全文获取类型
收费全文 | 61808篇 |
免费 | 3602篇 |
国内免费 | 5788篇 |
专业分类
林业 | 5502篇 |
农学 | 5046篇 |
基础科学 | 3841篇 |
7127篇 | |
综合类 | 26978篇 |
农作物 | 4292篇 |
水产渔业 | 2781篇 |
畜牧兽医 | 8872篇 |
园艺 | 3493篇 |
植物保护 | 3266篇 |
出版年
2024年 | 409篇 |
2023年 | 1037篇 |
2022年 | 2349篇 |
2021年 | 2613篇 |
2020年 | 2450篇 |
2019年 | 2412篇 |
2018年 | 1669篇 |
2017年 | 2767篇 |
2016年 | 2044篇 |
2015年 | 3037篇 |
2014年 | 3080篇 |
2013年 | 3556篇 |
2012年 | 5042篇 |
2011年 | 5414篇 |
2010年 | 5076篇 |
2009年 | 4448篇 |
2008年 | 4427篇 |
2007年 | 4062篇 |
2006年 | 3404篇 |
2005年 | 2671篇 |
2004年 | 1611篇 |
2003年 | 1203篇 |
2002年 | 1282篇 |
2001年 | 1185篇 |
2000年 | 1077篇 |
1999年 | 627篇 |
1998年 | 360篇 |
1997年 | 275篇 |
1996年 | 230篇 |
1995年 | 220篇 |
1994年 | 198篇 |
1993年 | 193篇 |
1992年 | 136篇 |
1991年 | 132篇 |
1990年 | 128篇 |
1989年 | 117篇 |
1988年 | 67篇 |
1987年 | 46篇 |
1986年 | 22篇 |
1985年 | 18篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1979年 | 5篇 |
1963年 | 4篇 |
1962年 | 10篇 |
1958年 | 3篇 |
1956年 | 17篇 |
1955年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
143.
144.
145.
AIM:To study the relationship between myocardial HSP70 and PKC during myocardial ischemic preconditioning(IPC). METHODS: PKC inhibitor, polymyxin B(PMB) and PKC activator, phorbol 12-myristate 13-acetate(PMA) were applied to the models of myocardial ischemia/reperfusion in vivo and in vitro in rabbits, respectively, and the ventricular functions, PLA2 in the serum, and the expression of mycardial HSP70 mRNA were examined. RESULTS:IPC decreased PLA2 activity, improved the left ventricular function and increased the expression of myocardial HSP70 mRNA. Howerer, all these effects of IPC could be blocked by PMB. Interestingly, PMA mimicked IPC with attenuating the injuries of cardial myocytes and increasing myocardial HSP70 mRNA expression. CONCLUSION:PKC is involved in the myocardial HSP70 expression in case of ischemic preconditioning. 相似文献
146.
AIM:To examine the effect of external counterpulsation(ECP) on renin-angiotensin system(RAS) and hemodynamics in dogs with myocardial ischemia and their relationship. METHODS:Acute myocardial ischemia was induced by occluding the left anterior descending of the dogs. The local renin activity, angiotensin Ⅱ(AngⅡ) level, angiotension-converting enzyme(ACE) activity were tested by biochemical methods and hemodynamics was recorded by a 8-channel physiological recorder.RESULTS:Ischemia could actiivate renin,ACE and AngⅡ in cardiovasculature and ECP reduced them except for renin in ischemic myocardium. Ischemia also could activate RAS in lung and kidney, which play an important role on circulating RAS, and ECP reduced them. Furthermore, ECP could improve hemodynamics and there existed a close relationship between local AngⅡlevel and hemodynamics. CONCLUSION:ECP can reduce local RAS and improve hemodynamics in dogs with myocardial ischemia, which might be one of mechanisms underlying the protective effect of ECP on ischemic myocardium. 相似文献
147.
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
148.
AIM: To examine the expression of human endostatin in E.coli, produce its fusion protein antibody and observe its biological activity. METHODS: Endostatin gene was amplified by polymerase chain reaction,recombined with plasmid vector pGEX-2T and induced expression with IPTG.The protein activity was tested by endothelial cell proliferation inhibitory assay.Inclusion body crudely purified was used to generate polyclonal antibody to detect its expression at mouse's liver and kidney etc. RESULTS: The protein expressed was 20kD after digestion by thrombin,it appeared the anti-angiogenesis activity and Western blotting indicated the expression of endostatin in liver and kidney of mouse. CONCLUSION: The successful expression of human endostatin and the preparation of polycolonal antibody indicated its potential application in anti-angiogenesis therapy and diagnosis tumors. 相似文献
149.
150.