全文获取类型
收费全文 | 25988篇 |
免费 | 365篇 |
国内免费 | 213篇 |
专业分类
测绘学 | 520篇 |
大气科学 | 1939篇 |
地球物理 | 5199篇 |
地质学 | 9057篇 |
海洋学 | 2107篇 |
天文学 | 6011篇 |
综合类 | 47篇 |
自然地理 | 1686篇 |
出版年
2021年 | 161篇 |
2020年 | 197篇 |
2019年 | 209篇 |
2018年 | 497篇 |
2017年 | 462篇 |
2016年 | 566篇 |
2015年 | 437篇 |
2014年 | 606篇 |
2013年 | 1211篇 |
2012年 | 731篇 |
2011年 | 1015篇 |
2010年 | 875篇 |
2009年 | 1219篇 |
2008年 | 1052篇 |
2007年 | 1053篇 |
2006年 | 978篇 |
2005年 | 818篇 |
2004年 | 837篇 |
2003年 | 799篇 |
2002年 | 739篇 |
2001年 | 688篇 |
2000年 | 637篇 |
1999年 | 571篇 |
1998年 | 576篇 |
1997年 | 576篇 |
1996年 | 440篇 |
1995年 | 419篇 |
1994年 | 380篇 |
1993年 | 335篇 |
1992年 | 311篇 |
1991年 | 276篇 |
1990年 | 304篇 |
1989年 | 281篇 |
1988年 | 235篇 |
1987年 | 311篇 |
1986年 | 257篇 |
1985年 | 346篇 |
1984年 | 384篇 |
1983年 | 371篇 |
1982年 | 335篇 |
1981年 | 310篇 |
1980年 | 312篇 |
1979年 | 282篇 |
1978年 | 311篇 |
1977年 | 263篇 |
1976年 | 267篇 |
1975年 | 275篇 |
1974年 | 234篇 |
1973年 | 238篇 |
1972年 | 158篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
P.E. Villagra G.E. Defossé H.F. del Valle S. Tabeni M. Rostagno E. Cesca E. Abraham 《Journal of Arid Environments》2009,73(2):202-211
The complex interactions between human activity and natural processes determine non-linear dynamics in ecosystems that can difficult their management. Human settlements in arid lands contribute to the modification of disturbance regimes, including the introduction of new disturbances and the elimination of others. In consequence, they can alter the functional mechanisms that allow systems to overcome limiting factors, leading to desertification. In this revision, we evaluated the effects of the changes on disturbance regimes produced by the different forms of land transformation on the structure and function of ecosystems of the Monte Biogeographical Province, in Argentinean arid west. Two approaches were used: the analysis of land use history and the analysis of the effects of the main disturbances on the dynamics of different communities. We concluded that throughout the history of the Monte Desert, the joint action of natural and anthropic agents has resulted in complex dynamics that lead most area of the Monte to a moderate to severe status of desertification. The modification of the disturbance regime had strong consequences for several aspects of the dynamics of communities, such as species composition and diversity, water dynamics, soil conditions, trophic structure and productivity of Monte Desert ecosystems. However, disturbance regimes could be managed to promote favorable transitions in ecosystems and, therefore, could be a tool for optimizing productivity of agro-ecosystems, and recovering and conserving natural ecosystems. 相似文献
232.
233.
The Geology and Petroleum Resources of Kansas: A Review From Alpha to Omega or From the Pleistocene to the Precambrian 总被引:1,自引:0,他引:1
Daniel F. Merriam 《Natural Resources Research》2010,19(4):293-316
The geological story of Kansas is told through the rocks that are present. It is a simple story in generalities but complex
in detail. Knowing the story, gives insight into understanding the occurrence and location of possible economic valuable minerals,
such as petroleum. This is a brief review of Kansas geology with respect to the known occurrence of oil and gas. Kansas is
part of the Midcontinent oil province with oil having been discovered 150 years ago and commercial production commencing in
1873. Although many prospects remain in Kansas, the state has gone from the number 1 producer in the U.S. in 1916 to 8th today.
Exploration for new oil and gas production therefore is going to have to be more imaginative and utilize new approaches and
techniques to find the elusive petroleum. There are possibilities however for the prospector who can search diligently. Although
the big fields probably have been discovered, the prospects today are deeper, in more undetectable traps, and in essentially
untested places. 相似文献
234.
235.
Ohne Zusammenfassung 相似文献
236.
F. García-Rodríguez N. Mazzeo P. Sprechmann D. Metzeltin F. Sosa H.C. Treutler M. Renom B. Scharf C. Gaucher 《Journal of Paleolimnology》2002,28(4):457-468
Paleolimnological techniques were used to assess human impacts onLake Blanca, a small (0.6 km2), coastal fresh waterbodyin southern Uruguay, which is the drinking water source for 100,000 localresidents. We retrieved a core that extends to about 1100 14Cyr BP. 210Pb ages, organic mater, CO3, totalcarbon, nutrients, fossil pigments and diatoms allowed us to establishlimnological conditions before and after cultural impacts. Soil removal(1880–1960) and intensive cattle and sheep grazing (1943–1966) ledto gully formation in the catchment. This watershed erosion resulted inincreased sedimentation rates. The aquatic system appeared to be mesotrophicwith dominance of epibenthic diatoms until 1966, at which timeeutrophication intensified with forestry activities. Increases in nutrients, aswell as blooms of planktonic diatoms, were observed. During the last decade,tourist/urban development as well as high drinking water demand caused areduction in lake area. Subsequent marked increases in rainfall led to furtherphytoplankton blooms and macrophyte proliferation. 相似文献
237.
238.
S. Oreshin L. Vinnik L. Makeyeva G. Kosarev R. Kind F. Wentzel 《Geophysical Journal International》2002,151(2):393-402
239.
240.
F. Wippermann 《Meteorology and Atmospheric Physics》1951,4(1):112-121
Zusammenfassung Zur Erklärung der Lage der großen quasistationären Tröge wird einem Rechnungsgang vonCharney undEliassen folgend, neben dem Einfluß der Erhebung der Erdoberfläche auch noch derjenige der Wärmeaufnahme und-abgabe herangezogen, der sich noch größer als der erstgenannte erweist. Erst nach seiner Berücksichtigung steht das Resultat in befriedigender Übereinstimmung mit den beobachteten Werten.
Mit 3 Textabbildungen. 相似文献
Summary In order to explain the position of the great quasi-stationary troughs and ensuing a computation ofCharney andEliassen, the author takes into consideration, apart from the influence of the upheavals of the earth's surface, also the supply and loss of heat. The latter influence proves to be more powerful than the first one, and taking it into consideration the result is in satisfactory agreement with the observed values.
Résumé Afin d'expliquer la situation des grands creux quasistationnaires sont pris en considération, en suivant une méthode deCharney etEliassen, à part l'influence des élévations de la surface terrestre, celle due à l'apport et la perte de chaleur, qui se révèle encore plus efficace que la première. Seulement en en tenant compte le résultat correspond d'une façon satisfaisante aux conditions observées.
Mit 3 Textabbildungen. 相似文献