全文获取类型
收费全文 | 709篇 |
免费 | 35篇 |
国内免费 | 54篇 |
专业分类
林业 | 64篇 |
农学 | 60篇 |
基础科学 | 52篇 |
101篇 | |
综合类 | 232篇 |
农作物 | 31篇 |
水产渔业 | 28篇 |
畜牧兽医 | 116篇 |
园艺 | 88篇 |
植物保护 | 26篇 |
出版年
2024年 | 4篇 |
2023年 | 14篇 |
2022年 | 28篇 |
2021年 | 34篇 |
2020年 | 27篇 |
2019年 | 40篇 |
2018年 | 30篇 |
2017年 | 34篇 |
2016年 | 43篇 |
2015年 | 33篇 |
2014年 | 40篇 |
2013年 | 44篇 |
2012年 | 40篇 |
2011年 | 42篇 |
2010年 | 43篇 |
2009年 | 36篇 |
2008年 | 31篇 |
2007年 | 37篇 |
2006年 | 37篇 |
2005年 | 22篇 |
2004年 | 28篇 |
2003年 | 19篇 |
2002年 | 12篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
排序方式: 共有798条查询结果,搜索用时 759 毫秒
131.
AIM:To investigate the effect of extracellular heat-shock protein 70 (HSP70)/HSP70-peptide complexes (HSP70-PCs) on epithelial-mesenchymal transition (EMT) of human hepatocellular carcinoma HepG2 cells and its probable mechanism. METHODS:HepG2 cells were divided into 3 groups: control group, HSP70/HSP70-PCs (2 mg/L) group and LY294002+HSP70/HSP70-PCs group. The mRNA and protein expression of epithelial cell surface marker E-cadherin, mesenchymal cell surface marker α-smooth muscle actin (α-SMA), phosphatidylinositol 3-kinase (PI3K) and hypoxia-inducible factor 1α (HIF-1α) was examined by real-time RT-PCR and Western blotting. RESULTS:Extracellular HSP70/HSP70-PCs promoted the initiation of EMT of HepG2 cells. The expression of HIF-1α and PI3K significantly increased in the process of EMT of HepG2 cells. After PI3K was blocked by LY294002, EMT did not occur and HIF-1α was not up-regulated in HepG2 cells. CONCLUSION:Extracellular HSP70/HSP70-PCs may promote EMT of hepatocellular carcinoma cells via PI3K/HIF-1α signaling pathway. 相似文献
132.
《Communications in Soil Science and Plant Analysis》2012,43(21):2572-2585
A transition period of at least 2 years is required for annual crops before the produce may be certified as organically grown. There is a need to better understand the various management options for a smooth transition from conventional to organic production. The purpose of this study was to evaluate the effects of different organic amendments and biofertilizers (BFs) on productivity and profitability of a bell pepper–french bean–garden pea system as well as soil fertility and enzymatic activities during conversion to organic production. For this, the following six treatments were established in fixed plots: composted farmyard manure (FYMC, T1); vermicompost (VC, T2); poultry manure (PM, T3) along with biofertilizers (BF) [Rhizobium/Azotobacter + phosphorus solubilizing bacteria (Pseudomonas striata)]; mix of three amendments (FYMC + PM + VC + BF, T4); integrated nutrient management (FYMC + NPK, T5); and unamended control (T6). The yields of bell pepper and french bean under organic nutrient management were markedly lower (25.2–45.9% and 29.5–46.2%, respectively) than with the integrated nutrient management (INM). Among the organic treatments, T4 and T1 produced greater yields of both bell pepper (27.96 Mg ha?1) and french bean (3.87 Mg ha?1) compared with other treatments. In garden pea, however, T4 gave the greatest pod yield (7.27 Mg ha?1) and was significantly superior to other treatments except T5 and T1. The latter treatment resulted in the lowest soil bulk density (1.19 Mg m?3) compared with other treatments. Similarly, soil organic C was significantly greater in all the treatments (1.21–1.30%) except T2 compared to T6 (1.06%). Plots under INM, however, had greater levels of available nitrogen–phosphorus–potassium (NPK) than those under organic amendments. T1 plots showed greater dehydrogenase and acid phosphatase activities compared with other treatments. However, T4 and T5 plots had greater activities of β-glucosidase and urease activities, respectively. The cost of cultivation was greater under organic nutrient management (except T2) compared with INM. The latter treatment gave greater gross margin and benefit/cost (B/C) ratio for all vegetables, except that T2 gave greater B/C ratio in garden pea compared with other treatments. We conclude that T1 and T4 were more suitable for enhancing the productivity of bell pepper–french bean–garden pea system, through improved soil properties, during transition to organic production. 相似文献
133.
