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   451篇
  免费   18篇
林业   32篇
农学   21篇
基础科学   3篇
  121篇
综合类   68篇
农作物   6篇
水产渔业   19篇
畜牧兽医   173篇
园艺   5篇
植物保护   21篇
  2023年   4篇
  2022年   7篇
  2021年   11篇
  2020年   5篇
  2019年   5篇
  2018年   10篇
  2017年   9篇
  2016年   12篇
  2015年   13篇
  2014年   11篇
  2013年   9篇
  2012年   35篇
  2011年   32篇
  2010年   15篇
  2009年   18篇
  2008年   24篇
  2007年   26篇
  2006年   33篇
  2005年   30篇
  2004年   21篇
  2003年   22篇
  2002年   17篇
  2001年   5篇
  2000年   8篇
  1999年   7篇
  1998年   2篇
  1997年   2篇
  1996年   4篇
  1995年   4篇
  1994年   2篇
  1992年   2篇
  1991年   4篇
  1989年   2篇
  1988年   4篇
  1986年   2篇
  1982年   2篇
  1981年   2篇
  1979年   2篇
  1976年   4篇
  1974年   2篇
  1973年   3篇
  1972年   7篇
  1971年   11篇
  1970年   2篇
  1969年   2篇
  1968年   1篇
  1967年   1篇
  1963年   1篇
  1940年   1篇
  1938年   1篇
排序方式: 共有469条查询结果,搜索用时 15 毫秒
61.
62.
63.
The federally threatened Florida Scrub-Jay (Aphelocoma coerulescens) has suffered dramatic losses in recent years primarily because of overdevelopment of its unique scrub habitat. Ensuring the survival of this species will require not only measures to reduce habitat loss, but also efforts to increase the numbers of birds in small scattered populations to a point at which they are resilient to extinction from stochastic population fluctuations. Here we evaluate the utility of providing supplementary food during the pre-breeding season as a means of increasing the reproductive output of Florida Scrub-Jays. Data collected from 2000 to 2007 at Archbold Biological Station in south-central Florida indicate a marked effect of supplemental feeding on reproductive output. This increased output appeared to result primarily from larger clutch sizes produced by supplemented female breeders as a result of their advanced laying. Supplementation also increased offspring survival probabilities and the early laying permitted more renesting attempts. Furthermore, annual variation in several reproductive measures was dampened in supplemented birds, suggesting that supplemental feeding may reduce environmental or stochastic effects on reproductive output. Although a number of potential problems may be associated with supplemental feeding (e.g., predator entrainment and increased opportunity for disease transmission), it can serve as a valuable tool for management agencies that wish to rapidly increase local carrying capacity. In addition, food supplementation might benefit translocation efforts both by increasing the number of potential translocation candidates from a donor population and then by supplementing the newly established population to promote rapid growth.  相似文献   
64.
65.
Journal of Plant Diseases and Protection - The following text summarizes the different perspectives of presenters participating in the section Plant Protection in the Tropics and Subtropics, 61st...  相似文献   
66.
To obtain microbiological data from rabbits at slaughter, 500 fecal samples and 500 carcasses samples were examined. All samples tested negative for Listeria and Salmonella. Campylobacter were detected in two fecal samples. Of the 500 fecal samples, 45.8% tested positive for eae (intimin), 1.2% for stx (Shiga toxin), and 1.8% for both eae and stx. By colony hybridization, 56 eae positive Escherichia coli strains were isolated. Among them, 27 strains (48.2%) were of the serotypes O178:H7 and O153:H7, whereas 15 strains (26.8%) belonged to a serogroup that has not yet been described (O(CB10681):H7). All strains possessed intimin beta1 and the translocated intimin receptor (tir) capable of being tyrosine phosphorylated. None of the strains harbored the genes for Shiga toxins, EAST1 (astA), bundlin (bfpA), or the EAF plasmid. Slaughter rabbits therefore constitute a reservoir for certain atypical enteropathogenic Escherichia coli. On rabbit carcasses, average total bacterial counts accounted for 3.3 log CFU cm(-2). Enterobacteriaceae and coagulase positive staphylococci (CPS) were detected on 118 (23.6%) and 153 (30.6%) carcasses, respectively. Enterobacteriaceae and CPS counts of positive samples were mainly <1.5 log CFU cm(-2). Among 153 selected CPS isolates, 98.7% were identified as Staphylococcus aureus. None of the 151 isolated strains harbored the gene for methicillin resistance (mecA). Genes for staphylococcal enterotoxins (SE) were detected in 102 strains. The combinations of seg and sei (53 strains) and sed, seg, sei, and sej (27 strains) dominated.  相似文献   
67.
