首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   166篇
  免费   10篇
林业   14篇
农学   7篇
  35篇
综合类   18篇
农作物   10篇
水产渔业   12篇
畜牧兽医   61篇
园艺   2篇
植物保护   17篇
  2023年   1篇
  2022年   1篇
  2021年   5篇
  2020年   4篇
  2019年   4篇
  2018年   3篇
  2017年   4篇
  2016年   5篇
  2015年   5篇
  2014年   5篇
  2013年   12篇
  2012年   18篇
  2011年   19篇
  2010年   7篇
  2009年   6篇
  2008年   10篇
  2007年   8篇
  2006年   9篇
  2005年   12篇
  2004年   6篇
  2003年   5篇
  2002年   5篇
  2001年   1篇
  2000年   1篇
  1999年   2篇
  1997年   2篇
  1996年   1篇
  1995年   2篇
  1994年   3篇
  1987年   1篇
  1977年   1篇
  1976年   1篇
  1974年   1篇
  1972年   1篇
  1969年   1篇
  1966年   1篇
  1955年   1篇
  1950年   1篇
  1949年   1篇
排序方式: 共有176条查询结果,搜索用时 13 毫秒
61.
BACKGROUND: Japanese beetles, Popillia japonica Newman, are a quarantine challenge for nursery shipments from infested to non‐infested states. Marathon (imidacloprid) and Discus (imidacloprid + cyfluthrin) are approved preharvest nursery treatments (US Domestic Japanese Beetle Harmonization Plan; DJHP). This study evaluated approved and non‐approved (acephate, carbaryl, clothianidin, dinotefuran, halofenozide, thiamethoxam, trichlorfon) preharvest treatments, optimal rates (labeled 1×, 0.3–0.75× or 2–3×) and optimal timings (June, July, August and September) to control early‐instar (grubs) P. japonica in field nurseries. RESULTS: Most insecticides effectively reduced grub densities, except for acephate, carbaryl and trichlorfon. Clothianidin, thiamethoxam and halofenozide provided grub control equivalent to DJHP standards during most years. Across all test years and timings, percentage grub reductions were: Marathon (1×: 59.2–100; 3×: 78.9–100), Discus (1×: 60.7–100), clothianidin (1×: 96.1–100; 3×: 97.4–100), thiamethoxam (1×: 75.0–100; 3×: 80.0–100), halofenozide (1×: 70.0–100; 3×: 90.0–100) and dinotefuran (1×: 13.2–88.2; 3×: 71.1–93.4). CONCLUSIONS: July application was more consistent and effective than other timings, and higher rates (2× and 3×) did not generally improve grub control. Overall, clothianidin, thiamethoxam and halofenozide (and dinotefuran applied in August) were equivalent to current DJHP standards. These insecticides may be suitable for DJHP Category 2 states, potentially lowering grower costs. Copyright © 2009 Society of Chemical Industry  相似文献   
62.
The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.  相似文献   
63.
This experiment was conducted to investigate the effects of dietary ratios of n-6:n-3 polyunsaturated fatty acids (PUFA) on the performance of lactating sows and their piglets. Thirty pregnant Landrace sows were assigned to one of three treatments from d 108 of gestation until weaning (26–29 d) and were fed diets containing different ratios of n-6:n-3 PUFA including 3:1, 9:1 and 13:1. The effects on sow and litter production traits were examined together with an assessment of sow body condition. No differences were detected among the treatments for the daily feed intake of sows or changes in sow weight and back-fat levels during lactation (P > 0.05). Litter size at d 14 and d 21 were tended to increase in 3:1 treatment compared with 9:1 and 13:1 treatments (P < 0.10). Litter weight gain (1.77 kg/d) from d 0 to d 14 was tended to increase in 9:1 groups compared with the other two treatments (P < 0.10). A significant difference was observed for the content of α -linolenic acid, total n-3 PUFA, and the ratio of n-6:n-3 PUFA in the colostrum, milk, and piglets plasma (P < 0.01). The effects of different ratios of n-6:n-3 PUFA in sow diets on colostrum, milk, and piglet plasma immunoglobulin concentrations are studied. No difference was observed among treatments in the concentrations of IgM, and IgA in colostrum (P > 0.05). A great significant difference for IgG concentration was observed among 3 group in colostrum. A great significant difference for IgA, and IgM (P < 0.01) concentrations in piglet plasma at d14 and a significant difference for IgG(P < 0.05) was observed at d14. Furthermore, at d 21 of lactation, piglet plasma IgG and IgA concentration were greater in 3:1 compared with 13:1 group (P < 0.01).In summary, the current study demonstrated that altering the ratio of n-6:n-3 PUFA in lactating sow diet had an effect on the immune component including immunoglobulin and cytokines, and it tended to increase the litter average daily gain and improve the immune status of piglets when dietary ratio of n-6:n-3 PUFA was 9:1.  相似文献   
64.
