全文获取类型
收费全文 | 55522篇 |
免费 | 3584篇 |
国内免费 | 5356篇 |
专业分类
林业 | 4171篇 |
农学 | 3109篇 |
基础科学 | 2818篇 |
5996篇 | |
综合类 | 26216篇 |
农作物 | 4083篇 |
水产渔业 | 3080篇 |
畜牧兽医 | 8303篇 |
园艺 | 4228篇 |
植物保护 | 2458篇 |
出版年
2024年 | 480篇 |
2023年 | 1247篇 |
2022年 | 2676篇 |
2021年 | 2645篇 |
2020年 | 2439篇 |
2019年 | 2447篇 |
2018年 | 1828篇 |
2017年 | 2921篇 |
2016年 | 1954篇 |
2015年 | 2815篇 |
2014年 | 2982篇 |
2013年 | 3311篇 |
2012年 | 4677篇 |
2011年 | 4816篇 |
2010年 | 4637篇 |
2009年 | 3893篇 |
2008年 | 4001篇 |
2007年 | 3567篇 |
2006年 | 2901篇 |
2005年 | 2247篇 |
2004年 | 1503篇 |
2003年 | 970篇 |
2002年 | 977篇 |
2001年 | 922篇 |
2000年 | 827篇 |
1999年 | 297篇 |
1998年 | 61篇 |
1997年 | 38篇 |
1996年 | 41篇 |
1995年 | 44篇 |
1994年 | 45篇 |
1993年 | 33篇 |
1992年 | 34篇 |
1991年 | 33篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 4篇 |
1981年 | 6篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1966年 | 3篇 |
1965年 | 4篇 |
1964年 | 3篇 |
1963年 | 3篇 |
1962年 | 9篇 |
1956年 | 23篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
83.
新疆棉区转Bt基因棉对棉田主要害虫及其天敌种群数量的影响 总被引:19,自引:0,他引:19
20 0 0~ 2 0 0 1年 ,在新疆棉区系统地研究了转Bt基因棉田主要害虫及其天敌的发生规律。结果表明 :转Bt基因棉对棉铃虫有良好的控制作用 ,发生高峰期百株落卵量和百株幼虫数量都显著低于常规对照 ,转Bt自控田和转Bt化防田棉蚜和棉盲蝽发生数量则显著高于常规棉对照田。在天敌方面 ,转Bt自控田和转Bt化防田较常规棉对照田 ,丽草蛉种群数量有所增加 ,而小花蝽和黑食蚜盲蝽等 5种捕食性和几种寄生性天敌数量都有所下降。转Bt基因棉田棉蚜和棉盲蝽等刺吸性害虫发生数量加重而多种天敌数量减少的趋势值得引起重视。鉴于新疆地区棉铃虫发生数量较低目前无需专门防治的特点 ,作者建议 :可以考虑推广农艺性状较好的常规棉品种并保护天敌 ,以达到控制害虫、丰产丰收的目的。 相似文献
84.
85.
86.
87.
88.
AIM:To explore the changes of L-selectin expression on peripheral blood polymorphonuclear leukocytes (PMNs) and their significance in rats with acute lung injury (ALI). METHODS:ALI model in rat was established by intravonous injection of E. coli endotoxin (ET). The expression of L-selectin on peripheral blood PMNs was measured by immunofluorescence and flow cytometry.RESULTS:The contribution of L-selectin fluorescence signal was on the surface of PMNs membrane. The expression of L-selectin on poeripheral blood PMN was significantly lower at 5 min after injection of ET and the lowest during 15 min to 30 min, then gradually increased, but the expression of L-selectin on PMN was lower at 60 min after injection of ET than that of control animal.CONCLUSION:In physiological state, L-selectin were expressed on the surface of PMN membrane. The protein expression of L-selectin on PMNs reduced rapidly after injection of ET and the lowest at 15 min, then gradually increased. L-selectin may play a role in the development of ALI. 相似文献
89.
AIM:To investigate the effect of lansoprazole on gastric ulceration in rats. METHODS:Using the gastric ulcer model induced by hemorrhagic shock, restraint water-immersion stress and pylorus-ligature, the protective effect of lansoprazole (iv) on gastric ulceration was observed. RESULTS:Pretreatment with lansoprazole (7.5-60 mg/kg) significantly inhibited the formation of gastric ulcer in the three models in a dose-dependent manner. The autiulcer efficacy of lansoprazole was similar to that of omeprazole in the equal dose, but stronger than that of omeprazole for ulcer induced by water-immersion stress.CONCLUSION:The intravenously administered lansoprazole inhibited formation of experimental gastric ulcer in rats. 相似文献
90.
AIM: To investigate the effect of berberine (Ber) on the activation and proliferation of T lymphocytes and its mechanism of action. METHODS: Whole peripheral blood from normal subjects was stimulated with phytohemagglutinin (PHA) or phorbol ester (PDB) plus ionomycin (Ion) and the expression levels of CD69 and CD25 were evaluated with flow cytometry after the staining with appropriate fluorescent monoclonal antibody. The distribution of cell cycles was analyzed by propidium iodide staining and dead cells by 7-aminoactinomycin live staining. RESULTS: 100 μmol/L and 50 μmol/L of Ber had significant inhibition of the expression of CD69 on T cells stimulated with PDB plus Ion or PHA, while effect of 25 μmol/L Ber was not significant. And as time of action extended, the extent of inhibition decreased. For the expression of CD25, Ber at the concentrations as above all exerted significant inhibitory effect in a dose-dependent manner. Moreover, Ber could block lymphocytes cell cycle progression from G0/G1 phase to S and G2/M phase without phase specificity. Besides, live staining analysis revealed that Ber did not have significant cytotoxicity on lymphocytes. CONCLUSIONS: Ber significantly inhibits the expression of early and mid activation antigens of T cells and also blocks the progression of lymphocytes cell cycles. These results suggest that Ber exerts immunosuppression effect through inhibiting the activation and proliferation of T cells. 相似文献