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   475篇
  免费   45篇
  国内免费   6篇
林业   31篇
农学   22篇
基础科学   9篇
  73篇
综合类   39篇
农作物   8篇
水产渔业   110篇
畜牧兽医   175篇
园艺   7篇
植物保护   52篇
  2022年   3篇
  2021年   9篇
  2020年   9篇
  2019年   14篇
  2018年   14篇
  2017年   23篇
  2016年   18篇
  2015年   12篇
  2014年   10篇
  2013年   18篇
  2012年   23篇
  2011年   36篇
  2010年   25篇
  2009年   22篇
  2008年   30篇
  2007年   32篇
  2006年   28篇
  2005年   26篇
  2004年   28篇
  2003年   14篇
  2002年   25篇
  2001年   14篇
  2000年   6篇
  1999年   3篇
  1998年   12篇
  1997年   4篇
  1996年   7篇
  1995年   8篇
  1994年   9篇
  1993年   5篇
  1991年   2篇
  1990年   4篇
  1989年   5篇
  1988年   3篇
  1985年   2篇
  1984年   2篇
  1981年   1篇
  1980年   4篇
  1978年   2篇
  1976年   1篇
  1974年   1篇
  1972年   1篇
  1969年   1篇
  1948年   1篇
  1943年   1篇
  1940年   1篇
  1939年   1篇
  1938年   1篇
  1937年   1篇
  1933年   1篇
排序方式: 共有526条查询结果,搜索用时 0 毫秒
101.
Agroforestry systems have been recognized as areas with high conservation potential, and there is a need to quickly assess the biodiversity and tree stocking density available in these systems. However, it is not clear if the commonly used fixed area plot is most efficient for sampling such landscapes, or if a different method could provide equivalent data with less effort. Thus, a field and simulation-based study was carried out to compare the efficiency and accuracy of a variable area transect versus the fixed area square plot. Field efficiency tests were carried out in three habitat types, robusta coffee plantations, arabica coffee plantations and a privately owned forest fragment, in Kodagu, southern India. A simulation study of bias, precision and accuracy of the two methods for tree density estimation also was carried out using various spatial distribution patterns and densities. The variable area transect was significantly more efficient per unit effort in the field than the fixed area square plot. In the simulation tests both methods performed equally well under random spatial distribution. However, under simulated aggregated distribution both methods were positively biased (square plot up to 12% at low density, variable area transect 9–12% at all densities), and under simulated regular distribution the variable area transect was slightly negatively biased (−5 to −7% at medium to high density). The variable area transect thus can be recommended over the square plot for rapid assessment of tree diversity and density, when the vegetation is expected to be randomly dispersed.  相似文献   
102.
Canine atopic dermatitis is a multifaceted disease, whose clinical presentation may be affected by numerous factors, including the genetic background of the animal, the environment, the offending allergens and flare factors. In particular, breed-associated differences have often been mentioned but never defined precisely. Using a large data set of atopic dogs, we document in this study the clinical presentation of nine often-affected breeds and demonstrate the existence of substantial differences between the clinical phenotype of each breed and the whole population. Some of the differences may be due to genetic differences while others are most likely to be associated with variations in environmental factors.  相似文献   
103.
Gérard PR  Husson C  Pinon J  Frey P 《Phytopathology》2006,96(9):1027-1036
ABSTRACT The aims of this study were, first, to compare the genetic and virulence diversity between populations of the rust fungus Melampsora larici-populina on wild and cultivated poplar stands and, second, to investigate the influence of the presence of the alternate host of the pathogen, larch, on which its sexual reproduction occurs, on these diversities. Nine French M. larici-populina populations collected from poplar trees in autumn and four populations collected from larch trees during the following spring were analyzed using both virulence factors and neutral markers. In all, 30 pathotypes were identified within the 13 populations studied. The pathotypic structure clearly distinguished the cultivated stands with high richness and complexity from the wild stands with low richness and complexity. High linkage disequilibria between virulences indicated preferential virulence associations, probably due to selection by the host. In all, 19 random amplified polymorphic DNA (RAPD) markers were used, which revealed a very high genetic diversity in the 743 isolates analyzed. The nine populations from poplar appeared moderately differentiated, indicating long-distance gene flow, and no isolation by distance was found. Linkage disequilibria between RAPD markers generally were low, indicating frequent recombination, but they were not lower in populations located near larch, probably due to long-distance dispersal.  相似文献   
104.
