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   326篇
  免费   36篇
林业   21篇
农学   16篇
  54篇
综合类   25篇
农作物   18篇
水产渔业   12篇
畜牧兽医   181篇
园艺   4篇
植物保护   31篇
  2023年   4篇
  2022年   11篇
  2021年   9篇
  2020年   9篇
  2019年   19篇
  2018年   16篇
  2017年   12篇
  2016年   9篇
  2015年   15篇
  2014年   14篇
  2013年   20篇
  2012年   18篇
  2011年   32篇
  2010年   20篇
  2009年   9篇
  2008年   13篇
  2007年   14篇
  2006年   12篇
  2005年   14篇
  2004年   16篇
  2003年   11篇
  2002年   16篇
  2001年   5篇
  2000年   7篇
  1999年   5篇
  1998年   2篇
  1997年   5篇
  1995年   2篇
  1994年   1篇
  1992年   4篇
  1991年   2篇
  1989年   1篇
  1988年   2篇
  1983年   1篇
  1974年   2篇
  1973年   1篇
  1971年   4篇
  1967年   2篇
  1963年   1篇
  1954年   1篇
  1940年   1篇
排序方式: 共有362条查询结果,搜索用时 15 毫秒
21.
Congenital vertebral malformations are common in brachycephalic “screw‐tailed” dog breeds such as French bulldogs, English bulldogs, Boston terriers, and pugs. The aim of this retrospective study was to determine whether a radiographic classification scheme developed for use in humans would be feasible for use in these dog breeds. Inclusion criteria were hospital admission between September 2009 and April 2013, neurologic examination findings available, diagnostic quality lateral and ventro‐dorsal digital radiographs of the thoracic vertebral column, and at least one congenital vertebral malformation. Radiographs were retrieved and interpreted by two observers who were unaware of neurologic status. Vertebral malformations were classified based on a classification scheme modified from a previous human study and a consensus of both observers. Twenty‐eight dogs met inclusion criteria (12 with neurologic deficits, 16 with no neurologic deficits). Congenital vertebral malformations affected 85/362 (23.5%) of thoracic vertebrae. Vertebral body formation defects were the most common (butterfly vertebrae 6.6%, ventral wedge‐shaped vertebrae 5.5%, dorsal hemivertebrae 0.8%, and dorso‐lateral hemivertebrae 0.5%). No lateral hemivertebrae or lateral wedge‐shaped vertebrae were identified. The T7 vertebra was the most commonly affected (11/28 dogs), followed by T8 (8/28 dogs) and T12 (8/28 dogs). The number and type of vertebral malformations differed between groups (P = 0.01). Based on MRI, dorsal, and dorso‐lateral hemivertebrae were the cause of spinal cord compression in 5/12 (41.6%) of dogs with neurologic deficits. Findings indicated that a modified human radiographic classification system of vertebral malformations is feasible for use in future studies of brachycephalic “screw‐tailed” dogs.  相似文献   
22.
Due mainly to alterations in plant metabolism, lack of oxygen and excess salts are disturbances that affect crop yields. In different parts of the world crops are subjected t o those disttirbances, simultaneously or successively. Our objective was to determine the effects of a winter waterlogging followed by a spring salt peak on rapeseed yield, A pot experiment, combining waterlogging and salinization was carried out. The waterlogging duration was: 0 (control), 3, 7 and 14 days and the sahnity treatments were peaks of Electrical Conductivity of 5 and 8 dSm−1 and the control. The yield started decreasingfrotn 3 days during waterlogging, mainly due to the lower number of seeds per plant. The salt peak from 5 dSm−1 affected the yield only in plants which had suffered a waterlogging lower than 7 days, showing interaction between salinity and waterlogging, Only salinity reduced oil content. The saline peak affected the K, Ca and Na concentration in plant tissues, but the effect of salinity on rapeseed could be more related to soil water potential than specific ion toxicities or imbalance.  相似文献   
23.
