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   85688篇
  免费   1221篇
  国内免费   477篇
测绘学   1763篇
大气科学   5633篇
地球物理   16272篇
地质学   30883篇
海洋学   7879篇
天文学   19975篇
综合类   251篇
自然地理   4730篇
  2022年   631篇
  2021年   1086篇
  2020年   1168篇
  2019年   1250篇
  2018年   2559篇
  2017年   2365篇
  2016年   2723篇
  2015年   1358篇
  2014年   2622篇
  2013年   4491篇
  2012年   2865篇
  2011年   3698篇
  2010年   3373篇
  2009年   4265篇
  2008年   3721篇
  2007年   3831篇
  2006年   3552篇
  2005年   2522篇
  2004年   2446篇
  2003年   2283篇
  2002年   2274篇
  2001年   1969篇
  2000年   1955篇
  1999年   1535篇
  1998年   1597篇
  1997年   1466篇
  1996年   1245篇
  1995年   1243篇
  1994年   1043篇
  1993年   1007篇
  1992年   934篇
  1991年   967篇
  1990年   935篇
  1989年   817篇
  1988年   751篇
  1987年   883篇
  1986年   773篇
  1985年   947篇
  1984年   1070篇
  1983年   1032篇
  1982年   950篇
  1981年   891篇
  1980年   793篇
  1979年   748篇
  1978年   727篇
  1977年   618篇
  1976年   626篇
  1975年   613篇
  1974年   589篇
  1973年   656篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
231.
The studies carried out throughout the world have indicated that there are differences between environmental attitudes and environmentally responsible behaviors of undergraduate students. In what ways the environmental attitudes and behaviors of the students who will protect and manage the resources of the country in the future have changed is an important issue? This study was aimed at determining the environmental attitudes and environmentally responsible behaviors of the undergraduate students of Abant Ýzzet Baysal University toward environmental issues. In addition, the effects of the faculty in which the students are enrolled, locality and gender on the determined environmental attitudes and environmentally responsible behaviors of the students were investigated. The data were gathered from 507 students in 2005. To explain the environmental attitudes and environmentally responsible behaviors of undergraduate students toward environmental issues, factor analysis was used with Varimax Rotation method. To determine the changes of the environmental attitudes and environmentally responsible behaviors of the students with regard to the faculty, locality and gender, one-way analysis of variance was used. According to the results, students highly support the environmental attitudes and highly participate only in consumerism behaviors. Finally, it was determined if faculty and gender had an effect on the environmental attitudes and behaviors of the students.  相似文献   
232.
233.
Studies of three deposits of neo-Archean banded iron formations from the West Karelian domain (the Kostomuksha deposit) and from the Central Kola block (the Olenegorsk and Kirovogorsk deposits) showed a pronounced difference in the isotope compositions of Nd from quartz and magnetite–hematite interlayers. The less radiogenic Nd of iron-containing layers compared to that of the quartz component may be considered as an indication of the formation mechanism of the treated banded iron formations. Thus, silicon-containing layers are related to submarine volcanism and iron was supplied to the sedimentation zone from other sources.  相似文献   
234.
235.
Fildes Peninsula, in King George Island, Antarctica, has a great concentration of international facilities, and it has clearly been affected by human activities. The objective of this 5-year study was ...  相似文献   
236.
The International Year of Forests, declared by the UN, is a good occasion to discuss approaches to reducing forest degradation in developing countries. The articles collected in Thematic Forest Series form a diversity of ideas which is essential for setting the levels below which the countries' reduced emissions could be measured and credited. This editorial calls attention to the use of Land-Use/Land-Cover Change models.  相似文献   
237.
238.
Data of long-term observations of Roshydromet and the studies of the authors’ studies of hydrochemical, hydrobiological, and bioassaying characteristics and appropriate publications in the areas of megalopolises—the cities of Rostov-on-Don and Novosibirsk are analyzed. Similar and distinctive characteristics of water quality by these ecological-toxicological characteristics are identified; trends in the long-term year-to-year variations in water quality are established, criteria and characteristics reflecting the effect of cities on water bodies in their territory are determined. The identity of some chemical-toxicological criteria and the characteristics of the influence of cities in southern Russia and Siberia on water bodies suggest that they can also be used in urban area in other regions. The Lower Don is used as an example to show that water pollution by metals is mostly due to wastewater discharge, while water pollution by petroleum products and sulfates has no direct relation to that.  相似文献   
239.
The Wadi Bayhan mafic-ultramafic intrusions associated with magmatic PGE-bearing Cu-Ni sulphide deposit are located in the south margin of the Arabian-Nubian Shield,SW Yemen.The intrusions consist of dunite,olivine-pyroxenite,lherzolite,hornblendite,gabbro and gabbronorite.The dunite and lherzolite are the main host rock for the Cu-Ni ores.The new data of the chemical compositions of the rocks have SiO2(50%-53.6%),Al2O3(0-32%) and MgO(4%-28%),and relatively low TiO2(0-3.2%) and K2O+Na2O(0.04%-5.2%).The geoc...  相似文献   
240.
The Wadi Sharis orogenic gold deposit in northwestern Yemen is related to the fault and shear zones vein at medium depth in the crust in the Neoproterozoic meta-sedimentary and meta-volcanosedimentary succession of greenschist to amphibolite facies metamorphism.Three distinct fluid inclusion types have been identified in the gold-bearing quartz sulphide veins of the deposit:(1) type I:vapour-liquid two-phase(VH2O-LH2O),(2) type II:three-phase CO2(VCO2-LH2O-LCO2) and(3) type III:vapour-rich(LCO2-VCO2) inclus...  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