全文获取类型
收费全文 | 5897篇 |
免费 | 269篇 |
国内免费 | 771篇 |
专业分类
林业 | 681篇 |
农学 | 822篇 |
基础科学 | 390篇 |
775篇 | |
综合类 | 2115篇 |
农作物 | 443篇 |
水产渔业 | 314篇 |
畜牧兽医 | 858篇 |
园艺 | 182篇 |
植物保护 | 357篇 |
出版年
2024年 | 25篇 |
2023年 | 56篇 |
2022年 | 155篇 |
2021年 | 223篇 |
2020年 | 190篇 |
2019年 | 196篇 |
2018年 | 130篇 |
2017年 | 190篇 |
2016年 | 158篇 |
2015年 | 193篇 |
2014年 | 210篇 |
2013年 | 290篇 |
2012年 | 387篇 |
2011年 | 371篇 |
2010年 | 381篇 |
2009年 | 370篇 |
2008年 | 326篇 |
2007年 | 361篇 |
2006年 | 366篇 |
2005年 | 310篇 |
2004年 | 159篇 |
2003年 | 194篇 |
2002年 | 274篇 |
2001年 | 279篇 |
2000年 | 214篇 |
1999年 | 168篇 |
1998年 | 100篇 |
1997年 | 91篇 |
1996年 | 81篇 |
1995年 | 87篇 |
1994年 | 85篇 |
1993年 | 74篇 |
1992年 | 59篇 |
1991年 | 46篇 |
1990年 | 42篇 |
1989年 | 30篇 |
1988年 | 25篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有6937条查询结果,搜索用时 15 毫秒
61.
Here we report the adaptation optimization of an efficient accurate inexpensive assay that employs custom-designed silicon-based optical thin-film biosensor chips to detect unique transgenes in genetically modified 《分子植物育种》2007,5(2):241-241
Here we report the adaptation and optimization of an efficient, accurate and inexpensive assay that employs custom-designed silicon-based optical thin-film biosensor chips to detect unique transgenes in genetically modified (GM) crops and SN-P markers in model plant genomes. Briefly, aldehyde-attached sequence-specific singlestranded oligonucleotide probes are arrayed and covalently attached to a hydrazine-derivatized biosensor chip surface. Unique DNA sequences (or genes) are detected by hybridizing biotinylated PCR amplicons of the DNA sequences to probes on the chip surface. In the SN-P assay, target sequences (PCR amplicons) are hybridized in the presence of a mixture of biotinylated detector probes and a thermostable DNA ligase. Only perfect matches between the probe and target sequences, but not those with even a single nucleotide mismatch, can be covalently fixed on the chip surface. In both cases, the presence of specific target sequences is siL, nified by a color change on the chip surface (gold to blue/purple) after brief incubation with an anti-biotin IgG horseradish peroxidase (HRP) to generate a precipitable product from an HRP substrate. 相似文献
62.
63.
64.
The high-valued utilization of Ulva (previously known as Enteromorpha) bioresources has drawn increasing attention due to the periodic blooms of world-wide green tide. The polysaccharide is the main functional component of Ulva and exhibits various physiological activities. The Ulva oligosaccharide as the degradation product of polysaccharide not only possesses some obvious activities, but also possesses excellent solubility and bioavailability. Both Ulva polysaccharides and oligosaccharides hold promising potential in the food industry as new functional foods or food additives. Studies on Ulva polysaccharides and oligosaccharides are increasing and have been the focus of the marine bioresources field. However, the comprehensive review of this topic is still rare and do not cover the recent advances of the structure, isolation, preparation, activity and applications of Ulva polysaccharides and oligosaccharides. This review systematically summarizes and discusses the recent advances of chemical composition, extraction, purification, structure, and activity of Ulva polysaccharides as well as oligosaccharides. In addition, the potential applications as new functional food and food additives have also been considered, and these will definitely expand the applications of Ulva oligosaccharides in the food and medical fields. 相似文献
65.
温度影响下的稻纵卷叶螟实验种群动态的系统动力学模拟 总被引:1,自引:0,他引:1
温度是影响稻纵卷叶螟(Cnaphalocrocis medinalis Guenee)发育、存活和繁殖的关键生态因子之一。研究温度与稻纵卷叶螟种群数量变动的关系,可为害虫种群的控制提供科学依据。本文根据稻纵卷叶螟在不同温度处理下(19.0℃,22.0℃,25.0℃,28.0℃,31.0℃)的实验种群生命表,利用系统动力学的相关理论和方法构建仿真模型,对稻纵卷叶螟实验种群的数量动态进行了模拟,在此基础上预测成虫的产卵量,并通过敏感性分析确定了成虫产卵的最适温度。结果显示,在初始卵量均为100标准粒的情况下,温度过高(〉25.0℃)不利于稻纵卷叶螟实验种群低龄幼虫的生存和发育,温度过低或过高均不利于实验种群后期的发育和繁殖;随着温度的上升,稻纵卷叶螟的存活率和生殖力迅速提高,温度为25.0℃时世代存活率、次代产卵量达到最高值,分别为19.67%和1488.4头;稻纵卷叶螟成虫的最高产卵量出现在24.9℃。研究表明了系统动力学模型在害虫种群发育动态及预测方面有着良好的应用潜力。 相似文献
66.
