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   626篇
  免费   50篇
  国内免费   67篇
安全科学   62篇
废物处理   1篇
环保管理   60篇
综合类   368篇
基础理论   188篇
污染及防治   10篇
评价与监测   9篇
社会与环境   20篇
灾害及防治   25篇
  2023年   11篇
  2022年   12篇
  2021年   20篇
  2020年   18篇
  2019年   11篇
  2018年   9篇
  2017年   10篇
  2016年   17篇
  2015年   22篇
  2014年   19篇
  2013年   26篇
  2012年   26篇
  2011年   50篇
  2010年   41篇
  2009年   42篇
  2008年   35篇
  2007年   41篇
  2006年   51篇
  2005年   38篇
  2004年   36篇
  2003年   31篇
  2002年   35篇
  2001年   29篇
  2000年   34篇
  1999年   8篇
  1998年   8篇
  1997年   8篇
  1996年   3篇
  1995年   12篇
  1994年   9篇
  1993年   2篇
  1992年   7篇
  1991年   4篇
  1990年   4篇
  1989年   4篇
  1988年   1篇
  1987年   2篇
  1986年   2篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
排序方式: 共有743条查询结果,搜索用时 843 毫秒
711.
Approximately one in five subjects in Finland carries some gene defect associated with 30 diseases belonging to the Finnish disease heritage, and about one in 500 children born is affected. Almost all carriers, women and men, are unaware of their condition. Recent advances in molecular medicine have offered the possibility of population-based carrier screening for recessive disorders. We studied acceptance and attitudes to antenatal screening for aspartylglucosaminuria (AGU) and infantile neuronal ceroid lipofuscinosis (INCL). From January 1995 until December 1996 carrier tests were offered at Kuopio City Health Center, free of charge to all pregnant women attending maternity care units. Women found to be carriers of AGU (n=47) or INCL (n=14) underwent detailed genetic counseling, and their male partners were also offered the test. If both partners appeared to be carriers we offered prenatal testing (n=1). No affected fetuses were detected. Attitudes towards the gene test were elicited by means of a questionnaire. Altogether 87% of pregnant women elected to undertake the gene tests. Antenatal screening for gene defects was feasible and well accepted, and it provided an effective way to find carriers of genetic diseases and to incorporate prenatal testing into this process. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
712.
Should we continue to support publicly funded research on genetically engineered herbicide resistant crops? In Part One, I discussed the difference between science and ethics, presented a brief history of weed control, and explained three moral principles undergirding my environmentalist perspective. I then argued that unqualified endorsement (E) of the research is unjustified, as is unqualified opposition (O). In Part Two, I argue against qualified endorsement (QE), and for qualified opposition (QO).  相似文献   
713.
贵州省安龙县地质灾害发育特征及成因分析   总被引:3,自引:0,他引:3  
安龙县位于贵州省西南部,地处扬子陆块与右江造山带的过渡地带。该县境内山地、丘陵地貌发育,地形切割较强烈,地质构造、地层岩性复杂。在自然因素、人为因素的作用下,引发了多种地质灾害,使区内生态地质环境遭受严重破坏,给工农业生产和人民生命财产带来较大的损失和严重危害。本文分析研究了因降雨为主引发的滑坡、崩塌,因岩溶充水矿床疏排地下水所引起的岩溶塌陷,因矿山企业采矿形成的采空区为主引发的采空塌陷等地质灾害发育特征及成因分析。地质环境是一个复杂多变的、不稳定的开放系统,其变化就构成了地质灾害形成与发展的基础与条件。地质灾害的发育、分布、致灾程度与地质环境中的地形地貌、地质构造、岩土体地质类型、水文地质条件等因素及人类工程活动强度有着密切的关系。并针对存在的地质灾害隐患提出防治措施及建议。  相似文献   
714.
江西省潭坑铅锌(银)矿区位于北武夷铅锌银成矿带内,本文系统阐述了矿区地质和矿床特征,并对矿床的成因进行了探讨。认为本区铅锌(银)矿床,经历了火山喷发沉积和后期热液充填两大成矿期,与次火山岩体(流纹斑岩)有密切的关系,属次火山热液矿床。  相似文献   
715.
