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   262篇
  免费   8篇
  国内免费   5篇
测绘学   4篇
大气科学   18篇
地球物理   57篇
地质学   87篇
海洋学   7篇
天文学   48篇
自然地理   54篇
  2023年   1篇
  2021年   4篇
  2020年   3篇
  2019年   8篇
  2018年   5篇
  2017年   7篇
  2016年   10篇
  2015年   7篇
  2014年   4篇
  2013年   7篇
  2012年   8篇
  2011年   17篇
  2010年   7篇
  2009年   16篇
  2008年   22篇
  2007年   24篇
  2006年   18篇
  2005年   9篇
  2004年   8篇
  2003年   10篇
  2002年   8篇
  2001年   8篇
  2000年   7篇
  1999年   5篇
  1998年   3篇
  1997年   6篇
  1996年   3篇
  1995年   2篇
  1994年   3篇
  1992年   2篇
  1991年   6篇
  1990年   1篇
  1989年   2篇
  1988年   4篇
  1987年   1篇
  1986年   4篇
  1985年   2篇
  1984年   5篇
  1983年   2篇
  1981年   2篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
排序方式: 共有275条查询结果,搜索用时 15 毫秒
1.
2.
3.
Cross-inoculation experiments were conducted in the greenhouse to test the rhizobia isolated from nodules of seven tree legumes for their effectiveness in Vigna mungo plants. The tree legumes included Albizia lebbeck, Dalbergia sissoo, Leucaena leucocephala, Pithecellobium dulce, Prosopis cineraria, Prosopis glandulosa and Prosopis juliflora, all growing under arid environment. Rhizobia from these legumes formed nodules on the roots of Vigna mungo except isolates from Albizia lebbeck. Dry weight and nitrogen contents of Vigna mungo plants increased significantly (P<0.05) in response to cross inoculation as compared to uninoculated control. Rhizobia from Leucaena leucocephala and Prosopis glandulosa showed significant increase in dry weight (P<0.05) and nitrogen contents (P<0.05) than other inoculated treatments. The natural rhizobia of wild tree legumes growing under arid environment show higher tolerance to prevailing adverse conditions like salt stress, elevated temperatures and drought. These rhizobia may be used to inoculate wild as well as crop legumes cultivated in reclaimed desert lands. These rhizobia may have specific traits that can be transferred to other rhizobia through genetic engineering tools. The cross infection of agriculturally important legumes with isolates from wild legumes may prove a useful means of increasing nitrogen contents within these plants.  相似文献   
4.
The objective of the present study is to determine the bioaccumulation of heavy metals in various organs of the fresh water fish exposed to heavy metal contaminated water system. The experimental fish was exposed to Cr, Ni, Cd and Pb at sublethal concentrations for periods of 32 days. The elements Cd, Pb, Ni and Cr were assayed using Shimadzu AA 6200 atomic absorption spectrophotometery and the results were given as μ/g dry wt. The accumulation of heavy metal gradually increases in liver during the heavy metal exposure period. All the results were statistically significant at p < 0.001. The order of heavy metal accumulation in the gills and liver was Cd > Pb > Ni > Cr and Pb > Cd > Ni > Cr. Similarly, in case of kidney and flesh tissues, the order was Pb > Cd > Cr > Ni and Pb > Cr > Cd > Ni. In all heavy metals, the bioaccumulation of lead and cadmium proportion was significantly increased in the tissues of Cyprinus carpio (Common carp).  相似文献   
5.
We have mapped the nuclear region of the starburst galaxy NGC 253 in the3 P 1 3 P 0 line of neutral carbon using the JCMT. Carbon is widespread across the nuclear region with a similiar distribution to CO as expected. Previous studies of Galactic star-forming regions showed that carbon emission is enhanced in photon-dominated regions (where UV photons impinge upon molecular clouds). Previous observations of other PDR tracers such as ionized carbon and FIR continuum constrain the physical conditions in the PDR gas of NGC 253. The carbon we have observed is far brighter than predicted by theoretical models of PDRs with solar elemental values. This indicates that carbon emission is not a reliable diagnostic of the physical conditions in the nuclear region of a galaxy undergoing a burst of star formation.  相似文献   
6.
Sago industry is one of the major small-scale sectors in India and over 800 units are located in the southern State of Tamilnadu. Processing of sago generates enormous quantities of high strength wastewater requiring systematic treatment prior to disposal. The present study is an attempt to treat the sago wastewater using Hybrid Upflow Anaerobic Sludge Blanket (HUASB) reactor, which offers the advantages of both fixed film and up flow anaerobic sludge blanket treatment. HUASB reactor with a volume of 5.6 L was operated at Organic Loading Rates varying from 10.7 to 24.7 kg COD/m3.day. After 130 days of startup, the reactor produced appreciable decrease in COD of wastewater and removed solids efficiently. The COD removal varied from 91–87%. While the removal of Total Solids was in the range of 61–57%, that of volatile solids varied from 70–67%. The ideal OLR for the reactor was 23.5 kg COD/m3.day. The findings of the study open up newer possibilities of design low cost and compact onsite treatment systems with very short retention periods.  相似文献   
7.
8.
9.
Phil Dunham 《Area》1997,29(2):141-150
Summary This paper calls for the incorporation of pre-1872 (and especially early Victorian) elections into the electoral geography research agenda. It argues that early Victorian elections provide a rare opportunity to examine actual voting behaviour at the individual level and also constitute a valid focus of enquiry in their own right. The paper concludes by discussing some of the principal methodological implications of an historical electoral geography.  相似文献   
10.
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