Peng XW Ren JL Zhong LX Peng F Sun RC 《Journal of agricultural and food chemistry》2011,59(15):8208-8215
Exploitation of biomaterials derived from renewable resources is an important approach to address environmental and resource problems in the world today. In this paper, novel ionic hydrogels based on xylan-rich hemicelluloses were prepared by free radical graft copolymerization of acrylic acid (AA) and xylan-rich hemicelluloses (XH) by using N,N-methylene-bis(acrylamide) (MBA) as cross-linker and ammonium persulfate/N,N,N',N'-tetramethylethylenediamine (APS/TMEDA) as redox initiator system. The network characteristics of the ionic hydrogels were investigated by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM), as well as by determination of mechanical properties, swelling, and stimuli responses to pH, salts, and organic solvents. The results showed that an increase in the MBA/XH or AA/XH ratio resulted in higher cross-linking density of the network and thus decreased the swelling ratio. Expansion of the network hydrogels took place at high pH, whereas shrinkage occurred at low pH or in salt solutions as well as in organic solvents. The ionic hydrogels had high water adsorption capacity and showed rapid and multiple responses to pH, ions, and organic solvents, which may allow their use in several areas such as adsorption, separation, and drug release systems. 相似文献
67.
Home-field advantage of litter decomposition and nitrogen release in forest ecosystems 总被引:1,自引:0,他引:1
Litter decomposition is a major fundamental ecological process that regulates nutrient cycling, thereby affecting net ecosystem carbon (C) storage as well as primary productivity in forest ecosystems. Litter decomposes in its home environment faster than in any other environment. However, evidence for this phenomenon, which is called the home-field advantage (HFA), has not been universal. We provide the first HFA quantification of litter decomposition and nutrient release through meta-analysis of published data in global forest ecosystems. Litter mass loss was 4.2 % faster on average, whereas nitrogen (N) release was 1.7 % lower at the home environment than in another environment. However, no HFA of phosphorus (P) release was observed. Broadleaf litter (4.4 %) had a higher litter mass loss HFA than coniferous litter (1.0 %). The positive HFA of N release was found in the coniferous litter. Mass loss HFA was significantly and negatively correlated with the initial lignin:N litter ratio. The litter decomposition and N release HFAs were obtained when mesh size ranged from 0.15 mm to 2.0 mm. The HFA of litter decomposition increased with decomposition duration during the early decomposition stage. The HFA of N release was well correlated with mass loss, and the greatest HFA was at mass loss less than 20 %. Our results suggest that the litter decomposition and N release HFAs are widespread in forest ecosystems. Furthermore, soil mesofauna is significantly involved in the HFA of litter decomposition. 相似文献
68.
为深入了解添加含氧燃料和废气再循环技术(exhaust gas recirculation,EGR)共同作用对颗粒结构及分形特征的影响,运用颗粒分级采样装置采集了EGR率分别为0、10%、20%时,柴油机燃用正丁醇质量百分比为10%的正丁醇/柴油混合燃料(N10)的燃烧颗粒(N10EGR0、N10EGR10%、N10EGR20%),通过电镜试验和图像处理技术,开展了不同EGR率对正丁醇/柴油燃烧颗粒的影响研究,分析了颗粒群的微观结构、平均粒径、分形维数,基本碳粒子的层面间距、微晶尺寸等物理结构参数的变化规律,结果表明,N10EGR0、N10EGR10%、N10EGR20%燃烧颗粒群整体呈现团簇状结构,颗粒粒径范围主要集中在30~70 nm之间,呈正态单峰分布;随着EGR率的增加,粒径范围向大粒径方向移动,平均粒径逐渐增大,N10EGR20%与N10EGR0相比,平均粒径增大约为19%;计盒维数逐渐减小,表明颗粒间的团簇程度逐渐减弱。不同EGR条件下的基本碳粒子结构相似,呈指纹状球形碳层结构,随EGR率的增加,基本碳粒子的内核碳层排列无序性和外壳石墨晶体结构无规则性增强,平均层面间距和弯曲度逐渐增大,微晶尺寸逐渐减小。该研究为含氧燃料与EGR共同作用对颗粒的形成机理以及降低柴油机颗粒排放的措施提供理论参考。 相似文献
69.
70.
连作对花生土壤酶活性、养分含量和植株产量的影响 总被引:4,自引:2,他引:4
通过盆栽试验,设置4个不同连作年限处理,研究连作对花生栽培种桂花17和野生种A.correntina土壤酶活性、养分含量和植株干物质产量影响的差异。结果表明:与对照相比,两个花生品种不同连作年限土壤有效养分含量和植株干物质产量均降低,A.correntina相比桂花17下降幅度小。桂花17各连作年限处理土壤的脲酶、转化酶、酸性磷酸酶活性随连作年限的增加有下降的趋势,处理间变幅大。而A.correntina各生育期土壤的脲酶、转化酶、酸性磷酸酶活性总体表现无一致性上升或下降的规律,处理间变幅小。两个花生品种在不同的连作年限间的过氧化氢酶活性的变化无规律性。连作条件下,花生野生种A.correntina的土壤理化和生物学性状的变化幅度更小。 相似文献