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   3771篇
  免费   310篇
  国内免费   628篇
安全科学   483篇
废物处理   263篇
环保管理   650篇
综合类   1928篇
基础理论   679篇
环境理论   5篇
污染及防治   295篇
评价与监测   199篇
社会与环境   154篇
灾害及防治   53篇
  2024年   12篇
  2023年   41篇
  2022年   86篇
  2021年   122篇
  2020年   154篇
  2019年   125篇
  2018年   102篇
  2017年   134篇
  2016年   170篇
  2015年   180篇
  2014年   247篇
  2013年   286篇
  2012年   327篇
  2011年   343篇
  2010年   288篇
  2009年   234篇
  2008年   190篇
  2007年   254篇
  2006年   244篇
  2005年   192篇
  2004年   138篇
  2003年   145篇
  2002年   112篇
  2001年   108篇
  2000年   79篇
  1999年   94篇
  1998年   49篇
  1997年   40篇
  1996年   28篇
  1995年   27篇
  1994年   27篇
  1993年   22篇
  1992年   21篇
  1991年   11篇
  1990年   15篇
  1989年   4篇
  1987年   3篇
  1986年   4篇
  1985年   3篇
  1984年   6篇
  1983年   6篇
  1982年   3篇
  1981年   5篇
  1979年   5篇
  1978年   4篇
  1974年   1篇
  1973年   4篇
  1972年   2篇
  1971年   6篇
  1970年   1篇
排序方式: 共有4709条查询结果,搜索用时 31 毫秒
101.
The purpose this study was to improve operational planning and management of national parks in Turkey to balance conservation use and sustainable management. Souksu National Park (SNP) was chosen as the study area. The data were obtained from interviews of 182 visitor groups (in total, 819 people) and analyzed using correlation, factor, discriminant, and regression analyses. It was found that the most important factors affecting operational planning and management of SNP are (1) travel cost, (2) visitor welfare level, (3) intensity of use, (4) size of visitor group, (5) type of recreational demand. The main source of visitors to SNP is from a zone within a 0–90-km radius. This region comprised 53.85% of total visitors to the park. The capital of Turkey (Ankara) is the most important source of visitors from within this zone. The optimum activity mix in SNP is also determined. Picnicking, viewing the scenery, and nature walks or trekking comprised the main uses of the park. It is anticipated that these findings will help to improve operational planning and sustainable management of the national park and the environment.  相似文献   
102.
李艳丰 《安全》2019,40(6):72-75,79
本文根据采油厂生产过程风险特点,以生产单元为对象,通过建立全员参与的HSE监督检查体系,实现对采油厂HSE监督检查标准的统一规范,利用开发的HSE监督检查信息集成平台,创建完成采油厂HSE监督检查管理系统。在大庆油田第五采油厂的应用实践显示,其能为采油厂带来巨大的风险管理效益,是全面落实直线与属地HSE责任的有效载体。对于采油厂有效实施HSE监督检查具有重大意义,是HSE管理制度的一种创新。  相似文献   
103.
张轩豪 《安全》2019,40(4):69-71
论文结合现有文献分析了大学校园存在周边环境复杂、学生安全意识薄弱、未能落实安防制度和安全责任、安全设备运用不足等问题,提出大学校园的安全工作应遵循人防与技防相结合的原则,建议通过安全人防的岗位责任制、培训机制、安保部门和公安机关联动机制、奖励机制,以及技防的安防设备配置全面规划、意外安全事故风险防范、安防设备和技术的自主创新等方式,来改善大学校园的安全水平。  相似文献   
104.
The causes of species rarity are of critical concern because of the high extinction risk associated with rarity. Studies examining individual rare species have limited generality, whereas trait‐based approaches offer a means to identify functional causes of rarity that can be applied to communities with disparate species pools. Differences in functional traits between rare and common species may be indicative of the functional causes of species rarity and may therefore be useful in crafting species conservation strategies. However, there is a conspicuous lack of studies comparing the functional traits of rare species and co‐occurring common species. We measured 18 important functional traits for 19 rare and 134 common understory plant species from North Carolina's Sandhills region and compared their trait distributions to determine whether there are significant functional differences that may explain species rarity. Flowering, fire, and tissue‐chemistry traits differed significantly between rare and common, co‐occurring species. Differences in specific traits suggest that fire suppression has driven rarity in this system and that changes to the timing and severity of prescribed fire may improve conservation success. Our method provides a useful tool to prioritize conservation efforts in other systems based on the likelihood that rare species are functionally capable of persisting.  相似文献   
105.
This paper outlines a complete review on modifications made on the absorber plate of solar air heaters in order to improve the turbulence and heat transfer rate, thereby efficiency. Corrugated sheets, fins, extended surfaces, wire mesh, porous medium, etc., are a few of the modifications used. Most of such alterations in the absorber plate resulted with an increase in efficiency but associated with drawback of increased pumping power due to raising friction factor. Pumping power is considered here as a predominant comparison parameters of various solar air heaters with different absorber plate in terms of effective efficiency.  相似文献   
106.