S. P. Singh    J. A. Gutierrez    C. A. Urrea    A. Molina  C. Cajiao 《Plant Breeding》1992,109(4):320-328
Two populations of common bean, Phaseolus vulgaris L., were used to make three independent location-specific selections at Palmira, Quilichao, and Popayán, Colombia. Also, three across-location selections were made by alternating generations between Palmira and Popayan, between Quilichao and Popayán, and among Palmira, Quilichao, and Popayán. The seven highest yielding lines selected from each environment and population along with 14 parents and two checks were evaluated for seed yield, seed weight, maturity, and reaction to an-thracnose, angular leaf spot, and common bacterial blight. Mean squares due to evaluation and selection environments, selected lines, and their interactions were significant for all traits. Mean yields of selected lines were higher than the mean of parents in both populations. Among location-specific selections, lines yielded higher at their respective selection site. Moreover, selections made at Popayán were higher yielding than those made at Quilichao or Palmira when tested across locations and years. Use of Popayán, a relatively wetter and cooler site, either alone or in combination with other locations resulted in higher yield, higher seed weight, and higher resistance to anthracnose. On the average, location-specific selections were lower yielding than the across-location selections. Among across-location selections, those selected between Palmira and Popayán were the highest yielding in both populations. Selections at Palmira and across all three locations resulted in greater stability.  相似文献   
24.
Huitlacoche is the ethnic name of the young fruiting bodies of Ustilago maydis, a common parasite of maize. In Mexico and other Latin American countries, this fungus has been traditionally appreciated as a local delicacy. In this work a metallomics approach was used with the determination of eight elements in huitlacoche by electrothermal atomic absorption spectrometry as one facet of this approach. The results obtained indicated relatively lower concentrations of commonly analyzed metals, as referred to the data reported for other mushroom types. This effect was ascribed to different accessibilities of elements, depending on fungus substrate (lower from plant than from soil). Subcellular fractionation was accomplished by centrifugation of cell homogenates suspended in Tris-HCl buffer. Recoveries of the fractionation procedure were in the range of 71-103%. For six elements (Cr, Cu, Fe, Mn, Ni, and Pb), the mean relative contributions in cytosol, cell walls, and mixed membrane fraction were 50.7, 48.2, and 1.1% respectively. To attain the molecular weight distribution of compounds containing target elements as an additional aspect of the metallomics approach, the fungus extract (1% sodium dodecyl sulfate in Tris-HCl, 30 mmol L(-)(1), pH 7.0) was analyzed by size exclusion chromatography with UV and ICP-MS detection. With spectrophotometric detection (280 nm), the elution of high molecular weight compounds was observed in the form of one peak (MW > 10 kDa), and several lower peaks appeared at higher retention times (MW < 10 kDa). On ICP-MS chromatograms, a coelution of (59)Co, (63)Cu, (57)Fe, (202)Hg, (60)Ni, and (80)Se with the first peak on the UV chromatogram was clearly observed, indicating that a fraction of each element incorporated with high molecular weight compounds (12.7, 19.8, 33.7, 100, 19.4, and 45.8%, respectively, based on the peak area measurements). From a comparison of (80)Se and (33)S chromatograms (for sulfur analysis, the extract was obtained in the absence of SDS), both elements coeluted with the first UV peak, but their lower molecular weight compounds were apparently different. These findings may contribute to a better understanding of the accumulation of elements in mushrooms.  相似文献   
25.
26.
Deep Impact observations by OSIRIS onboard the Rosetta spacecraft   总被引:1,自引:0,他引:1  
The OSIRIS cameras (optical, spectroscopic, and infrared remote imaging system) onboard the European Space Agency's Rosetta spacecraft observed comet 9P/Tempel 1 for 17 days continuously around the time of NASA's Deep Impact mission. The cyanide-to-water production ratio was slightly enhanced in the impact cloud, compared with that of normal comet activity. Dust particles were flowing outward in the coma at >160 meters per second, accelerated by the gas. The slope of the brightness increase showed a dip about 200 seconds after the impact. Dust Afrho values before and long after the impact confirm the slight decrease of cometary activity. The dust-to-water mass ratio was much larger than 1.  相似文献   
27.
