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   33395篇
  免费   343篇
  国内免费   220篇
安全科学   813篇
废物处理   1400篇
环保管理   4260篇
综合类   6424篇
基础理论   8710篇
环境理论   15篇
污染及防治   8345篇
评价与监测   2104篇
社会与环境   1711篇
灾害及防治   176篇
  2022年   214篇
  2021年   238篇
  2018年   397篇
  2017年   405篇
  2016年   649篇
  2015年   506篇
  2014年   763篇
  2013年   2470篇
  2012年   899篇
  2011年   1302篇
  2010年   1029篇
  2009年   1125篇
  2008年   1327篇
  2007年   1410篇
  2006年   1253篇
  2005年   1072篇
  2004年   1067篇
  2003年   1034篇
  2002年   1000篇
  2001年   1244篇
  2000年   881篇
  1999年   555篇
  1998年   406篇
  1997年   443篇
  1996年   452篇
  1995年   520篇
  1994年   484篇
  1993年   444篇
  1992年   424篇
  1991年   442篇
  1990年   440篇
  1989年   413篇
  1988年   380篇
  1987年   351篇
  1986年   330篇
  1985年   320篇
  1984年   397篇
  1983年   349篇
  1982年   403篇
  1981年   335篇
  1980年   298篇
  1979年   300篇
  1978年   281篇
  1977年   239篇
  1976年   217篇
  1975年   226篇
  1974年   244篇
  1973年   230篇
  1972年   224篇
  1971年   220篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
The recent intensification of human disturbances in the Caribbean has increased the prevalence of partial mortality on coral colonies. Partial mortality can change colony size by directly shrinking colonies or by splitting colonies into fragments. A reduction in colony size can also adversely affect fecundity and fitness as internal resources shift away from reproduction toward colony maintenance. This study aimed to determine whether three Caribbean coral species, Siderastrea siderea, Montastraea faveolata, and Diploria strigosa, along the reef tract in Puerto Morelos, Mexico (20o52′N, 86o51′W), continued to dedicate resources to reproduction when colonies were fragmented to pre-maturation size. Contrary to expectations, eggs were found in colonies that were smaller than the maturation size and had been subjected to partial mortality. The continued dedication of resources toward reproduction, even in the smallest colonies, suggests that resource trade-offs away from reproduction are not as rigid as previously suggested in stressed corals.  相似文献   
983.
Earthquakes are separated from other hazards in meaning, significance, and risk perception throughout the Islamic World due to their specific focus in their own chapter or surah “al-Zalzala” (99th) in the Qur'an. Unlike earthquakes that are discussed in terms or the Judgment Day or as divine punishment or retribution against the disbelieving or hypocritical—other natural hazards like floods, tornadoes, and landslides are rarely discussed. An extensive survey of earthquake survivors and longtime residents was undertaken to better understand the perceptions of seismic risk in Agadir, Morocco where two moderate earthquakes razed the city in 1960 leaving 15,000 dead and 25,000 injured. Most of the deaths were attributed to faulty construction (along with standards and enforcement), inaddition to poor evacuation plans.

During the summer of 2002, more than 250 earthquake survivors and residents were surveyed and interviewed for their knowledge and perception of the disaster forty years before. Surveys were conducted in Arabic, French and English and included questions and Likertscaled responses including extensive interviews in the hopes of obtaining ideas of their potential quake recurrence, seismology, current construction standard policies, and local and regional planning strategies. In addition, reviews the Qur'an, Hadith and classical and contemporary tafasir texts were used to investigate the guiding passages used in Islamic discussions of “al-Zalzala”.

It was found that younger persons (<25yo) were more likely to believed that brick, mortar and cement structures were always safer and stronger during and after a tremor, regardless as to whether they are iron-reinforced or sub-standard (and hazardous) stone or brick infilled. After the 1960 disaster, speedy recovery efforts often undermined concrete construction and reinforcement techniques since such ‘rebar’ was relatively unavailable. Even today, inferior and seismically unstable construction practices are widely used.

