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   596篇
  免费   41篇
  国内免费   3篇
林业   28篇
农学   13篇
基础科学   2篇
  159篇
综合类   139篇
农作物   26篇
水产渔业   36篇
畜牧兽医   199篇
园艺   6篇
植物保护   32篇
  2023年   4篇
  2021年   10篇
  2020年   9篇
  2019年   9篇
  2018年   11篇
  2017年   11篇
  2016年   15篇
  2015年   20篇
  2014年   16篇
  2013年   21篇
  2012年   30篇
  2011年   32篇
  2010年   24篇
  2009年   11篇
  2008年   26篇
  2007年   23篇
  2006年   22篇
  2005年   34篇
  2004年   26篇
  2003年   18篇
  2002年   19篇
  2001年   22篇
  2000年   23篇
  1999年   21篇
  1998年   12篇
  1997年   6篇
  1996年   4篇
  1995年   8篇
  1994年   4篇
  1993年   10篇
  1992年   12篇
  1991年   7篇
  1990年   10篇
  1989年   12篇
  1988年   9篇
  1987年   7篇
  1986年   6篇
  1985年   12篇
  1984年   7篇
  1983年   3篇
  1981年   5篇
  1979年   3篇
  1978年   3篇
  1977年   3篇
  1976年   5篇
  1975年   3篇
  1974年   6篇
  1973年   4篇
  1972年   4篇
  1971年   3篇
排序方式: 共有640条查询结果,搜索用时 31 毫秒
111.
A polysaccharide (GSP-6B) with a molecular mass of 1.86 × 10? Da was isolated from the fruiting bodies of Ganoderma sinense . Chemical composition analysis, methylation analysis, infrared spectroscopy, and nuclear magnetic resonance spectroscopy were conducted to elucidate its structure. GSP-6B contains a backbone of (1→6)-linked-β-D-glucopyranosyl residues, bearing branches at the O-3 position of every two sugar residues along the backbone. The side chains contain (1→4)-linked-β-D-glucopyranosyl residues, (1→3)-linked-β-D-glucopyranosyl residues, and nonreducing end β-D-glucopyranosyl residues. An in vitro immunomodulating activity assay revealed that GSP-6B could significantly induce the release of IL-1β and TNF-α in human peripheral blood mononuclear cell (PBMC) and showed no toxicity to either PBMC or a human macrophage cell line THP-1. GSP-6B could also activate dendritic cells (DC) by stimulating the secretion of IL-12 and IL-10 from DC.  相似文献   
112.
The objective of this study was to investigate and compare the kinetic photocatalytic degradation of mono azo dyes Acid Orange 7 (AO7) and Methyl Orange (MO) under solar light irradiation with titanium dioxide (TiO2) as a photocatalyst. Several operational parameters affecting the photocatalytic degradation of dye were evaluated such as different azo dyes, initial dye concentration, TiO2 dosage, with and without aeration and sunlight irradiation. The data obtained was well fitted with the Langmuir?CHinshelwood kinetic model. It was observed that the pseudo-first-order rate constants for AO7 were higher than MO in all cases, indicating that the photocatalytic degradation of AO7 was easier and more rapid than MO. The analysis of chemical oxygen demand and UV?CVis spectra shows the AO7 and MO not only being decolorized due to the breakdown of azo bond but also being mineralized if the azo dye solutions were continually exposed to solar light irradiation after the decolorization process.  相似文献   
113.
114.
