全文获取类型
收费全文 | 119402篇 |
免费 | 10363篇 |
国内免费 | 69篇 |
出版年
2022年 | 494篇 |
2021年 | 1527篇 |
2020年 | 962篇 |
2019年 | 1200篇 |
2018年 | 1547篇 |
2017年 | 1417篇 |
2016年 | 2455篇 |
2015年 | 4102篇 |
2014年 | 4607篇 |
2013年 | 6159篇 |
2012年 | 7445篇 |
2011年 | 7703篇 |
2010年 | 4974篇 |
2009年 | 4435篇 |
2008年 | 6581篇 |
2007年 | 6696篇 |
2006年 | 6313篇 |
2005年 | 6330篇 |
2004年 | 6375篇 |
2003年 | 5884篇 |
2002年 | 5801篇 |
2001年 | 1435篇 |
2000年 | 1079篇 |
1999年 | 1430篇 |
1998年 | 1766篇 |
1997年 | 1323篇 |
1996年 | 1205篇 |
1995年 | 1140篇 |
1994年 | 1090篇 |
1993年 | 1043篇 |
1992年 | 1051篇 |
1991年 | 982篇 |
1990年 | 898篇 |
1989年 | 928篇 |
1988年 | 846篇 |
1987年 | 795篇 |
1986年 | 735篇 |
1985年 | 941篇 |
1984年 | 1106篇 |
1983年 | 940篇 |
1982年 | 1128篇 |
1981年 | 1089篇 |
1980年 | 987篇 |
1979年 | 731篇 |
1978年 | 814篇 |
1977年 | 764篇 |
1976年 | 725篇 |
1975年 | 592篇 |
1974年 | 717篇 |
1973年 | 655篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
Cystine Deprivation Induces Oligodendroglial Death: Rescue by Free Radical Scavengers and by a Diffusible Glial Factor 总被引:4,自引:0,他引:4
Mihoko Yonezawa Stephen A. Back Xiaodong Gan Paul A. Rosenberg Joseph J. Volpe 《Journal of neurochemistry》1996,67(2):566-573
Abstract: In this study we examined the effect on oligodendroglial survival of exogenous cystine deprivation. Oligodendroglia isolated from mixed glial primary cultures derived from brains of 1-day-old rats, and then grown for 3 days, were markedly dependent on extracellular cystine for survival. The EC50 values for cystine for a 24-h exposure ranged from 2 to 65 µ M . After 6 h of cystine deprivation, the cellular glutathione level decreased to 21 ± 13% of the control. Free radical scavengers (α-tocopherol, ascorbate, idebenone, and N-tert -butyl-α-phenylnitrone) were protective against cystine deprivation but had no effect on the glutathione level. An iron chelator, desferrioxamine mesylate, also was protective. These findings suggest that intracellular hydroxyl radicals are important for this toxicity. In contrast to the observations in 3-day-old cultures, the dependence on exogenous cystine for cell viability was not observed consistently in oligodendroglia cultured for 6 days before the onset of cystine deprivation. Several observations suggested that this loss of cystine dependence was due to a diffusible factor. Sensitivity to the toxicity of cystine deprivation in day 6 cultures increased as the volume of medium was increased from 0.3 to 2 ml. Furthermore, preincubation of cystine-depleted medium with astrocyte cultures eliminated the toxicity of the cystine deprivation. HPLC assay of the conditioned cystine-depleted medium showed no significant change in cystine or cysteine concentration. We conclude that oligodendroglia are highly susceptible to cystine deprivation in day 3 cultures and that this susceptibility is due to the accumulation of intracellular free radicals in the setting of glutathione depletion. The resistance of day 6 oligodendroglial cultures is caused at least in part by a diffusible factor. 相似文献
103.
This overview summarizes the data for how epithelial cells sort and deliver proteins and lipids to the apical and basolateral cell surface domains. The basolateral pathway uses a Rab-SNARE mechanism for docking and fusion, while the apical route employs a different machinery. This latter mechanism is based on lipid microdomains, composed of clusters of sphingolipids and cholesterol, which function as rafts for apical delivery. The sphingolipid-cholesterol raft mechanism seems to be employed generally by mammalian cells to transport raft-associated proteins to their post-Golgi destinations. 相似文献
104.
105.
106.
107.
108.
109.
110.
Susan Morrison Grace John-Stewart John J. Egessa Sezi Mubezi Sylvia Kusemererwa Dennis K. Bii Nulu Bulya Francis Mugume James D. Campbell Jonathan Wangisi Elizabeth A. Bukusi Connie Celum Jared M. Baeten Partners PrEP Study Team 《PloS one》2015,10(10)
During an HIV-1 prevention clinical trial in East Africa, we observed 16 cases of primary HIV-1 infection in women coincident with pregnancy or breastfeeding. Nine of eleven pregnant women initiated rapid combination antiretroviral therapy (ART), despite having CD4 counts exceeding national criteria for ART initiation; breastfeeding women initiated ART or replacement feeding. Rapid ART initiation during primary HIV-1 infection during pregnancy and breastfeeding is feasible in this setting. 相似文献