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   67篇
  免费   0篇
安全科学   1篇
环保管理   8篇
基础理论   56篇
评价与监测   1篇
灾害及防治   1篇
  2014年   6篇
  2013年   7篇
  2012年   1篇
  2011年   2篇
  2010年   4篇
  2009年   1篇
  2008年   4篇
  2007年   7篇
  2006年   1篇
  2005年   2篇
  2004年   8篇
  2003年   2篇
  2001年   2篇
  2000年   1篇
  1997年   2篇
  1995年   2篇
  1994年   1篇
  1993年   3篇
  1991年   1篇
  1989年   2篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1983年   1篇
  1982年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有67条查询结果,搜索用时 15 毫秒
31.
32.
The improvements made by developing countries in the 1970s in petroleum and mineral agreements with transnational corporations have been well documented, and substantial evidence exists to show that some real gains, in terms of host country control over operations, distribution of economic benefits, better employment and training requirements, etc., have in fact been made. In the case of the energy-related minerals, uranium and coal, however, relatively few contracts between Third World governments and transnational corporations have become public, and it is thus difficult to document whether the same gains made in the case of petroleum or non-fuel minerals have been achieved in relation to these energy resources. This article reviews a number of such recent coal and uranium agreements in developing countries. In overall terms, these agreements do not go as far in providing for the interests of host countries as do those negotiated for petroleum or hard minerals. The reasons for this apparent weakness in developing countries' bargaining power in the case of uranium and coal include the specific nature of the markets for these minerals, the structure of transnational corporations in the industry, and the very secrecy which has kept most of these contracts from public view. In the light of the relatively weak markets expected for export sales of coal and uranium through the remainder of the 1980s, it appears unlikey that developing countries can make significant advances in their negotiations to the extent of achieving terms which are more favourable than those contained in the best of the agreements reviewed in this article. It should, however, be possible for host governments to use the more favourable of the agreements reviewed here as standards for future negotiations. Une solide documentation existe sur les améliorations apportées par les pays en développement dans les années '70 dans le domaine des accords pétroliers et miniers avec les sociétés multinationales et il est maintenant bien etabli que des gains réels ont été acquis en ce qui concerne le contrôle des opérations par le pays hôte, la répartition des bénéfices, une meilleure utilisation de la main-d'oeuvre et les obligations de formation professionnelle. Cependant, dans le cas des minerais énergétiques uranium et charbon, relativement très peu de contrats intervenus entre les gouvernements du Tiers Monde et les sociétés multinationales sont tombés dans le domaine public de sorte qu'il est difficile d'établir si des gains semblables à ceux réalisés dans le cadre du pétrole et des minerais métalliques ont été obtenus. Cet article passe en revue certains des accords intervenus récemment dans les domaines du charbon et de l'uranium dans les pays en développement. En termes généraux, ces accords ne vont pas aussi loin dans la protection des intérêts des pays hôtes que ceux qui ont été négociés pour le pétrole et les minerais. La marge de manoeuvre des pays en développement dans le cadre des négociations d'accords portant sur le charbon et l'uranium est limitée en apparence du fait de la nature particulière des marchés de ces minerais, de la place qu'occupent les sociétés multinationales dans l'industrie minière et du caractère confidentiel qui entoure les transactions et les isole de la vue du grand public. Etant donné les tendances baissières des marchés du charbon et de l'uranium à l'exportation pour le reste de cette décennie, il semble peu probable que les pays en développement puissent réaliser des progrès sensibles dans leurs négociations pour atteindre des conditions plus favorables que celles qui figurent dans les meilleurs accords examinés dans cet article. Cependant, les pays hôtes devraient se prévaloir des accords qui leur sont les plus favorables parmi ceux qui sont passés en revue pour les utiliser comme base de leurs futures négociations et tout au moins pour éviter de signer des accords léonins. Los progresos alcanzados en la década del setenta por los países en desar-rollo en los acuerdos con las compañias transnacionales sobre el desarrollo del petróleo y de los minerales ha sido bien documentado y existe evidencia sustantiva de que ha habido ganancias reales en aspectos tales como control del país sobre las operaciones, distribución de beneficios económicos, mejores condiciones para el empleo y el entrenamiento, etc. Sin embargo, en el caso de minerales energéticos, tales como el uranio y el carbón, pocos contratos han sido hechos públicos y es difícil documentar si se tuvieron similares ganancias como en el caso de minerales no energéticos y petróleo. Este artículo pasa revista a un número de dichos contratos recientes sobre carbón y uranio. En términos generales estos contratos no son tan favorables a los países en desarrollo en comparación con los contratos para petróleo y minerales no energéticos. Las razones para esta aparente debilidad del poder de negociación en el caso del carbón y del uranio se debe, entre otras, a la naturaleza específica del mercado para estos minerales, la estruc-tura de las compañías transnacionales dentro de la indústria y el carácter secreto que ha tenido la mayoría de estos contratos con respecto al público en general. A la luz de la relativa debilidad del mercado para las exportaciones de carbón y uranio que se cree que imperará durante el resto de la década del ochenta, parece poco probable que los países en desarrollo puedan hacer avances significativos en sus negociaciones con el objeto de alcanzar términos que sean más favorables que los que se alcanzaron en el mejor de los contratos revisados en el presente artículo. Debería ser posible, sin embargo, que los gobiernos puedan usar como patrón para futuras negociaciones el contrato mas favorable revisado en este artículo y evitar la firma de acuerdos totalmente desfavorables al pais.  相似文献   
33.
