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   5454篇
  免费   3篇
  国内免费   3篇
测绘学   17篇
大气科学   1012篇
地球物理   1234篇
地质学   3115篇
海洋学   23篇
天文学   20篇
综合类   3篇
自然地理   36篇
  2013年   64篇
  1998年   29篇
  1997年   33篇
  1996年   73篇
  1995年   46篇
  1994年   41篇
  1993年   60篇
  1992年   146篇
  1991年   152篇
  1990年   140篇
  1989年   134篇
  1988年   136篇
  1987年   176篇
  1986年   132篇
  1985年   114篇
  1984年   152篇
  1983年   170篇
  1982年   188篇
  1981年   185篇
  1980年   152篇
  1979年   185篇
  1978年   160篇
  1977年   150篇
  1976年   116篇
  1975年   139篇
  1974年   125篇
  1973年   143篇
  1972年   129篇
  1971年   137篇
  1970年   143篇
  1969年   100篇
  1968年   130篇
  1967年   123篇
  1966年   85篇
  1965年   96篇
  1964年   100篇
  1963年   44篇
  1962年   91篇
  1960年   104篇
  1959年   35篇
  1957年   41篇
  1956年   37篇
  1955年   40篇
  1954年   67篇
  1953年   38篇
  1952年   49篇
  1951年   38篇
  1950年   61篇
  1949年   44篇
  1948年   33篇
排序方式: 共有5460条查询结果,搜索用时 406 毫秒
321.
322.
323.
324.
325.
Modern geography is based on ecological thinking. In this paper some geoecological notions are discussed: the scales and levels regarding spatial magnitude and complexity, the “hierarchy” of landscape units and espcially the scale of time and the concept of the supper-imposing “stamps”. This last mentioned concept is very important in relation to the problem regarding regionalization and its possibilities. Three “stamps” are recognized: 1. the substrate, 2. the climatic conditions, 3. the human (noötic) influence. Holistic regionalization in which all elements (including the human influences) are telling to full advantage, is unsatisfactory.  相似文献   
326.
Every man has to consume a certain quatity of water every day. This use constitutes the most basic need for water. In households water is also used for basic hygiene, washing, cleaning, and for the transport of sewage. Water is used in industry for cooling, generating electric power, for the production of a large variety of goods, and other purposes. The greatest demand for water results from irrigation. To satisfy these demands, an increasing quantity of ground-water is used. It is available at many places, where far extended subsurface reservoirs exist; it is better protected against pollution than surface water. But even though ground-water exists in many geological formations, which seem to be infinite, the availability is limited. The recharge of ground-water is dependent on the supply of atmospheric moisture. Especially in semiarid and arid zones this component of the hydrologic cycle determines the availability of ground-water. Besides natural conditions, technical and economic factors such as drilling of boreholes and the cost of pumping of ground-water have to be considered. Also political decisions can limit the availability of ground-water. If, for instance, wetlands are destroyed by drawdown of ground-water, nontechnical and non-economical aspects are involved. We face undesirable effects of ground-water pumping. Whether these effects are tolerable or intolerable depends on the decision-making processes on a political level.  相似文献   
327.
J. Chazeau Dr. 《GeoJournal》1983,7(6):527-532
This paper is an attempt to sum up our knowledge of the coccinellid fauna in the Pacific area. About 560 species have been recorded from the area, in which Australia has been included because it is essential for a proper understanding of the Melanesian insular faunas. Major points emerging from this study are: a significant reduction in the number of species from west to east; the prevalence of Oriental and Australian influences over American influences; the difficulty of determining faunal characteristics for most sub-regional units; the great difference between the New Guinean and Australian faunas, the former, though not well investigated as yet, displaying a much stronger Oriental influence and a wide variety of endemic forms; recent artificial dispersal by man for purposes of biological control, which many sometimes completely mask the original fauna. It must be admitted that a great deal of taxonomic work remains to be done before we can claim to have cocomprehensive biogeographic synthesis of this family in the Pacific.  相似文献   
328.
329.
330.
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