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   86篇
  免费   6篇
  国内免费   10篇
测绘学   2篇
大气科学   1篇
地球物理   15篇
地质学   35篇
海洋学   36篇
天文学   5篇
自然地理   8篇
  2023年   3篇
  2022年   2篇
  2021年   4篇
  2020年   2篇
  2019年   1篇
  2018年   3篇
  2017年   4篇
  2016年   5篇
  2015年   4篇
  2014年   3篇
  2013年   4篇
  2012年   1篇
  2011年   4篇
  2010年   3篇
  2009年   5篇
  2008年   2篇
  2007年   1篇
  2006年   5篇
  2005年   4篇
  2004年   2篇
  2003年   7篇
  2002年   2篇
  2001年   2篇
  2000年   2篇
  1999年   2篇
  1998年   3篇
  1997年   1篇
  1995年   2篇
  1994年   3篇
  1993年   4篇
  1992年   1篇
  1990年   2篇
  1986年   1篇
  1984年   2篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1977年   1篇
  1967年   1篇
排序方式: 共有102条查询结果,搜索用时 31 毫秒
31.
Malaysia's rapid economic development in the two decades since independence has brought benefits to the nation as a whole. However, it has also produced problems in relation to the natural resources and the environment, particularly in Peninsular Malaysia. The urgency with which economic, social and political objectives have to be achieved through development has greatly taxed the nation's natural resources, such as land, forests and water, whilst the discharge of wastes of various kinds has resulted in the degradation of rivers, the seas and air. Serious pollution problems have surfaced in various forms and these have prompted the government to formulate policy guidelines on the environment vis-á-vis development. This paper reviews the different kinds of problems relating to resource exploitation and environmental deterioration and their implications with particular reference to Peninsular Malaysia.  相似文献   
32.
33.
Snow is an important component of the Earth's climate system and is particularly vulnerable to global warming. It has been suggested that warmer temperatures may cause significant declines in snow water content and snow cover duration. In this study, snowfall and snowmelt were projected by means of a regional climate model that was coupled to a physically based snow model over Shasta Dam watershed to assess changes in snow water content and snow cover duration during the 21st century. This physically based snow model requires both physical data and future climate projections. These physical data include topography, soils, vegetation, and land use/land cover, which were collected from associated organizations. The future climate projections were dynamically downscaled by means of the regional climate model under 4 emission scenarios simulated by 2 general circulation models (fifth‐generation of the ECHAM general circulation model and the third‐generation atmospheric general circulation model). The downscaled future projections were bias corrected before projecting snowfall and snowmelt processes over Shasta Dam watershed during 2010–2099. This study's results agree with those of previous studies that projected snow water equivalent is decreasing by 50–80% whereas the fraction of precipitation falling as snowfall is decreasing by 15% to 20%. The obtained projection results show that future snow water content will change in both time and space. Furthermore, the results confirm that physical data such as topography, land cover, and atmospheric–hydrologic data are instrumental in the studies on the impact of climate change on the water resources of a region.  相似文献   
34.
Zhang  Runhong  Goh  Anthony Teck Chee  Li  Yongqin  Hong  Li  Zhang  Wengang 《Acta Geotechnica》2021,16(5):1615-1626
Acta Geotechnica - The evaluation of strut forces is critical to ensure the system stability of braced excavation in urban areas. The most common empirical approach to determine the forces in the...  相似文献   
35.
36.
ADCP观测得到的2008年4月吕宋海峡流速剖面结构   总被引:1,自引:0,他引:1  
基于2008年4月22—26日吕宋海峡调查航次的下放式声学多普勒流速剖面仪(LADCP)和船载ADCP(SADCP)等观测资料,并采用潮波模式模拟结果去除潮流对观测资料的影响,观测结果表明:调查期间黑潮入侵南海的位置与1992年春季比较接近,其分支位于调查海区中部C2、C7、C8和C9站,表层黑潮在C8站分离为两支,分别流向C9和C2站,C9站北向流明显比C8站减弱。在C2站,黑潮分支位于400m层以浅,其最大西向流速为77cm/s,而在C7、C8和C9站黑潮分支位于500m层以浅,黑潮在入侵南海的过程中其核心深度逐渐变浅。上层黑潮明显作反气旋弯曲。本调查航次的观测结果在定性上支持吕宋海峡水交换有"三明治"垂直结构的特性。  相似文献   
37.
