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   246篇
  免费   1篇
  国内免费   1篇
系统科学   5篇
教育与普及   1篇
现状及发展   60篇
研究方法   19篇
综合类   152篇
自然研究   11篇
  2014年   1篇
  2013年   2篇
  2012年   9篇
  2011年   18篇
  2010年   5篇
  2008年   12篇
  2007年   4篇
  2006年   8篇
  2005年   4篇
  2004年   4篇
  2003年   7篇
  2002年   11篇
  2001年   8篇
  2000年   5篇
  1999年   3篇
  1997年   1篇
  1996年   1篇
  1994年   1篇
  1992年   4篇
  1991年   7篇
  1990年   2篇
  1989年   5篇
  1988年   2篇
  1987年   8篇
  1986年   3篇
  1985年   5篇
  1984年   5篇
  1983年   4篇
  1982年   5篇
  1981年   2篇
  1980年   2篇
  1979年   5篇
  1978年   6篇
  1977年   4篇
  1976年   6篇
  1975年   7篇
  1974年   6篇
  1973年   2篇
  1972年   3篇
  1971年   3篇
  1970年   16篇
  1969年   3篇
  1968年   10篇
  1967年   6篇
  1966年   2篇
  1965年   3篇
  1962年   1篇
  1961年   1篇
  1960年   1篇
  1955年   1篇
排序方式: 共有248条查询结果,搜索用时 15 毫秒
51.
Calcitonin release from 6.23 rat medullary thyroid carcinoma C-cells was stimulated by dibutyryl cyclic AMP and inhibited by dibutyryl cyclic GMP in concentration dependent fashion. Histamine, isoproterenol, prostaglandin E2 and Bay K 8644 stimulated calcitonin release, while acetylcholine and serotonin had no significant effect on CT release.  相似文献   
52.
C Calés  J F Hancock  C J Marshall  A Hall 《Nature》1988,332(6164):548-551
About 30% of human tumours contain a mutation in one of the three ras genes leading to the production of p21ras oncoproteins that are thought to make a major contribution to the transformed phenotype of the tumour. The biochemical mode of action of the ras proteins is unknown but as they bind GTP and GDP and have an intrinsic GTPase activity, they may function like regulatory G proteins and control cell proliferation by regulating signal transduction pathways at the plasma membrane. It is assumed that an external signal is detected by a membrane molecule (or detector) that stimulates the conversion of p21.GDP to p21.GTP which then interacts with a target molecule (or effector) to generate an internal signal. Recently a cytoplasmic protein, GAP, has been identified that interacts with the ras proteins, dramatically increasing the GTPase activity of normal p21 but not of the oncoproteins. We report here that GAP appears to interact with p21ras at a site previously identified as the 'effector' site, strongly implicating GAP as the biological target for regulation by p21.  相似文献   
53.
Dosages of either 1 or 2 mg daily of 16beta-hydroxy-dehydroepiandrosterone, given to mononephrectomized, salt-loaded female rats, had no detectable effect upon saline consumption, blood pressure, kallikrein excretion or heart and kidney weight. Its alleged mineralocorticoid properties, as judged by these criteria, were not demonstrable.  相似文献   
54.
Summary Dosages of either 1 or 2 mg daily of 16-hydroxy-dehydroepiandrosterone, given to mononephretomized, salt-loaded female rats, had no detectable effect upon saline consumption, blood pressure, kallikrein excretion or heart and kidney weight. Its alleged mineralocorticoid properties, as judged by these criteria, were not demonstrable.This study was supported by a grant No. HL 15319 from the United States Public Health Service.  相似文献   
55.
The present research brings new insights on the role of admixed corrosion inhibitors in the processes of cement hydration and rebar corrosion.The admixing of NaCl and the corrosion inhibitors in fresh mortar was found to alter the morphology and microstructure of the hardened mortar at the steel-mortar interfacial region.The admixing of the inhibitors increased the risk of carbonation of cement hydrates at the steel-mortar interfacial region,but partially displaced chloride ions. Chloride and the admixed in...  相似文献   
56.
57.
The International Human Genome Sequencing Consortium (IHGSC) recently completed a sequence of the human genome. As part of this project, we have focused on chromosome 8. Although some chromosomes exhibit extreme characteristics in terms of length, gene content, repeat content and fraction segmentally duplicated, chromosome 8 is distinctly typical in character, being very close to the genome median in each of these aspects. This work describes a finished sequence and gene catalogue for the chromosome, which represents just over 5% of the euchromatic human genome. A unique feature of the chromosome is a vast region of approximately 15 megabases on distal 8p that appears to have a strikingly high mutation rate, which has accelerated in the hominids relative to other sequenced mammals. This fast-evolving region contains a number of genes related to innate immunity and the nervous system, including loci that appear to be under positive selection--these include the major defensin (DEF) gene cluster and MCPH1, a gene that may have contributed to the evolution of expanded brain size in the great apes. The data from chromosome 8 should allow a better understanding of both normal and disease biology and genome evolution.  相似文献   
58.
Hall JG 《Nature genetics》2003,33(4):440-442
  相似文献   
59.
60.
Kyriacou CP  Hall JC 《Nature》1984,308(5954):62-65
The courtship song in Drosophila melanogaster has two components, a low-frequency hum and a train of pulses with a species-specific interpulse interval (IPI) of 30-40 ms(1,2). The IPIs oscillate rhythmically, with periods between 50 and 60 s in wild-type males(3). When females are stimulated with artificial songs in the presence of courting but silent (wingless) males, the 'pulse song' and its oscillation can enhance mating success(4?6). If separated males and females are first simultaneously primed with invariant 34-ms IPIs, their subsequent mating success is improved(7). However, exclusive prestimulation of females leads to faster mating only when the hum component of the song is applied, not constant 34-ms IPIs(5). We have re-examined these findings by testing whether prior exposure of females to a rhythmic pulse song speeds up subsequent mating performance. We report here that it does. Furthermore, learning and memory mutations(8), expressed in the females to whom songs are being played, either 'block' or attenuate the effectiveness of acoustical priming.  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