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   14篇
  免费   7篇
  国内免费   2篇
测绘学   2篇
大气科学   2篇
地球物理   4篇
地质学   7篇
海洋学   3篇
综合类   2篇
自然地理   3篇
  2023年   1篇
  2020年   1篇
  2019年   2篇
  2018年   1篇
  2017年   2篇
  2016年   2篇
  2012年   1篇
  2011年   1篇
  2010年   2篇
  2009年   2篇
  2006年   2篇
  2005年   1篇
  2004年   2篇
  1994年   1篇
  1975年   1篇
  1931年   1篇
排序方式: 共有23条查询结果,搜索用时 15 毫秒
1.
The International Whaling Commission's (IWC) Scientific Committee provides important advice to the IWC on a large variety of cetacean species, sub-species and populations and the issues affecting them. Cetaceans are facing increasing, non-whaling-related threats, and the Scientific Committee (SC), in accordance with the Commission's requests, has strengthened its conservation-oriented research work. A selection of the reports of the Scientific Committee from between 1986 and 2012 was assessed for its: (i) fundamental research; (ii) management; (iii) conservation; and (iv) administrative content, and to identify potential trends over time. Recommendations and their urgency were also examined, as implied from the language used by the SC in its reports. The analysis showed that the work of the Scientific Committee has increasingly been oriented towards conservation issues over the period reviewed, but at the same time this conservation work has received little funding. Increased support for conservation-related research projects is warranted to promote the long-term survival of cetaceans. Based on this review of the content and focus of the Committee reports, the analysis suggested that its issued advice be made clearer, whenever possible, and governments are urged to give due consideration to this science-based advice particularly when urgent conservation actions are needed. In addition, more consistent funding of the IWC's conservation-related research should be pursued to improve international conservation outputs regarding cetacean populations.  相似文献   
2.
3.
When insufficient data are available for measuring operational risk faced by a financial institute, most of the models depending on the probability theory are failure. Differing from that we use a probability distribution to depict random uncertainty, in this paper we use a number to represent the naive uncertainty in a phase serving for operational risk identification. The simplest form of the naive uncertainty model for measuring operational risk with multiple phases is the weighted mean with the uncertainties. It is also valid when we have a rough judgment for the uncertainties with intervals or fuzzy values. In this paper, we give a calculation case in lending operational risk to demonstrate the model validity.  相似文献   
4.
Regional‐scale 40Ar–39Ar data presented in this paper reveal significant across‐strike and along‐strike age differences in the Committee Bay belt (CBb), Rae Province, Nunavut, Canada, that complement variations in observed monazite ages. 40Ar–39Ar hornblende ages are c. 1795, 1775, and 1750 Ma in the western, eastern and central parts of the Prince Albert Group (PAG) domain respectively. The migmatite domain and Walker Lake intrusive complex are characterized by c. 1750–1730 40Ar–39Ar hornblende ages without significant along‐strike variation. The 40Ar–39Ar data provide important constraints on the cooling history and on thermal modelling that elucidates the controls on diachroneity and metamorphic patterns within the belt. In the western CBb, prograde monazite growth occurred 26 ± 10 Myr earlier in the migmatite domain (1864 ± 9 Ma; peak P–T = 5 kbar?700 °C) than in the PAG domain (1838 ± 5 Ma; peak P–T = 5 kbar?580 °C). Calculations indicate that this earlier monazite growth results from tectonic thickening of higher heat productivity Archean lithologies in the migmatite domain, which undergoes more rapid prograde heating than the less radiogenetic and lower grade rocks of the PAG domain. Granite generation via biotite dehydration melting at 800 °C and 20 km depth is predicted to occur c. 1835 Ma, in agreement with geochronological constraints. The tectonic burial of crustal domains with contrasting radiogenic properties also explains the general congruence of lower to upper amphibolite facies metamorphic zones generated during the two main orogenic cycles (i.e. M2–D1 and M3–D2). The modelled timing of prograde monazite growth in the migmatite domain suggests that D2 tectonic thickening began at 1872 ± 9 Ma, some 8 ± 3 Myr before monzazite growth, coeval with the inferred time of collision of the Meta Incognita terrane with the southern Rae Province. Along‐strike diachroneity, reflected in 25 Myr younger monazite and 40Ar–39Ar hornblende ages in the eastern relative to the western PAG domain, cannot be accounted for by heat productivity contrasts along the belt. Instead the younger deformation and metamorphism in the eastern CBb was driven by its proximity to the eastern promontory of the Superior Province which collided with the Rae Province at c. 1820 Ma. The 40Ar–39Ar data presented here support the interpretation that the youngest monazite in the CBb crystallized at c. 1790 Ma in the central CBb when this part of the belt was downfolded into a gentle synformal structure while the western part of the belt cooled through 40Ar–39Ar hornblende closure. The results of this study illustrate the important influence of contrasting rock properties on the thermal evolution of orogenic belts and on the temporal record of this evolution.  相似文献   
5.