Much of the biodiversity‐related climate change impacts research has focused on the direct effects to species and ecosystems. Far less attention has been paid to the potential ecological consequences of human efforts to address the effects of climate change, which may equal or exceed the direct effects of climate change on biodiversity. One of the most significant human responses is likely to be mediated through changes in the agricultural utility of land. As farmers adapt their practices to changing climates, they may increase pressure on some areas that are important to conserve (conservation lands) whereas lessening it on others. We quantified how the agricultural utility of South African conservation lands may be altered by climate change. We assumed that the probability of an area being farmed is linked to the economic benefits of doing so, using land productivity values to represent production benefit and topographic ruggedness as a proxy for costs associated with mechanical workability. We computed current and future values of maize and wheat production in key conservation lands using the DSSAT4.5 model and 36 crop‐climate response scenarios. Most conservation lands had, and were predicted to continue to have, low agricultural utility because of their location in rugged terrain. However, several areas were predicted to maintain or gain high agricultural utility and may therefore be at risk of near‐term or future conversion to cropland. Conversely, some areas were predicted to decrease in agricultural utility and may therefore prove easier to protect from conversion. Our study provides an approximate but readily transferable method for incorporating potential human responses to climate change into conservation planning. Uso de Cambios en la Utilidad Agrícola para Cuantificar Riesgos Futuros para la Conservación Inducidos por el Clima  相似文献   
34.
Abstract: Chytridiomycosis is linked to the worldwide decline of amphibians, yet little is known about the demographic effects of the disease. We collected capture–recapture data on three populations of boreal toads (Bufo boreas [Bufo = Anaxyrus]) in the Rocky Mountains (U.S.A.). Two of the populations were infected with chytridiomycosis and one was not. We examined the effect of the presence of amphibian chytrid fungus (Batrachochytrium dendrobatidis [Bd]; the agent of chytridiomycosis) on survival probability and population growth rate. Toads that were infected with Bd had lower average annual survival probability than uninfected individuals at sites where Bd was detected, which suggests chytridiomycosis may reduce survival by 31–42% in wild boreal toads. Toads that were negative for Bd at infected sites had survival probabilities comparable to toads at the uninfected site. Evidence that environmental covariates (particularly cold temperatures during the breeding season) influenced toad survival was weak. The number of individuals in diseased populations declined by 5–7%/year over the 6 years of the study, whereas the uninfected population had comparatively stable population growth. Our data suggest that the presence of Bd in these toad populations is not causing rapid population declines. Rather, chytridiomycosis appears to be functioning as a low‐level, chronic disease whereby some infected individuals survive but the overall population effects are still negative. Our results show that some amphibian populations may be coexisting with Bd and highlight the importance of quantitative assessments of survival in diseased animal populations.  相似文献   
35.
Two studies examined whether the previously documented coping strategy of social withdrawal in response to chronic crowding is related to changes in social information processing. In both studies we found evidence that individuals residing in crowded homes in comparison to uncrowded homes were less cognizant of personal information about strangers in an incidental encounter under naturalistic, uncrowded conditions as well as under highly crowded conditions, occurring in the laboratory. Furthermore, we show in the experimental study that interference with this social withdrawal process has significant effects on social information processing. In study 2 we also demonstrate that social withdrawal in response to acute crowding is an effective coping strategy for reducing short-term stress for those who have learned to employ this strategy while living under chronically crowded conditions. All of these results occur independently of income levels.  相似文献   
36.
