全文获取类型
收费全文 | 12726篇 |
免费 | 1049篇 |
国内免费 | 8篇 |
专业分类
13783篇 |
出版年
2022年 | 85篇 |
2021年 | 135篇 |
2020年 | 84篇 |
2019年 | 130篇 |
2018年 | 177篇 |
2017年 | 196篇 |
2016年 | 258篇 |
2015年 | 424篇 |
2014年 | 446篇 |
2013年 | 615篇 |
2012年 | 723篇 |
2011年 | 731篇 |
2010年 | 501篇 |
2009年 | 522篇 |
2008年 | 671篇 |
2007年 | 750篇 |
2006年 | 714篇 |
2005年 | 698篇 |
2004年 | 682篇 |
2003年 | 669篇 |
2002年 | 688篇 |
2001年 | 194篇 |
2000年 | 188篇 |
1999年 | 217篇 |
1998年 | 238篇 |
1997年 | 176篇 |
1996年 | 159篇 |
1995年 | 154篇 |
1994年 | 139篇 |
1993年 | 167篇 |
1992年 | 203篇 |
1991年 | 159篇 |
1990年 | 157篇 |
1989年 | 137篇 |
1988年 | 108篇 |
1987年 | 106篇 |
1986年 | 85篇 |
1985年 | 122篇 |
1984年 | 108篇 |
1983年 | 85篇 |
1982年 | 102篇 |
1981年 | 88篇 |
1980年 | 78篇 |
1979年 | 84篇 |
1978年 | 66篇 |
1977年 | 80篇 |
1976年 | 74篇 |
1975年 | 51篇 |
1974年 | 49篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
D Hernández S Guerrero M Morales 《Comparative biochemistry and physiology. A, Comparative physiology》1987,87(3):649-656
1. The cardiac pacemaker cells of the frog Caudiverbera caudiverbera are centrally located in the sinus venosus. These cells are rounded, smaller than contractile fibres and have large nuclei. 2. Intracellular recording confirmed the existence of primary and transitional pacemaker cells. 3. Action potentials from primary cells were resistant to blockade by tetrodotoxin (TTX), but were abolished by verapamil suggesting that their bioelectric activity is dependent on a slow inward current. 4. Transitional cells appeared to have two different inward currents contributing to the upstroke: a fast TTX-sensitive and a slow verapamil-sensitive current. 相似文献
14.
15.
Growth of the hopanoid-producing bacterium Zymomonas mobilis was inhibited at low concentrations of the cationic detergent octadecyltrimethylammoniumchloride (OTAC). A relationship between sensitivity of Zymomonas mobilis to OTAC, presence of hopanoids and ethanol tolerance was postulated. Mutants resistant to OTAC were isolated from strains ZM1 and ZM4. They did not present any alteration of the hopanoid content and their squalene cyclases showed the same sensitity to OTAC as the parent enzymes. Resistance to OTAC paralleled pleiotropic effects including, enhanced accessibility of the membrane-bound alkaline phosphatase, important release of proteins from cells by Tris/HCl treatment, increased resistance to antibiotics and increased sensitivity to ethanol. In addition, OTACR mutants were also characterized by the synthesis or the overproduction of an outer membrane protein (F53) not detected on 2D-PAGE maps of parent strains and by a normal heat shock response. The role of hopanoids, heat shock proteins, protein F53 and membrane organization in ethanol tolerance is discussed.Abbreviations OTAC
octadecyltrimethylammoniumchloride
- SLS
sodium lauryl sarcosinate 相似文献
16.
17.
18.
Sylvie Cablé Michèle Kedinger Michel Dauça 《Differentiation; research in biological diversity》1993,54(2):99-108
Abstract. The development of peroxisomes and expression of their enzymes were investigated in differentiating intestinal epithelial cells during their migration along the crypt-villus axis. Sequential cell populations harvested by a low-temperature method were identified by microscopy, determination of alkaline phosphatase and sucrase activities and incorporation of [3 H]-thymidine into DNA. Ultrastructural cytochemistry after staining for catalase activity, revealed the presence of peroxisomes in undifferentiated stem cells located in the crypt region. Morphometry indicated that the number of these organelles increased as intestinal epithelial cells differentiate. Catalase activity was higher in the crypt cells than in the mature enterocytes harvested from villus tips. On the other hand, an increasing gradient of activity was observed from crypts to villus tips for peroxisomal oxidases, i.e. fatty acyl coA oxidase, D-amino acid oxidase and polyamine oxidase. These findings indicate that biogenesis of peroxisomes occurs during migration of intestinal epithelial cells along the crypt-villus axis and that peroxisomal oxidases contribute substantially to the biochemical maturation of enterocytes. 相似文献
19.
20.