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   187篇
  免费   0篇
  国内免费   1篇
系统科学   3篇
教育与普及   2篇
现状及发展   56篇
研究方法   13篇
综合类   114篇
  2020年   1篇
  2018年   2篇
  2016年   2篇
  2013年   5篇
  2012年   4篇
  2011年   12篇
  2010年   1篇
  2009年   2篇
  2008年   10篇
  2007年   5篇
  2006年   3篇
  2005年   7篇
  2004年   8篇
  2003年   8篇
  2002年   5篇
  2001年   8篇
  2000年   7篇
  1995年   2篇
  1994年   2篇
  1992年   2篇
  1991年   3篇
  1990年   2篇
  1989年   1篇
  1988年   2篇
  1987年   3篇
  1986年   4篇
  1984年   2篇
  1983年   3篇
  1982年   2篇
  1981年   3篇
  1980年   3篇
  1979年   1篇
  1978年   3篇
  1977年   4篇
  1975年   3篇
  1974年   7篇
  1973年   7篇
  1972年   3篇
  1971年   7篇
  1970年   7篇
  1969年   3篇
  1968年   8篇
  1967年   3篇
  1966年   1篇
  1965年   2篇
  1961年   1篇
  1960年   1篇
  1958年   1篇
  1955年   1篇
  1954年   1篇
排序方式: 共有188条查询结果,搜索用时 812 毫秒
181.
Zusammenfassung Äthylenglykol-dimethansulfonat (EDS) wird von der Ratte zu N-Acetyl-S-(-hydroxyäthyl)-cystein (V), N-Acetyl-S-(-hydroxyäthyl)-cystein-S-oxyd (VI), und Methansulfonsäure abgebaut. Äthylendibromid (EDB) gibt ausser V und VI, S-(-Hydroxyäthyl)-cystein (III) und wird weiter zu Kohlendioxyd und anorganischem Sulphat via S-(-Hydroxyäthyl)-cystein-S-oxyd (IV) abgebaut. Keine der erwähnten Stoffwechselprodukte sind gegen Tumoren oder gegen Spermatogenese wirksam.

This work was supported by grants from the Ford Foundation and the Wellcome Trust (A. R. J.) and the British Empire Cancer Campaign for Research (K. E.).  相似文献   
182.
A W Edwards 《Nature》1986,324(6096):417-418
  相似文献   
183.
Ohne Zusammenfassung Vorgelegt von M. Kline The work of H. Edwards was supported by part by the U. S. National Science Foundation Grant SOC-7905162 and by the Vaughn Foundation.  相似文献   
184.
The middle-Holocene was a period of profound cul- ture transitions: the Neolithic culture around Central China[1], Mesopotamia[2] and India[3] all mysteriously collapsed around 4 ka . It is plausible that this civiliza-tion collapse can be contributed to …  相似文献   
185.
The geographical origin of modern humans is the subject of ongoing scientific debate. The 'multiregional evolution' hypothesis argues that modern humans evolved semi-independently in Europe, Asia and Africa between 100,000 and 40,000 years ago, whereas the 'out of Africa' hypothesis contends that modern humans evolved in Africa between 200 and 100 kyr ago, migrating to Eurasia at some later time. Direct palaeontological, archaeological and biological evidence is necessary to resolve this debate. Here we report the discovery of early Middle Stone Age artefacts in an emerged reef terrace on the Red Sea coast of Eritrea, which we date to the last interglacial (about 125 kyr ago) using U-Th mass spectrometry techniques on fossil corals. The geological setting of these artefacts shows that early humans occupied coastal areas and exploited near-shore marine food resources in East Africa by this time. Together with similar, tentatively dated discoveries from South Africa this is the earliest well-dated evidence for human adaptation to a coastal marine environment, heralding an expansion in the range and complexity of human behaviour from one end of Africa to the other. This new, wide-spread adaptive strategy may, in part, signal the onset of modern human behaviour, which supports an African origin for modern humans by 125 kyr ago.  相似文献   
186.
187.
Microbial activities shape the biogeochemistry of the planet and macroorganism health. Determining the metabolic processes performed by microbes is important both for understanding and for manipulating ecosystems (for example, disruption of key processes that lead to disease, conservation of environmental services, and so on). Describing microbial function is hampered by the inability to culture most microbes and by high levels of genomic plasticity. Metagenomic approaches analyse microbial communities to determine the metabolic processes that are important for growth and survival in any given environment. Here we conduct a metagenomic comparison of almost 15 million sequences from 45 distinct microbiomes and, for the first time, 42 distinct viromes and show that there are strongly discriminatory metabolic profiles across environments. Most of the functional diversity was maintained in all of the communities, but the relative occurrence of metabolisms varied, and the differences between metagenomes predicted the biogeochemical conditions of each environment. The magnitude of the microbial metabolic capabilities encoded by the viromes was extensive, suggesting that they serve as a repository for storing and sharing genes among their microbial hosts and influence global evolutionary and metabolic processes.  相似文献   
188.
Microfluidic diagnostic technologies for global public health   总被引:2,自引:0,他引:2  
Yager P  Edwards T  Fu E  Helton K  Nelson K  Tam MR  Weigl BH 《Nature》2006,442(7101):412-418
The developing world does not have access to many of the best medical diagnostic technologies; they were designed for air-conditioned laboratories, refrigerated storage of chemicals, a constant supply of calibrators and reagents, stable electrical power, highly trained personnel and rapid transportation of samples. Microfluidic systems allow miniaturization and integration of complex functions, which could move sophisticated diagnostic tools out of the developed-world laboratory. These systems must be inexpensive, but also accurate, reliable, rugged and well suited to the medical and social contexts of the developing world.  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