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   165篇
  免费   0篇
  国内免费   1篇
大气科学   7篇
地球物理   70篇
地质学   79篇
天文学   6篇
自然地理   4篇
  2021年   2篇
  2020年   2篇
  2019年   2篇
  2016年   2篇
  2014年   3篇
  2012年   4篇
  2011年   4篇
  2009年   2篇
  2008年   2篇
  2000年   3篇
  1998年   3篇
  1991年   6篇
  1990年   5篇
  1989年   8篇
  1988年   7篇
  1987年   13篇
  1985年   5篇
  1984年   5篇
  1983年   12篇
  1982年   5篇
  1981年   3篇
  1978年   3篇
  1976年   2篇
  1974年   2篇
  1973年   2篇
  1959年   2篇
  1954年   2篇
  1953年   1篇
  1950年   1篇
  1943年   1篇
  1941年   1篇
  1940年   2篇
  1939年   1篇
  1936年   2篇
  1935年   2篇
  1933年   2篇
  1932年   1篇
  1931年   3篇
  1930年   3篇
  1928年   2篇
  1926年   2篇
  1925年   2篇
  1924年   3篇
  1922年   1篇
  1921年   1篇
  1919年   1篇
  1916年   3篇
  1914年   2篇
  1913年   1篇
  1912年   2篇
排序方式: 共有166条查询结果,搜索用时 15 毫秒
31.
Zusammenfassung Die komplexen tertiären Vulkangebiete lassen sich auf Grund der Störungsphasen und Reliefgenerationen in verschiedene natürliche Gruppen gliedern. An Beispielen (Westerwald, Vogelsberg, Habichtswald, Hegau, Böhmisches Mittelgebirge) wird gezeigt, wie man durch Ermittlung der Reliefgenerationen die bisher zugrunde gelegte, rein petrographische Unterscheidung der Vulkangebilde ergänzen, berichtigen oder ersetzen kann und dabei zu einer richtigen Analyse des Aufbaues und der vulkanischen Ereignisse gelangt.  相似文献   
32.
33.
34.
35.
The oil content of oil-contaminated porous media is an important parameter for the assessment and remediation of oil pollution in soil and groundwater. However, an accurate measurement method is not available. In this study, we propose a new equation to calculate the oil content of water-bearing media based on traditional extraction–ultraviolet spectroscopy. Further, an improved experimental method was developed. The results indicate that the pure solid weight and oil content of oil-contaminated media can be accurately determined by introducing the oil drying loss coefficient (γ). The average relative errors of the improved method range from −0.14% to −0.96%. They are much smaller than errors of −4.49% to −10.97% of the original methods, indicating that the accuracy of measured oil content is enhanced. In addition, the accuracy of the new method does not depend on oil volatility and oil content.  相似文献   
36.
Abstract

Small dams fragment river landscapes, disrupting channel connectivity and impacting water quality and quantity. Although they impound volumetrically less total water than large dams, the ubiquity of small dams suggests their cumulative impacts could be significant. Documenting the distribution and characteristics of small dams is necessary to understanding and mitigating their impacts. In this study, we compare datasets of small dams in Oregon, compile a new comprehensive dataset, and document geographic variations in small dam distributions between different ecoregions. We used Oregon Water Resources Department dam and Oregon Department of Fish and Wildlife fish passage barrier datasets to compare dam heights and contributing drainage areas between different ecoregions. Over 61% of Oregon’s land area is above one or more small dam. We highlight the location of Oregon’s small dams at valley margins, transition zones between flat plains and mountains, and areas of high population density. Given the hidden nature of small dams, evaluation of small dam impacts using public imagery is not effective. However, knowledge of small dam distributions given their association with landforms can aid in finding unrecorded dams, assessing approaches for evaluating their geomorphic impacts, and informing their management.  相似文献   
37.
38.
In order to evaluate the Holocene palaeoenvironmental evolution of the Ugii Nuur basin, central Mongolia, investigations on chemical and mineralogical properties of lacustrine sediments were carried out on a 630 cm sediment core from lake Ugii Nuur. The interpretation of the record is based on a principal component analysis (PCA) of the elemental composition of the samples. The results show that lacustrine deposition started at 10.6 kyr BP. Low lake level conditions were identified during the Early Holocene (10.6-7.9 kyr BP). The Mid Holocene (7.9-4.2 kyr BP) was characterized by generally higher lake levels and thus higher moisture supply, but it experienced strong climatic fluctuations. Arid conditions prevailed from 4.2-2.8 kyr BP and were followed by a stable, more humid phase until today.  相似文献   
39.
40.
On the laboratory scale investigations are carried out into the action of singlet oxygen, which is generated in water by addition of sodium-hypochlorite and hydrogen-peroxide solution, on Elbe river water and model waters. DOC does not change; COD, however, decreases considerably. The advantages and drawbacks of the treatment are stated.  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