It was found that television-watchers considered themselves less knowledgeable about earthquakes, when in fact many aspects of the1960 event and earthquakes in general, were more widely understood by this group, supporting the notion that the medium of televisionis the most widely used, efficient, and fastest mass communication and education tool.

Less-educated respondents in general tended to attribute earthquakes to divine action and retribution. All questions, however, concerning the possibility of quake recurrence frequency or magnitude caused an overwhelming refusal to answer, or with the reply of ‘Allahu a'lam’ or “God is wisest”—implying or directly stating that any attempt at earthquake forecasting, quake-related construction, advanced architectural standards for seismic safety, and/or related education was ‘haram’ or prohibited by Islam.

Further discussions with participants in Agadir indicated that any guess, awareness or prediction was in fact, fortune-telling and therefore an act forbidden by the Qur'an and Hadith.

Finally, the less educated were more likely to say that Allah protected those who were devout and considered scientific assessment as futile, forecasting as forbidden, or new construction technologies as a waste since only the ‘kafir’ (non-Muslim) or ‘munafiq’ (hypocrite) were at risk to death or injury from an earthquake. These conclusions are important toward gaining an insight of perception and risky behavior in a questionably constructed city with now more than 600,000 people 40 years later, and in a region laced by active faulting.  相似文献   
984.
985.
Air pollutants in exhaust gas produced from LP-gas (propane) were studied using both laboratory engines and vehicles. The objective of the study was both to evaluate propane as a low-pollution fuel and to provide information on adjustment of engine parameters for advantageous use of propane as a low-pollution fuel. Variables in the study were air-fuel ratio (A/F), ignition timing schedule, and ambient temperature. Data comparable to that for propane relating A/F and ambient temperature to emissions are shown for natural gas and for gasoline.  相似文献   
986.
Whereas most estimates of material damage are based on industrial surveys, the estimates produced in this study were derived from material damage experiments and ambient air quality data. Air quality data on SO2 were obtained from 200 or more monitoring sites primarily located in heavily populated or polluted areas. Material threshold damage function data were then compared with SO2 levels, and an estimate of losses, as reflected in increased maintenance and replacement costs, was determined. Estimates of the total stock of various materials in use were derived from census and industry data and allocated geographically according to population. A substantial decrease in the ambient SO2 levels, particularly in larger urban areas, has occurred during the past five years. From 1968 to 1972, the estimated amount of material damage from SO2 in the U. S. decreased from $900 million/yr to less than $100 million. During this period, the estimated percentage of man made materials exposed to SO2 levels exceeding the proposed secondary annual average standard (60 μg/m3) and primary annual average standard (80 μg/m3) in the U. S. fell respectively, from 20% to less than 5% and from more than 10% to less than 1%. Most of the present loss is attributed to corrosion damage of metallic surfaces that are normally exposed to the ambient environment.  相似文献   
987.
Abstract: Most protected areas are too small to sustain populations of wide‐ranging mammals; thus, identification and conservation of high‐quality habitat for those animals outside parks is often a high priority, particularly for regions where extensive land conversion is occurring. This is the case in the vicinity of Emas National Park, a small protected area in the Brazilian Cerrado. Over the last 40 years the native vegetation surrounding the park has been converted to agriculture, but the region still supports virtually all of the animals native to the area. We determined the effectiveness of scat‐detection dogs in detecting presence of five species of mammals threatened with extinction by habitat loss: maned wolf (Chrysocyon brachyurus), puma (Puma concolor), jaguar (Panthera onca), giant anteater (Myrmecophaga tridactyla), and giant armadillo (Priodontes maximus). The probability of scat detection varied among the five species and among survey quadrats of different size, but was consistent across team, season, and year. The probability of occurrence, determined from the presence of scat, in a randomly selected site within the study area ranged from 0.14 for jaguars, which occur primarily in the forested areas of the park, to 0.91 for maned wolves, the most widely distributed species in our study area. Most occurrences of giant armadillos in the park were in