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   347篇
  免费   1篇
  国内免费   2篇
系统科学   5篇
丛书文集   1篇
教育与普及   1篇
现状及发展   71篇
研究方法   34篇
综合类   226篇
自然研究   12篇
  2018年   3篇
  2017年   3篇
  2016年   1篇
  2015年   2篇
  2014年   3篇
  2013年   2篇
  2012年   25篇
  2011年   44篇
  2010年   15篇
  2009年   3篇
  2008年   11篇
  2007年   15篇
  2006年   24篇
  2005年   10篇
  2004年   10篇
  2003年   6篇
  2002年   7篇
  2001年   10篇
  2000年   11篇
  1999年   7篇
  1997年   1篇
  1996年   3篇
  1995年   1篇
  1994年   1篇
  1992年   11篇
  1991年   4篇
  1990年   7篇
  1989年   6篇
  1987年   10篇
  1986年   5篇
  1985年   4篇
  1984年   4篇
  1983年   3篇
  1982年   4篇
  1981年   4篇
  1980年   3篇
  1979年   9篇
  1978年   4篇
  1977年   1篇
  1976年   5篇
  1975年   2篇
  1974年   4篇
  1973年   7篇
  1971年   4篇
  1970年   9篇
  1969年   3篇
  1968年   5篇
  1967年   7篇
  1966年   1篇
  1965年   5篇
排序方式: 共有350条查询结果,搜索用时 15 毫秒
261.
Cytogenic changes are becoming increasingly important in understanding the pathogenesis of human malignancies. The t(9;22) (q34;q11) translocation is one of the most consistent and generates the Philadelphia chromosome (Ph1) (ref. 1) in chronic myeloid leukaemia (CML); it has also been observed in some acute lymphoblastic leukaemias (ALL) (ref. 2). In CML the breakpoints occur on chromosome 22 in the region designated bcr (ref. 3) and result in the expression of a bcr-abl fusion product of relative molecular mass (MT) 210,000 (210K) with associated in vitro tyrosine kinase activity (P210bcr-abl). In some cases of Ph1-positive ALL, a novel abl-related protein (P190all-abl) of 190K has been shown to have tyrosine kinase activity. In this report we demonstrate that the P190all-abl protein has a bcr determinant from the amino-terminal region, but is lacking a bcr determinant normally found in the P210bcr-abl near the bcr-abl junction. The chimaeric nature of the P190all-abl was confirmed by sequential immunoprecipitation with antisera against abl and bcr peptides.  相似文献   
262.
263.
4',6-Dichloroflavan (BW683C), a new anti-rhinovirus compound   总被引:10,自引:0,他引:10  
  相似文献   
264.
香港海域海洋沉积物的放射性测量   总被引:1,自引:2,他引:1  
本文报导了香港海域8个采样站位表层沉积物样品总α,总β和高纯锗γ谱放射性核素分析的测量结果。α/β比值平均为1.23. ̄(238)U, ̄(226)Ra, ̄(232)Th和 ̄(10)K的含量均值分别为39.7,32.5,48.1和625Bq·kg ̄(-1),裂变产物 ̄(135)Cs含量均值为2.00Bq·kg ̄(-1),其量甚微,但易于检出。  相似文献   
265.
266.
Y Zhang  B Heym  B Allen  D Young  S Cole 《Nature》1992,358(6387):591-593
Tuberculosis is responsible for one in four of all avoidable adult deaths in developing countries. Increased frequency and accelerated fatality of the disease among individuals infected with human immunodeficiency virus has raised worldwide concern that control programmes may be inadequate, and the emergence of multidrug-resistant strains of Mycobacterium tuberculosis has resulted in several recent fatal outbreaks in the United States. Isonicotinic acid hydrazide (isoniazid, INH) forms the core of antituberculosis regimens; however, clinical isolates that are resistant to INH show reduced catalase activity and a relative lack of virulence in guinea-pigs. Here we use mycobacterial genetics to study the molecular basis of INH resistance. A single M. tuberculosis gene, katG, encoding both catalase and peroxidase, restored sensitivity to INH in a resistant mutant of Mycobacterium smegmatis, and conferred INH susceptibility in some strains of Escherichia coli. Deletion of katG from the chromosome was associated with INH resistance in two patient isolates of M. tuberculosis.  相似文献   
267.
268.
Contraction of single smooth muscle cells from Bufo marinus stomach   总被引:10,自引:0,他引:10  
R M Bagby  A M Young  R S Dotson  B A Fisher  K McKinnon 《Nature》1971,234(5328):351-352
  相似文献   
269.
Rotating at over twice the angular speed of Earth, Saturn imposes a rapid spin on its magnetosphere. As a result, cold, dense plasma is believed to be flung outward from the inner magnetosphere by centrifugal force and replaced by hotter, more tenuous plasma from the outer magnetosphere. The centrifugal interchange of plasmas in rotating magnetospheres was predicted many years ago and was conclusively demonstrated by observations in Jupiter's magnetosphere, which--like that of Saturn (but unlike that of Earth)--is rotationally dominated. Recent observations in Saturn's magnetosphere have revealed narrow injections of hot, tenuous plasma believed to be the inward-moving portion of the centrifugal interchange cycle. Here we report observations of the distribution of the angle between the electron velocity vector and the magnetic field vector ('pitch angle') obtained in the cold, dense plasma adjacent to these inward injection regions. The observed pitch-angle distributions are indicative of outward plasma flow and consistent with centrifugal interchange in Saturn's magnetosphere. Further, we conclude that the observed double-peaked ('butterfly') pitch-angle distributions result from the transport of plasma from regions near the orbits of Dione and Tethys, supporting the idea of distinct plasma tori associated with these moons.  相似文献   
270.
Identification of the cellular receptor for anthrax toxin.   总被引:44,自引:0,他引:44  
K A Bradley  J Mogridge  M Mourez  R J Collier  J A Young 《Nature》2001,414(6860):225-229
The tripartite toxin secreted by Bacillus anthracis, the causative agent of anthrax, helps the bacterium evade the immune system and can kill the host during a systemic infection. Two components of the toxin enzymatically modify substrates within the cytosol of mammalian cells: oedema factor (OF) is an adenylate cyclase that impairs host defences through a variety of mechanisms including inhibiting phagocytosis; lethal factor (LF) is a zinc-dependent protease that cleaves mitogen-activated protein kinase kinase and causes lysis of macrophages. Protective antigen (PA), the third component, binds to a cellular receptor and mediates delivery of the enzymatic components to the cytosol. Here we describe the cloning of the human PA receptor using a genetic complementation approach. The receptor, termed ATR (anthrax toxin receptor), is a type I membrane protein with an extracellular von Willebrand factor A domain that binds directly to PA. In addition, a soluble version of this domain can protect cells from the action of the toxin.  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