全文获取类型
收费全文 | 17336篇 |
免费 | 1081篇 |
国内免费 | 1242篇 |
专业分类
林业 | 966篇 |
农学 | 1429篇 |
基础科学 | 147篇 |
2023篇 | |
综合类 | 6612篇 |
农作物 | 1416篇 |
水产渔业 | 1603篇 |
畜牧兽医 | 3850篇 |
园艺 | 927篇 |
植物保护 | 686篇 |
出版年
2024年 | 113篇 |
2023年 | 243篇 |
2022年 | 529篇 |
2021年 | 632篇 |
2020年 | 663篇 |
2019年 | 795篇 |
2018年 | 544篇 |
2017年 | 814篇 |
2016年 | 902篇 |
2015年 | 704篇 |
2014年 | 804篇 |
2013年 | 1099篇 |
2012年 | 1279篇 |
2011年 | 1323篇 |
2010年 | 996篇 |
2009年 | 994篇 |
2008年 | 884篇 |
2007年 | 1019篇 |
2006年 | 801篇 |
2005年 | 568篇 |
2004年 | 503篇 |
2003年 | 400篇 |
2002年 | 338篇 |
2001年 | 324篇 |
2000年 | 282篇 |
1999年 | 274篇 |
1998年 | 222篇 |
1997年 | 197篇 |
1996年 | 222篇 |
1995年 | 188篇 |
1994年 | 146篇 |
1993年 | 131篇 |
1992年 | 120篇 |
1991年 | 126篇 |
1990年 | 113篇 |
1989年 | 107篇 |
1988年 | 73篇 |
1987年 | 47篇 |
1986年 | 28篇 |
1985年 | 28篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1962年 | 3篇 |
1956年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
多杀菌素的作用机理及其抗药性的研究进展 总被引:2,自引:0,他引:2
多杀菌素是一类新的杀虫剂,具有高效、低毒、选择性强、对环境安全的特点。其作用机制是通过激活烟碱型乙酰胆碱受体(nAChR),使正常昆虫神经细胞去极化,也可通过抑制γ-氨基丁酸受体(GABAR)使神经细胞超极化。本文综述了多杀菌素作用机理及其抗药性的研究进展。 相似文献
993.
A target-site mutation is present in a glyphosate-resistant Lolium rigidum population 总被引:2,自引:1,他引:2
Annual ryegrass (Lolium rigidum) is the only weed species to have evolved resistance to the broad‐spectrum herbicide glyphosate in Australia. A population that had failed to be controlled by glyphosate was collected from a vineyard in the Adelaide Hills region of South Australia. Dose–response experiments on this population (SLR 77) showed that it was glyphosate resistant, with an LD50 that was 1.9–3.4 times higher than that of a susceptible population (VLR 1). The movement of radiolabelled glyphosate within SLR 77 plants showed that this population did not have the differential glyphosate translocation mechanism of resistance common to several other Australian glyphosate‐resistant populations. Subsequent analysis of shikimic acid accumulation within the plant after glyphosate treatment showed that this population accumulated significantly less shikimic acid than a susceptible population, but more than a glyphosate‐resistant population with the translocation mechanism, indicating the possible involvement of another mechanism of resistance. Sequencing of a portion of the SLR 77 5‐enolpyruvylshikimate‐3‐phosphate synthase gene was carried out and a mutation causing an amino acid change at position 106 from proline to threonine was identified. This mutation is likely to be responsible for glyphosate resistance in this population, as mutations in this position have been found to be responsible for glyphosate resistance in goosegrass (Eleusine indica) from Malaysia. This paper represents the first report of target‐site glyphosate resistance in L. rigidum and provides evidence that this species has at least two mechanisms of glyphosate resistance present in Australia. 相似文献
994.
