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   1374424篇
  免费   120240篇
  国内免费   1450篇
  2021年   17784篇
  2019年   16181篇
  2018年   17967篇
  2017年   16671篇
  2016年   28177篇
  2015年   42569篇
  2014年   50527篇
  2013年   76970篇
  2012年   36531篇
  2011年   25097篇
  2010年   43860篇
  2009年   45230篇
  2008年   23919篇
  2007年   22130篇
  2006年   27320篇
  2005年   28383篇
  2004年   27736篇
  2003年   25324篇
  2002年   23566篇
  2001年   33653篇
  2000年   30948篇
  1999年   31374篇
  1998年   25486篇
  1997年   25308篇
  1996年   24899篇
  1995年   22993篇
  1994年   22817篇
  1993年   21890篇
  1992年   27742篇
  1991年   26216篇
  1990年   25224篇
  1989年   26055篇
  1988年   24118篇
  1987年   22700篇
  1986年   21704篇
  1985年   23782篇
  1984年   23440篇
  1983年   20735篇
  1982年   20963篇
  1981年   20145篇
  1980年   18762篇
  1979年   19549篇
  1978年   18228篇
  1977年   17585篇
  1976年   16894篇
  1975年   16370篇
  1974年   16992篇
  1973年   17325篇
  1972年   14852篇
  1971年   13585篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
931.
932.
933.
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   
934.
935.
936.
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   
937.
An approach to the synthesis of cationic carbohydrate surfactants with potential antimicrobial and transfecting activities is proposed.  相似文献   
938.
939.
940.
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