Mixtures of turkey herpesvirus (HVT) and Rispens poultry vaccines have been used worldwide for over 20 yr, mainly for vaccination of future layers and breeders. With increasing virulence of Marek's disease (MD) virus strains, vaccination strategies are evolving toward the use of vaccines combining HVT and Rispens. A single vaccination either in ovo or at 1 day of age with the HVT + infectious bursal disease (IBD) vector vaccine is efficient against IBD. However, with vaccination programs that include a hatchery administration of the HVT + IBD vaccine, additional protection against very virulent and very virulent-plus MD viruses is needed, especially for layers and breeders. This study looked at the combination of four commercially available Rispens vaccines with the HVT + IBD vector vaccine injected at 1 day of age. MD challenge tests that were superior to 90% in relative score in all the groups vaccinated with both vaccines showed that the mixture of HVT + IBD and Rispens vaccines had no effect on clinical protection against MD, and IBD challenge tests showed that the mixture of HVT + IBD and Rispens vaccines had no effect on clinical protection against IBD, which was equal to 100% protection in all the groups vaccinated with both vaccines.  相似文献   
115.
Hatchery vaccination protocols in day-old chicks are designed to provide early priming and protection against several poultry diseases including, but not limited to, Marek's disease (MD), infectious bursal disease (IBD), and Newcastle disease (ND). The constraint of concomitant administration of live MD and IBD vaccines plus ND inactivated oil-adjuvanted vaccines (IOAVs) requires improvements in vaccine technology. Single-needle concomitant subcutaneous (SC) application of IBD/MDV and killed NDV vaccine and the use of viral vectors for expression of immunogenic proteins are a current trend in the industry. The objective of this work was to assess the compatibility of a turkey herpesvirus (HVT)-infectious bursal disease (vHVT-IBD) vector vaccine applied simultaneously with IOAV and to evaluate the consequences for vaccine intake, the need for additional immunizations with the respective vaccines, and protection. Five separate trials were performed using double- and/or single-needle injectors. The levels and persistence of vaccine intake, serologic response, vHVT-IBD virus combination with the MD Rispens strain, and/or live NDV vaccination were also assessed. Histopathology and PCR at injection sites showed adequate vaccine intake detected up to 44 days postvaccination. Serologic evidence of vaccine priming was observed, and all vaccinated groups differed (P < 0.05) from the control at different time points. MD, NDV, and IBD protection results after concomitant double-shot single-needle vaccination were near 85%, 95%, and 100%, respectively. Taken together the results indicate no deleterious effects on the efficacy of the vHVT-IBD vaccine monitored by vaccine intake, serologic and challenge results, and combinations after concomitant live/killed vaccination, suggesting the suitability of its use in hatchery vaccination. All types of injectors used as well as injection techniques, vaccines injected separately or together, gave the same results.  相似文献   
116.
Objectives : To review the success rates for liposuction of lipomas in dogs, report early complications and medium‐term outcomes and formulate recommendations on the most appropriate candidates for liposuction. Methods : Retrospective study of 20 dogs with 76 lipomas diagnosed by cytology, in which dry liposuction was attempted. Case records were reviewed for number and size of the lipomas, efficacy of liposuction, frequency and types of complication and likelihood of recurrence. Results : Liposuction was successful in removing 73 of 76 lipomas (96%). Simple, encapsulated lipomas less than 15 cm in diameter were most easily removed, with minimal risk of complication. Giant lipomas contained fibrous trabeculae that hindered liposuction and resulted in poor fat retrieval. Giant lipomas were also associated with a high risk of bruising, haematoma and seroma, especially when inguinal in location. Regrowth was noted at follow‐up between 9 and 36 months in 28% of lipomas. Clinical Significance : Liposuction may be less invasive and more attractive to owners than conventional surgery for lipomas up to 15 cm in diameter. Liposuction is not recommended for infiltrative or giant inguinal lipomas. Regrowth can be expected in a high proportion of lipomas, which should be considered when choosing liposuction over conventional excision.  相似文献   
117.
