全文获取类型
收费全文 | 16884篇 |
免费 | 1277篇 |
国内免费 | 1277篇 |
专业分类
19438篇 |
出版年
2024年 | 49篇 |
2023年 | 248篇 |
2022年 | 598篇 |
2021年 | 994篇 |
2020年 | 593篇 |
2019年 | 797篇 |
2018年 | 786篇 |
2017年 | 579篇 |
2016年 | 807篇 |
2015年 | 1069篇 |
2014年 | 1318篇 |
2013年 | 1444篇 |
2012年 | 1545篇 |
2011年 | 1388篇 |
2010年 | 841篇 |
2009年 | 759篇 |
2008年 | 860篇 |
2007年 | 715篇 |
2006年 | 572篇 |
2005年 | 506篇 |
2004年 | 419篇 |
2003年 | 364篇 |
2002年 | 276篇 |
2001年 | 250篇 |
2000年 | 223篇 |
1999年 | 231篇 |
1998年 | 158篇 |
1997年 | 135篇 |
1996年 | 121篇 |
1995年 | 110篇 |
1994年 | 105篇 |
1993年 | 87篇 |
1992年 | 102篇 |
1991年 | 100篇 |
1990年 | 53篇 |
1989年 | 55篇 |
1988年 | 41篇 |
1987年 | 32篇 |
1986年 | 22篇 |
1985年 | 28篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Thymic stromal cell clone with nursing activity supports the growth and differentiation of murine CD4+8+ thymocytes in vitro 总被引:2,自引:0,他引:2
T Nishimura Y Takeuchi Y Ichimura X H Gao A Akatsuka N Tamaoki H Yagita K Okumura S Habu 《Journal of immunology (Baltimore, Md. : 1950)》1990,145(12):4012-4017
Thymic stromal cell clone, TNC-R3.1 cell, was established from spontaneous AKR/J mouse thymoma. TNC-R3.1 cell, which has the similar properties to thymic nurse cells, formed a unique complex with normal thymocyte subpopulations. Flow cytometry analysis demonstrated that CD4+8+ and CD4-8- immature thymocytes preferentially interacted with TNC-R3.1 stromal cell clone. CD4+8+ thymocytes, which interacted with TNC-R3.1 stromal cell clone, contained a higher proportion of large size and cycling T cells than did noninteracting CD4+8+ thymocytes. As is generally accepted, CD4+8+ thymocytes did not respond to any stimulation such as IL-2, anti-CD3 mAb (2C11), or IL-2 plus 2C11. However, culture of isolated CD4+8+ thymocytes on TNC-R3.1 stromal cell monolayer in the presence of suboptimal dose of IL-2 induced a significant cell growth. Moreover, the addition of 2C11 and IL-2 into this coculture system resulted in a dramatic increase of the proliferative response of thymocytes. Flow cytometry analysis showed the proliferating cells on TNC-R3.1, which originated from CD4+8+ thymocytes, were mostly TCR-alpha beta+ CD3+CD4-8+ T cells. These results provide in vitro evidence that CD4+8+ thymocytes are at an intermediate stage of T cell maturation and TNC-R3.1 stromal cell clone induces the growth and differentiation of CD4+8+ thymocytes into CD4-8+ T cells. 相似文献
103.
104.
105.
106.
107.
浙江西门岛海洋特别保护区大型底栖动物功能群特征及其与环境的关系 总被引:4,自引:0,他引:4
为研究浙江西门岛海洋特别保护区大型底栖动物功能群的变化规律及其与环境因子的关系,作者分别于2010年4月(春季)、11月(秋季),2011年8月(夏季)和2012年2月(冬季)进行了4个航次的大型底栖动物调查,共鉴定出大型底栖动物78种,根据其食性类型划分为浮游生物食者、植食者、肉食者、杂食者、碎屑食者5种功能群.各功能群平均密度从高到低依次为浮游生物食者>肉食者>植食者>碎屑食者>杂食者,平均生物量从高到低依次为浮游生物食者>碎屑食者>肉食者>杂食者>植食者.单因素方差分析结果表明,大型底栖动物各功能群的密度和生物量季节间均无显著性差异.典范对应分析结果表明,影响大型底栖动物功能群的主要环境因子包括温度、溶解氧、溶解态无机磷和表层沉积物的中值粒径,排序轴对功能群-环境关系的贡献率计算结果表明环境变量可以较好地解释功能群的变化情况. 相似文献
108.
