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   261篇
  免费   39篇
  国内免费   20篇
安全科学   94篇
废物处理   10篇
环保管理   44篇
综合类   99篇
基础理论   21篇
污染及防治   16篇
评价与监测   16篇
社会与环境   5篇
灾害及防治   15篇
  2024年   1篇
  2023年   1篇
  2022年   5篇
  2021年   5篇
  2020年   10篇
  2019年   6篇
  2018年   6篇
  2017年   12篇
  2016年   9篇
  2015年   12篇
  2014年   16篇
  2013年   12篇
  2012年   25篇
  2011年   24篇
  2010年   13篇
  2009年   19篇
  2008年   7篇
  2007年   20篇
  2006年   15篇
  2005年   16篇
  2004年   20篇
  2003年   12篇
  2002年   10篇
  2001年   7篇
  2000年   4篇
  1999年   9篇
  1998年   3篇
  1997年   5篇
  1996年   3篇
  1994年   2篇
  1993年   2篇
  1992年   3篇
  1988年   4篇
  1987年   1篇
  1981年   1篇
排序方式: 共有320条查询结果,搜索用时 31 毫秒
121.
为应对民航突发情况,保障民航运行安全,提出应急调度这一概念。阐述常规情况下航班调度基本模型,分析其在应急情况下的弊端。引入机会约束,构建应对突发状况的应急调度模型。研究兼顾航空公司成本、航班运行安全及旅客随机需求的机型分配问题(FAP)模型和机组排班问题(CSP)模型。比较混合智能算法、隐枚举法、等价转化法的优缺点及适用度。根据案例数据,使用Matlab软件编程,并采用随机模拟与粒子群(PSO)算法相结合的智能算法对模型求解。结果表明,机会约束规划模型在考虑随机因素的情况下,比基本模型更符合实际动态环境。  相似文献   
122.
目前矿山空区探测方法众多,但缺乏对其进行优化选择的分析模型。为了提高特定条件下空区探测方法选择的科学性、合理性,采用网络分析法(ANP)将决策问题分解成控制层和网络层。就这些层中的元素而言,用一种标度对人的主观判断进行客观量化后,对其实施定性、定量分析。综合考虑空区探测方法的技术、经济、人机设计及环境指标,构建空区探测方法综合评价体系,确定各判断准则间的相互影响关系,建立空区探测方法优选决策问题的ANP结构,借助Super Deci-sions软件计算参选方法基于各影响因素的综合优先权,从而确定适用于特定条件下的空区探测方法。结果表明,该模型能够随着工作环境的改变而计算影响因素优先权,使空区探测方法根据工作环境的改变而调整。  相似文献   
123.
根据KR搅拌式铁水脱硫的工艺流程、设备及操作特点,对铁水脱硫自动控制系统软件进行编制,并对软件调试中出现的问题加以解决,确保系统安全、可靠、高效运行。  相似文献   
124.
介绍了应用挪威DNV船级社SESAM软件进行海上平台导管架结构的评估方法和程序,并得出评估结论.  相似文献   
125.
气溶胶采样头在无人机上安装位置的模拟   总被引:1,自引:0,他引:1       下载免费PDF全文
利用流体力学软件CFD对固定翼无人机在海拔1000m高处以30m/s速度飞行时采样头的最佳安装位置进行了模拟.首先利用ICEM CFD前处理软件对无人机模型进行了网格划分;然后利用FLUENT软件及其中的DPM模型先后对气相(连续相)和颗粒相(离散相)分别进行了数值模拟,最后用DPM模型模拟了从速度入口方向以30m/s速度释放粒径为1,2.5,10μm的颗粒物,由颗粒物的轨迹图得到了颗粒物在机身周围的阴影区和密集区厚度.得到主要结论如下:对于本研究中的无人机,在海拔1000m高处,采集PM1,PM2.5,PM10时的气溶胶采样头的最佳安装位置为机身下部距机头距离约42~75cm,采样头探头距机身下部壁面的距离分别应大于4,4,4.3cm,但不超过26cm(机身下部距地面距离).  相似文献   
126.