奶牛日粮中添加油菜籽、菜油及脂肪酸钙对奶牛产奶量及奶品质的影响 总被引:2,自引:0,他引:2
试验选用泌乳3~5个月,2~5胎次,体重相近,健康无病,产奶量相近(P>0.05)的奶牛36头,随机分为4组,其中:对照组喂给基础日粮,试验1、2和3组分别在基础日粮中添加油菜籽(350 g/d·头)、菜油(150 g/d·头)和脂肪酸钙(200 g/d·头)。通过30 d对比饲养试验。结果表明:试验1、2、3组的奶牛日均产奶量分别比对照组相对提高0.88(P<0.05)、0.31(P>0.05)、0.70 kg/d·头(P<0.05)。各组间奶牛干物质采食量及饲料干物质利用率均无显著差异(P>0.05);试验1、2、3组牛奶中乳蛋白和非脂乳固体有增加的趋势,但不明显(P>0.05);试验1、2、3组与对照组的乳脂率无明显变化(P>0.05)。与对照组相比试验1组每头奶牛每天可增加纯收入1.08元,试验2组亏损0.06元,试验3组亏损0.14元;从而认为在日粮中添加油菜籽、菜油、脂肪酸钙可以提高奶牛产奶量,其中以添加油菜籽的经济效益最好。 相似文献
995.
《The Journal of Applied Poultry Research》2007,16(3):420-428
The present study was conducted to investigate the effect of long-term feeding of conjugated linoleic acid (CLA) and fish oil on egg quality characteristics, production performance, liver pathology, and egg fatty acid content of laying hens. Single Comb White Leghorn laying hens (n = 112), 21 wk old, were placed in cages and randomly assigned to 4 diets (28 hens/diet, 4 replicates of 7 hens) containing 3.0% yellow grease (control), 2.75% yellow grease + 0.25% CLA (YG-CLA), 2.5% yellow grease + 0.25% CLA + 0.25% fish oil (YG-CLA-FO), and 2.75% yellow grease + 0.25% fish oil (YG-FO). The experimental diets were fed for 12 mo. Eggs were collected daily for 12 mo. Feed consumption, hen-day egg production, and feed efficiency were monitored. At the end of the trial, hepatic tissue was collected for histopathology. No effect of diet was found on feed consumption, hen-day egg production, feed efficiency, egg weight, yolk weight, shell weight, or Haugh unit. The YG-CLA and YG-CLA-FO diets produced an increase in CLA and saturated fatty acids in the egg and liver tissue with a concomitant reduction in monounsaturated fatty acids (P < 0.05). Feeding YG-CLA-FO and YG-FO increased the n-3 fatty acids in egg yolk and liver of hens (P < 0.05). No difference was observed in the number of fat vacuoles in the liver tissue. The total fat content of hepatic and abdominal fat pads did not differ among treatments (P > 0.05). Regardless of the diet, as the hens aged, egg weight, yolk weight, and egg total fat increased, and shell weight decreased (P < 0.05). These data demonstrate that eggs with increased n-3 fatty acids and CLA can be generated by minor diet modifications without affecting the production performance or health of birds. 相似文献
996.
997.
本试验选用五龙鹅蛋用系与快长系各150只进行网床育肥试验,测定血浆总蛋白质含量,并进行PAGE电泳。结果显示:初生雏鹅血浆总蛋白质含量较高,随着日龄(1~90 d)增加呈先下降后升高趋势,以对数函数和抛物线函数分段拟合效果较佳,R2为0.9445、0.9568;血浆总蛋白质含量在性别间差异不显著,品系间差异显著。PAGE电泳结果表明:血浆中蛋白质种类在品系、性别间没有差异,随日龄的增加亦没有条带变化。清蛋白含量的变化是引起血浆总蛋白质含量变化的主要因素。 相似文献
998.
了解牛磺胆酸对发热大鼠体温的影响,并研究其解热作用机理.分别以细菌内毒素、异体蛋白和2,4-二硝基酚致热大鼠,采用荧光分光光度法测定大鼠下丘脑组织中去甲肾上腺素(NE)、多巴胺(DA)和5-羟色胺(5-HT)含量;ELISA法测定下丘脑组织中肾上腺素E2(PGE2)含量.牛磺胆酸对细菌内毒素和2,4-二硝基酚所致发热大鼠的体温具有显著的降低作用,而对蛋白胨所致的发热体温作用时间较短;给药组下丘脑中的NE、DA、5-HT和PGE2的含量显著低于对照组.试验证明牛磺胆酸具有显著的解热作用,其作用机理与影响下丘脑组织中NE、DA、5-HT和PGE2的含量有关. 相似文献
999.
1000.