Revealing the geological history of microbial life is very challenging. Microbes rarely are preserved with morphological fidelity, and even when they are, morphology is a poor guide to phylogeny and metabolism. Biological studies of environments considered analogous to those of paleobiological interest on the ancient Earth can inform interpretations and suggest new approaches. This paper reviews recent advances in our understanding of the biological diversity of two environments relevant to Archean paleobiology: those of extreme acidity and temperature (the Mt. Hood and White Island volcanoes), and high salinity (living stromatolites in Shark Bay). The combination of traditional microbial isolation with the use of modern molecular techniques has revealed that the microbial communities in these environments are much more diverse than originally thought. Through the extraction of whole microbial community DNA, enzymatic amplification of evolutionarily conserved genes, and cloning and sequencing of these genes, more specific and informed inferences concerning functional complexity in these extreme environments have now been made. Studies of the modern stromatolites have demonstrated that they have a very diverse range of micoorganisms, and contrary to previous interpretations, cyanobacteria are not the most abundant microbes present. In addition, many of the microorganisms are unique with no known close relatives, and these microorganisms may also possess novel physiologies vital to the integrity and persistence of stromatolites through space and time. Microbes in the volcanoes studied are present ubiquitously and include geochemically significant sulfur- and iron-cycling taxa. The findings from the studies reviewed here suggest that the Archean biota may have been functionally diverse and much more complex than has yet been revealed. The importance of studying modern analogues is stressed in that the biogeochemical processes occurring in these communities leave morphological, mineralogical, lipid and isotopic signals that could be sought in the rock record.  相似文献   
38.
The interaction of freshly abraded surfaces of cuprite, Cu2O, with neutral or mildly alkaline aqueous solutions of diethyl or di-n-butyl dithiophosphate (DTP) has been investigated by means of conventional and synchrotron X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. It was confirmed that DTP adsorbs readily on Cu atoms in the surface layer of the mineral treated with solutions of the collector at pH values near 7 and 9 in the presence of air, and renders the surface hydrophobic. When cuprite is treated with relatively high concentrations of DTP for sufficiently long periods, collector can also be adsorbed as CuDTP, but the coverage does not exceed a thin layer of CuDTP on the adsorbed DTP monolayer, unlike the situation with Cu metal or chalcocite where a thick multilayer can be formed.  相似文献   
39.
Time-dependent cross-flow was studied around cylinders with circular and noncircular cross-sections. The numerical approach for the analysis was a low-order panel method based on constant source and dipole values along each panel. The method was previously used successfully for several applications, such as calculation of the added mass and damping coefficients. In simulating the viscous time-dependent flow around the cylinder, the time-dependent wake feature of the code was used. For the circular and D-cylinders, the results agreed well with the experiments. Suggestions for improving the results for T-cylinders with angle of attack are included.  相似文献   
40.
Tides and short-term variabilities in the Kuroshio west of Yonakuni-jima   总被引:1,自引:0,他引:1  
INTRODUCFIONTheKuroshioeastofTaiwanIslandflowsnorthwardandenterstheEastChinaalgathroughapaSSagebetweenTaiwanIslandandlriomote-shima.TOstudyfurthertheKuroshiothereandestimateitstransPOrt,itisnecessarytoobservetheKuroshioCurrentdirectly.Therehavebeen*ThisstudywassupportedbytheNationalNaturalaudienceFoundationofChinaundercontractNo.49476278.severaldirectobservationsoftheKuroshionearTaiwanIsland.Forexample,thedirectcurrentmeasurementat(24'24'N1123'35'E)byinabaetal.(1981)showedtheapp…  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