全文获取类型
收费全文 | 5134篇 |
免费 | 224篇 |
国内免费 | 437篇 |
专业分类
林业 | 231篇 |
农学 | 364篇 |
基础科学 | 124篇 |
737篇 | |
综合类 | 1872篇 |
农作物 | 437篇 |
水产渔业 | 191篇 |
畜牧兽医 | 1094篇 |
园艺 | 406篇 |
植物保护 | 339篇 |
出版年
2024年 | 13篇 |
2023年 | 82篇 |
2022年 | 153篇 |
2021年 | 179篇 |
2020年 | 158篇 |
2019年 | 173篇 |
2018年 | 136篇 |
2017年 | 262篇 |
2016年 | 245篇 |
2015年 | 259篇 |
2014年 | 275篇 |
2013年 | 343篇 |
2012年 | 344篇 |
2011年 | 389篇 |
2010年 | 319篇 |
2009年 | 316篇 |
2008年 | 292篇 |
2007年 | 319篇 |
2006年 | 287篇 |
2005年 | 195篇 |
2004年 | 177篇 |
2003年 | 111篇 |
2002年 | 107篇 |
2001年 | 88篇 |
2000年 | 94篇 |
1999年 | 91篇 |
1998年 | 47篇 |
1997年 | 47篇 |
1996年 | 51篇 |
1995年 | 39篇 |
1994年 | 23篇 |
1993年 | 31篇 |
1992年 | 36篇 |
1991年 | 24篇 |
1990年 | 17篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1956年 | 4篇 |
1955年 | 2篇 |
排序方式: 共有5795条查询结果,搜索用时 62 毫秒
61.
锌元素对籼稻成熟胚愈伤组织绿苗分化率的影响 总被引:1,自引:0,他引:1
本实验就锌元素对籼稻成熟胚愈伤组织绿苗分化率的影响进行了研究,结果指出:(1)锌元素能明显提高籼稻成熟胚愈伤组织绿苗分化频率,且使用浓度范围较广(0.5~10μmol/L),其中以锌浓度1μmol/L效果较好;(2)在本实验范围内各籼稻品种对锌元素的反应是一致的,但品种间差异很大,其中中早14绿苗分化率较高;(3)锌脉冲试验指 相似文献
62.
波特竞争战略侧重从外部行业环境角度解释企业运营问题,但是实证分析结果证明资源对企业发展影响重大。针对目前尚无具体模式研究企业如何立足现有资源进行发展问题,本文基于资源基础论,将企业资源具体分为物质、信息、资金和知识资源(MICK),提出了MICK-4FI(四流集成)资源运营模式,借助投入产出模型构建MICK-4FI模式分析框架。文中利用聚焦和杠杆作用定性地解释了企业培育或者集成资源,即企业获取资源形成竞争优势的机理。本模式将资源基础论应用到企业实践层次,解决了企业通过集成运营内外部资源以求快速发展的路径依赖问题。资源运营理论从微观资源角度分析企业经营,与波特从宏观行业分析的理论共同构成一套系统的企业运营理论体系。 相似文献
63.
AIM To observe the effect of Fuzilizhong decoction on the inflammatory damage of non-alcoholic fatty liver disease (NAFLD) rats and to explore its mechanism. METHODS SPF male SD rats were randomly divided into 6 groups: control group, model group, high dose (20 mg·kg-1·d-1), middle dose (10 mg·kg-1·d-1), low dose (5 mg·kg-1·d-1) Fuzilizhong decoction group and Yishanfu (30 mg·kg-1·d-1)group, 8 rats in each group. A NAFLD rat modelwas established by intragastric administration of fat emulsion for 4 weeks. Then the drug was given for 4 weeks in each treatment group. HE staining was performed to observe the histopathological changes of the rat liver.The serum levels of interleukin-2(IL-2), IL-6 and tumor necrosis factor-α(TNF-α) were measured by ELISA. The expression of toll like receptor 4(TLR4) and NF-κB p65 in liver tissues at mRNA and protein levels was determined by RT-qPCR and Western bolt,respectively. RESULTS Compared with control group, the inflammatory damage of liver tissue was more serious, the serum levels of IL-2, IL-6 and TNF-α, the mRNA expression TLR4 and NF-κB p65 in liver tissues were significantly increased in model group(P <0.05). However, compared with model group, the liver pathological changes in each treatment group were significantly relieved, the serum levels of IL-2, IL-6 and TNF-α, the mRNA expression of TLR4 and NF-κB p65 in liver tissues were significantly reduced(P <0.05).In addition, the changes of TLR4 and p-NF-κB p65 protein levels in liver tissue were consistent with the changes of TLR4 and NF-κB p65 mRNA. CONCLUSION Fuzilizhong decoction attenuates the inflammatory damages of NAFLD in rats by inhibiting TLR4/NF-κB p65 signaling pathway. 相似文献
64.
