全文获取类型
收费全文 | 8365篇 |
免费 | 942篇 |
国内免费 | 1篇 |
出版年
2021年 | 100篇 |
2019年 | 65篇 |
2018年 | 110篇 |
2017年 | 102篇 |
2016年 | 139篇 |
2015年 | 269篇 |
2014年 | 283篇 |
2013年 | 378篇 |
2012年 | 421篇 |
2011年 | 422篇 |
2010年 | 278篇 |
2009年 | 224篇 |
2008年 | 372篇 |
2007年 | 410篇 |
2006年 | 349篇 |
2005年 | 367篇 |
2004年 | 326篇 |
2003年 | 303篇 |
2002年 | 294篇 |
2001年 | 166篇 |
2000年 | 177篇 |
1999年 | 143篇 |
1998年 | 126篇 |
1997年 | 122篇 |
1996年 | 104篇 |
1995年 | 97篇 |
1994年 | 115篇 |
1993年 | 100篇 |
1992年 | 160篇 |
1991年 | 128篇 |
1990年 | 113篇 |
1989年 | 119篇 |
1988年 | 109篇 |
1987年 | 125篇 |
1986年 | 97篇 |
1985年 | 137篇 |
1984年 | 144篇 |
1983年 | 106篇 |
1982年 | 125篇 |
1981年 | 115篇 |
1980年 | 102篇 |
1979年 | 93篇 |
1978年 | 65篇 |
1977年 | 70篇 |
1976年 | 79篇 |
1975年 | 63篇 |
1974年 | 76篇 |
1973年 | 65篇 |
1972年 | 57篇 |
1971年 | 55篇 |
排序方式: 共有9308条查询结果,搜索用时 0 毫秒
1.
2.
Keratinocyte growth-promoting activity from human placenta 总被引:4,自引:0,他引:4
Extracts of term human placenta were tested for enhancement of proliferative growth of primary cultures of human keratinocytes. Saline extracts or supernatants from homogenates were dialyzed extensively, lyophilized, and tested in subcultures of keratinocytes in MCDB 153 medium with 0.1 mM Ca++ containing only defined supplements (insulin, hydrocortisone, transferrin, ethanolamine, phosphoethanolamine). Cells plated in the absence of EGF at moderately high densities (1000-3000 cells per cm2) formed colonies and grew in the presence of placental extract at 25-500 micrograms/ml. Extracts of cord serum or maternal serum were inactive, suggesting that the activity is derived from placental tissue. The activity is not EGF, since the activity in the placental extract, unlike EGF, did not promote growth at low cell density, was synergistic with EGF under some conditions, and did not produce changes in colonial morphology which occurred in the presence of EGF. Unlike keratinocyte growth-promoting activity in bovine hypothalamic extract, the activity is non-dialyzable and is destroyed at 100 degrees C. Placental extract could not replace any of the defined components of the medium and is therefore distinct from them. The presence of activity in the placenta with distinctive properties suggests that this is a previously undescribed material with growth-promoting properties for epithelium. 相似文献
3.
4.
5.
6.
William Russell 《BMJ (Clinical research ed.)》1985,290(6485):1914
7.
8.
We have investigated the time course of the degradation of a supported dipalmitoylphosphatidylcholine bilayer by phospholipase A2 in aqueous buffer with an atomic force microscope. Contact mode imaging allows visualization of enzyme activity on the substrate with a lateral resolution of less than 10 nm. Detailed analysis of the micrographs reveals a dependence of enzyme activity on the phospholipid organization and orientation in the bilayer. These experiments suggest that it is possible to observe single enzymes at work in small channels, which are created by the hydrolysis of membrane phospholipids. Indeed, the measured rate of hydrolysis of phospholipids corresponds very well with the enzyme activity found in kinetic studies. It was also possible to correlate the number of enzymes at the surface, as calculated from the binding constant to the number of starting points of the hydrolysis. In addition, the width of the channels was found to be comparable to the diameter of a single phospholipase A2 and thus further supports the single-enzyme hypothesis. 相似文献
9.
10.