is a rapidly evolving focus for catchment‐based science and management.  相似文献   
997.
We sketch four possible pathways how carbon dioxide capture and storage (CCS) (r)evolution may occur in the Netherlands, after which the implications in terms of CO2 stored and avoided, costs and infrastructural requirements are quantified. CCS may play a significant role in decarbonising the Dutch energy and industrial sector, which currently emits nearly 100 Mt CO2/year. We found that 15 Mt CO2 could be avoided annually by 2020, provided some of the larger gas fields that become available the coming decade could be used for CO2 storage. Halfway this century, the mitigation potential of CCS in the power sector, industry and transport fuel production is estimated at maximally 80–110 Mt CO2/year, of which 60–80 Mt CO2/year may be avoided at costs between 15 and 40 €/t CO2, including transport and storage. Avoiding 30–60 Mt CO2/year by means of CCS is considered realistic given the storage potential represented by Dutch gas fields, although it requires planning to assure that domestic storage capacity could be used for CO2 storage. In an aggressive climate policy, avoiding another 50 Mt CO2/year may be possible provided that nearly all capture opportunities that occur are taken. Storing such large amounts of CO2 would only be possible if the Groningen gas field or large reservoirs in the British or Norwegian part of the North Sea will become available.  相似文献   
998.
Coconut, sisal and jute fibers were added as reinforcement materials in a biodegradable polymer matrix comprised of starch/gluten/glycerol. The content of fibers used in the composites varied from 5% to 30% by weight of the total polymers (starch and gluten). Materials were processed in a Haake torque rheometer (120 °C, 50 rpm) for 6 min. The mixtures obtained were molded by heat compression and further characterized. Addition of lignocellulosic fibers in the matrix decreased the water absorption at equilibrium. The diffusion coefficient decreased sharply around 5% fiber concentration, and further fiber additions caused only small variations. The thermogravimetric (TG) analysis revealed improved thermal stability of matrix upon addition of fibers. The Young’s modulus and ultimate tensile strength increased with fiber content in the matrix. The storage modulus increased with increasing fiber content, whereas tanδ curves decreased, confirming the reinforcing effect of the fibers. Morphology of the composites analyzed under the scanning electron microscope (SEM) exhibited good interfacial adhesion between the matrix and the added fibers. Matrix degraded rapidly in compost, and addition of increased amounts of coconut fiber in the matrix caused a slowdown the biodegradability of the matrix. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may be suitable.  相似文献   
999.
Long-lived species are particularly susceptible to bioaccumulation of lead in bone tissues. In this paper we gain insights into the sublethal effects of lead contamination on Egyptian vultures (Neophron percnopterus). Our approach was done on the comparison of two populations (Canary Islands and Iberian Peninsula) differing in exposures to the ingestion of lead ammunition. Blood lead levels were higher in the island population (Canary Islands range: 5.10-1780 μg L−1n = 137; Iberian Peninsula range: 5.60-217.30 μg L−1n = 32) showing clear seasonal trends, peaking during the hunting season. Moreover, males were more susceptible to lead accumulation than females. Bone lead concentration increased with age, reflecting a bioaccumulation effect. The bone composition was significatively altered by this contaminant: the mineralization degree decreased as lead concentration levels increased. These results demonstrate the existence of long-term effects of lead poisoning, which may be of importance in the declines of threatened populations of long-lived species exposed to this contaminant.  相似文献   
1000.
Background, aim, and scope  The Yunnan snub-nosed monkey is one of the most endangered primates in the world. It is experiencing a range of ongoing threats and the persisting effects of past disturbances. The prospects for this species are not very optimistic because habitat corridors are severely damaged by logging, grazing, and mining. Each group of the monkeys in different areas is facing a unique variety of threats. Based on genetic analysis, Rhinopithecus bieti should be separated into three management units for conservation, of which the Mt. Laojun management unit involves the most endangered primates. Despite the fact that the vegetation on Mt. Laojun is in a relatively pristine state, only two groups of monkeys, of a total of fewer than 300, survive in the area. With this paper, we aimed to address the capacity of the monkeys’ habitat at the study site and the possible reasons for the small populations. Materials and methods  Rapid ecological assessment based on a SPOT 5 image and field survey was used to simulate the vegetation of the whole area based on reference ecological factors of the GIS system. The vegetation map of the site was thus derived from this simulation. Based on the previous studies, the three vegetation types were identified as the suitable habitat of the monkeys. The confusion matrix-based field GPS points were applied to analyze the precision of the habitat map. Based on the map of suitable habitat of the monkeys, the utilization of the habitat and the carrying capacity were analyzed in the GIS. Results  The confusion matrix-based field GPS points were applied to the habitat analysis process, and it was found that the habitat map was 81.3% precise. Then, with the current habitat map, we found that the mixed forest currently used by the monkeys is only a very small fraction (2.65%) of the overall potential habitat of the population, while the dark conifer forest is 4.09%. Discussion  Poaching is the greatest short-term threat to this species, particularly in the southern range where local residents have a strong tradition of hunting. Quite a few individual monkeys are still trapped accidentally due to the high density of traps. These problems are hard to mitigate because it is difficult to enforce laws due to the extremely rugged terrain. Conclusions  The results show that there is a great ecological capacity of the area for the monkey’s survival and a great potential for an expansion of the monkey population at the site. Based on the current population and its geographical range, it can be estimated that the suitable habitat area defined by this study can support more monkeys, about many times the current population. Thus, at least in the Mt. Laojun Area, poaching pressure is the main factor to be responsible for the low density of Yunnan snub-nosed monkeys instead of habitat alteration. Recommendations and perspectives  Based on these results, some suggestions relating to conservation can be made: Focus conservation efforts on the current distribution area of the monkeys and create a 20 km buffer zone; design a long-term plan for the suitable habitat outside the buffer zone to set up a wildlife corridor in the long run; establish an association for the local hunters exploiting, their knowledge on the animals to promote monkey conservation and stop poaching. Also, the map derived from the study helps managers to allocate conservation resources more efficiently and enhances the overall outcomes of conservation measures.  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