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   444篇
  免费   27篇
林业   26篇
农学   19篇
基础科学   1篇
  172篇
综合类   19篇
农作物   27篇
水产渔业   35篇
畜牧兽医   121篇
园艺   10篇
植物保护   41篇
  2024年   2篇
  2023年   2篇
  2022年   8篇
  2021年   12篇
  2020年   14篇
  2019年   10篇
  2018年   10篇
  2017年   11篇
  2016年   11篇
  2015年   12篇
  2014年   20篇
  2013年   27篇
  2012年   42篇
  2011年   47篇
  2010年   16篇
  2009年   19篇
  2008年   33篇
  2007年   31篇
  2006年   29篇
  2005年   25篇
  2004年   20篇
  2003年   22篇
  2002年   13篇
  2001年   5篇
  2000年   1篇
  1999年   7篇
  1998年   3篇
  1997年   3篇
  1996年   2篇
  1995年   2篇
  1993年   1篇
  1992年   1篇
  1990年   2篇
  1989年   2篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1972年   1篇
排序方式: 共有471条查询结果,搜索用时 31 毫秒
1.
A 29-yr-old chimpanzee (Pan troglodytes) presented after an acute onset of right facial and forearm paresis that progressed to paralysis within 24 hr, with subsequent development of right leg paresis. Magnetic resonance imaging (MRI) of the head revealed an abnormal region of increased signal intensity in the left frontal, parietal, and temporal cerebral hemispheres, corresponding to the vascular territory of the middle cerebral artery, with resultant compression of the left lateral ventricle. The findings were consistent with a cerebral infarct (stroke). MRI is the most sensitive test for early detection of cerebral changes due to ischemia and was essential in obtaining a diagnosis in this case. The chimpanzee responded well to treatment with long-term anticoagulant aspirin and a short, tapered course of prednisone and regained full gross motor function.  相似文献   
2.
3.
Cefquinome is a fourth‐generation cephalosporin that is used empirically in goats. Different physiologic factors like pregnancy or lactation could determine the pharmacokinetic behavior of drugs in the organism. The objectives of this study are to (a) compare the pharmacokinetics of cefquinome after intravenous and intramuscular administration in adult nonpregnant (n = 6), pregnant (n = 6), and lactating goats (n = 6), at a dose of 2 mg/kg, with rich sampling by nonlinear mixed‐effects modeling, (b) conduct a pharmacokinetic/pharmacodynamic analysis to evaluate the efficacy of the recommended posology in goats with different physiological states, and (c) determine the optimal posology that achieve a PTA value ≥ 90%, taking into account a T > MIC ≥ 60% of a MIC value ≤ 0.25 µg/ml, in the different subpopulations of goats for both routes. Gestation significantly increased Ka and V1, while reduced F0, Cl, and Q. On the other hand, lactation significantly increased V1 and reduced Tk0. Cefquinome concentrations achieved in placental cotyledon, amniotic fluid, and fetal serum indicate a minimal penetration across the placental barrier. Moreover, milk penetration of cefquinome was minimal. The total body clearance of cefquinome for goats was 0.29 L kg?1 hr?1, that is apparently higher than the reported for cows (0.13 L kg?1 hr?1) and pigs (0.16 L kg?1 hr?1). So, the optimal dose regimen for cefquinome after intravenous and intramuscular administration required higher dose and frequency of administration compared with recommendations for cows or pigs. Therefore, 2 mg kg?1 8 hr?1 and 5 mg kg?1 12 hr?1 could be used for IV and IM routes, respectively, for the treatment of respiratory infections caused by P. multocida and M. haemolytica, but only 5 mg kg?1 12 hr?1 by both routes should be recommended for Escherichia coli infections.  相似文献   
4.
