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   521篇
  免费   21篇
林业   30篇
农学   61篇
基础科学   5篇
  135篇
综合类   33篇
农作物   28篇
水产渔业   18篇
畜牧兽医   157篇
园艺   16篇
植物保护   59篇
  2023年   3篇
  2022年   7篇
  2021年   7篇
  2020年   16篇
  2019年   12篇
  2018年   19篇
  2017年   16篇
  2016年   21篇
  2015年   10篇
  2014年   11篇
  2013年   50篇
  2012年   17篇
  2011年   23篇
  2010年   17篇
  2009年   16篇
  2008年   15篇
  2007年   31篇
  2006年   30篇
  2005年   10篇
  2004年   19篇
  2003年   7篇
  2002年   10篇
  2001年   11篇
  2000年   5篇
  1999年   11篇
  1997年   3篇
  1996年   4篇
  1995年   6篇
  1994年   6篇
  1993年   4篇
  1992年   8篇
  1991年   3篇
  1990年   11篇
  1989年   11篇
  1988年   8篇
  1987年   8篇
  1986年   6篇
  1985年   8篇
  1983年   5篇
  1981年   6篇
  1979年   5篇
  1978年   4篇
  1977年   4篇
  1974年   2篇
  1973年   3篇
  1971年   4篇
  1970年   4篇
  1969年   4篇
  1968年   2篇
  1967年   3篇
排序方式: 共有542条查询结果,搜索用时 890 毫秒
501.
502.
Immunological release of histamine from the whole blood of the sensitized chickens was demonstrated. Compound 48/80 (a potent histamine releaser) released histamine from isolated chicken lung. The sensitizing antigens (bovine albumin or horse plasma) did not release histamine from the lung. Bovine albumin and horse plasma released slow-reacting substance of anaphylaxis only from the lungs of adult domestic fowl and not from ileum or lungs of immature chickens.  相似文献   
503.
504.
Pentobarbital-anesthetized and spontaneously breathing, bovine albumin (BA)-sensitized adult domestic fowl showed acute systemic anaphylaxis to IV injection of antigen (BA), which was characterized by arterial hypotension, central venous hypertension, and bradycardia. Large doses of pyrilamine maleate (/1-receptor antagonist) partially inhibited acute systemic anaphylaxis. On the other hand, metiamide (a specific H2-antagonist) and propranolol (beta-adrenergic antagonist) markedly enhanced the anaphylactic response. Terbutaline (beta 2-agonist), dimaprit (a highly selective H2-agonist), and compound FPL 55712 (a slow-reacting substance of anaphylaxis receptor antagonist) either significantly inhibited or reversed the anaphylactic response. Cimetidine (a newer H2-antagonist) enhanced only central venous pressor response to BA. This investigation appears to suggest a minor role of histamine and a major role of slow-reacting substance of anaphylaxis as chemical mediatiors of anaphylaxis. A protective role of beta 2-adrenergic and H2-histaminergic receptors seem to operate in immediate hypersensitivity reactions in adult domestic fowl.  相似文献   
505.
Streptococcus equi was found to adhere to tongue, cheek and nasal epithelial cells of ponies, in vitro. Maximum adherence was observed at pH 7.5 after one hour of incubation of bacteria with epithelial cells. This adherence was more on epithelial cells from adult animals than foals. Streptococci exposed to heat (60°C for 10 min) or treated with pepsin or trypsin showed a reduced adherence, whereas an increase occurred on treatment with hyaluronidase. Antibodies against whole S. equi cells or M-like protein blocked the adherence, whereas antibodies against group-specific carbohydrate or lipoteichoic acids did not. Pretreatment of epithelial cells with either the M-like protein or crude extract of S. equi lowered the adherence, whereas an extract of S. zooepidemicus did not. Adherence of S. equi to the epithelial cells was considered to be mediated by structures specific to S. equi.  相似文献   
506.
507.