134.
借助石蜡切片技术对无籽西瓜胚轴进行连续切片和系统镜检。在根茎过渡区连续横切面上,可看到由根部四原型外始式初生木质部与初生韧皮部相间排列的维管束转变到茎部成为四原型、内始式和双韧并生排列的维管束。转化经过分叉、倒转和合并,是不同步的,从左到右沿顺时针力向逐步转变。中胚轴子叶迹发生处延伸出2个小束。根、茎维管束转换区发生在下胚轴。该区外形较粗大,生理活性较强,对外界条件变化较敏感,是瓜苗抗性最弱部位,也是组培择取外植体最合适的节段。可为瓜苗耕作管理和择取外植体提供形态学参考指标。 相似文献
135.
分析研究了人口、生态和技术的变迁对农地规模经营的影响。在长期的历史变迁中,中国农业的发展在人口压力下形成了与追求产量最大化相一致的小规模经营,且随着集约化技术的发展,小规模经营愈加强化。技术变迁的历史表明:完善的市场化措施和社会化服务体系的建立,完全可以在目前小农经营基础上改造传统农业并促进农业生产的进一步发展。 相似文献
136.
杨玲 《西北农林科技大学学报(自然科学版)》2001,29(5):124-126
用差示扫描量热法分析了 6种作物幼苗线粒体极性脂和磷脂酰甘油 (PG)的热致相变。结果发现 ,抗冷性作物小麦发生相变的温度比其他冷敏感作物的低得多 ;小麦和花生线粒体 PG混合后 ,显著改变了各自的相变温度。线粒体 PG脂肪酸组成分析表明 ,脂肪酸饱和度决定其相变温度。线粒体 PG的脂肪酸饱和度与作物幼苗的冷敏感性相关 相似文献
137.
根据水轮机甩负荷过渡过程中导叶或阀门的关闭规律与水击压力变化率ξ、机组转速变化率β的变化关系分析,运用蕴涵确定模糊关系的方法,建立模糊控制规则,以此形成一个闭环回路控制输入输出信息,经模糊控制器作出控制决策 相似文献
138.
基于1980-2007年陕西省安塞县统计数据,分析了生态退耕对农民收入、产业结构、种植结构等的影响,并运用灰色关联度分析法,阐明了安塞县农村产业结构调整的动态变化过程和农业结构调整的方向.探讨了生态退耕后安塞县的农村经济转型问题.结果表明:(1)生态退耕政策的实施显著增加了农民人均收入,促进了农业结构调整和农村剩余劳动力转移.(2)现阶段安塞县农村经济转型的目标在于巩固生态退耕成果,实现农村经济的可持续发展,其根本任务是农业产业结构调整.(3)促进第二产业发展是安塞县农村经济结构调整的重点;种植业、畜牧业、林业是农业内部结构调整的重点.(4)解决农民增收问题和实现农村剩余劳动力稳妥转移是安塞县农村经济转型的关键. 相似文献
139.
一维马尔可夫链模拟黑河中游流域土壤质地垂向变异 总被引:1,自引:1,他引:0
黑河中游地区土壤剖面砂、黏层次相间排列的特点及部分区域剖面中出现的不透水层对土壤中的水分运动和溶质迁移具有重要影响。该研究调查了黑河中游100km2区域内土壤剖面的质地分层情况,运用一维嵌入马尔可夫链模型模拟该地区的土壤质地剖面。研究表明,研究区土壤剖面共出现砂土、壤质砂土、砂质壤土、壤土、黏质壤土、粉黏壤土和粉黏土7种质地类型,层次厚度呈对数正态分布。粉黏土未在表层土壤出现,而砂土在表层出现的概率明显高于其余质地类型,剖面某一质地层之下多出现细粒含量比其高的下一质地类型。剖面上相邻两质地层之间的转移具有明显的马尔可夫链特征(简称马氏性),且马氏链是平稳的。一维嵌入马尔可夫链模型能够较好地描述研究区土壤质地层次的垂向变化,剖面主要的质地层次组合为:砂—壤、壤—砂、壤—黏、黏—壤。对土壤质地剖面的定量模拟,可以为开展该区域土壤水循环、转化和溶质迁移等相关研究提供参考。 相似文献
140.