ObjectiveVarious drugs administered to horses undergoing surgical procedures can release histamine. Histamine concentrations were evaluated in horses prepared for surgery and administered butorphanol or morphine intraoperative infusions.Study designProspective studies with one randomized.AnimalsA total of 44 client-owned horses.MethodsIn one study, anesthesia was induced with xylazine followed by ketamine–diazepam. Anesthesia was maintained with guaifenesin–xylazine–ketamine (GXK) during surgical preparation. For surgery, isoflurane was administered with intravenous (IV) morphine (group M: 0.15 mg kg–1 and 0.1 mg kg–1 hour–1; 15 horses) or butorphanol (group B: 0.05 mg kg–1 and 0.01 mg kg–1 hour–1; 15 horses). Histamine and morphine concentrations were measured using enzyme-linked immunoassay before opioid injection (time 0), and after 1, 2, 5, 30, 60 and 90 minutes. In a subsequent study, plasma histamine concentrations were measured in 14 horses before drug administration (baseline), 15 minutes after IV sodium penicillin and 15 minutes after starting GXK IV infusion. Statistical comparison was performed using anova for repeated measures. Pearson correlation compared morphine and histamine concentrations. Data are presented as mean ± standard deviation. Significance was assumed when p ≤ 0.05.ResultsWith histamine, differences occurred between baseline (3.2 ± 2.4 ng mL–1) and GXK (5.2 ± 7.1 ng mL–1) and between baseline and time 0 in group B (11.9 ± 13.4 ng mL–1) and group M (11.1 ± 12.4 ng mL–1). No differences occurred between baseline and after penicillin or between groups M and B. Morphine concentrations were higher at 1 minute following injection (8.1 ± 5.1 ng mL–1) than at 30 minutes (4.9 ± 3.1 ng mL–1) and 60 minutes (4.0 ± 2.5 ng mL–1). Histamine correlated with morphine at 2, 30 and 60 minutes.Conclusions and clinical relevanceGXK increased histamine concentration, but concentrations were similar with morphine and butorphanol.  相似文献   
5.
Agriculture has a close relationship with nature, but it can also be the source of negative and permanent environmental effects. The use of pesticides in modern agriculture is a common practice, but their side effects on the environment cannot be disregarded. In this study, we evaluated a combination of solarization and ozonation techniques for the elimination of six amide pesticides (boscalid, chlorantraniliprole, cyflufenamid, fluopyram, napropamide, and propyzamide) in soil. Initial experiments were performed with four different soils to assess the efficiency of this methodology at different soil temperatures and ozone dosages under laboratory conditions, and then a greenhouse pot experiment was conducted under controlled conditions during summer. Fifty days after the onset of the experiments, higher degradation percentages of amide pesticides were observed in ozonized soils than in other treated soils, particularly when ozone was applied at 10 cm soil depth. The results show that the utilization of ozonation, along with solarization, represents a valid method for degrading residues of the studied pesticides and suggest that this combined technology may be a promising tool for remediating pesticide-polluted soils.  相似文献   
6.
An inexpensive and portable surface plasmon resonance (SPR) sensor, SPReeta Evaluation Kit SPR3, has been used to develop a biosensor for the determination of fluoroquinolone antibiotics (FQs) and to demonstrate its performance analyzing FQ residues in milk samples. The SPReeta three-channel gold chips were activated with a mixed self-assembled monolayer (m-SAM) and functionalized with a FQ haptenized protein. Binding of the antibody produced a concentration-dependent increase of the SPR signal as a result of the change in the refraction index. Similarly, the presence of the FQ produced a dose-dependent decrease of the response, which allowed a good limit of detection (LOD) to be obtained (1.0 ± 0.4 μg L(-1) for enrofloxacin in buffer). The response was reproducible in all three channels, on different injections and days, and also between chips. Milk samples could be analyzed after a simple sample treatment involving fat removal by centrifugation and dilution with water. Under these conditions calibration curves were obtained showing that FQ residues can be analyzed in milk samples with an IC(50) value of 26.4 ± 7.2 μg L(-1) and a LOD of 2.0 ± 0.2 μg L(-1) (for enrofloxacin), far below the European Union regulations for this antibiotic family in this matrix. Finally, the paper also demonstrates that the biosensor is able to selectively detect the presence of FQs in milk samples, even in the presence of other antibiotics. Enrofloxacin, ciprofloxacin, and norfloxacin residues were detected in blind samples supplied by Nestle? Co.  相似文献   
7.
