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   30篇
  免费   0篇
测绘学   1篇
大气科学   1篇
地球物理   1篇
地质学   9篇
海洋学   13篇
天文学   1篇
自然地理   4篇
  2018年   1篇
  2016年   2篇
  2015年   1篇
  2013年   9篇
  2005年   1篇
  2002年   1篇
  2001年   1篇
  1998年   1篇
  1996年   2篇
  1995年   1篇
  1992年   1篇
  1991年   3篇
  1989年   2篇
  1986年   1篇
  1985年   2篇
  1975年   1篇
排序方式: 共有30条查询结果,搜索用时 421 毫秒
1.
Jowett AJ 《GeoJournal》1991,23(2):135-146
Pre-1949 China was The Sick Man of Asia, The Land of Famine. In 1949 Mao brought the communists to power and in the re-ordered world, all such problems were supposedly overcome — but not so. Thirty years ago China suffered one of the world's worst famines. Over the four years 1958–61, China suffered some 25–30 million more deaths and experienced some 30–35 million fewer births than might have been expected under normal conditions. Yet for almost a quarter of a century there would be few, outside of China, who were aware of the existence let alone the dimensions of the disaster. Access to Chinese census data since the mid-1980s has permitted a preliminary analysis of the demographic impact of the famine.Abbreviations JPRS-CEA-81-128 Joint Publications Research Service, China Economic Affairs Report 128, 1981 - JPRS-CPS-85-028 Joint Publications Research Service. China Report, Political, Sociological & Military Affairs 28, 1985  相似文献   
2.
The author presents a selection of cartograms designed to illustrate aspects of the demography of China. Topics covered include population growth, density, regional variations in fertility, and age distribution. A discussion of the advantages of using cartograms (maps drawn proportional to a given variable) as opposed to conventional, area-based maps, is included.  相似文献   
3.
"While 'closed-door' immigration policies are adopted by most countries, 'exceptionalist' legislation is often made to permit entry of special immigrant groups. An example is the British Nationality (Hong Kong) Act 1990, which was passed in the run-up to the change in sovereignty of Hong Kong in 1997. Britain's increasingly restrictive immigration policies prior to 1990 [have] resulted in the majority of Hong Kong citizens having British nationality (as British Dependent Territories citizens) but without the right of abode in the U.K. The 1990 Act conferred full British citizenship status on 50,000 heads of households in Hong Kong." The authors conclude that "in a world of marked global inequalities, immigration pressure will become even more extreme and is likely to produce an increasing number of cases of exceptionalist immigration legislation in countries with both ?open' and 'closed'-door policies.'  相似文献   
4.
Jowett AJ  Li Y 《GeoJournal》1992,28(4):427-442
Detailed examination of China's 1982 census data confirms that the standard of age reporting among the Han Chinese, and among many of the ethnic minorities, is very good. Furthermore the quality of age reporting is unaffected by large variations in levels of literacy which exist between men and women, between young and old, and between rural and urban areas. Much of the credit for the high quality of China's age reporting stems from the distinctive nature of Chinese traditional calendars. However, in the far west of China, in the Xinjiang Autonomous Region, age heaping and age exaggeration are as bad as they are in many other developing countries. The authors show that the poor quality of age reporting in Xinjiang is confined to three of the region's ethnic communities, the Uygur, Kirgiz and Tajik, who appear to neither know, nor care, how old they are.  相似文献   
5.
In newly burnt and unburnt pine and eucalyptus forest in Portugal, overland flow and soil losses were monitored to assess the impacts of the following post-fire treatments: application of different quantities of logging litter; rip-ploughing compared with minimum tillage prior to planting eucalyptus seedlings; and clearance of pine needles and vegetation. Eucalyptus logging litter reduced soil losses by up to 95 per cent. The impact of pine logging litter was equivocal, but removal of pine needles increased soil losses elevenfold. Implications for soil longevity, soil quality and land management strategy are discussed.  相似文献   
6.
