收费全文 | 2395篇 |
免费 | 265篇 |
国内免费 | 1篇 |
林业 | 192篇 |
农学 | 108篇 |
基础科学 | 13篇 |
413篇 | |
综合类 | 75篇 |
农作物 | 149篇 |
水产渔业 | 335篇 |
畜牧兽医 | 1104篇 |
园艺 | 58篇 |
植物保护 | 214篇 |
2024年 | 3篇 |
2023年 | 35篇 |
2022年 | 62篇 |
2021年 | 129篇 |
2020年 | 149篇 |
2019年 | 178篇 |
2018年 | 176篇 |
2017年 | 151篇 |
2016年 | 185篇 |
2015年 | 88篇 |
2014年 | 138篇 |
2013年 | 142篇 |
2012年 | 183篇 |
2011年 | 172篇 |
2010年 | 102篇 |
2009年 | 93篇 |
2008年 | 113篇 |
2007年 | 107篇 |
2006年 | 80篇 |
2005年 | 51篇 |
2004年 | 58篇 |
2003年 | 44篇 |
2002年 | 43篇 |
2001年 | 25篇 |
2000年 | 35篇 |
1999年 | 23篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1967年 | 2篇 |
1963年 | 1篇 |
1958年 | 1篇 |
The South American tomato pinworm, Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae), is heavily targeted by insecticide applications. Methoxyfenozide is highly effective against T. absoluta with reduced side effects to natural enemies. This work aimed to (1) genetically and biochemically characterize resistance of the T. absoluta GBN population to methoxyfenozide, (2) establish cross resistance profiles with other insecticide groups and (3) monitor resistance in populations with the goal of improving T. absoluta insecticide resistance management (IRM). Methoxyfenozide resistance was completely recessive, polyfactorial and autosomal. Effective dominance revealed that 10 mg methoxyfenozide/L would be enough to eliminate susceptible homozygotes and heterozygotes, thus used to diagnose resistance in field populations. The synergism of methoxyfenozide toxicity in the resistant population for PBO (SR?=?95×), DEF (SR?=?51×) and DEM (SR?=?45×), suggested monooxygenases, esterases and glutathione S-transferases as resistance mechanisms. However, only monooxygenase activity appeared to be involved in methoxyfenozide resistance. Resistance ratio for methoxyfenozide (2352-fold) after selection and cross-resistance ratios of a lab-selected GBN strain (“GBN-Sel”) were significant relative to a susceptible strain “JDR1-Sus” for tebufenozide (656-fold), cartap hydrochloride (10.68-fold), deltamethrin (4.70-fold), abamectin (2.65-fold), lufenuron (2.22-fold) and indoxacarb (1.92-fold), with negative cross-resistance to spinetoram (0.32-fold). Evidence of control failures was observed in 10 field populations of T. absoluta (mortalities between 13 and 76%), and all populations showed frequencies of resistant phenotypes (percentage survivorship ranging between 4 and 96%). A rational basis for managing resistance to bisacylhydrazines is discussed, along with details of recommended T. absoluta resistance management tactics.
相似文献Pinus plantations have increased in Brazil, and native forest areas have been converted for timber production. The clearing and the long-term loblolly pine (Pinus taeda L.) land-use effects on soil carbon and nitrogen stocks were evaluated in a natural broadleaved forest and in loblolly pine sites cultivated for 29, 35, 38 and 49 years, as well the soil contribution as ecosystem carbon pool. According to the exponential-decay model fitted to changes in carbon stock, the initial soil carbon stock of 200 Mg ha?1 to a depth of 100 cm in the natural forest decreased by 36% over 49 years of pine cultivation (around 72.4 Mg ha?1 of C). Around two-thirds of this decrease occurred in the top 30 cm of the soil and intensively in the first 12 years of cultivation, but slowly faded as carbon stock tended to reach a new steady state after approximately 49 years of cultivation. The soil nitrogen stock in the natural forest was 14.2 Mg ha?1 to a depth of 100 cm and decreased by 36% over the 49 years. This decrease was linear according to the fitted model, especially in the top 30 cm where nitrogen decline was 83% and was proportionally more intense than the carbon decline. Despite the soil carbon decrease, soil remained the largest carbon reservoir in the ecosystem for the growing rotation time of loblolly pine in this region.
相似文献