The variation in soil organic carbon density(SOCD) has been widely documented at various spatial and temporal scales. However, an accurate method for examining the attribution of explanatory factors for change in SOCD is still lacking. This study aims to attribute and quantify the key climatic factors, anthropogenic activities, and soil properties associated with SOCD change in the native grasslands of Inner Mongolia, China, by comparing data between the 1960s and the 2010s. In 2007 and 2011, we resampled 142 soil profiles which were originally sampled during 1963–1964 in the native grasslands of Inner Mongolia. SOCD was determined in A horizon(eluvial horizon) of the soil. We selected the explanatory factors based on a random forest method, and explored the relationships between SOCD change and each of the explanatory factors using a linear mixed model. Our results indicated that the change in SOCD varied from the east to the west of Inner Mongolia, and SOCD was 18% lower in the 2010s than in the 1960s. The lower SOCD in the 2010s may primarily be attributed to the increasing in mean annual water surface evaporation, which explained approximately 10% and 50% of the total variation and explainable variation in the change in SOCD, respectively. The sand content of the soil is also a significant explanatory factor for the decrease in SOCD, which explained about 4% and 21% of the total variation and explainable variation in the change in SOCD, respectively. Furthermore, the collection of quantitative information on grazing frequency and duration may also help to improve our understanding of the anthropogenic factors that govern the change in SOCD.  相似文献   
65.
The effects of chlorpyrifos on aquatic systems are well documented. However, the consequences of the pesticide on soil food webs are poorly understood. In this field study, we hypothesised that the addition of a soil insecticide to an area of upland grassland would impact spider and Collembola communities by decreasing numbers of spiders, consequently, causing an increase in detritivore numbers and diversity.Chlorpyrifos was added to plots on an upland grassland in a randomised block design. Populations of Collembola and spiders were sampled by means of pitfall traps (activity density) and identified to species.Twelve species of Collembola were identified from the insecticide-treated and control plots. Species diversity, richness and evenness were all reduced in the chlorpyrifos plots, although the total number of Collembola increased ten-fold despite the abundance of some spider species being reduced. The dominant collembolan in the insecticide-treated plots was Ceratophysella denticulata, accounting for over 95% of the population.Forty-three species of spider were identified. There were a reduced number of spiders in insecticide-treated plots due mainly to a lower number of the linyphiid, Tiso vagans. However, there was no significant difference in spider diversity between the control and insecticide treatments.We discuss possible explanations for the increase in abundance of one collembolan species in response to chlorpyrifos and the consequences of this. The study emphasises the importance of understanding the effects of soil management practices on soil biodiversity, which is under increasing pressure from land development and food production. It also highlights the need for identification of soil invertebrates to an ‘appropriate’ taxonomic level for biodiversity estimates.  相似文献   
66.
BACKGROUND: Predatory mites (Amblyseius swirskii Athias‐Henriot, Typhlodromips montdorensis Schicha, Neoseiulus cucumeris (Oudemans) and Iphiseius degenerans Berlese) were investigated for their potential to act as control agents for Thrips palmi Karny. Prey consumption rates and compatibility with pesticides were assessed. RESULTS: Second‐instar larvae were the preferred life stage. Typhlodromips montdorensis consumed the most larvae (2.8) and also an average of 1.2 adult T. palmi per 5 day period. Both 24 and 48 h assessments following application of abamectin, spinosad and imazalil demonstrated mortality of predatory mites (across all species), which was significantly higher than with the other treatments (P < 0.001). Spraying with pymetrozine did not provide any increased mortality when compared with the water control. Application of thiacloprid proved detrimental only to I. degenerans. Following indirect exposure of predatory mites to pymetrozine and imazalil, no significant differences in mite mortality were obtained. Indirect exposure to spinosad was identified as the most detrimental treatment (P < 0.001) to all mites. Abamectin also proved detrimental, with only T. montdorensis showing any potential tolerance. CONCLUSION: All predatory mites investigated offer potential for controlling T. palmi. Compatibility with chemicals varied between the mites. The potential of incorporating the mites into eradication strategies for T. palmi is discussed. Copyright © 2012 Society of Chemical Industry  相似文献   
67.
