全文获取类型
收费全文 | 6186篇 |
免费 | 373篇 |
国内免费 | 438篇 |
专业分类
林业 | 755篇 |
农学 | 503篇 |
基础科学 | 144篇 |
1037篇 | |
综合类 | 2916篇 |
农作物 | 404篇 |
水产渔业 | 131篇 |
畜牧兽医 | 490篇 |
园艺 | 125篇 |
植物保护 | 492篇 |
出版年
2024年 | 28篇 |
2023年 | 126篇 |
2022年 | 218篇 |
2021年 | 259篇 |
2020年 | 260篇 |
2019年 | 237篇 |
2018年 | 167篇 |
2017年 | 292篇 |
2016年 | 339篇 |
2015年 | 266篇 |
2014年 | 328篇 |
2013年 | 389篇 |
2012年 | 484篇 |
2011年 | 424篇 |
2010年 | 325篇 |
2009年 | 350篇 |
2008年 | 272篇 |
2007年 | 307篇 |
2006年 | 308篇 |
2005年 | 243篇 |
2004年 | 169篇 |
2003年 | 155篇 |
2002年 | 118篇 |
2001年 | 129篇 |
2000年 | 116篇 |
1999年 | 98篇 |
1998年 | 98篇 |
1997年 | 64篇 |
1996年 | 63篇 |
1995年 | 69篇 |
1994年 | 52篇 |
1993年 | 54篇 |
1992年 | 54篇 |
1991年 | 44篇 |
1990年 | 26篇 |
1989年 | 17篇 |
1988年 | 19篇 |
1987年 | 12篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有6997条查询结果,搜索用时 15 毫秒
101.
The dose-response curve was quantified for the avian repellency of cinnamamide, a derivative of the plant secondary compound cinnamic acid, using a three-day, ‘short-term no-choice’ test. This test was designed to resemble more closely the availability of alternative food in the birds' natural environment than in previous no-choice studies. Cinnamamide reduced food consumption by feral pigeons (Columba livia Gmelin) at concentrations as low as 6.17 μmole g?1 food (0.09% w/w) and this reduction increased with concentration. An R50 index, the concentration at which food consumption was reduced by 50% was interpolated from the dose-response curve as 18.4 (±0.38) μmole g?1 food 10.26% w/w). This index can now be matched with those of related compounds in future structure-activity studies. The birds' response to cinnamamide changed over the three-day trial with respect to concentration. Repellency declined at concentrations < R50 and increased at concentrations > R50. This suggests that pigeons become habituated to cinnamamide at low concentrations but at high concentrations they may develop a conditioned aversion. This study provides quantitative confirmation of previous laboratory and field demonstrations of cinnamamide's effectiveness as a non-lethal chemical repellent suitable for reducing avian pest damage. 相似文献
102.
Gengmei?Xing Jun?Zhang Jing?Liu Xiaoyan?Zhang Genxuan?WangEmail author Yafu?Wang 《Phytoparasitica》2003,31(5):499-514
The impacts of elevated CO2 and soil water on the population dynamics, adult fecundity and nymphal period of the bird cherry-oat aphidRhopalsiphum padi (Linnaeus) were evaluated in three experiments: (i)Combined effects of CO
2
and soil water on aphid populations. Spring wheat was grown in pots at three CO2 concentrations (350, 550 and 700 ppm) and three soil water levels (40%, 60% and 80% of field water capacity, FWC) in field
open-top chambers (OTC) and infested with the bird cherry-oat aphid. Aphid population dynamics were recorded throughout the
growing season; at the same time, adult fecundity and duration of the nymphal period were recorded. Chemical composition of
spring wheat leaves was also analyzed. (ii)Indirect effects of CO
2
concentrations and soil water on aphid adult fecundity and nymphal period. The experiment was conducted with the leaf discs method in the laboratory. Aphids were reared on leaf discs excised from
the treated wheat in OTC with different CO2 and soil water levels. (iii)Direct effects of CO
2
concentrations on aphid adult fecundity and nymphal period. Aphids were reared on leaf discs excised from the wheat grown under natural conditions. The experiment was conducted with
the leaf disc method in OTC with the three CO2 concentrations. It was found that the direct effect of CO2 concentration on aphid population parameters was minor. CO2 and soil water affected aphid population indirectly through their effects on wheat characteristics. The aphid population
under 550 ppm CO2 was far larger than the one under 350 ppm CO2, whereas the population under 700 ppm CO2 was slightly higher than that under 550 ppm CO2. The largest aphid population was obtained with the 60% soil water treatment, regardless of CO2 treatment. The effects of CO2 concentration on aphid population were, however, not significantly correlated with soil water level. Adult fecundity increased
with CO2 concentration, the highest fecundity being achieved under 60% FWC treatments. The nymphal period was not affected by CO2 concentration. The shortest period occurred under 60% FWC. Atmospheric CO2 and soil water had significant effects on the chemical composition of the wheat leaves. Aphid population size was positively
correlated with leaf water content, concentrations of soluble proteins, soluble carbohydrates and starch, and negatively correlated
with DIMBOA and tannins concentrations.
http://www.phytoparasitica.org posting Oct. 20, 2003. 相似文献
103.
104.
105.
106.
107.
中药凤尾草的研究进展 总被引:3,自引:0,他引:3
凤尾草是一种传统的药用植物,具有很高的药用价值,应用前景广阔。本文综述了凤尾草的鉴定、临床应用、药理作用和化学成分的研究概况,为中药凤尾草资源开发与合理利用提供依据。 相似文献
108.
桉树化学成分及药理作用研究进展 总被引:6,自引:0,他引:6
桉树作为世界上三大速生丰产树种之一,已被人们所公认.近年来,桉树及其副产物的综合利用研究取得了一定的进展,桉树的药理作用研究方兴未艾.文章在介绍桉树的主要化学成分的基础上,详细综述了桉树在抗菌、抗炎、杀虫以及促渗等方面的药理作用研究进展,使人们对桉树能有更加全面的了解和认识,拓宽了人们在桉树药用价值等相关领域的研究视野. 相似文献
109.
110.
新疆污灌区重金属含量及形态研究 总被引:6,自引:0,他引:6
本文对新疆污灌区土壤中Cu、Zn、N i、Cr、Pb五种重金属元素的含量和形态特征进行了研究。结果表明,Cu、Zn、N i、Cr、Pb主要富集在0—20cm表土中。以《土壤环境质量标准》GB15618—1995二级标准为评价标准,污染综合指数评价均为安全级。新疆污灌表土中Cu、Zn、N i、Cr、Pb以残渣态为主,水溶态和可交换态比例低,其中Cu、Zn、Pb的潜在生物可利用性较高。 相似文献