为了解决移动变电站低压侧为变频器供电时漏电保护装置误动的问题,提出了基于傅式算法的附加直流原理漏电保护新方法。通过理论分析和MATLAB/Simulink仿真,研究了具有变频器的矿井低压供电系统附加直流原理漏电保护,提出由傅式算法分解出采样电压直流分量以反映电缆绝缘水平的保护方法;同时分析了其他因素对直流分量的影响。研究结果表明:变频器对传统附加直流保护整定值有较大影响,易造成漏电保护装置误动且无法实现电缆的在线绝缘监测;所提出的直流分量法能准确测量电缆对地绝缘电阻,且可消除电缆分布电容、变频器载波频率、变频器输出频率等其他因素的干扰;采用该漏电保护方法,可承受变频器投入时对采样电压造成的较大冲击,不必在启动期间解除漏电保护装置,能够消除在此期间存在的人身触电安全隐患。  相似文献   
107.
Since the first product became commercially available in 1995, biotechnology has become the fastest growing crop technology, dominating large shares of the global agricultural market. The development of biotechnology, however, has given rise to questions regarding human and ecological safety, culminating in local and global political battles. While researchers interested in biotech politics have focused on areas such as media framing, social movements, and campaign work, less attention has been paid to how the industry has historically promoted and legitimized this swift proliferation. In this study, we conduct a discourse analysis of documents available on live and archived websites to discern the legitimation strategies employed by one important corporate actor, Monsanto. Findings show that for nearly two decades, Monsanto consistently employed discursive resources that concealed details about actors and action, reflected trends among experts in global sustainability discourse, and reshaped narratives to promote itself, products, and biotechnology in general.  相似文献   
108.
城市电力供应系统与城市公共安全关系紧密,文章分析了导致城市电力供应系统故障或事故的主要风险因素、事故类型及其风险程度,建立了城市电力供应系统公共安全风险评估体系。利用建立的风险评估体系,对某市电力供应系统的安全性进行了风险评估,同时验证了该体系在城市电力供应系统风险评估中的良好适用性。  相似文献   
109.
Abstract: Parks are cornerstones of conservation; and non‐native invasive species drive extensive changes to biological diversity in parks. Knowing this, national park staff at Lake Mead National Recreation Area in the southwestern United States had a program in place for early detection of the non‐native, invasive quagga mussel (Dreissena rostriformis bugensis). Upon finding the mussel in January 2007, managers moved quickly to access funding and the best available science to implement a response. Managers considered four options—doing nothing, closing the park, restricting movement on the lakes, and educating and enforcing park visitors—and decided to focus on education and enforcing existing laws. Nonetheless, quagga spread throughout the park and soon began to appear throughout the western United States. I examined why efforts to control the expansion failed and determined the general lessons to be learned from this case. Concentrating human visitation on the lakes through land‐use zoning opened a pathway for invasion, reduced management options, and led to the rapid spread of quagga. To reconcile competing mandates to protect nature and provide recreation, zoning in parks has become a common practice worldwide. It reduces stress on some areas of a park by restricting and thus concentrating human activity in particular areas. Concentrating the human activity in one area does three things: cements pathways that repeatedly import and export vectors of non‐native invasive species; creates the disturbed area necessary to enable non‐native invasive species to gain a foothold; and, establishes a source of invasions that, without appropriate controls, can quickly spread to a park's wilderness areas.  相似文献   
110.
The comprehensive control efficiency for the formation potentials(FPs) of a range of regulated and unregulated halogenated disinfection by-products(DBPs)(including carbonaceous DBPs(C-DBPs), nitrogenous DBPs(N-DBPs), and iodinated DBPs(I-DBPs)) with the multiple drinking water treatment processes, including pre-ozonation, conventional treatment(coagulation–sedimentation, pre-sand filtration), ozone-biological activated carbon(O_3-BAC) advanced treatment, and post-sand filtration, was investigated. The potential toxic risks of DBPs by combing their FPs and toxicity values were also evaluated.The results showed that the multiple drinking water treatment processes had superior performance in removing organic/inorganic precursors and reducing the formation of a range of halogenated DBPs. Therein, ozonation significantly removed bromide and iodide,and thus reduced the formation of brominated and iodinated DBPs. The removal of organic carbon and nitrogen precursors by the conventional treatment processes was substantially improved by O_3-BAC advanced treatment, and thus prevented the formation of chlorinated C-DBPs and N-DBPs. However, BAC filtration leads to the increased formation of brominated C-DBPs and N-DBPs due to the increase of bromide/DOC and bromide/DON.After the whole multiple treatment processes, the rank order for integrated toxic risk values caused by these halogenated DBPs was haloacetonitriles(HANs)》haloacetamides(HAMs) haloacetic acids(HAAs) trihalomethanes(THMs) halonitromethanes(HNMs) 》I-DBPs(I-HAMs and I-THMs). I-DBPs failed to cause high integrated toxic risk because of their very low FPs. The significant higher integrated toxic risk value caused by HANs than other halogenated DBPs cannot be ignored.  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