Liver fibrosis is a morphologic alteration that accompanies chronic liver diseases. Apart from analysis of liver biopsy specimens, there has been no means of diagnosing and evaluating the course of liver fibrosis in the dog. Several plasma markers, including transforming growth factor beta-1 (TGF-β1), are used to indicate liver fibrosis in humans, but none has been validated for use in dogs. There is a significant correlation between the presence and severity of hepatic fibrosis and the plasma concentration of TGF-β1 in humans with hepatic fibrosis and cirrhosis. The feasibility of using TGF-β1 as a marker for hepatic fibrosis in dogs was evaluated by comparing plasma concentrations in 29 healthy dogs and 18 dogs with liver disease. The plasma concentrations of TGF-β1, were 193 to 598 pg/mL in the healthy dogs, 143 to 475 pg/mL in the 7 dogs with mild hepatic fibrosis or none at all, and 427 to 1289 pg/mL in 11 dogs with moderate to severe hepatic fibrosis. The plasma concentrations of TGF-β1 in the dogs with moderate to severe fibrosis differed significantly (P < 0.001) from those in the other 2 groups, whereas the concentrations in the dogs with mild or no fibrosis did not differ significantly from those in the healthy dogs (P > 0.05). It was concluded that TGF-β1 is a potential plasma marker for hepatic fibrosis in dogs.  相似文献   
68.
Liver disease can influence the metabolism of various other organs. Regarding the influence of liver diseases on muscles, only a few studies done on people exist. The goal of our study was to investigate the influence of liver diseases on muscles in dogs. Twenty-eight dogs with different liver diseases were investigated in this study. The diagnosis of muscle alteration was based on electromyography (EMG), creatine kinase serum activity, 3-methylhistidine serum concentration and a muscle biopsy in some cases. Our results suggest that liver diseases in dogs can be accompanied with muscle alteration. 3-Methylhistidine serum concentration as a new parameter for muscle destruction in dogs was significantly increased compared to clinical healthy dogs and was comparable to those concentrations in dogs with histologically confirmed myopathy of different types. The differentiation of the liver diseases into severe hepatitis, moderate hepatitis and liver tumours showed a significant elevation of 3-methylhistidine serum concentration in cases of liver tumours (P=0.03) and a tendency in cases of severe hepatitis (P=0.07). Based on our study we can conclude that liver diseases have an influence on muscles in dogs and 3-methylhistidine could be a useful parameter for muscle destruction.  相似文献   
69.
70.
A total of 142 S. aureus strains isolated from pig carcasses from abattoirs A (n = 98) and B (n = 44) were characterized by phenotypic and genotypic traits. Phenotypically, 96% showed yellow-pigmented colonies, 63% β/δ hemolysis, 85% were egg yolk-positive and 99% were positive for clumping factor/protein A. Only 25% of the strains were resistant to the antimicrobials tested (abattoir A: 19%; abattoir B: 39%), especially to penicillin and ampicillin. None of the strains harbored the mecA gene, which is conserved in methicillin-resistant S. aureus. The biofilm associated genes icaA, icaD and bap were present in 100%, 100% and 0% of the strains. Genes for staphylococcal enterotoxin (SE) were detected in 51% (abattoir A) and 14% of the strains (abattoir B). Among strains harboring SE genes (n = 56), 63%, 31%, 4% and 2% tested positive for seg/sei, seg, sei and sec, respectively. The amplification of the 3′ end of the coagulase gene (coa) yielded amplicons of 400, 436, 602, 682 or 776 bp. Coa restriction profile (CRP) analysis using HaeIII resulted in seven patterns (a–d, e1–e3). CRP (c) was detected most frequently at both abattoirs, whereas CRP (a) was restricted to abattoir A and CRP (e3) to abattoir B. In the slaughter process (abattoir B), (i) two CRPs (b and d) were only found before dehairing/singeing, and (ii) four CRPs (c, e1–e3) were identified throughout the process. The genotyping revealed a remarkable homogeneity in S. aureus strains from the two different abattoirs and the slaughter process stages. These results may be explained by the distribution of a limited number of S. aureus genotypes in the pig population. Moreover, as the predominant CRPs (c, e1–e3) persisted throughout the slaughter process in abattoir B, it may be hypothesized that these types are characterized by colonization advantages.  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