ObjectiveTo assess the population pharmacokinetics of methadone in deer.Study designProspective non-randomized experimental trial.AnimalsTwelve healthy adult sika deer (nine males and three females).MethodsDeer received intramuscular administration of racemic methadone hydrochloride at 0.5 mg kg−1 or 1 mg kg−1. Plasma methadone and its metabolite 2-Ethylidene-1,5-Dimethyl-3,3-Diphenyl-Pyrolidine (EDDP) concentrations were determined by validated liquid chromatography coupled to tandem mass spectrometry methods, at times 0, 30 minutes, 1, 2, 3, 4, 5, 6, 8, 12 and 24 hours. Population pharmacokinetics analysis was undertaken using a non-linear mixed effects modelling (NONMEM).ResultsA two-compartment linear disposition model best described observed time-concentration profiles of methadone and EDDP. Population parameter estimates of methadone were elimination clearance (17.3 L hour−1), metabolic clearance (34.6 L hour−1), volume of distribution of compartment 1 (216.0 L) and volume of distribution of compartment 2 (384.0 L). Population parameter estimates of EDDP were elimination clearance (121.0 L hour−1), volume of distribution of compartment 3 (1.08 L) and volume of distribution of compartment 4 (499.5 L). The total clearance and total volume of distribution of methadone and EDDP were 51.9 L hour−1, 121.0 L hour −1, 600.0 L and 500.6 L, respectively. The methadone terminal elimination half-life was 8.19 hours. No adverse effects were observed after methadone administration.Conclusions and Clinical relevanceFollowing intramuscular injection, methadone was characterized by a large total volume of distribution, high systemic clearance and intermediate terminal half-life in sika deer.  相似文献   
105.
106.
A 1.5-year-old male castrated dog was presented in anaphylactic shock after suffering an apparent bee sting. Immunotherapy with bee venom was initiated based upon history, skin testing and serological testing for allergen-specific immunoglobulin (Ig)E. The dog was maintained on venom immunotherapy for five years and showed no signs of adverse effects from therapy or from repeated bee stings.  相似文献   
107.
依据淋巴细胞脉络丛脑膜炎病毒(LCMV)主要保护性抗原CD8 T细胞表位VRRPQASGVYMGNLTAQ和卵清白蛋白(OVA)CD8 T细胞表位SIINFEKL,设计、合成两条编码LCMV和OVA CD8 T细胞表位的寡核苷酸片段,经退火后,克隆入绿色荧光蛋白表达质粒pYAGFP,经PCR扩增和序列测定分析,证实成功构建T细胞表位与绿色荧光蛋白融合表达的重组质粒pYAGFPL-O,将此重组质粒pYAGFPL-O转化减毒鼠伤寒沙门氏菌X4550,获得重组沙门氏菌X4550(pYAGFPL-O).用SDS-PAGE电泳测得重组菌表达的融合蛋白约为30kD.同时,荧光显微镜下观察到X4550(pYAGFPL-O)发出黄绿色荧光.这些结果表明LCMV和OVA T细胞表位已成功表达.重组菌X4550(pYAGFPL-O)的获得为研究沙门氏菌载体携带外源抗原的T细胞应答规律及调控机理打下了重要基础.  相似文献   
108.
109.
110.
The following question arises: Do the glycolysis and the pentose phosphate cycle operate in the fruit during its maturity? The different results obtained yet with the banana and particularly with the apple and the pear suggest that the pentose phosphate cycle may operate in the preclimacteric fruit and then, decreases with a shift toward the glycolysis. Experiences were conducted with banana and with a non climacteric fruit: the cherry. It seems that cherry does not exhibit such a shift. It may be a difference between climacteric fruits and non climacteric ones.  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