The prosperity and well-being of human societies relies on healthy ecosystems and the services they provide. However, the biodiversity crisis is undermining ecosystems services and functions. Vultures are among the most imperiled taxonomic groups on Earth, yet they have a fundamental ecosystem function. These obligate scavengers rapidly consume large amounts of carrion and human waste, a service that may aid in both disease prevention and control of mammalian scavengers, including feral dogs, which in turn threaten humans. We combined information about the distribution of all 15 vulture species found in Europe, Asia, and Africa with their threats and used detailed expert knowledge on threat intensity to prioritize critical areas for conserving vultures in Africa and Eurasia. Threats we identified included poisoning, mortality due to collision with wind energy infrastructures, and other anthropogenic activities related to human land use and influence. Areas important for vulture conservation were concentrated in southern and eastern Africa, South Asia, and the Iberian Peninsula, and over 80% of these areas were unprotected. Some vulture species required larger areas for protection than others. Finally, countries that had the largest share of all identified important priority areas for vulture conservation were those with the largest expenditures related to rabies burden (e.g., India, China, and Myanmar). Vulture populations have declined markedly in most of these countries. Restoring healthy vulture populations through targeted actions in the priority areas we identified may help restore the ecosystem services vultures provide, including sanitation and potentially prevention of diseases, such as rabies, a heavy burden afflicting fragile societies. Our findings may guide stakeholders to prioritize actions where they are needed most in order to achieve international goals for biodiversity conservation and sustainable development.  相似文献   
127.
The outcome of analyses that prioritize locations for conservation on the basis of distributions of species, land cover, or other elements is influenced by the spatial resolution of data used in the analyses. We explored the influence of data resolution on prioritization of Finnish forests with Zonation, a software program that ranks the priority of cells in a landscape for conservation. We used data on the distribution of different forest types that were aggregated to nine different resolutions ranging from 0.1 × 0.1 km to 25.6 × 25.6 km. We analyzed data at each resolution with two variants of Zonation that had different criteria for prioritization, with and without accounting for connectivity and with and without adjustment for the effect on the analysis of edges between areas at the project boundary and adjacent areas for which data do not exist. Spatial overlap of the 10% of cells ranked most highly when data were analyzed at different resolutions varied approximately from 15% to 60% and was greatest among analyses with similar resolutions. Inclusion of connectivity or edge adjustment changed the location of areas that were prioritized for conservation. Even though different locations received high priority for conservation in analyses with and without accounting for connectivity, accounting for connectivity did not reduce the representation of different forest types. Inclusion of connectivity influenced most the outcome of fine-resolution analyses because the connectivity extents that we based on dispersal distances of typical forest species were small. When we kept the area set aside for conservation constant, representation of the forest types increased as resolution increased. We do not think it is necessary to avoid use of high-resolution data in spatial conservation prioritization. Our results show that large extent, fine-resolution analyses are computationally feasible, and we suggest they can give more flexibility to implementation of well-connected reserve networks.  相似文献   
128.
基于OpenFOAM的城市街区毒气扩散模拟   总被引:1,自引:0,他引:1       下载免费PDF全文
为了对毒气扩散过程进行及时、有效的模拟,将开源计算流体动力学软件OpenFOAM与PISO算法(pressure implicit with splitting of operators,压力隐式算子分割算法)相结合,进行城市街区毒气扩散模拟研究. 将SIMPLE(semi-implicit method for pressure linked equations,压力耦合方程组的半隐式算法)与PISO算法进行了对比,指出以PISO算法为基础的数值模拟在城市街区这类大范围毒气扩散模拟中具有容差性强、计算较为稳定等优点. 以福州大学怡山校区为扩散区虚拟地理环境,选用氯气为假定毒气,利用OpenFOAM对氯气的扩散传播过程进行了模拟, 并与商用软件FLUENT在相同条件下的ρ(Cl2)模拟结果进行了对比. 结果表明,结合PISO算法的OpenFOAM能够较好地完成复杂虚拟地理环境下的毒气扩散过程模拟,其ρ(Cl2)模拟结果与FLUENT模拟结果的平均偏差小于5%,但在计算效率上却提高了41.89%.   相似文献   
129.
本文系统地介绍了有关水环境主要的形态模型、表面络合模型、点源和非点源污染模型及其计算机模型软件,并着重阐述了生态模型的发展及应用等  相似文献   
130.
针对原有的基于模糊综合评价法建立的油库安全度评估模型存在的不足,结合油库安全管理现状,从油库安全评估的内容、方法、实现形式等方面进行了油库安全度评估体系的完善,并以软件形式实现。通过实际应用,表明所建立的油库安全评估模型合理可行,评估软件可操作性强、实用。  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