全文获取类型
收费全文 | 26048篇 |
免费 | 1497篇 |
国内免费 | 2458篇 |
专业分类
林业 | 2165篇 |
农学 | 2075篇 |
基础科学 | 1517篇 |
2769篇 | |
综合类 | 11407篇 |
农作物 | 1789篇 |
水产渔业 | 1133篇 |
畜牧兽医 | 4263篇 |
园艺 | 1696篇 |
植物保护 | 1189篇 |
出版年
2024年 | 134篇 |
2023年 | 380篇 |
2022年 | 959篇 |
2021年 | 1018篇 |
2020年 | 947篇 |
2019年 | 916篇 |
2018年 | 677篇 |
2017年 | 1009篇 |
2016年 | 804篇 |
2015年 | 1141篇 |
2014年 | 1253篇 |
2013年 | 1542篇 |
2012年 | 2053篇 |
2011年 | 2141篇 |
2010年 | 2103篇 |
2009年 | 1891篇 |
2008年 | 1894篇 |
2007年 | 1855篇 |
2006年 | 1529篇 |
2005年 | 1293篇 |
2004年 | 862篇 |
2003年 | 605篇 |
2002年 | 782篇 |
2001年 | 743篇 |
2000年 | 538篇 |
1999年 | 302篇 |
1998年 | 106篇 |
1997年 | 83篇 |
1996年 | 70篇 |
1995年 | 48篇 |
1994年 | 55篇 |
1993年 | 39篇 |
1992年 | 51篇 |
1991年 | 43篇 |
1990年 | 27篇 |
1989年 | 29篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1986年 | 12篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1962年 | 7篇 |
1956年 | 4篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
AIM:To study the effect of TGF-β1 and TNF-α antisense PS-ODNS on ex vivo expansion of hematopoietic stem/progenitor cells (HSPC). METHODS:CD34+cells were purified from fresh umbilical cord blood by immunomagnetic beads, and mononuclear cells were purified from bone marrow by Ficoll-hypaque. The effects of TGF-β1 and /or TNF-α antisense PS-ODNS on ex vivo expansion of CD34+ cells、CFU-GEMM、CFU-GM、CFU-E and BFU-E were detected by using liquid and semi-solid culture systems.RESULTS:TGF-β1 antisense PS-ODNS cooperated with cytokines increased the number of CD34+ cells, CFU-GEMM, CFU-GM, CFU-E and BFU-E, which was as 4, 2.6, 2.7, 1.8, 2.1 times as that of the control (the cytokines combination), respectively. TNF-α antisense PS-ODNS cooperated with cytokines respectively increased the number of CD34+ cells, CFU-GEMM, CFU-GM, CFU-E and BFU-E by 4, 2.9, 2.6, 1.7, 1.8 times as that of the control. The above two antisense PS-ODNS cooperated with cytokines could respectively increased the number of CD34+ cells, CFU-GEMM, CFU-GM, CFU-E and BFU-E by 5.3, 2.1, 2.7, 1.9, 1.8 times as that of the control.CONCLUSION:Inhibition of endogenous TGF-β1 and TNF-α by antisense PS-ODNS will be one of the effective methods to expand HSPC ex vivo. 相似文献
82.
83.
84.
85.
AIM and METHODS: Total RNA was extracted from 6th rat subcultured pulmonary artery smooth muscle cells(PASMC) exposed to continual chronic hypoxia or normoxia and the effects of chronic hypoxia on the changes of Kv1.3,Kv2.1,Kv3.1 mRNA in cultured PASMC induced by acute hypoxia were studied by semiquantitative RT-PCR in vitro. RESULTS:①Kv1.3,Kv2.1,Kv3.1 genes were found to be expressed in PASMC of rats exposed either to hypoxia or normxia.②The expression of Kv2.1 and Kv3.1 in 6th subcultured of PASMC in normaxia group could be upregulated by exposure to acute hypoxia,the levels of Kv2.1 and Kv3.1 mRNA were significantly increased from 0.646±0.092, 0.782±0.104 to 1.059±0.134, 0.985±0.116,respectively (P<0.01,n=5). ③PASMC cultured continuously in chronic hypoxia for 6 subcultures and then exposed to normoxia for 12 h,thereafter the expression of Kv2.1 and Kv3.1 were downregulated by acute hypoxia for 6 hours.The level of Kv2.1 mRNA was significantly decreased from 1.008±0.117 to 0.649±0.097 (P<0.01,n=5). CONCLUSION:Kv2.1,Kv3.1 genes might be oxygen sensitive genes.Chronic hypoxia might change the response of these Kv genes of PASMC to acute hypoxia and down-regulate its expression,which might probably decrease the role of Kv in HPV. 相似文献
86.
87.
88.
89.
本试验选用24只3-3.5月龄的波德代(♂)×蒙古羊(♀)和陶赛特(♂6)×蒙古羊(♀)杂交一代羔羊,按2×2×2因子设计,研究了两个营养水平下以高果胶的甜菜粕取代小麦的全混合颗粒饲料对两种羔羊瘤胃pH值的影响。结果表明,低营养水平组的pH值显著高于高营养水平组(P=0.015);食后4 h(P-0.019)、6 h(P=0.009)的pH值在营养水平和饲料间存在互作,高营养水平组,小麦组羔羊的瘤胃液pH高于甜菜粕组,而低营养水平组、甜菜粕组的pH高于小麦组;羊品种对pH值无影响。 相似文献
90.