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   210篇
  免费   25篇
  国内免费   21篇
安全科学   22篇
废物处理   1篇
环保管理   36篇
综合类   76篇
基础理论   51篇
污染及防治   7篇
评价与监测   8篇
社会与环境   27篇
灾害及防治   28篇
  2023年   4篇
  2022年   8篇
  2021年   8篇
  2020年   8篇
  2019年   8篇
  2018年   11篇
  2017年   7篇
  2016年   7篇
  2015年   13篇
  2014年   6篇
  2013年   20篇
  2012年   6篇
  2011年   18篇
  2010年   17篇
  2009年   15篇
  2008年   9篇
  2007年   9篇
  2006年   15篇
  2005年   10篇
  2004年   13篇
  2003年   5篇
  2002年   7篇
  2001年   2篇
  2000年   6篇
  1999年   2篇
  1998年   1篇
  1997年   2篇
  1996年   2篇
  1995年   2篇
  1994年   3篇
  1993年   2篇
  1992年   2篇
  1990年   1篇
  1989年   2篇
  1983年   2篇
  1981年   1篇
  1979年   1篇
  1972年   1篇
排序方式: 共有256条查询结果,搜索用时 109 毫秒
181.
以儒家文化为核心内涵的传统主流价值观与中国现代文学的发生、发展有着非常微妙而复杂的联系.一方面,传统主流价值观启示着现代作家在其审美活动中高张“人”的个性,从而实现对传统主流价值的反拨;另一方面又导引着作家以启蒙和救亡为主题担负起对社会的责任与义务,由此而实现对主流价值的归属.  相似文献   
182.
BACKGROUND: Potential exposure of ground troops in Vietnam to Agent Orange and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) remains controversial despite the passage of 30 years since the Vietnam War. Because of uncertainty over the serum dioxin levels in ground troops at the end of their service in Vietnam, attempts have been made to develop a methodology for characterizing exposure of ground troops in Vietnam to Agent Orange and other herbicides based upon historical reconstruction from military records. Historical information is often useful in evaluating and modeling exposure, but such information should be reasonably accurate, complete, and reliable. METHODS: This paper reviews the procedures and supporting historical information related to the spraying of herbicides in Vietnam. The historical information is classified into two categories: procedural information and operational information. Procedural information covered the process and procedures followed in spraying herbicides from US Air Force fixed wing aircraft (Operation RANCH HAND) in Vietnam, and included approval procedures for spray missions, the criteria required to conduct a mission, the control exercised by the Forward Air Controller and the Tactical Air Control Center and the characteristics of the equipment used to apply the herbicides. Operational information includes data from the RANCH HAND Daily Air Activities Reports, which included geographic locations of specific spray missions, the amount of herbicide sprayed by a specific mission, reports of battle damage to spray aircraft, reports of fighter aircraft support for aerial spray missions, and any comments, such as reasons for canceling a mission. RESULTS: Historical information demonstrates that herbicide spray missions were carefully planned and that spraying only occurred when friendly forces were not located in the target area. RANCH HAND spray missions were either not approved or cancelled if approved when there were friendly forces in the area designated for spraying. Stringent criteria had to be met before spray missions could be approved. The operational information shows that spray missions for both defoliation and crop destruction were conducted in an extremely hostile environment. Heavy 'fighter suppression' with antipersonnel ordnance was used to minimize the impact of hostile ground fire on RANCH HAND aircraft. Procedures were in place that prohibited movement of troops into sprayed areas immediately after a mission due to the possible presence of unexploded ordnance delivered by fighter aircraft supporting RANCH HAND missions. The optimal nature of the spray equipment and application procedures minimized the possibility of significant spray drift. Conclusions. Few friendly troops were sprayed by fixed wing aircraft during Operation RANCH HAND, which delivered 95% of all defoliants used in Vietnam. Similarly, few troops were sprayed during helicopter or surface-based spray operations, which constituted the remaining 5% of defoliants. Detailed policies and procedures for approval and execution of spray missions ensured that friendly forces were not located in the areas targeted for spraying. Fighter aircraft assigned to accompany each spray mission frequently suppressed much of the hostile fire with bombs and other ordnance. Confirmed clearance of the target area was necessary to avoid friendly casualties. Historical records establish that these policies and procedures were strictly followed. Exposure of troops whether from direct spraying or movement through areas recently sprayed was very unlikely. The wartime military records of troop positions and herbicide operations are valuable for some purposes, but have specific limitations in exposure reconstruction. The completeness and accuracy of the geographic data (maps used by RANCH HAND and military ground units) were dependent upon the inherent precision of the map, the accuracy with which it depicted surface features, and the completeness and accuracy of the information on which it is based. Navigation by the crew using visual orientation and reference to the map was the only means that aircrew on spray missions had for establishing their locations. A Forward Air Controller independent of Operation RANCH HAND was present at the location of each spray target immediately before and during spraying operations to verify the target location and ensure that friendly forces were clear of the target area. Anecdotal reports of direct spraying of troops in Vietnam likely reflect the RANCH HAND missions spraying insecticide for mosquito control at regular intervals from March 1967 through February 1972. Outlook. The distribution and levels of serum dioxin in RANCH HAND veterans and the US Army Chemical Corps Vietnam veterans (the unit responsible for helicopter and ground-based spray operations) are distinguishable from typical levels in the population decades after the Vietnam conflict. An exposure model similar to that proposed in the 2003 report of the Institute of Medicine's Committee on 'Characterizing Exposure of Veterans to Agent Orange and Other Herbicides Used in Vietnam' was tested in 1988 by the Centers for Disease Control and Prevention and found to be a poor predictor of absorbed dose of TCDD. Military records during the Vietnam War lack the precision to determine that troops were directly sprayed with herbicides during Operation RANCH HAND, especially given the procedures in place to ensure clearance of friendly forces from the target area and the lack of elevated serum levels of TCDD in ground troops judged to have operated in heavily sprayed areas.  相似文献   
183.