A stand-level optimisation problem formulated to determine a set of efficient thinning regimes satisfying two objectives, i.e. value production for sawlog harvesting and volume production for a pulpwood market, was demonstrated for a Eucalyptus fastigata trial in Kaingaroa Forest, New Zealand. Genetic algorithms were used to estimate the set of efficient thinning regimes (i.e. regimes that occur when it is not possible to increase the achievement of one objective without reducing another) known as a Pareto frontier. Each thinning regime specified a unique combination of initial planting density; frequency, timing and intensity of thinning; final crop number; and rotation length. Specifications for the “best” regime in the Pareto set (i.e. the one that satisfied a balanced trade-off between value and volume production) were similar to those recommended through professional judgment based on pooled long-term field observations from different eucalypt species grown throughout New Zealand. The advantage of Pareto optimality was the ability of not only identifying a unique thinning regime, but equally efficient regimes each providing a different combination of value and volume production. Research on this approach has the potential of being applied to other forest sites, providing there is sufficient re-measurement data to reflect stand growth dynamics.  相似文献   
716.
Advances in electronic integration and radio communication have led to the emergence of a new kind of safety systems, i.e. Wireless Sensor Network (WSN). This network-based safety-related system is becoming more and more present in the domain of safety due to its easy deployment. It does not need a wire infrastructure and its range of applications is wide. Usually, such a system is composed of various nodes (sensors) collaborating to monitor a targeted phenomenon. In most cases, nodes are battery powered and this is the weakness of the system makes it necessary to design an energy saving policy. The present paper gives a dependability viewpoint of such a system. A modeling framework is suggested integrating the interdependency of the components. Stochastic Petri nets are used to implement this model and two heuristics to schedule component activity. The first is based on the proposed importance measures, the second on a multi-objective genetic algorithm. The aim is to conserve energy and so to extend WSN dependability.  相似文献   
717.
随着民航运输业的发展,航班密度不断增加,相邻停机位间推出冲突概率不断增加。为合理分配大型繁忙机场停机位,兼顾安全与效率,建立基于运行安全的停机位分配问题优化模型。在模型中加入约束条件以避免潜在的推出冲突,以及考虑将重要航班优先分配到指定的旅客行走距离较短的停机位,来提高旅客的整体满意度。通过分析机位分配特点,选择性能比较优越的遗传算法进行求解。最后用实际算例进行验证,得到停机位分配甘特图以及算法收敛曲线。从结果中可以看到,停机位分配比较合理,算法收敛性能良好。就整体而言,达到了预期的要求。  相似文献   
718.
基于改进VRP模型的危险品配送路径优化及其求解研究   总被引:1,自引:0,他引:1  
危险品道路运输高风险性,一直受到人们的广泛关注。危险品道路运输路径优化的研究,对于降低运输风险具有十分重要的意义。本文针对危险品运输配送过程中的路径优化问题,提出综合考虑道路运输的风险和费用两方面指标改进VRP模型路径优化目标,并设计遗传算法对改进模型进行了求解。最后通过实例进行了验证。结果表明:用遗传算法对改进VRP模型的求解结果与实际分析结果相符。因此,改进VRP模型及其遗传算法求解设计可以应用于危险品运输的路径优化分析。  相似文献   
719.
Abstract Stability and accuracy of retrieving the aerosol size-distribution by using the linear-regression (LR), genetic algorithm (GA), and annealing genetic algorithm (AGA) were studied in detail. It was found that by using the AGA, retrieval results are quite stable and accurate; using the GA, stability and accuracy of the retrieval results decreased mildly but were still acceptable; and using the LR, retrieval results were too unstable to be acceptable. This conclusion is verified by both of the numeric simulation and the experiment.  相似文献   
720.
An appropriate logistics network is an important element of the infrastructure of any product recovery company. Small and medium enterprises (SMEs) constitute a major fraction of the product recovery industry with a different business objective and scale of operation from those of original equipment manufacturers. This paper addresses the network design issues for SMEs involved in product recovery activities. A mathematical formulation is presented in an SME context and a subsequent simulation model is developed. A genetic algorithm approach is presented for optimising the network for a single product scenario.  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