Yang Wang Xu Li Xiaoliang Wang Waynebond Lau Yajing Wang Yuan Xing Xing Zhang Xinliang Ma Feng Gao 《PloS one》2013,8(8)
Evidence suggests Ginsenoside Rd (GSRd), a biologically active extract from the medical plant Panax Ginseng, exerts antioxidant effect, decreasing reactive oxygen species (ROS) formation. Current study determined the effect of GSRd on myocardial ischemia/reperfusion (MI/R) injury (a pathological condition where ROS production is significantly increased) and investigated the underlying mechanisms. The current study utilized an in vivo rat model of MI/R injury and an in vitro neonatal rat cardiomyocyte (NRC) model of simulated ischemia/reperfusion (SI/R) injury. Infarct size was measured by Evans blue/TTC double staining. NRC injury was determined by MTT and lactate dehydrogenase (LDH) leakage assay. ROS accumulation and apoptosis were assessed by flow cytometry. Mitochondrial membrane potential (MMP) was determined by 5, 5′, 6, 6′-tetrachloro-1, 1′, 3, 3′-tetrathylbenzimidazol carbocyanine iodide (JC-1). Cytosolic translocation of mitochondrial cytochrome c and expression of caspase-9, caspase-3, Bcl-2 family proteins, and phosphorylated Akt and GSK-3β were determined by western blot. Pretreatment with GSRd (50 mg/kg) significantly augmented rat cardiac function, as evidenced by increased left ventricular ejection fraction (LVEF) and ±dP/dt. GSRd reduced myocardial infarct size, apoptotic cell death, and blood creatine kinase/lactate dehydrogenase levels after MI/R. In NRCs, GSRd (10 µM) inhibited SI/R-induced ROS generation (P<0.01), decreased cellular apoptosis, stabilized the mitochondrial membrane potential (MMP), and attenuated cytosolic translocation of mitochondrial cytochrome c. GSRd inhibited activation of caspase-9 and caspase-3, increased the phosphorylated Akt and GSK-3β, and increased the Bcl-2/Bax ratio. Together, these data demonstrate GSRd mediated cardioprotective effect against MI/R–induced apoptosis via a mitochondrial-dependent apoptotic pathway. 相似文献
109.
110.
Gao JX Zhang J Awaraji C Bhatia M Jevnikar A Singh B Bell D Delovitch TL 《Cellular immunology》2000,202(1):41-53
The identification of factors that regulate the proliferation and differentiation of double-positive (DP) into CD4(+) and CD8(+) single-positive (SP) thymocytes has proven difficult due to the inability of DP thymocytes to proliferate, expand, and differentiate into SP thymocytes in available cell culture media. Here we report on the ability of DP thymocytes to differentiate in a novel conditioned medium, termed XLCM, derived from the supernatant of mitogen activated human cord blood mononuclear cells. During a 5-day culture in XLCM in the absence of thymic stromal cells, DP thymocytes from normal mice and MHC double knockout mice (lack SP thymocytes) proliferate, expand, and differentiate into several (alphabetaTCR(+), NK1.1(+)alphabetaTCR(+), and gammadeltaTCR(+)) subsets of CD4(+) and predominantly CD8(+) SP thymocytes. These studies suggest that the use of XLCM may aid in the characterization of factors that regulate the differentiation of DP thymocytes into CD8(+) SP thymocytes. 相似文献