We studied the relative value of natural habitats, river and coastal wetlands, and artificial habitats, irrigation canal and ponds, for the conservation of an endangered fish, Iberian toothcarp, in its southernmost area of distribution, characterised by agricultural intensification. Our results show that the bulk of the population of the Iberian toothcarp is concentrated in irrigation ponds. Natural habitats sustained null or impoverished subpopulations, and individuals showed signs of low metabolic activity. This coincided with the relatively high habitat quality observed in ponds, particularly those with submerged aquatic vegetation, in contrast with the chronic eutrophication of the coastal lagoons. In spite of a generalised aggressive management in the irrigation system, featured by periodic vegetation clearance, desiccation and biocide treatment, the subpopulation of the Iberian toothcarp thrives in it probably thanks to adequate water quality and to an active path dynamics maintained by connectivity through the canal. Agro-environmental measures are discussed for the improvement of this species conservation in natural and artificial habitats.  相似文献   
28.
A study was carried out on the pH values obtained from bulk (wet and dry) precipitation samples collected simultaneously in two cities in Cantabria (Spain), Santander and Torrelavega over a period of a year. It was observed that the annual weighted average values for the pH of precipitation, 4.42 and 4.21, respectively, differ significantly although the difference is less than that existing between their pollution levels. The difference is greater when total annual H+ depositions are compared. The study also demonstrated the strong influence of long-range transport effect on acidity and to a lesser degree the effect of mid-range transport.  相似文献   
29.
Pharmacokinetic variables of amikacin in cows were determined after administration of amikacin sulphate either intravenously (IV) or intramuscularly (IM) at a dose of 25 mg/kg per day for three days. Amikacin concentrations at time zero and maximum serum concentrations were 240.8 microg/mL and 122.53 microg/mL, respectively. The elimination half-life remained unchanged during the three days of administration (T1/2beta = 1.33 +/- 0.029 h for the IV route and T1/2beta = 2.75 +/- 0.38 h for the IM route). Apparent volumes of distribution suggest limited distribution out of the central compartment (VdAUC = 0.154 +/- 0.005 L/kg; Vdc = 36.50 +/- 2.35 L; Vdss = 0.092 +/- 0.004 L/kg). Bioavailability after IM administration was 95%. Serum profiles of urea, creatinine, albumin, electrolytes and pH after 5-day treatment with amikacin at a dose of 25 mg/kg per day IM revealed no changes. Assessment of diffusion of amikacin to milk by a commercially available screening method to detect antibiotic residues revealed that amikacin could not be detected by the fifth milking period after the last treatment. These results suggest that it would be rational to use a large single-daily dose of amikacin for future clinical trials in cows.  相似文献   
30.
Porcine circovirus diseases   总被引:21,自引:0,他引:21  
Porcine circovirus type 2 (PCV2) is a member of the family Circoviridae, a recently established virus family composed of small, non-enveloped viruses, with a circular, single-stranded DNA genome. PCV2, which is found all over the world in the domestic pig and probably the wild boar, has been recently associated with a number of disease syndromes, which have been collectively named porcine circovirus diseases (PCVD). Postweaning multisystemic wasting syndrome (PMWS), porcine dermatitis and nephropathy syndrome (PDNS) and reproductive disorders are the most relevant ones. Among them, only PMWS is considered to have a severe impact on domestic swine production. PMWS mainly affects nursery and/or fattening pigs; wasting is considered the most representative clinical sign in this disease. Diagnosis of this disease is confirmed by histopathological examination of lymphoid tissues and detection of a moderate to high amount of PCV2 in damaged tissues. Since PMWS is considered a multifactorial disease in which other factors in addition to PCV2 are needed in most cases to trigger the clinical disease, effective control measures have focused on the understanding of the co-factors involved in individual farms and the control or elimination of these triggers. PDNS, an immuno-complex disease characterized by fibrino-necrotizing glomerulonephritis and systemic necrotizing vasculitis, has been linked to PCV2, but a definitive proof of this association is still lacking. PCV2-associated reproductive disease seems to occur very sporadically under field conditions, but it has been characterized by late-term abortions and stillbirths, extensive fibrosing and/or necrotizing myocarditis in fetuses and the presence of moderate to high amounts of PCV2 in these lesions. Taking into account that scientific information on PCV2 and its associated diseases has been markedly expanded in the last 8 years, the objective of this review is to summarize the current state of knowledge of the most relevant aspects of PCV2 biology and PCVD.  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