open grasslands, but in the agricultural matrix they tended to occur in riparian woodlands. At least one target species occurred in every survey quadrat, and giant armadillos, jaguars, and maned wolves were more likely to be present in quadrats located inside than outside the park. The effort required for detection of scats was highest for the two felids. We were able to detect the presence for each of five wide‐ranging species inside and outside the park and to assign occurrence probabilities to specific survey sites. Thus, scat dogs provide an effective survey tool for rare species even when accurate detection likelihoods are required. We believe the way we used scat‐detection dogs to determine the presence of species can be applied to the detection of other mammalian species in other ecosystems.  相似文献   
988.
Abstract:  The Society for Conservation Biology (SCB) can enhance conservation of biodiversity in North America by increasing its engagement in public policy. Toward this end, the North America Section of SCB is establishing partnerships with other professional organizations in order to speak more powerfully to decision makers and taking other actions—such as increasing interaction with chapters—geared to engage members more substantively in science-policy issues. Additionally, the section is developing a North American Biodiversity Blueprint, which spans the continental United States and Canada and is informed by natural and social science. This blueprint is intended to clarify the policy challenges for protecting continental biodiversity, to foster bilateral collaboration to resolve common problems, and to suggest rational alternative policies and practices that are more likely than current practices to sustain North America's natural heritage. Conservation scientists and practitioners can play a key role by drawing policy makers' attention to ultimate, as well as proximate, causes of biodiversity decline and to the ecological and economic consequences of not addressing these threats.  相似文献   
989.
Abstract: As zebra mussels (Dreissena polymorpha) continue to spread among inland lakes of the United States and Canada, there is growing interest from professionals, citizens, and other stakeholders to know which lakes are likely to be colonized by zebra mussels. Thus, we developed a classification of lake suitability for zebra mussels on the basis of measured or estimated concentrations of dissolved calcium in lake water and applied the classification to >11,500 lakes in Wisconsin and the Upper Peninsula of Michigan. The majority of lakes (58%) were classified as unsuitable (<10 mg/L Ca) for survival and reproduction of zebra mussels, 27% were identified as suitable (≥21 mg/L Ca), and 15% were classified as borderline suitable (≥10 and <21 mg/L Ca). Of the 77 inland lakes with confirmed zebra mussel records for which data on dissolved calcium were available, our method classified 74 as suitable and 3 as borderline suitable. To communicate this lake‐specific suitability information and to help prioritize regional efforts to monitor and prevent the expansion of zebra mussels and other invasive species, we developed a web‐based interface (available from http://www.aissmartprevention.wisc.edu/ ). Although we are still uncertain of how access to suitability information ultimately affects decision making, we believe this is a useful case study of building communication channels among researchers, practitioners, and the public.  相似文献   
990.
Mountain ecosystems are considered vulnerable to early impacts of climate change. Whether and how local residents of these areas perceive these changes, however, remain under-studied questions. By conducting a household survey in the Khumbu region of Nepal, this study assessed local residents’ experience-based perception of changes in climate trends and patterns, perceived risk, and attitudes towards climate issues. Multivariate cluster analysis based on residents’ climate change beliefs revealed three segments: “Cautious,” “Disengaged,” and “Alarmed.” A comparison of these segments along key psychosocial constructs of Protection Motivation Theory (PMT) revealed significant inter-segment differences in residents’ perception of severity, vulnerability, response efficacy, self-efficacy, and response cost associated with engaging in mitigating behavior. Results shed light on how residents of high elevation areas that are considered to be exposed to early impacts of climate change perceive the risk and intend to respond. These findings could also assist stakeholders working in other similar mountain ecosystems in understanding vulnerability and in working towards climate readiness.Electronic supplementary materialThe online version of this article (10.1007/s13280-020-01369-x) contains supplementary material, which is available to authorized users.  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