全文获取类型
收费全文 | 240551篇 |
免费 | 24645篇 |
国内免费 | 42111篇 |
专业分类
林业 | 19191篇 |
农学 | 15568篇 |
基础科学 | 16819篇 |
48107篇 | |
综合类 | 110775篇 |
农作物 | 17299篇 |
水产渔业 | 12219篇 |
畜牧兽医 | 36969篇 |
园艺 | 16446篇 |
植物保护 | 13914篇 |
出版年
2024年 | 2359篇 |
2023年 | 4850篇 |
2022年 | 9699篇 |
2021年 | 9272篇 |
2020年 | 9923篇 |
2019年 | 12170篇 |
2018年 | 9894篇 |
2017年 | 13713篇 |
2016年 | 11834篇 |
2015年 | 15056篇 |
2014年 | 14635篇 |
2013年 | 16719篇 |
2012年 | 21071篇 |
2011年 | 20871篇 |
2010年 | 19338篇 |
2009年 | 17268篇 |
2008年 | 16713篇 |
2007年 | 15445篇 |
2006年 | 12693篇 |
2005年 | 10264篇 |
2004年 | 7466篇 |
2003年 | 5232篇 |
2002年 | 5006篇 |
2001年 | 4441篇 |
2000年 | 4050篇 |
1999年 | 2230篇 |
1998年 | 1324篇 |
1997年 | 1320篇 |
1996年 | 1143篇 |
1995年 | 1211篇 |
1994年 | 1190篇 |
1993年 | 945篇 |
1992年 | 979篇 |
1991年 | 814篇 |
1990年 | 618篇 |
1989年 | 599篇 |
1988年 | 538篇 |
1987年 | 417篇 |
1986年 | 432篇 |
1985年 | 215篇 |
1984年 | 196篇 |
1983年 | 191篇 |
1982年 | 191篇 |
1981年 | 261篇 |
1980年 | 192篇 |
1979年 | 153篇 |
1978年 | 130篇 |
1965年 | 137篇 |
1964年 | 140篇 |
1955年 | 119篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
81.
AIM:To investigate the effects of FK506 on anti-glomerular basement membrane(GBM) nephritis in rats. METHODS: Anti-GBM nephritis model was elaborated by rabbit anti-rat GBM antibody injection in SD rats in this study. The rats were divided into three groups: FK506 treated group(0.5 mg·kg-1·d-1, sc), untreated nephritis control group and normal control group. FK506 was administered daily six hours after injection of anti-GBM IgG. All the rats were observed urinary protein at the 4th day, the 14th day and the 21st day. At the same time, the kidney specimens were collected, and T cell transforming function was also monitored.RESULTS:Rats injected with rabbit anti-GBM Ab developed heavy proteinuria by 4 days, and serum creatinine and serum urea appeared which kept on the rising. Glmerular hypercellularity, crescents, and protein casts were observed in nephritic rats. By electron microscopy, the thickening of GBM and loss of foot processes were seen. T cell transforming function was higher than normal. But, all pathological changes obviously turned for the better in FK506 treated group. CONCLUSION:FK506 could inhibit the progression of rat anti-GBM nephritis. 相似文献
82.
AIM:To study the effect of cilazapril on pulmonary vascular endothelial dysfunction in hypoxic rats. METHODS:The structure and function of endothelium in hypoxic rats were studied by biochemical analysis, radioimmunoassay, transmission electron microscope and correlated with hemodynamic. RESULTS:1) The change and damage of ultrastructure in endothelial cell (EC) were obsevered in hypoxic rats. 2) The contents of plasma nitric oxide (NO) and superoxide dismutase (SOD) activity in blood as well as endothelial nitric oxide synthase (eNOS) activity in the lung tissue were significantly lower in the hypoxic rat than those in contral animals. The concentrations of plasma endothelin-1(ET-1) and angiotensin converting enzyme(ACE) as well as malondialdehyde(MDA) were significantly higher in the hypoxic rat than these in contral animals. The relaxing and contracting factors had a significant positive/negative correlation with mean pulmonary artery pressure (mPAP). 3) Cilazapril significantly decreased the level of ET-1 and ACE and significantly increased the level of NO and activity of eNOS and SOD. At the same time, cilazapril extenuated hypoxia-induced injuries of EC. CONCLUSION:The results indicate that damaging structure and dysfunction of EC existes in hypoxic rats. The cilazapril effectively preventes and treates the chronic hypoxic PH by relieving the injury and improving secretion in EC. 相似文献
83.