Review of environmental monitoring methods: survey designs   总被引:1,自引:0,他引:1  
During the past decade and a half, environmental monitoring programshave increased in numberand importance. Large scale environmental monitoring programs often present design difficulties because they tend to measure many(sometimes hundreds) of parameters through space and time. Thispaper reviewed and summarized one important component of environmental monitoring programs, the statistical survey design. Survey designsused for long-term monitoring programs lasting multiple (3)occasions were reviewed, paying specialattention to those published after 1985. During this review, two key components of the overall survey design were identified. The first key component wasthe membership design. Groups of population units sampled the same occasionwere called panels here, and the membership design specified which units were members of which panels. The second component was the revisit design that specified when panels were to be revisited. Membership designs varied, butsome form of simple random or systematic design was popular.Among revisit designs, four basicpatterns were found in the literature and their relative strengths andweaknesses were summarized. To efficiently discuss revisit designs, anew unified short-hand notation was proposed and adopted.  相似文献   
184.
苍洱地区居址环境的历史变迁   总被引:1,自引:0,他引:1  
根据民族学和考古学资料进行的综合研究,可将苍洱地区居址环境划为4个历史变迁时期:4000多年前的先民们居住在沿海拔2500~2200米一线的一些向阳避风的苍山台地上。海拔2200~2000米一线的苍山脚下为汉晋时期先民们的聚居点。海拔2000米左右,沿滇藏公路一线的白族村落大致在唐宋南诏大理国时期形成。海拔1975米左右,今洱海边的白族村落大多数在元明清时期形成。其趋势是从高处往低处下移,随苍山上升,洱海水位下降,利用滩地形成新的居民群。其形成的间隔时间越来越短,加强洱海保护是迫切的任务。  相似文献   
185.
从环境类学术文献看中国环境教育存在的问题   总被引:5,自引:0,他引:5  
根据我国环境科学类期刊上刊登的环境教育文献的比重和内容的调查结果来看,我国环境科学界对环境以重视程度与环境教育的重要性不成比例,环境教育研究的落后已成为制约我国环境教育可持续发展的关键问题。  相似文献   
186.
This paper evaluates the influence of different policy-related and scientific choices on the calculated regional contributions to global climate change (the “Brazilian Proposal”). Policy-related choices include the time period of emissions, the mix of greenhouse gases and different indicators of climate change impacts. The scientific choices include historical emissions and model representations of the climate system. We generated and compared results of several simple climate models. We find that the relative contributions of different nations to global climate change—from emissions of greenhouse gases alone—are quite robust, despite the varying model complexity and differences in calculated absolute changes. For the default calculations, the average calculated contributions to the global mean surface temperature increase in 2000 are about 40% from OECD, 14% from Eastern Europe and Former Soviet Union, 24% from Asia and 22% from Africa and Latin America. Policy-related choices, such as time period of emissions, climate change indicator and gas mix generally have larger influence on the results than scientific choices. More specifically, choosing a later attribution start date (1990 instead of 1890) for historical emissions, decreases the contributions of regions that started emitting early, such as the OECD countries by 6 percentage points, whereas it increases the contribution of late emitters such as Asia by 8 percentage points. However, only including the fossil CO2 emissions instead of the emissions of all Kyoto gases (fossil and land use change), increases the OECD contributions by 21 percentage points and decreases the contribution of Asia by 14 percentage points.  相似文献   
187.
重视现代信息技术的应用是专业图书馆的一个特点。本文从图书馆业务工作的自动化及文献信息服务的自动化两方面,阐述了如何利用新技术手段为科研人员服务。  相似文献   
188.
湖北省历史时期洪、旱灾害统计特征分析   总被引:10,自引:0,他引:10  
基于近2000年来的历史资料,对湖北省历史时期洪、旱灾害的统计特征及其演变规律进行了分析.结果表明:湖北省历史时期的洪、旱灾害经历了"少灾时期、增多时期与多灾时期"3个阶段,灾害出现的频率和影响的范围均呈增大趋势;洪旱灾害的空间分布呈现"洪水连江,干旱依山"的特点;洪旱灾害发生的季节集中性较强,中、大区域性洪水灾害集中在6-7月的梅雨季节,具有"梅汛"的特点,而旱灾以夏旱为多、春秋旱次之,严重的旱情多具有跨季节性的特点;总的来看,历史时期的洪旱灾害系交替进行,洪灾多于并重于旱灾.  相似文献   
189.
190.
该文基于名人文化旅游产品开发建设热潮背景下,全面剖析了名人文化旅游产品开发中存在的问题,并有针对性地提出了名人文化旅游产品开发对策.参12.  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