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   70813篇
  免费   142414篇
  国内免费   29723篇
  2019年   2792篇
  2018年   2398篇
  2017年   2157篇
  2016年   2349篇
  2015年   2610篇
  2014年   2689篇
  2013年   2661篇
  2012年   3098篇
  2011年   3637篇
  2010年   4897篇
  2009年   9947篇
  2008年   4146篇
  2007年   4083篇
  2006年   2993篇
  2005年   2988篇
  2004年   2889篇
  2003年   2453篇
  2002年   3211篇
  2001年   4186篇
  1999年   6696篇
  1998年   8915篇
  1997年   9109篇
  1996年   8471篇
  1995年   8766篇
  1994年   8148篇
  1993年   7813篇
  1992年   7741篇
  1991年   7762篇
  1990年   8595篇
  1989年   7837篇
  1988年   7144篇
  1987年   6242篇
  1986年   5782篇
  1985年   5216篇
  1984年   4057篇
  1983年   3254篇
  1982年   3585篇
  1981年   3248篇
  1980年   3188篇
  1979年   3267篇
  1978年   2986篇
  1977年   2921篇
  1976年   2741篇
  1975年   2320篇
  1974年   2470篇
  1973年   2475篇
  1972年   2817篇
  1971年   2602篇
  1970年   2346篇
  1969年   2398篇
排序方式: 共有10000条查询结果,搜索用时 538 毫秒
181.
Chromatography of soluble proteins from rat heart on phosphocellulose columns separates two 5'-nucleotidases. The first to emerge from the column shows a preference for AMP over IMP as substrate, whereas the second shows a preference for IMP over AMP. The properties of the IMP-preferring enzyme, including the conditions under which it is eluted from phosphocellulose columns, show it to be the enzyme studied by Itoh, Oka & Ozasa [Biochem. J. (1986) 235, 847-851]. The kinetic properties of the AMP-preferring enzyme indicate that it is likely to be the enzyme responsible for the production of adenosine under conditions of hypoxia and increased work load, and with metabolic stresses such as a high load of acetate.  相似文献   
182.
Vaccination with DNA and recombinant vaccinia viruses (rec.VV) has been studied with the coxsackievirus B3 (CVB3) model system. Plasmids encoding all structural proteins of CVB3, when injected intramuscularly, induced only low levels of virus-specific antibodies. However, DNA vaccination with the major structural protein VP1 protected 72.2% of mice from lethal challenge, whereas VP1 expressed by rec.VV was much less efficient.  相似文献   
183.
184.
Using a combination of a primary growth retardant, mefluidide, a synergistic additive, chlorsulfuron, a detergent to enhance penetration (X-77), and a herbicide, 2,4-D, to provide for control of broadleaf weeds, full-season management of bluegrass (Poa pratensis L.)—tall fescue (Festuca arundinaceae Schreb.) mixtures along roadsides has been achieved. A single spray application is made in the spring, and no additional herbicide applications or mechanical mowing are needed. The treatment is effective with greater than 90% control of fescue seed heads. Those few seed heads that do form remain short. It is economical. The costs of materials and application are equal to or less than the cost of a single mowing cycle. The treatment is environmentally safe when applied in early spring before most agricultural crops have been planted. The effectiveness and low cost of the combination derive from laboratory and greenhouse observations that various materials, herein referred to as additives, often only weakly effective as growth retardants themselves, will interact synergistically with mefluidide to provide overall treatment effectiveness at application rates that are economical. Using this principle, a combination suitable for roadside vegetation management was devised, field-tested for 2 years under actual use conditions, and found to be effective for full-season vegetation management of mixed bluegrass—tall fescue turf to permit considerable cost savings when compared to three-cycle mechanical mowing.  相似文献   
185.
186.
187.
188.
189.
190.
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