84.
十种常用农药与球孢白僵菌的生物学相容性 总被引:24,自引:2,他引:24
球孢白僵菌孢子粉与10种常用农药相容性的测定结果显示,随着孢子浓度上升,所试农药对孢子的抑制作用均有不同程度的增强。在1/10田间常规使用浓度下,百菌清和代森锰锌均能抑制或杀死孢子(萌发率<1%)。除阿维菌素外,所有杀虫剂均与白僵菌孢子相容,在常规使用浓度的10倍稀释液中孢子萌发率达90%以上。吡虫啉、蚜虱灵、灭多威和氟虫腈与孢子的相容性最好,其中吡虫啉和蚜虱灵对孢子萌发率的影响不明显随药剂浓度的变化而变化,即使在田间常规使用浓度下孢子萌发率也在95%以上,而阿维菌素与白僵菌的相容性极差。因此,应用白僵菌制剂防治害虫,选择生物学相容性好的农药以低剂量与白僵菌制剂混用,既可使菌剂增效,又可大幅度降低化学药剂用量。 相似文献
85.
变叶海棠种群多样性的形成与分化研究 总被引:9,自引:2,他引:9
采用杂种指数和形象化散点图法, 探明了变叶海棠以兼性无融合生殖方式与陇东海棠和花叶海棠产生渗入杂交变异, 又以无融合生殖方式保持新产生变异的遗传, 经过数千万年的世代繁衍,形成现今这样极其复杂多样的渗入杂交群体, 该群体为3 个种的杂交复合体。由于杂种的全部或部分能育子代中发生的基因重组和增加基因的突变, 丰富了物种的基因库, 从而深入的揭示了变叶海棠具有多种高抗性的遗传机理。在变叶海棠居群内保护或栽植适量的陇东海棠和花叶海棠, 对于保持和促进变叶海棠多样性的形成与分化具有重要意义。 相似文献
86.
入世后我国甜樱桃面临的机遇与挑战及发展对策 总被引:5,自引:0,他引:5
甜樱桃作为一种早熟、优质、保健果品,而且种植效益较高,在国内国际都正处于发展时期。根据世界甜樱桃生产和贸易情况,指出了我国在甜樱桃科学技术与生产上与世界先进甜樱桃生产国的差距,分析了我国加入WTO之后,我国甜樱桃面临的机遇和挑战,并且机遇大于挑战。如果有适当的科技投入,我国甜樱桃产业将可克服现在科技滞后的状态,发挥我国劳动力低廉和国土辽阔的优势,迅速扩大其生产总量,提高品质,扩大出口,增加农民的收入,2015年可望形成32.4~43.2亿元的社会总产值。 相似文献
87.
AIM: To investigate the changes of myocardium glycogen content and the relation ship between changes of the myocardial glycogen content and the myocardial function. METHODS: Male Wistar rats were placed in (hypoxia rats) and made to swim in (hypoxia swimming rats) a hypobaxic chamber simulating an altitude of 5 000 m above sea level. The content of myocardium glycogens was determined by colorimetry. RESULTS: The myocardium
glycogen content of rats significantly reduced along with the prolongation of hypoxic exposure and approached to control level in hypoxia swimming rats. The myocardial function of right ventricule was improved significantly compared with control group.CONCLUSION: Moderate exercise (swimming) is beneficial to hypoxic adaptation of rats under the condition of chronic hypoxia. 相似文献
88.
89.
90.