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   525036篇
  免费   66657篇
  国内免费   173篇
  2016年   5525篇
  2015年   7795篇
  2014年   9343篇
  2013年   13230篇
  2012年   14712篇
  2011年   14790篇
  2010年   9740篇
  2009年   9235篇
  2008年   13200篇
  2007年   13962篇
  2006年   12970篇
  2005年   12610篇
  2004年   12511篇
  2003年   12106篇
  2002年   11647篇
  2001年   22690篇
  2000年   23199篇
  1999年   18591篇
  1998年   6643篇
  1997年   7039篇
  1996年   6829篇
  1995年   6567篇
  1994年   6552篇
  1993年   6468篇
  1992年   16237篇
  1991年   16126篇
  1990年   15803篇
  1989年   15370篇
  1988年   14359篇
  1987年   13810篇
  1986年   12918篇
  1985年   13062篇
  1984年   10972篇
  1983年   9692篇
  1982年   7476篇
  1981年   7007篇
  1980年   6585篇
  1979年   10963篇
  1978年   8518篇
  1977年   7849篇
  1976年   7454篇
  1975年   8261篇
  1974年   8562篇
  1973年   8404篇
  1972年   7950篇
  1971年   6918篇
  1970年   6050篇
  1969年   5715篇
  1968年   5211篇
  1967年   4526篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
141.
142.
143.
144.
A new gas-liquid chromatographic method was developed for the determination of diethylether in whole blood. Ether was quantitated by peak area ratio analysis with n-propanol as the internal standard using a flame ionization detector. Blood ether concentrations were determined in cats undergoing inhalational anesthesia by ether in oxygen. In normal spontaneously breathing cats, anesthesia began at ether concentrations of about 0.6 g/l, and respiratory arrest occurred at 2.4 g/l and above. Mean arterial blood pressure was well maintained throughout the entire anesthetic range. In spinal artificially respired animals, mean arterial blood pressure correlated inversely with blood ether concentration. The data suggest that decline in blood pressure may be a useful sign of ether toxicity in spinal cats.  相似文献   
145.
ABSTRACT   The phrase persistent vulnerability reflects the enduring relationship of the rural population in Ceará with a highly variable climate. Persistence underscores the historical and unyielding nature of this vulnerability. Yet contrary to once-catastrophic rates of mortality etched in a public consciousness, no one dies from severe droughts and few people flee them as in the past. Government relief and social transfers have become the institutionalized form of adaptation, giving way to the counterintuitive reality that drought stabilizes the food and income supply for poor people. We analyze how maladaptive risk reduction, which is embedded in clientilistic social relations, undermines resilience, and we examine pathways toward a more sustainable adaptive relationship.  相似文献   
146.
Ffh is a component of a bacterial ribonucleoprotein complex homologous to the signal recognition particle (SRP) of eukaryotes. It comprises three domains that mediate both binding to the hydrophobic signal sequence of the nascent polypeptide and the GTP-dependent interaction of Ffh with a structurally homologous GTPase of the SRP receptor. The X-ray structures of the two-domain 'NG' GTPase of Ffh in complex with Mg2+GDP and GDP have been determined at 2.0 A resolution. The structures explain the low nucleotide affinity of Ffh and locate two regions of structural mobility at opposite sides of the nucleotide-binding site. One of these regions includes highly conserved sequence motifs that presumably contribute to the structural trigger signaling the GTP-bound state. The other includes the highly conserved interface between the N and G domains, and supports the hypothesis that the N domain regulates or signals the nucleotide occupancy of the G domain.  相似文献   
147.
148.
149.
Burials and mummies of dogs from the Arica, Chile, area are described. It is concluded that these dogs were brought to this area 2500 years ago by shepherds from the highlands and are still present, relatively unchanged.  相似文献   
150.
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