正确认识和对待天气气候预报的不确定性   总被引:3,自引:2,他引:1  
王东海  杜钧  柳崇健 《气象》2011,37(4):385-391
美国国家科学发展的指导机构同家研究顾问委员会(NRC)不久前发表了一份关于天气、气候和水文预报的不确定性的凋研报告.报告强调了预报不确定性信息在终端用户应用气象预报作决策中的重要性,同时指出一个预报如果没有定量地估计它的不确定性,那么该预报是不完全的.该报告中文版的出版工作正在进行中,现藉此机会向读者综合地介绍一下预报不确定性的问题.文中首先讨论了预报不确定性的缘由以及应该如何来科学地对待它.然后介绍了要应对这一问题所要进行的一些具体措施和策略.最后,简要地介绍了美国气象界为此所做的一些努力和计划以供参考.通过上述讨论和介绍,希望引起更多的人对预报不确定性问题的重视并科学应对以更好地服务社会.  相似文献   
6.
To settle the difficulties of the shortage of oceanographic research vessels in our country, the National Natural Science Foundation Committee of China founded Oceanographic Research Vessel Sharing Plan in 2009. It is aimed at enhancing efficiency and optimization of the vessel resources,and coordinating the use demands of vessels for the different foundation projects and the efficient use of the research vessels. We have summarized the achievements made in the Plan from 2010 to 2014, as well as the use system of the research vessels sharing, the specific operating mode ,the organization and the management framework of the Plan. In the end, we put forward our suggestions on the improvement of the Plan after the primary analysis of the present situation of the sharing of the survey data and the existing problems.  相似文献   
7.
8.
It has been asserted by Clough (1952) , amongst others, that British Military Survey was poorly prepared for the outbreak of war in 1939. An examination of the work carried out between the wars by the Air Survey Committee would seem to contradict that view. In this paper, the work of the Air Survey Committee is discussed and a brief assessment made of the impact of its work on British mapping during the Second World War.  相似文献   
9.
Since 1991 volunteers from the Canadian Gas Potential Committee (CGPC) have conducted assessments of undiscovered gas potential in Canada. Reports were published in 1997 and 2001. The 2001 CGPC report assessed all established and some conceptual exploration plays in Canada and incorporated data from about 29,000 discovered gas pools and gas fields. Mainly year-end 1998 data were used in the analysis of 107 established exploration plays. The CGPC assessed gas in place without using economic cut offs. Estimates of nominal marketable gas were made, based on the ratio between gas in place and marketable gas in discovered pools. Only part of the estimated nominal marketable gas actually will be available, primarily because of restrictions on access to exploration and the small size of many accumulations. Most plays were assessed using the Petrimes program where it could be applied. Arps-Roberts assessments were made on plays where too many discovered pools were present to use the Petrimes program. Arps-Roberts assessments were corrected for economic truncation of the discovered pool sample. Several methods for making such corrections were tried and examples of the results are shown and compared with results from Petrimes. In addition to assessments of established plays, 12 conceptual plays, where no discoveries have been made, were assessed using Petrimes subjective methodology. An additional 65 conceptual plays were recognized, discussed, and ranked without making a quantitative assessment. No nominal marketable gas was attributed to conceptual plays because of the high risk of failure in such plays. Nonconventional gas in the form of coalbed methane, gas hydrates, tight gas, and shale gas are discussed, but no nominal marketable gas is attributed to those sources pending successful completion of pilot study projects designed to demonstrate commercially viable production. Conventional gas resources in Canada include 340 Tcf of gas in place in discovered pools and fields and 252 Tcf of undiscovered gas in place. Remaining nominal marketable gas includes 96 Tcf in discovered pools and fields and 138 Tcf of undiscovered nominal marketable gas. The Western Canada Sedimentary Basin holds 61% of the remaining nominal marketable gas. Future discoveries from that area will be mainly in pools smaller than 2.5 Bcf of marketable gas and increasing levels of exploratory drilling will be required to harvest this undiscovered resource. A pragmatic, geologically focussed approach to the assessment of undiscovered gas potential by the CGPC provides a sound basis for future exploration and development planning. Peer reviewed assessment on a play-by-play basis for entire basins provides both detailed play information and the ability to evaluate new exploration results and their impact on overall potential.  相似文献   
10.
六十年前召开的第一届全国地层会议对我国的地层学、古生物学发展起了非常大的推动作用,带来了我国地层古生物学科发展的第一个黄金时期,为改革开放之后我国地层古生物学的辉煌发展打下了坚实的基础。这次会议上成立的全国地层委员会作为全国地层工作的组织、协调单位至今仍然在发挥着重要而且积极的作用。  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