Cai S  Li J  Wong MT  Jiao P  Fan H  Liu D  Liao M  Jiang J  Shi M  Lam TT  Ren T  Leung FC 《Veterinary microbiology》2011,152(1-2):46-54
Complete genomes of four Newcastle disease virus (NDV) strains, isolated from ducks and wild birds in Guangdong province of China from 2003 to 2007, were sequenced and analyzed in this study. Pathogenicity tests in chicken embryos and chickens illustrate that D3 and R8 are lentogenic, and W4 and P4 are mesogenic strains. Phylogenetic analysis using all six genes provides a high resolution profile for genotype designation as genotype I for D3 and R8 strains and genotype VI for W4 and P4 strains. In addition, molecular dating based on different genes suggests that D3 and R8 diverged from their common ancestor at around 1998; W4 and P4 diverged from their common ancestor at around 1999. Subsequent selective pressure analysis displayed specific traits of genes evolution in all 4 strains since their divergence from the recent common ancestor. Furthermore, the geographic origins of 4 strains were deduced to be from Europe via two independent introduction events by phylogeographical analysis. This provides insights to the potential influence of waterfowl migration on NDV epidemiology.  相似文献   
118.
Seven FDA pesticide laboratories collaborated to develop and validate an LC-MS/MS method to determine 173 pesticides in <20 min. The average determination coefficient (r2) was >0.99 for all but two compounds tested. The limits of detection were <20 ng/mL for all compounds and <10 ng/mL for 363 of the 368 transitions reported. The method was used to determine pesticides in two AOAC sponsored proficiency samples. The LC-MS/MS determination was used for the analysis of oranges, carrots and spinach using the QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) method. Each matrix was fortified at 20, 100, 400, and 1000 ng/g. No false positive responses were detected in controls of the three matrices. 165 pesticides had recoveries between 70 and 130%, and 161 had minimum detection levels less than 10 ng/g. Recoveries of 169 compounds for the 1000 ng/g spikes were within 50-150%. A matrix effect study indicated all three matrices caused a small net suppressing effect, the most pronounced attributable to the citrus matrix. The procedure proved to be accurate, precise, linear, sensitive and rugged, and adds 100 pesticides to the scope of the FDA pesticide program.  相似文献   
119.
Sulphuric acid-modified bagasse has been used as low-cost adsorbent for the removal of methylene blue (MB) dye from aqueous solution. In order to remove organic compounds that contribute to chemical oxygen demand (COD), pretreatment with thorough washing of adsorbent using boiling distilled water was performed instead of conventional washing using distilled water at room temperature only. This has resulted in the highest efficiency of color removal of 99.45% and COD reduction of 99.36% for MB dye solution at pH 9. Effects of initial pH, dye concentration, adsorbent dosage, temperature, and contact time have been studied. The adsorption of MB dye was pH dependent. Langmuir and Freundlich isotherm models were tested on the adsorption data. The kinetic experimental data were analyzed using pseudo-first order, pseudo-second order, and the intraparticle diffusion model in order to examine the adsorption mechanisms. The adsorption process followed the Langmuir isotherm as well as the Freundlich isotherm and pseudo-second-order kinetic model. The process was found to be endothermic in nature.  相似文献   
120.
为充分利用林区的自然资源,1986—1987年先后在帽儿山实验林场和依兰县先锋林场进行了养鱼试验,经过120天的饲养期,鱼产量在帽儿山为3094.5kg/ha,在先锋为1882.5kg/ha。 林区水资源丰富,水质稳定;水的pH值偏低,多为软水,水中营养盐类贫乏。用石灰清塘可使pH值由6.5升至8.3。施肥可促进浮游生物的增殖,藻类的优势种为隐藻,浮游动物为近邻剑水蚤。灯光诱虫既能使鲤鱼生长明显加快,又能除去部分森林害虫。林区水体污染较轻,故家养鱼类病害也较少。 在帽儿山、鱼的增重倍数为5.33,饵料系数为2.14;在先锋则分别为7.68和1.35。由于鲤鱼适应低温环境,所以长势较鲢鳙鱼为好。在帽儿山鲤鱼平均重0.31kg,在先锋则为0.40kg。 林区宜主养鲤鱼,也应放养草食和腐食性的鱼类,以充分利用水体中的生态位。  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