全文获取类型
收费全文 | 613篇 |
免费 | 11篇 |
国内免费 | 19篇 |
专业分类
系统科学 | 11篇 |
丛书文集 | 2篇 |
教育与普及 | 2篇 |
理论与方法论 | 4篇 |
现状及发展 | 136篇 |
研究方法 | 82篇 |
综合类 | 396篇 |
自然研究 | 10篇 |
出版年
2021年 | 3篇 |
2019年 | 6篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 4篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 14篇 |
2012年 | 59篇 |
2011年 | 64篇 |
2010年 | 25篇 |
2009年 | 19篇 |
2008年 | 42篇 |
2007年 | 46篇 |
2006年 | 43篇 |
2005年 | 42篇 |
2004年 | 38篇 |
2003年 | 30篇 |
2002年 | 27篇 |
2001年 | 18篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1997年 | 3篇 |
1994年 | 2篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1971年 | 4篇 |
1970年 | 2篇 |
1969年 | 4篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 7篇 |
1965年 | 3篇 |
排序方式: 共有643条查询结果,搜索用时 109 毫秒
641.
Seandel M James D Shmelkov SV Falciatori I Kim J Chavala S Scherr DS Zhang F Torres R Gale NW Yancopoulos GD Murphy A Valenzuela DM Hobbs RM Pandolfi PP Rafii S 《Nature》2007,449(7160):346-350
Adult mammalian testis is a source of pluripotent stem cells. However, the lack of specific surface markers has hampered identification and tracking of the unrecognized subset of germ cells that gives rise to multipotent cells. Although embryonic-like cells can be derived from adult testis cultures after only several weeks in vitro, it is not known whether adult self-renewing spermatogonia in long-term culture can generate such stem cells as well. Here, we show that highly proliferative adult spermatogonial progenitor cells (SPCs) can be efficiently obtained by cultivation on mitotically inactivated testicular feeders containing CD34+ stromal cells. SPCs exhibit testicular repopulating activity in vivo and maintain the ability in long-term culture to give rise to multipotent adult spermatogonial-derived stem cells (MASCs). Furthermore, both SPCs and MASCs express GPR125, an orphan adhesion-type G-protein-coupled receptor. In knock-in mice bearing a GPR125-beta-galactosidase (LacZ) fusion protein under control of the native Gpr125 promoter (GPR125-LacZ), expression in the testis was detected exclusively in spermatogonia and not in differentiated germ cells. Primary GPR125-LacZ SPC lines retained GPR125 expression, underwent clonal expansion, maintained the phenotype of germline stem cells, and reconstituted spermatogenesis in busulphan-treated mice. Long-term cultures of GPR125+ SPCs (GSPCs) also converted into GPR125+ MASC colonies. GPR125+ MASCs generated derivatives of the three germ layers and contributed to chimaeric embryos, with concomitant downregulation of GPR125 during differentiation into GPR125- cells. MASCs also differentiated into contractile cardiac tissue in vitro and formed functional blood vessels in vivo. Molecular bookmarking by GPR125 in the adult mouse and, ultimately, in the human testis could enrich for a population of SPCs for derivation of GPR125+ MASCs, which may be employed for genetic manipulation, tissue regeneration and revascularization of ischaemic organs. 相似文献
642.
SMRT-mediated repression of an H3K27 demethylase in progression from neural stem cell to neuron 总被引:3,自引:0,他引:3
Jepsen K Solum D Zhou T McEvilly RJ Kim HJ Glass CK Hermanson O Rosenfeld MG 《Nature》2007,450(7168):415-419
643.
The mammalian hair follicle is a complex 'mini-organ' thought to form only during development; loss of an adult follicle is considered permanent. However, the possibility that hair follicles develop de novo following wounding was raised in studies on rabbits, mice and even humans fifty years ago. Subsequently, these observations were generally discounted because definitive evidence for follicular neogenesis was not presented. Here we show that, after wounding, hair follicles form de novo in genetically normal adult mice. The regenerated hair follicles establish a stem cell population, express known molecular markers of follicle differentiation, produce a hair shaft and progress through all stages of the hair follicle cycle. Lineage analysis demonstrated that the nascent follicles arise from epithelial cells outside of the hair follicle stem cell niche, suggesting that epidermal cells in the wound assume a hair follicle stem cell phenotype. Inhibition of Wnt signalling after re-epithelialization completely abrogates this wounding-induced folliculogenesis, whereas overexpression of Wnt ligand in the epidermis increases the number of regenerated hair follicles. These remarkable regenerative capabilities of the adult support the notion that wounding induces an embryonic phenotype in skin, and that this provides a window for manipulation of hair follicle neogenesis by Wnt proteins. These findings suggest treatments for wounds, hair loss and other degenerative skin disorders. 相似文献