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   1627篇
  免费   112篇
  国内免费   1篇
林业   116篇
农学   35篇
基础科学   3篇
  253篇
综合类   224篇
农作物   62篇
水产渔业   113篇
畜牧兽医   797篇
园艺   52篇
植物保护   85篇
  2023年   13篇
  2022年   6篇
  2021年   40篇
  2020年   44篇
  2019年   48篇
  2018年   44篇
  2017年   55篇
  2016年   43篇
  2015年   43篇
  2014年   52篇
  2013年   85篇
  2012年   101篇
  2011年   130篇
  2010年   61篇
  2009年   54篇
  2008年   111篇
  2007年   96篇
  2006年   80篇
  2005年   80篇
  2004年   83篇
  2003年   68篇
  2002年   77篇
  2001年   16篇
  2000年   19篇
  1999年   11篇
  1998年   19篇
  1997年   9篇
  1996年   5篇
  1995年   8篇
  1994年   9篇
  1993年   9篇
  1992年   13篇
  1991年   11篇
  1990年   17篇
  1989年   12篇
  1988年   7篇
  1987年   6篇
  1986年   5篇
  1985年   8篇
  1984年   8篇
  1983年   7篇
  1979年   14篇
  1978年   7篇
  1977年   4篇
  1975年   10篇
  1974年   9篇
  1973年   11篇
  1971年   6篇
  1967年   7篇
  1966年   5篇
排序方式: 共有1740条查询结果,搜索用时 296 毫秒
21.
Response of healthy dogs to infusions of human serum albumin   总被引:1,自引:0,他引:1  
OBJECTIVE: To evaluate the clinical and immunologic response in healthy dogs to infusions of human serum albumin (HSA). ANIMALS: 9 healthy purpose-bred mixed-breed dogs. PROCEDURES: Each dog was administered a 25% HSA solution once or twice. Various physical examination and laboratory variables were serially evaluated. Antibody against HSA was assayed before and after infusion by use of an ELISA. Intradermal testing was also conducted. A repeated-measures ANOVA or Friedman repeated-measures ANOVA on ranks was used to compare results for the variables. RESULTS: Adverse clinical reactions were observed after the first or second infusion in 3 dogs. Anaphylactoid reactions were observed in 1 of 9 dogs during the first infusion and in 2 of 2 dogs administered a second infusion. Two dogs developed severe edema and urticaria 6 or 7 days after an initial infusion. All dogs developed anti-HSA antibodies. Positive responses for ID tests were observed in 8 of 9 dogs. Short-term increases were detected in blood protein, total bilirubin, and calcium concentrations after HSA infusion. Serum cholesterol concentrations and platelet counts decreased after HSA infusion. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of HSA resulted in profound reactions in 2 of 9 dogs administered a single infusion and in 2 of 2 dogs administered a second infusion. This indicates that there is risk of life-threatening adverse reactions to HSA infusion in healthy dogs.  相似文献   
22.
CASE DESCRIPTION: A 1-month-old female alpaca was examined because of progressive clinical signs consistent with an intracranial lesion. CLINICAL FINDINGS: Clinical signs included signs of depression, lethargy, tetraparesis, and neck weakness. Two large isointense intracranial masses could be seen on T1-weighted magnetic resonance images. On T2-weighted images, the masses contained concentric rings of hypointense and hyperintense material. TREATMENT AND OUTCOME: 2 abscesses were removed via a craniotomy that incorporated removal of the sagittal crest and surrounding skull and transection of the sagittal sinus. The bony deficit was replaced with polypropylene mesh. The alpaca recovered within 2 weeks and was fully integrated into the herd within 1 month after surgery. CLINICAL RELEVANCE: Findings indicated that surgical removal is a feasible means of successfully treating intracranial abscesses in juvenile alpacas.  相似文献   
23.
The purpose of this study was to determine the serological and molecular prevalence of Bartonella spp. infection in a sick dog population from Brazil. At the S?o Paulo State University Veterinary Teaching Hospital in Botucatu, 198 consecutive dogs with clinicopathological abnormalities consistent with tick-borne infections were sampled. Antibodies to Bartonella henselae and Bartonella vinsonii subsp. berkhoffii were detected in 2.0% (4/197) and 1.5% (3/197) of the dogs, respectively. Using 16S-23S rRNA intergenic transcribed spacer (ITS) primers, Bartonella DNA was amplified from only 1/198 blood samples. Bartonella seroreactive and/or PCR positive blood samples (n=8) were inoculated into a liquid pre-enrichment growth medium (BAPGM) and subsequently sub-inoculated onto BAPGM/blood-agar plates. PCR targeting the ITS region, pap31 and rpoB genes amplified B. henselae from the blood and/or isolates of the PCR positive dog (ITS: DQ346666; pap31 gene: DQ351240; rpoB: EF196806). B. henselae and B. vinsonii subsp. berkhoffii (pap31: DQ906160; rpoB: EF196805) co-infection was found in one of the B. vinsonii subsp. berkhoffii seroreactive dogs. We conclude that dogs in this study population were infrequently exposed to or infected with a Bartonella species. The B. henselae and B. vinsonii subsp. berkhoffii strains identified in this study are genetically similar to strains isolated from septicemic cats, dogs, coyotes and human beings from other parts of the world. To our knowledge, these isolates provide the first Brazilian DNA sequences from these Bartonella species and the first evidence of Bartonella co-infection in dogs.  相似文献   
24.
