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   1949篇
  免费   136篇
林业   100篇
农学   97篇
基础科学   21篇
  384篇
综合类   64篇
农作物   208篇
水产渔业   221篇
畜牧兽医   686篇
园艺   62篇
植物保护   242篇
  2023年   17篇
  2022年   54篇
  2021年   73篇
  2020年   77篇
  2019年   120篇
  2018年   85篇
  2017年   121篇
  2016年   100篇
  2015年   69篇
  2014年   83篇
  2013年   145篇
  2012年   120篇
  2011年   132篇
  2010年   81篇
  2009年   61篇
  2008年   75篇
  2007年   61篇
  2006年   65篇
  2005年   70篇
  2004年   44篇
  2003年   43篇
  2002年   47篇
  2001年   27篇
  2000年   19篇
  1999年   25篇
  1998年   14篇
  1997年   14篇
  1996年   11篇
  1995年   11篇
  1994年   11篇
  1993年   19篇
  1992年   11篇
  1991年   14篇
  1990年   14篇
  1989年   8篇
  1988年   12篇
  1987年   11篇
  1985年   8篇
  1984年   11篇
  1983年   9篇
  1982年   7篇
  1979年   13篇
  1978年   5篇
  1977年   7篇
  1976年   8篇
  1975年   8篇
  1971年   6篇
  1969年   4篇
  1967年   7篇
  1966年   4篇
排序方式: 共有2085条查询结果,搜索用时 15 毫秒
991.
The aim of the study was to attempt the detection of West Nile virus (WNV) in wild birds in Poland. Forty-eight species of 1912 wild birds were used for the investigations. The birds were derived from various locations in Poland from early spring till late autumn of the years 2009-2011. The brain samples were homogenised and cellular RNA was isolated. Two methods (RT-PCR and nested RT-PCR) were used. The presence of WNV RNA was not detected in the samples examined. Additionally, a short analysis of the epizootiological situation regarding the presence of WNV in Poland is presented.  相似文献   
992.
Some aspects of the biology of the tick Hyalomma anatolicum fed on rabbits, sheep and goats were studied. The non-feeding stages were maintained under laboratory conditions at 20-36°C and 75% relative humidity. The longest feeding periods of larvae and nymphs of H. anatolicum were observed when fed on rabbits (mean 4.58 ± 0.51 and 7 ± 1.15 days, respectively) while the longest feeding periods of females were observed on goats (9.61 ± 1.21). The pre-oviposition period (4.8 ± 0.42 days) and pre-eclosion periods (mean 21.3 ± 1.16 days) were shortest for females fed on rabbits. Engorged females reached heavier engorgement weights (482.92 ± 88.08 mg), and produced more eggs (4881.8 ± 842.71) when fed on rabbits. However, no significant differences were observed between the percentages hatchability of eggs laid by ticks fed on the three hosts studied. Most (94.31%) of the larvae fed on rabbits underwent a 2-host life cycle, while few (5.69%) of them behaved as a 3-host ticks. Few larvae were able to complete feeding as 3-host pattern on both sheep and goats, while the majority of the larvae failed to complete feeding or died on their way to molt on both sheep and goats.  相似文献   
993.
This study was performed for the purpose of investigating the prevalence of Sarcocystis spp. in buffaloes in Beni-Suef Governorate, Egypt. Both macroscopic (Sarcocystis fusiformis) and microscopic (Sarcocystis levinei) cysts were recognized, and were differentiated by their morphological features and location in the tissues. Of 379 buffaloes examined in abattoirs in Beni-Suef, 299 were found to be infected, with an overall prevalence of 78.9%. Depending on age, three categorized groups of naturally infected buffaloes were examined: male buffalo calves aged 1.5–2 years, adult females aged 2–5 years, and females older than 5 years. Among these groups, infection rates were 74.5%, 82.3%, and 81.2%, respectively. Organs examined included esophagus, tongue, and heart. Macroscopic cysts were examined by the naked eye through meat inspection in abattoirs, while the pepsin-digestion method and the histological technique were applied to detect microscopic cysts. It has been found that esophagus showed the highest rate of infection among the infected organs, with both macroscopic and microscopic cysts seen in the infected buffaloes. Moreover, results of the pepsin-digestion method proved more accurate than those produced by the histological technique in terms of infection rates for the microscopic cysts. Our findings indicated that infected buffaloes aged 2–5 years showed the highest mixed infection rate (82.3%) for both types of cysts. The high prevalence of microscopic Sarcocystis spp. in Beni-Suef Governorate reflects a significant role played by stray dogs, rather than cats, in the transmission of these parasites.  相似文献   
994.
995.
