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   1267691篇
  免费   104815篇
  国内免费   1540篇
  2021年   17768篇
  2020年   12646篇
  2019年   16195篇
  2018年   17856篇
  2017年   16669篇
  2016年   28168篇
  2015年   42234篇
  2014年   50201篇
  2013年   76532篇
  2012年   33781篇
  2011年   22138篇
  2010年   43242篇
  2009年   44811篇
  2008年   21099篇
  2007年   18933篇
  2006年   24345篇
  2005年   25849篇
  2004年   24712篇
  2003年   22382篇
  2002年   20531篇
  2001年   29059篇
  2000年   26334篇
  1999年   27755篇
  1998年   24756篇
  1997年   24505篇
  1996年   24115篇
  1995年   22290篇
  1994年   22098篇
  1993年   21144篇
  1992年   24065篇
  1991年   22436篇
  1990年   21437篇
  1989年   22321篇
  1988年   20456篇
  1987年   19381篇
  1986年   18341篇
  1985年   20516篇
  1984年   20816篇
  1983年   18455篇
  1982年   19404篇
  1981年   18872篇
  1980年   17633篇
  1979年   16638篇
  1978年   16230篇
  1977年   15720篇
  1976年   15099篇
  1975年   14443篇
  1974年   14717篇
  1973年   15198篇
  1972年   12638篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
831.
832.
833.
Abstract— In contrast to mouse brain, the content of putrescine in fish brain considerably exceeds that of spermine and spermidine. While we observed constant protein, RNA and spermidine concentrations in fish brains of weights between 60 and 800 mg, DNA and spermine concentrations diminished with increasing brain weight, the content of spermine per cell being constant throughout life. It can be concluded from our results that growth of fish brain results both from cell enlargement and cell proliferation. The concomitant changes of spermine and DNA concentrations in the growing fish brain are the first example of a direct quantitative relationship between these cell constituents and provides evidence on their possible functional relationship in the cell nucleus.  相似文献   
834.
835.
836.
The potential of nisin F as an antimicrobial agent in treating subcutaneous skin infections was tested in vivo by infecting C57BL/6 mice with a bioluminescent strain of Staphylococcus aureus (Xen 36). Strain Xen 36 has the luxABCDE operon located on a native plasmid. Mice were grouped into four groups: Infected with strain Xen 36 and treated with nisin F, infected with strain Xen 36 and treated with saline (placebo), not infected and treated with nisin (control) and not infected and not treated (control). The immune systems of the mice were suppressed with deksamethasone. Mice were treated with either nisin F or sterile physiological saline 24 and 48 h after infection with subcutaneously injected S. aureus Xen 36 (4 × 106 CFU). Histology and bioluminescent flux measurements revealed no significant difference between infected mice treated with nisin and saline, respectively. However, infected mice treated with nisin F had an increased number of polymorphonuclear cells when compared with infected mice treated with saline. Also, not infected mice treated with nisin F had an influx of polymorphonuclear cells. Nisin F is thus ineffective in combating deep dermal staphylococcal infections. The apparent immune modulation of nisin when subcutaneously injected has to be investigated.  相似文献   
837.
An approach to the synthesis of cationic carbohydrate surfactants with potential antimicrobial and transfecting activities is proposed.  相似文献   
838.
839.
840.
Cotton seedlings raised under glass from seed pre-soaked in a water suspension of Xanthomonas malvacearum , and watered by sub-irrigation only, developed atypical dull green flaccid areas extending from the periphery of the cotyledons. Later symptoms that variably developed were: vascular discoloration, not necessarily continuous, in the petioles of affected cotyledons, in the hypocotyl, and in parts of the plant above the cotyledonary node; premature withering of cotyledons; dull green flaccid areas in true leaves, not necessarily the lowest, later turning brown and drying, with usually a chlorotic margin; parenchymatous attack in stems, petioles and leaves. Evidence is adduced, from the progression of symptoms and from associations between them, and from isolations of the pathogen from various parts of the plant at different stages, that the course of this type of infection is primarily vascular, progressing from the edges of cotyledons into the hypocotyl and thence upwards in vascular tissues. Thence the infection may break out at any time into parenchymatous tissues, leading to the more characteristic forms of the disease, of greater or less severity according to the susceptibility of the parenchyma at the time of its invasion. Similar symptoms have been observed in field plantings, and it is suggested that vascular infection is of greater and wider significance in the epidemiology of bacterial blight than has hitherto been commonly accepted.  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