This study was conducted to assess the effects of different dose levels of zinc oxide (ZnO) combined with probiotics complex supplementation on the growth, performance, nutrient digestibility, faecal lactobacillus and Enterobacteria counts, noxious gas emissions and faecal score of weaned piglets. A total of 180 crossbred weaning pigs ([Yorkshire × Landrace] × Duroc; 6.61 ± 1.29 kg [mean ± SE]; 28 days old) were used in a 42-day trial. All pigs were randomly allotted to 1 of 4 treatment diets based on initial BW and sex (9 replicate pens/treatment; 2 gilts and 3 barrows/pen). Dietary treatment groups were as follows: CON, basal diet +ZnO 3,000 ppm; BZS, basal diet +ZnO 2,100 ppm +0.1% SynerZymeF10; BZS1, basal diet +ZnO 1,200 ppm +0.1% SynerZymeF10; BZS2, basal diet +ZnO 300 ppm +0.1% SynerZymeF10. During the phase 3, decreasing the ZnO concentration led to a linear reduction in ADG (p = 0.044), and the ADG was lower (p < 0.05) in BZS2 compared with CON treatment during the whole experimental period. The effects of dietary ZnO with probiotics complex were not detected (p > 0.05) on nutrient digestibility, Lactobacillus and E. coli counts, faecal gas emissions and faecal scores. In conclusion, the diet supplementation of ZnO (1,200 ppm) with probiotics complex has been shown to have comparable efficacy to ZnO (3,000 ppm) diet on growth performance, nutrient digestibility, faecal microbiota, noxious gas emissions and faecal score of weaning pigs.  相似文献   
68.
69.
OBJECTIVE: To evaluate the use of measuring plasma concentrations of atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), and cardiac troponin-I (cTnI) to detect dogs with occult dilated cardiomyopathy (DCM). ANIMALS: 118 client-owned dogs. PROCEDURES: Dogs were prospectively examined by use of ECG; echocardiography; and evaluation of concentrations of ANP, BNP, and cTnI. Occult DCM was diagnosed by evaluation of echocardiographic left ventricular dimensions and detection of ventricular arrhythmias on ECG. Sensitivity and specificity of assays for measurement of plasma concentrations of ANP, BNP, and cTnI to detect dogs with occult DCM were determined. RESULTS: Occult DCM was diagnosed in 21 dogs. A concentration of > 6.21 pg/mL for BNP had a sensitivity of 95.2% and specificity of 61.9% for identifying dogs with occult DCM. In contrast, concentrations of ANP and cTnI had relatively low predictive values. CONCLUSIONS AND CLINICAL RELEVANCE: Blood-based screening for occult DCM in dogs can be accomplished by use of a BNP assay. Additional studies should be performed to optimize this method of screening dogs to detect occult DCM.  相似文献   
70.
We describe an experiment where cattle urine was applied at a rate of 420 kg N ha−1, equivalent to 10 L m−2, to mesocosm swards of a high lipid genetically modified perennial ryegrass line (HME) and its wild type (WT). We measured N pools and fluxes in the plant and soil, soil microbial populations and N2O production. HME plants produced 21% greater biomass than WT (p = .02), resulting in greater N uptake (27% higher in HME, p = .05). Urine N recovery in total plant biomass during the experiment in HME and WT swards were 54.7% and 33.9% respectively. The nitrification potential of soil was significantly lower (p = .01) in HME than WT. Partial least square-discriminant analysis using microbial gene abundance data indicated that HME and WT plant growth induced distinct microbial populations in the soil. These differences in plant soil microbial interactions between HME and WT swards resulted in significantly lower N2O emissions from the HME sward. Total N2O emissions over the 4 weeks after urine application was 38% lower (p < .03) in HME swards than in WT swards. The next step in this work is to identify the specific changes in HME traits that drive the reduction in N2O.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号