Haemophilus parasuis is the etiological agent of Gl?sser's disease, which is characterized by fibrinous polyserositis, polyarthritis and meningitis in pigs. This study was focused on the characterization of the acute-phase response after immunization and infection of colostrum-deprived pigs with H. parasuis serovar 5, by measuring serum concentrations of three positive acute-phase proteins (APPs) (pig major acute-phase protein pig, MAP; haptoglobin, HPG; C-reactive protein, CRP) and one negative APP (apolipoprotein A-I, ApoA-I). Six experimental groups were established: a non-immunized but infected control group (CTL); two groups immunized with either a recombinant transferrin-binding protein (Tbp) A or TbpB fragment from H. parasuis Nagasaki strain (rTbpA and rTbpB, respectively); two groups immunized with native outer membrane proteins with affinity to porcine transferrin (NPAPT), one of them inoculated intramuscularly (NPAPTim) and the other intratracheally (NPAPTit), and the last group receiving a commercially available bacterin (PG). The greatest concentrations of the three positive APPs and the lowest concentration of the negative APP were detected in CTL group, as well as in those animals belonging to rTbpA or rTbpB groups that died in response to challenge. Significant differences (P<0.005) were found in these groups when comparing challenge with the following days after it. However, no significant differences were seen for the remaining vaccinated groups (NPAPTim, NPAPTit and PG), which were effectively protected against Gl?sser's disease. Therefore, APPs could be used as useful biomarkers for both evaluating disease progression and determining vaccination effectiveness.  相似文献   
996.
Sheep poxvirus (SPPV), Goat poxvirus (GTPV) and Lumpy skin disease virus (LSDV) are Capripoxviruses (CaPVs) responsible for causing severe poxvirus disease in sheep, goats and cattle, respectively. Serological differentiation of CaPVs is not possible and strain identification has relied on the implicitly accepted hypothesis that the viruses show well defined host specificity. However, it is now known that cross infections can occur and authentication of identity based on the host animal species from which the strain was first isolated, is not valid and should be replaced with molecular techniques to allow unequivocal strain differentiation. To identify a diagnostic target for strain genotyping, the CaPV homologue of the Vaccinia virus E4L gene which encodes the 30 kDa DNA-dependent RNA polymerase subunit, RPO30 was analyzed. Forty-six isolates from different hosts and geographical origins were included. Most CaPVs fit into one of the three different groups according to their host origins: the SPPV, the GTPV and the LSDV group. A unique 21-nucleotide deletion was found in all SPPV isolates which was exploited to develop a RPO30-based classical PCR test to differentiate SPPV from GTPV that will allow rapid differential diagnosis of disease during CaPV outbreaks in small ruminants.  相似文献   
997.
Hemotrophic mycoplasmas (hemoplasmas) are bacteria that attach to red blood cells of mammals, leading to acute and/or subclinical disease in infected animals. It has been suggested that Mycoplasma ovis, a hemoplasma that infects sheep and goats worldwide, may also infect deer. The aim of this study was to evaluate whether South American deer are infected with M. ovis. EDTA-anticoagulated blood samples from a herd of 32 captive South American deer were collected. DNA extraction of blood samples was performed followed by PCR amplification of the 16S and 23S rRNA genes, and sequencing of products. Using M. ovis PCR, 27/31 (87%) were positive, including 21/22 Mazama nana; 2/3 Mazama americana and 4/6 Blastocerus dichotomus. Sequencing of the nearly entire 16S rRNA gene of 26/27 positive samples showed 98.2-98.8% identity to M. ovis of sheep (GenBank, AF338268) and 98.6-99.4% identity to M. ovis-like of a fawn (FJ824847); the 23S rRNA gene from one of these isolates and the fawn's had 97.6% identity. The remaining isolate had just 94.9% identity to the 16S rRNA gene of M. ovis and only 89.4% identity to the 23S rRNA gene of the fawn's M. ovis. This is the first report of M. ovis in captive South American deer, revealing a high prevalence of hemoplasma infection in these animals.  相似文献   
998.
Three camels aged 4–5 years were experimentally infected with Bluetongue virus serotype 1 (BTV-1) and were observed for 75 days. No clinical signs of disease were observed throughout the experiment, however all three animals seroconverted and developed BTV-1 specific neutralising antibodies after challenge. All three camels developed a viraemia from 7 days post infection albeit at a lower level than that usually observed in experimental infections of sheep and cattle. Virus was isolated from the blood of all three animals suggesting that camels may act as a reservoir for BTV and play an important role in its transmission.  相似文献   
999.
1000.
BACKGROUND: Upon emergence from their pupal cells, bollworm, Helicoverpa zea (Boddie), adults actively seek and feed on plant exudates before they disperse and reproduce on suitable host plants. This nocturnal behavior of the bollworm may be exploited as a pest management strategy for suppression of the insect by using an attractant/stimulant mixed with an insecticide to induce feeding to cause adult mortality or reproductive reduction/inhibition. This study aimed to determine in the laboratory whether or not spinosad when mixed with sucrose solution as a feeding stimulant and ingested by bollworm could influence mortality and reproduction of the insect. RESULTS: Sublethal concentrations of spinosad fed to laboratory‐reared females confined with males significantly reduced percentage hatch of eggs at 0.1 mg L?1, and it was reduced to near zero at 2.5 mg L?1 when compared with females fed 2.5 M sucrose solutions only. The lethal concentration (LC99) for males captured from the field in sex‐pheromone‐baited traps was 73 mg L?1 for 24 h response. Proboscis extension response was not inhibited significantly even at 10 g L?1. In spite of a 137‐fold increase in lethal dose concentration, spinosad did not inhibit feeding. CONCLUSION: A detailed study of laboratory‐reared and field‐collected bollworm adults relative to mortality and reproduction after ingestion of spinosad indicates that spinosad would be useful in an attract‐and‐kill strategy to control the insect when mixed with a feeding attractant/stimulant. Field validation of the data is warranted. Published 2010 by John Wiley & Sons, Ltd.  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