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   418篇
  免费   36篇
林业   15篇
农学   22篇
基础科学   2篇
  59篇
综合类   86篇
农作物   16篇
水产渔业   28篇
畜牧兽医   196篇
园艺   5篇
植物保护   25篇
  2021年   9篇
  2020年   16篇
  2019年   10篇
  2018年   14篇
  2017年   10篇
  2016年   15篇
  2015年   10篇
  2014年   13篇
  2013年   13篇
  2012年   21篇
  2011年   29篇
  2010年   23篇
  2009年   18篇
  2008年   15篇
  2007年   18篇
  2006年   16篇
  2005年   16篇
  2004年   8篇
  2003年   16篇
  2002年   10篇
  2001年   7篇
  2000年   15篇
  1999年   5篇
  1998年   4篇
  1995年   5篇
  1994年   3篇
  1992年   5篇
  1991年   5篇
  1990年   2篇
  1989年   15篇
  1988年   24篇
  1987年   4篇
  1986年   4篇
  1984年   2篇
  1983年   3篇
  1982年   2篇
  1981年   2篇
  1979年   3篇
  1976年   3篇
  1974年   2篇
  1972年   2篇
  1971年   3篇
  1969年   3篇
  1968年   2篇
  1967年   6篇
  1953年   2篇
  1943年   1篇
  1941年   1篇
  1940年   1篇
  1937年   1篇
排序方式: 共有454条查询结果,搜索用时 296 毫秒
1.
2.
Francisella tularensis type A is the primary cause of tularemia in animals and humans in North America. The majority of research on F. tularensis has been done with the attenuated live vaccine strain (LVS), which is a type B, but very few wild-type F. tularensis strains have been characterized. A gram-negative coccobacillus that was isolated in pure culture from the lungs of a cat that died after being lost for 5 days was received for identification at the Virginia-Maryland Regional College of Veterinary Medicine Teaching hospital. The isolate (strain TI0902) was not identified (or was misidentified) by commercial identification systems; however, it was identified as F. tularensis subspecies tularensis (type A) by sequencing a portion of the 16S ribosomal RNA gene. Furthermore, repetitive extragenic palindromic sequences-polymerase chain reaction amplified a 4-kb DNA fragment from TI0902 that was characteristic of F. tularensis type A but not type B. The electrophoretic profile of the lipopolysaccharide of strain TI0902 was identical to that of the LVS by Western blotting with antiserum to LVS. The protein-enriched outer membrane of strain TI0902 contained 6-8 proteins, which were similar in molecular size to those from the LVS. Electron microscopy of negatively stained and alcian blue-stained LVS and TI0902 cells showed that both strains were coccobacillary in shape and may be encapsulated. However, after mouse challenge, the TI0902 strain was clearly more virulent than the LVS strain. Results of this study indicate that the genotype and phenotype of wild-type F. tularensis type A strain TI0902 is similar, but not identical, to that of the LVS strain. Further studies will help determine whether pathogenesis and host-pathogen interactions are also similar between the 2 strains.  相似文献   
3.
4.
Seven sea otters received a single subcutaneous dose of cefovecin at 8 mg/kg body weight. Plasma samples were collected at predetermined time points and assayed for total cefovecin concentrations using ultra‐performance liquid chromatography and tandem mass spectrometry. The mean (±SD) noncompartmental pharmacokinetic indices were as follows: CMax (obs) 70.6 ± 14.6 μg/mL, TMax (obs) 2.9 ± 1.5 h, elimination rate constant (kel) 0.017 ± 0.002/h, elimination half‐life (t1/2kel) 41.6 ± 4.7 h, area under the plasma concentration‐vs.‐time curve to last sample (AUClast) 3438.7 ± 437.7 h·μg/mL and AUC extrapolated to infinity (AUC0→∞) 3447.8 ± 439.0 h·μg/mL. The minimum inhibitory concentrations (MIC) for select isolates were determined and used to suggest possible dosing intervals of 10 days, 5 days, and 2.5 days for gram‐positive, gram‐negative, and Vibrio parahaemolyticus bacterial species, respectively. This study found a single subcutaneous dose of cefovecin sodium in sea otters to be clinically safe and a viable option for long‐acting antimicrobial therapy.  相似文献   
5.
6.
7.
The metabolism of cis- and trans-1,3-dichloropropene (1,3-D) was studied in soybean plants grown in soil treated 24 days prior to planting with [U-14C]E- and Z-1,3-dichloropropene at 380 liters ha?1. Isolation and identification of the 14C residue from soybean plants at 84 days (forage) and 176 days (mature) after application showed that no 1,3-dichloropropene or its putative metabolites, 3-chloroallyl alcohol and 3-chloroacrylic acid, could be detected in any of the tissues. The components of the 14C residue included major plant constituents (i.e. fatty acids, protein, pigments, organic acids, sucrose and other carbohydrates, and lignin).  相似文献   
8.
Systemic uptake bioassays using excised cotton leaves confirmed resistance to imidacloprid in a Guatemalan population of the tobacco whitefly Bemisia tabaci Gennadius. Polyacrylamide gel electrophoresis of naphthyl esterases identified the insects as B-types. Upon collection from the field, resistance was determined to be 58-fold relative to a susceptible strain originating in the Imperial Valley of California. Resistance levels increased to 126-fold in this population during its continuous exposure to systemically treated cotton. In biochemical investigations, there was no detectable NADPH-dependent mixed function oxidase metabolism of 14C-imidacloprid at any time during the selection process. In contrast, microsomal preparations from housefly abdomens readily produced significant amounts of the mono-hydroxy and olefin derivatives of the parent compound. Detoxification of imidacloprid by housefly MFOs may account for reports of lower toxicity of the insecticide towards this insect compared with whiteflies, despite similar binding properties between imidacloprid and the nicotinic acetylcholine receptors in both species.  相似文献   
9.
10.
We estimated the population density of dogs by distance sampling and assessed the potential utility of two marking methods for capture-mark-recapture applications following a mass canine rabies-vaccination campaign in Sorsogon Province, the Republic of the Philippines. Thirty villages selected to assess vaccine coverage and for dog surveys were visited 1 to 11 days after the vaccinating team. Measurements of the distance of dogs or groups of dogs from transect lines were obtained in 1088 instances (N = 1278 dogs; mean group SIZE = 1.2). Various functions modelling the probability of detection were fitted to a truncated distribution of distances of dogs from transect lines. A hazard rate model provided the best fit and an overall estimate of dog-population density of 468/km2 (95% confidence interval, 359 to 611). At vaccination, most dogs were marked with either a paint stick or a black plastic collar. Overall, 34.8% of 2167 and 28.5% of 2115 dogs could be accurately identified as wearing a collar or showing a paint mark; 49.1% of the dogs had either mark. Increasing time interval between vaccination-team visit and dog survey and increasing distance from transect line were inversely associated with the probability of observing a paint mark. Probability of observing a collar was positively associated with increasing estimated density of the dog population in a given village and with animals not associated with a house. The data indicate that distance sampling is a relatively simple and adaptable method for estimating dog-population density and is not prone to problems associated with meeting some model assumptions inherent to mark-recapture estimators.  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