A dynamic optimization model was developed and used to evaluate alternative foot-and-mouth disease (FMD) control strategies. The model chose daily control strategies of depopulation and vaccination that minimized total regional cost for the entire epidemic duration, given disease dynamics and resource constraints. The disease dynamics and the impacts of control strategies on these dynamics were characterized in a set of difference equations; effects of movement restrictions on the disease dynamics were also considered. The model was applied to a three-county region in the Central Valley of California; the epidemic relationships were parameterized and validated using the information obtained from an FMD simulation model developed for the same region. The optimization model enables more efficient searches for desirable control strategies by considering all strategies simultaneously, providing the simulation model with optimization results to direct it in generating detailed predictions of potential FMD outbreaks.  相似文献   
25.
The occurrence of aspen (Populus tremuloides Michx.) patches within stands dominated by black spruce (Picea mariana Mill. BSP) has been shown to increase litter decomposition and nutrient cycling rates by improving soil physical and chemical properties. It is well known, however, that these processes are also influenced by the structure of the soil biota, but this factor has received less attention. In this study, relationships between forest floor properties and soil invertebrates were studied along black spruce–trembling aspen gradients in three stands of the eastern boreal forest of Canada. The forest floor layer of 36 plots differing in aspen basal area was sampled and analyzed to determine physical and chemical properties, the rates of decomposition of standard substrates, net N mineralization, as well as microbial basal respiration and metabolic quotient. Soil invertebrates were also collected using funnel-extraction and pitfall trapping methods. Based on redundancy analyses, we found that forest floor properties, the abundance and composition of soil invertebrates, and the rates of belowground processes changed along the spruce–aspen gradient. The increase in aspen basal area was associated with a reduction in forest floor thickness, moisture content and microbial biomass, and with an increase in the concentration of nutrients. It was also accompanied by changes in soil faunal communities, as soil invertebrates were associated with specific soil properties. In general, macroinvertebrates (i.e., Lumbricidae, Formicidae, Carabidae, Staphylinidae and Gastropoda) were related to the nutrient-rich forest floor associated with aspen, whereas microarthropods and Enchytraeidae tended to be negatively related to aspen basal area. According to mixed linear models, decomposition rates of standard substrates and net ammonification significantly increased along the spruce–aspen gradient. Given the functional significance of macroinvertebrates in soils, these results suggest that aspen favours the elaboration of a macrofaunal community, which in turn accelerates the rate of soil processes by having either direct or indirect influence on microbial activity. Moreover, this study shows that the changes in soil processes and in the biodiversity of soil organisms related to the presence of mixed stands can operate only in the immediate surroundings of a given tree species. Therefore, coarse-scale tree species mixing in a forest stand may have a different effect on soil biodiversity and soil processes than fine-scale mixing.  相似文献   
26.
Abstract –  Habitat requirements of lamprey ammocoetes (Petromyzon marinus and Lampetra genus) were investigated, for the first time, from shallow to deep waters, at different spatial scales across the Gironde‐Dordogne continuum, thanks to a water suction dredge. Fish‐habitat relationships were assessed through two complementary statistical analyses: habitat‐use curves and habitat suitability models using the Boosted Regression Trees (BRT) technique. Analyses were performed on a small‐size data set that was characterised by the low prevalence of lamprey. The sea lamprey larvae occurred in deeper areas than their Lampetra genus counterparts. ‘Pools’ of 2 m’ depth and more were optimal habitats for the former species. Among the environmental variables retained to model lamprey occurrences, the mesohabitat (a categorical variable) was demonstrated to be highly influential, in terms of fine grain‐size substratum and vegetation cover. These preliminary results suggest that monitoring using the water suction dredge method may contribute to sea lamprey conservation.  相似文献   
27.
28.
A new monodesmosidic spirostanol saponin, along with three known saponins was isolated from Agave macroacantha Zucc leaves. The structure of the new saponin was established as hecogenin-3-O-α-l-rhamnopyranosyl (1→4) β-d-xylopyranosyl (1→3)[β-d-glucopyranosyl (1→2)] β-d-glucopyranosyl (1→4) β-d-galactopyranoside. The 1H and 13C resonances of the four compounds were assigned using a combination of 1D and 2D NMR techniques including 1H, 13C, COSY, TOCSY, ROESY, HSQC and HMBC NMR and confirmed by mass spectrometry.  相似文献   
29.
A 4-year-old castrated male mixed-breed dog with a history of coccidioidomycosis was referred for evaluation of abdominal and pleural effusion. Results of radiography, ultrasonography, cytologic evaluation of thoracic fluid, and serologic testing supported a diagnosis of constrictive pericarditis secondary to infection with Coccidioides immitis. Aggressive treatment for presumptive coccidioidomycosis was begun, but the dog's condition continued to deteriorate, and the dog was euthanatized. At necropsy, the pericardium was thicker than normal and fibrotic and adhered to the epicardium. Microscopically, the pericardium and 1 section of epicardium contained lymphoplasmacytic infiltrates with a few macrophages and neutrophils. Coccidioides immitis was cultured from pericardial fluid. A search of records from the Arizona Veterinary Diagnostic Laboratory for 1988 through 1998 revealed that of 46 dogs in which a diagnosis of coccidioidomycosis was confirmed at necropsy, 13 had involvement of the heart or pericardium.  相似文献   
30.
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