The diatom Chaetoceros muelleri was grown in outdoor mass cultures under the winter, spring and summer conditions of Bahia Kino, Sonora, NW Mexico. The solar irradiance in winter was close to 60% of that available in spring and summer, but the cell concentrations and the harvestable biomass were one order of magnitude higher in spring and summer than in winter. There was no difference between the biomass harvested after 2 and 3 days in winter and summer, whereas in spring it was higher after 3 days. The protein content was significantly lower in winter, and carbohydrates and lipids were higher in winter and spring. The number of cells and the amount of harvestable biomass of outdoor cultures of C. muelleri depend on the temperature prevailing in each season, which causes significant differences in growth rates and in biochemical composition.  相似文献   
8.
Characterization of cider apples on the basis of their fatty acid profiles   总被引:1,自引:0,他引:1  
In the current study, the fatty acids composition of 30 monovarietal apple juices from six cider apple varieties belonging to two categories was analyzed. The different apple juices were obtained from three consecutive harvests (1997, 1998, and 1999). The fatty acids concentration in apple juice together with chemometric techniques such as principal components analysis (PCA), soft independent modeling of class analogy (SIMCA), and linear discriminant analysis (LDA), allowed us to differentiate apple juices on the basis of the sweet or sharp category to which the cider apple variety belongs. Fatty acids such as the unsaturated oleic and linoleic acids, and saturated caprylic, capric, stearic, and palmitic acids were related to the sweet cider apple category, while pentadecanoic acid is related to the sharp class.  相似文献   
9.
Vibrio spp. are the most common and harmful shrimp pathogenic bacteria; however, microalgae and cyanobacteria have the ability to produce antimicrobial substances against these species. In this study, the organic and aqueous extracts of 28 species of marine microalgae and cyanobacteria were screened against Vibrio campbellii M1. Two of these phytoplankton species with antibacterial activity in aqueous extracts (Dunaliella tertiolecta and Skeletonema costatum) and nontoxic to brine shrimp Artemia franciscana nauplii were used to evaluate their anti‐Vibrio effect when used as green‐water cultures in Vibrio‐challenged white shrimp Litopenaeus vannamei cultures. No differences in mortality of juvenile L. vannamei were observed between treatments tested, suggesting that the pathogenicity of V. campbellii could be related to the growth stage of shrimp. The proximal composition of D. tertiolecta and S. costatum was in the recommended range for penaeid shrimp nutrition, allowing shrimp supplemented with these microalgae to have significantly greater total length and weight than control shrimp. Shrimp supplemented with S. costatum presented the highest values of organic mass (11.48 mg/organism) and growth rate (0.31 mg/d) in comparison to D. tertiolecta. These results indicate that microalgae are not only capable of producing antibacterial compounds against Vibrio but can also help shrimp nutrition.  相似文献   
10.
One hundred and sixty strains of Pseudomonas syringae subsp. savastanoi from Olea europaea, Olea europaea var. sylvestris, Nerium oleander, Fraxinus angustifolia and Retama sphaerocarpa, and four type strains of other pathovars were studied, investigating 102 phenotypic traits, among which we include biochemical characteristics, assimilation of different carbon sources, sensitivity or resistance to antibiotics and indoleacetic acid (IAA) production. Results were analysed with an affinity dendrogram via the Jaccard coefficient. They indicate an influence of environmental factors on the formation of the 15 phenons obtained, since isolated (knot) strains from the same species but different geographical areas are segregated. Segregation, also detected in strains from different hosts within the same area, added to the pathogenicity test helps to characterise these strains as different pathovars.  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