The Picacho gold deposit, located in southeasternmost California, is a low-grade gold deposit in a nearly flat-lying denudational fault of regional extent and probable Oligocene age. The deposit is hosted by intensely fractured and faulted Mesozoic leucogranite and by chloritic augen gneiss and schist, and is overlain unconformably and in fault contact by unmineralized late Oligocene Quechan volcanic rocks. The deposit is structurally characterized by normal and normal-oblique faults of low to high dip at shallow depths in the mine, merging downward with a synchronous, low-dipping ore-stage extensional fault system (the Chocolate Mountains/Gatuna Fault) of probable Oligocene age in deeper portions of the deposit. The fault system was infiltrated during much of its active life by hot, dilute, highly exchanged meteoric water having temperatures of 170°–210° C, salinity <2 wt% NaCl equivalent and calculated δ18Ofluid between −2.6‰ and 5.2‰. This main-stage fluid precipitated quartz, pyrite, and specular hematite, accompanied by silicification and sericitization. Auriferous ore-stage pyrite was precipitated late in the fault evolution probably by mixing of reducing ore fluid with relatively oxidized main-stage fluid during regional Oligocene extension on the Chocolate Mountains/Gatuna Fault. The Picacho deposit is characterized by a gold–arsenic–antimony geochemical signature consistent with bisulfide complexing of gold in reducing fluid, in contrast with typical denudation fault-hosted base-metal-rich deposits associated with high-salinity fluids elsewhere in the southwestern United States. The deposit is overprinted by Miocene normal faults having a wide range of dips. These postore faults are associated with red earthy hematite precipitation, pyrite oxidation, and supergene enrichment of gold. Editorial handling: L. Meinert  相似文献   
7.
Jowett AJ 《GeoJournal》1989,18(4):417-427
The recent publication of data from the 1982 census permits an assessment of the patterns, progress and problems of illiteracy in China. Educational progress, since the communists came to power in 1949, has been particularly impressive, especially in relation to the low levels of income within the People's Republic. Nevertheless, nearly a third of the country's population are still unable to read and write and major variations in literacy exist between the developed and less developed regions, between men and women, between the urban and rural areas, between the various age groups and among the many ethnic groups that constitute the People's Republic of China. Among the most favoured people and places, literacy rates exceed 90% but among the most disadvantaged groups, retired women in rural areas for example, levels of literacy fall below 3%. Proposed educational reforms, targeted to provide nine years of compulsory education, offer the potential for boosting literacy levels and breaking the bondage of ignorance. However, such proposals are being undermined by the recent economic reforms in rural China. By stressing the value of labour, including child labour, the agricultural responsibility system has generated a surprising decline in school attendance which may jeopardise future improvements in literacy, particularly so among the poorer people in the poorer areas of China.  相似文献   
8.
The effects of small fractions ( < 30%) of open water covering a grid element are currently neglected even in atmospheric general circulation models (AGCMs) which incorporate complex land surface parameterization schemes. Here, a method for simulating sub-grid scale open water is proposed which permits any existing land surface model to be modified to account for open water. This new parameterization is tested as an addition to an advanced land surface scheme and, as expected, is shown to produce general increases in the surface latent heat flux at the expense of the surface sensible heat flux. Small changes in temperature are associated with this change in the partitioning of available energy which is driven by an increase in the wetness of the grid element. The sensitivity of the land surface to increasing amounts of open water is dependent upon the type of vegetation represented. Dense vegetation (with a high leaf area index) is shown to complicate the apparently simple model sensitivity and indicates that more advanced methods of incorporating open water into AGCMs need to be considered and compared against the parameterization suggested here. However, the sensitivity of one land surface model to incorporating open water is large enough to warrant consideration of its incorporation into climate models.  相似文献   
9.
Extracts of the viscera of Haliotis iris (Martyn, 1784) were shown to hydrolyse 2‐hydroxy‐5‐nitrophenyl sulphate at pH 5.5, and the p‐nitrophenyl derivatives of α‐ and β‐D‐galactose, α‐ and β‐D‐mannose, α‐L‐lucose, β‐D‐glucuronic acid, β‐N‐acetyl glucosamine and phosphate at pH 4.0 and 5.5: p‐nitrophenyl‐β‐L‐fucose was not hydrolysed.  相似文献   
10.
We examined the effects of sediment on fish communities at 38 sites in the East Cape region of New Zealand. Many streams in this region are subject to high sediment loads, a natural situation that has been exacerbated by the conversion of native forest to pasture. The fish community consisted of diadromous native species common throughout New Zealand that require access to and from the sea. We found that site altitude and distance inland were important factors in determining the abundance and composition of the fish community. We used four measures as indices of sediment load: suspended sediment concentration, median substrate size, substrate stability, and the ratio of the wetted width to the width of the active (non‐vegetated) stream channel. Although all indices were correlated, the ratio of wetted width to width of active channel was most closely related to fish abundance and diversity. Fish abundance and diversity reduced as sediment load increased among streams, with up to nine fish species in streams with low sediment loads and only two species in streams with high sediment loads. In‐stream habitat also varied with sediment load; as load increased, depth and substrate size decreased and velocity increased. These results suggest that activities that increase sediment loads in rivers will have a negative impact on native fish communities in New Zealand.  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