HUANG Zeng-yan HUANG Man-ping PENG Chun-li LIU Yong-yuan LI Chun-yan LIANG Dong-hui 《园艺学报》2021,37(1):34-40
AIM To observe effects of emotional stimulation on expression of stromal cell-derived factor-1(SDF-1) and CXC chemokine receptor 4 (CXCR4) in plasma, platelets, aortas, hippocampus and bone marrow of apolipoprotein E gene knockout (ApoE -/-) mice, and to reveal the possible mechanism of the aggravated atherosclerotic plaque vulnerability by emotional stimulation. METHODS Thirty 8-week-old male ApoE -/- mice were randomly divided into normal control group, high fat group, and emotional stimulation group. Ten 8-week-old inbred C57BL/6J mice served as blank control group. After 12 weeks of intervention, the serum levels of SDF-1 and CXCR4 were investigated by ELISA. The protein levels of SDF-1 and CXCR4 in platelets, aortas, hippocampus and bone marrow were determined by Western blot. The pathological damage of aortas was observed by oil red O staining. RESULTS Compared with blank control group, normal control group and high fat group, the mice subjected to emotional stimulation showed more serious atherosclerosis in aortas detected by oil red O staining, and increased levels of SDF-1 and CXCR4 in the plasma and aortas were also observed (P <0.05). The results of Western blot showed that the protein levels of SDF-1 and CXCR4 in platelets, aortas and hippocampus were increased in the mice subjected emotional stimulation, but the expression of SDF-1 and CXCR4 in the bone marrow was decreased (P <0.05). CONCLUSION Imbalance of SDF-1/CXCR4 may be the key target by which emotional stimulation accelerates the progression of atherosclerosis. 相似文献
65.
以白花芥蓝‘四季粗条’为材料克隆了Boa DFR基因,Gen Bank登录号为MT472647,CDS序列长为1158 bp,编码385个氨基酸,与甘蓝型油菜、甘蓝和白菜等具有高度同源性。Boa DFR表达水平在芥蓝不同发育时期、不同器官中存在显著差异,随植株发育总体呈现先下降后上升的趋势,在幼嫩种子中表达量最高。芥蓝原生质体的亚细胞定位结果显示Boa DFR定位在细胞核上。构建了农杆菌介导的芥蓝瞬时过表达体系,将Boa DFR转入白花芥蓝‘四季粗条’和黄花芥蓝‘福州黄花’中,发现Boa DFR在两种芥蓝中均高水平表达,转基因植株叶片颜色明显变紫,花青素苷显著积累,总含量最高达461.43μg·g-1 FW,而野生型和转空载体芥蓝叶片中几乎检测不到花青素苷。通过HPLC在转基因植株叶片中共检测到8种花青素苷,均为矢车菊花青素苷,其中矢车菊–3–阿魏酰–丙二酰–槐糖苷–5–葡萄糖苷占比最高。 相似文献
66.
Isao Tada Minoru Motoki Nobuyoshi Takahashi Tetsuji Miyata Tomoko Takechi Toshiro Uchida Yasushi Takagi 《Pest management science》1996,48(2):165-173
A series of novel 4,5-dihydropyrazole-5-thiones (DHPs) was synthesised by treating the corresponding dihydropyrazolones with ‘Lawesson’s reagent and evaluated for miticidal activity against two-spotted spider mites (Tetranychus urticae Koch). Of these, 3-(4-chlorophenyl)-4,4-dimethyl-1-phenyl-4,5-dihydropyrazole-5-thione, 3-(4-chlorophenyl)-4-ethyl-4-methyl-1-phenyl-4,5-dihydropyrazole-5-thione, 3-(4-chlorophenyl)-1-phenyl-4,5-dihydropyrazole-5-thione-4-spirocyclopentane and 4,4-dimethyl-1-phenyl-3-(4-trifluoromethyl-phenyl)-4,5-dihydropyrazole-5-thione were highly active (pEC50>4·0) and were more effective than the miticide dicofol (pEC50=3·879), which has traditionally been used for the control of phytophagous mites. Structure–activity relationship (SAR) studies were performed on each position of the pyrazole ring of DHPs. The results indicated that the unsubstituted phenyl, 4-substituted phenyl and thioxo groups on the 1-, 3- and 5-positions of DHPs respectively were required for activity. Quantitative SAR studies using physicochemical parameters of substituents and the capacity factor k′ as a hydrophobicity index suggested that: (a) the activities of all types of DHPs examined were mainly dominated by hydrophobicity, (b) the bulkiness of 4-substituents of the 3-phenyl ring favoured the activity and (c) the log k′ optimum for all DHPs was 1·675, equivalent to a log Pow value of c. 5·0. 相似文献
67.
智能单片机小车由于其智能、方便、快捷,被广泛应用于各行业.本研究的智能送药小车包括了Ardunio mega2560单片机、OpenMv4智能识别装置、寻迹装置、L298N模块、433M无线模块等装置.研究结果表明:智能送药小车通过识别地面安置路线以及相应的病房号,可以自动躲避障碍,自动沿设定的路线行驶,既可以实现单车... 相似文献
68.
69.
本研究以香蕉枯萎病菌尖镰孢古巴专化型4号小种为目标菌,采用PDA平板培养、土壤平板培养和盆栽试验三种方法来测定碱性硅肥对香蕉枯萎病病菌的影响。结果表明,使用第一种方法,硅肥在小于1000倍液的范围内对菌丝生长均显示抑制作用,其中原液的抑制率达到最高并与其他浓度处理,以及对照普通肥料有显著的差异(p<0.05);第二种方法显示与第一种方法的抑菌效果一致;第三种方法显示,硅肥处理的香蕉苗病情指数为43.85%,对照肥料处理的为68.57%,空白对照的为80.00%。本研究认为,碱性硅肥对香蕉枯萎病菌有一定的抑制作用,在生产上应用潜力。 相似文献
70.