A new species,Tamarixia sheebae, is described and illustrated.Tamarixia sheebae differs fromT. bicolor Mercet andT. radiata Waterston in having the apex of gaster tilted upwards. It emerged from leaf galls ofTerminalia arjuna (Roxb.) Wright & Arn. (Combretaceae), a tree with many medicinal properties in addition to its timber value.  相似文献   
508.
The disposition kinetics, urinary excretion and a dosage regimen for ciprofloxacin after a single intravenous administration of 5 mg/kg was investigated in 5 healthy buffalo calves. The disposition kinetics were best fitted to a three-compartment open model. After 1 min, the concentration of ciprofloxacin in plasma was 8.50±0.39 g/ml and the minimum therapeutic concentration was maintained for 10 h. The elimination half-life and volume of distribution were 3.88 and 0.08 h and 3.97±0.22 L/kg, respectively. The total body clearance and T/P ratio were 0.709±0.025 L/kg per h and 6.13±0.54, respectively. Approximately 28.3% of the total administered dose of ciprofloxacin was recovered in urine within 24 h of administration. To maintain a minimum therapeutic plasma concentration of 0.10 g/ml, a satisfactory intravenous dosage regimen of ciprofloxacin, computed on the basis of disposition kinetic data obtained in healthy buffalo calves, would be 3 mg/kg repeated at 12 h intervals.  相似文献   
509.
This study investigated the relationship between sorghum grain yield for a range of soil depths, with the seasonal crop water stress index based on relative evapotranspiration deficits and spectral vegetation indices. A root zone water balance model was used to evaluate seasonal soil water fluctuations and actual evapotranspiration within a toposequence; soil depth varied between 30 and 75 cm and available water capacity ranged from 6.9 to 12.6% (v/v, %). An empirical model was used to determine root growth. Runoff was estimated from rainfall data using the curve number techniques of the Soil Conservation Services, combined with a soil water-accounting procedure. The high r2 values between modeled and observed values of soil water in the root zone (r2 > 0.70, significant at P < 0.001) and runoff (r2 = 0.95, significant at P < 0.001) indicated good agreement between the model output and observed values. Canopy reflectance was measured during the entire crop growth period and the following spectral indices were calculated: simple ratio, normalized difference vegetation index (NDVI), green NDVI, perpendicular vegetation index, soil adjusted vegetation index (SAVI) and modified SAVI (MSAVI). All the vegetation indices, except for the perpendicular vegetation index, measured from booting to anthesis stage, were positively correlated with leaf area index (LAI) and yield. The correlation coefficient for spectral indices with dry biomass was relatively less than for LAI and yield. Modified SAVI recorded from booting to milk-grain stage gave the highest average correlation coefficient with grain yield. Additive and multiplicative forms of water-production functions, as well as water stress index calculated from water budget model, were used to predict crop yield. A multiple regression was carried out with yield, for the years 2001–2003, as the dependent variable and MSAVI, from the booting to the milk-grain stage of crop and relative yield values, calculated using both additive and multiplicative water production functions as well as water stress index, as the independent variables. The multiplicative model and MSAVI, recorded during the heading stage of crop growth, gave the highest coefficient of determination (r2 = 0.682, significant at P < 0.001). The multiple regression equation was tested for yield data recorded during 2004; the deviation between observed and estimated yields varied from −6.2 to 9.4%. The water budget model, along with spectral vegetation indices, gave satisfactory estimates of sorghum grain yields and appears to be a useful tool to estimate yield as a function of soil depth and available water.  相似文献   
510.
Present preliminary findings demonstrate in vitro stimulation of splenic lymphocytes of BALB/c mice after exposure to oligosaccharide fractions isolated from mare's milk during colostrum, transitional, and mature lactation periods, which shows immunostimulatory action of oligosaccharide content present in mares' milk. Oligosaccharide fractions caused more pronounced oxidative burst at a much lower concentration (0.1 μg/mL) compared with that shown by levamisole (standard immunostimulant) at a much higher concentration of 10 μg/mL. In this study, it was observed that oligosaccharides fraction of colostrum phase attaining high potency of immunostimulatory property.  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