Abstract:  Many riparian zones in the Sonoran Desert have been altered by elimination of the normal flood regime; such changes to the flow regime have contributed to the spread of saltcedar ( Tamarix ramosissma Ledeb.), an exotic, salt-tolerant shrub. It has been proposed that reestablishment of a natural flow regime on these rivers might permit passive restoration of native trees, without the need for aggressive saltcedar clearing programs. We tested this proposition in the Colorado River delta in Mexico, which has received a series of large-volume water releases from U.S. dams over the past 20 years. We mapped the vegetation of the delta riparian corridor through ground and aerial surveys (1999–2002) and satellite imagery (1992–2002) and related vegetation changes to river flood flows and fire events. Although saltcedar is still the dominant plant in the delta, native cottonwood (  Populus fremontii S. Wats.) and willow ( Salix gooddingii C. Ball) trees have regenerated multiple times because of frequent flood releases from U.S. dams since 1981. Tree populations are young and dynamic (ages 5–10 years). The primary cause of tree mortality between floods is fire. Biomass in the floodplain, as measured by the normalized difference vegetation index on satellite images, responds positively even to low-volume (but long-duration) flood events. Our results support the hypothesis that restoration of a pulse flood regime will regenerate native riparian vegetation despite the presence of a dominant invasive species, but fire management will be necessary to allow mature tree stands to develop.  相似文献   
37.
38.
Abstract:  International wildlife crime is burgeoning in this climate of global trade. We contend that the most effective way to contain this illegal trade is to determine where the wildlife is being removed. This allows authorities to direct law enforcement to poaching hot spots, potentially stops trade before the wildlife is actually killed, prevents countries from denying their poaching problems at home, and thwarts trade before it enters into an increasingly complex web of international criminal activity. Forensic tools have been limited in their ability to determine product origin because the information they can provide typically begins only at the point of shipment. DNA assignment analyses can determine product origin, but its use has been limited by the inability to assign samples to locations where reference samples do not exist. We applied new DNA assignment methods that can determine the geographic origin(s) of wildlife products from anywhere within its range. We used these methods to examine the geographic origin(s) of 2 strings of seizures involving large volumes of elephant ivory, 1 string seized in Singapore and Malawi and the other in Hong Kong and Cameroon. These ivory traffickers may comprise 2 of the largest poaching rings in Africa. In both cases all ivory seized in the string had common origins, which indicates that crime syndicates are targeting specific populations for intense exploitation. This result contradicts the dominant belief that dealers are using a decentralized plan of procuring ivory stocks as they became available across Africa. Large quantities of ivory were then moved, in multiple shipments, through an intermediate country prior to shipment to Asia, as a risk-reduction strategy that distances the dealer from the poaching locale. These smuggling strategies could not have been detected by forensic information, which typically begins only at the shipping source.  相似文献   
39.
Abstract: Many of the skills and resources associated with botanic gardens and arboreta, including plant taxonomy, horticulture, and seed bank management, are fundamental to ecological restoration efforts, yet few of the world's botanic gardens are involved in the science or practice of restoration. Thus, we examined the potential role of botanic gardens in these emerging fields. We believe a reorientation of certain existing institutional strengths, such as plant‐based research and knowledge transfer, would enable many more botanic gardens worldwide to provide effective science‐based support to restoration efforts. We recommend botanic gardens widen research to include ecosystems as well as species, increase involvement in practical restoration projects and training practitioners, and serve as information hubs for data archiving and exchange.  相似文献   
40.
Abstract: Climate change poses a particular threat to species with fragmented distributions and little or no capacity to migrate. Assisted colonization, moving species into regions where they have not previously occurred, aims to establish populations where they are expected to survive as climatic envelopes shift. However, adaptation to the source environment may affect whether species successfully establish in new regions. Assisted colonization has spurred debate among conservation biologists and ecologists over whether the potential benefits to the threatened species outweigh the potential disruption to recipient communities. In our opinion, the debate has been distracted by controversial examples, rather than cases where assisted colonization may be a viable strategy. We present a strategic plan for the assisted migration of tuatara (Sphenodon punctatus), an endemic New Zealand reptile. The plan includes use of extant populations as reference points for comparisons with assisted‐colonization populations with respect to demography, phenotypic plasticity, and phenology; optimization of genetic variation; research to fill knowledge gaps; consideration of host and recipient communities; and inclusion of stakeholders in the planning stage. When strategically planned and monitored, assisted colonization could meet conservation and research goals and ultimately result in the establishment of long‐term sustainable populations capable of persisting during rapid changes in climate.  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