全文获取类型
收费全文 | 190篇 |
免费 | 0篇 |
专业分类
教育与普及 | 1篇 |
理论与方法论 | 1篇 |
现状及发展 | 11篇 |
研究方法 | 12篇 |
综合类 | 161篇 |
自然研究 | 4篇 |
出版年
2018年 | 1篇 |
2013年 | 2篇 |
2012年 | 6篇 |
2011年 | 5篇 |
2010年 | 1篇 |
2008年 | 2篇 |
2007年 | 5篇 |
2006年 | 4篇 |
2005年 | 10篇 |
2004年 | 25篇 |
2003年 | 43篇 |
2002年 | 27篇 |
2001年 | 26篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 4篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有190条查询结果,搜索用时 828 毫秒
101.
Dynein structure and power stroke 总被引:11,自引:0,他引:11
Dynein ATPases are microtubule motors that are critical to diverse processes such as vesicle transport and the beating of sperm tails; however, their mechanism of force generation is unknown. Each dynein comprises a head, from which a stalk and a stem emerge. Here we use electron microscopy and image processing to reveal new structural details of dynein c, an isoform from Chlamydomonas reinhardtii flagella, at the start and end of its power stroke. Both stem and stalk are flexible, and the stem connects to the head by means of a linker approximately 10 nm long that we propose lies across the head. With both ADP and vanadate bound, the stem and stalk emerge from the head 10 nm apart. However, without nucleotide they emerge much closer together owing to a change in linker orientation, and the coiled-coil stalk becomes stiffer. The net result is a shortening of the molecule coupled to an approximately 15-nm displacement of the tip of the stalk. These changes indicate a mechanism for the dynein power stroke. 相似文献
102.
103.
Osteoblastic cells regulate the haematopoietic stem cell niche 总被引:2,自引:0,他引:2
Calvi LM Adams GB Weibrecht KW Weber JM Olson DP Knight MC Martin RP Schipani E Divieti P Bringhurst FR Milner LA Kronenberg HM Scadden DT 《Nature》2003,425(6960):841-846
Stem cell fate is influenced by specialized microenvironments that remain poorly defined in mammals. To explore the possibility that haematopoietic stem cells derive regulatory information from bone, accounting for the localization of haematopoiesis in bone marrow, we assessed mice that were genetically altered to produce osteoblast-specific, activated PTH/PTHrP receptors (PPRs). Here we show that PPR-stimulated osteoblastic cells that are increased in number produce high levels of the Notch ligand jagged 1 and support an increase in the number of haematopoietic stem cells with evidence of Notch1 activation in vivo. Furthermore, ligand-dependent activation of PPR with parathyroid hormone (PTH) increased the number of osteoblasts in stromal cultures, and augmented ex vivo primitive haematopoietic cell growth that was abrogated by gamma-secretase inhibition of Notch activation. An increase in the number of stem cells was observed in wild-type animals after PTH injection, and survival after bone marrow transplantation was markedly improved. Therefore, osteoblastic cells are a regulatory component of the haematopoietic stem cell niche in vivo that influences stem cell function through Notch activation. Niche constituent cells or signalling pathways provide pharmacological targets with therapeutic potential for stem-cell-based therapies. 相似文献
104.
105.
106.
107.
108.
Prevention of rapid immune elimination of anti-lymphocytic globulin in transplant patients 总被引:4,自引:0,他引:4
109.
110.