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   66篇
  免费   7篇
林业   11篇
农学   1篇
  14篇
综合类   10篇
农作物   9篇
水产渔业   2篇
畜牧兽医   20篇
植物保护   6篇
  2022年   3篇
  2021年   2篇
  2020年   1篇
  2019年   2篇
  2018年   2篇
  2017年   3篇
  2016年   3篇
  2015年   1篇
  2014年   3篇
  2013年   2篇
  2012年   2篇
  2011年   2篇
  2010年   3篇
  2009年   3篇
  2008年   2篇
  2007年   4篇
  2006年   2篇
  2005年   3篇
  2004年   5篇
  2003年   1篇
  2002年   1篇
  2001年   4篇
  2000年   3篇
  1999年   1篇
  1998年   2篇
  1996年   2篇
  1995年   1篇
  1993年   1篇
  1991年   1篇
  1987年   1篇
  1981年   2篇
  1978年   1篇
  1974年   1篇
  1964年   1篇
  1963年   2篇
排序方式: 共有73条查询结果,搜索用时 15 毫秒
61.
Horse chestnut extracts are widely used in pharmacy and cosmetic industries. The main active constituents are saponins of oleane type, but seeds of horse chestnut also contain flavonoids, being glycosides of quercetin and kaempferol. Their contribution to the overall activity of the extracts was not clear. In the present work, the main flavonoids from horse chestnut seeds were isolated and their structures established with spectral methods. Seven glycosides were isolated, out of which six ( 2, 3, 4, 7, 11, 13) were previously reported and one ( 9) was identified as a new tamarixetin 3- O- [beta- d-glucopyranosyl(1-->3)]- O-beta- d-xylopyranosyl-(1-->2)- O-beta- d-glucopyranoside. The structures of three additional compounds 1, 10, and 12, not previously reported, were deduced on the basis of their LC-ESI/MS/MS fragmentation characteristics. A new ultraperformance liquid chromatographic (UPLC) method has been developed for profiling and quantitation of horse chestnut flavonoids. The method allowed good separation over 4.5 min. Thirteen compounds could be identified in the profile, out of which di- and triglycoisdes of quercetin and kaempferol were the dominant forms and their acylated forms occurred in just trace amounts. The total concentration of flavonoids in the powdered horse chestnut seed was 0.88% of dry matter. The alcohol extract contained 3.46%, and after purification on C18 solid phase, this concentration increased to 9.40% of dry matter. The flavonoid profile and their content were also measured in the horse chestnut wastewater obtained as byproduct in industrial processing of horse chestnut seeds. The total flavonoid concentration in the powder obtained after evaporation of water was 2.58%, while after purification on solid phase, this increased to 11.23% dry matter. It was concluded that flavonoids are present in a horse chestnut extract in a relatively high amount and have the potential to contribute to the overall activity of these extracts. Industrial horse chestnut wastewater can be used to obtain quercetine and kaempferol glycosides for cosmetic, nutraceutical, and food supplement industries.  相似文献   
62.
OBJECTIVE: To develop and evaluate a marker cluster set for measuring sagittal and extrasagittal movement of joints in the distal portion of the forelimb in ponies. ANIMALS: 4 ponies. PROCEDURES: 5 infrared cameras were positioned on a concrete walkway in a frontal-sagittal arc and calibrated. Four segments were defined: hoof, middle phalanx, proximal phalanx, and metacarpus. Rigid clusters with 4 retroreflective markers were placed on each segment. A static trial was recorded with additional anatomic markers on the medial and lateral joint lines. Those anatomic markers were removed, and kinematic data were recorded at 240 Hz during walking. An ensemble mean was computed from the 4 ponies from 5 replicates of the walks. Joint kinematic variables were calculated by use of the calibrated anatomical system technique. The design and error dispersion of each marker were evaluated. RESULTS: Marker clusters were quasiplanar, but variation in orientation error was reduced because the mean radii were > 10 times the largest error dispersion values. Measurements of sagittal rotations of the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints were similar to measurements obtained with bone-fixed triads, but larger discrepancies between the 2 methods were found for extrasagittal rotations. CONCLUSIONS AND CLINICAL RELEVANCE: Development of noninvasive methods for quantifying data pertaining to 3-dimensional motion in horses is important for advancement of clinical analysis. The technique used in the study enabled identification of flexion-extension motions with an acceptable degree of accuracy. Appropriate correction algorithms and improvements to the technique may enable future quantification of extrasagittal motions.  相似文献   
63.
Enterotoxigenic Escherichia coli (ETEC) infection results in fluid and electrolyte losses in the small intestine. We investigated the effect of non-starch polysaccharides (NSP) hydrolysis products of wheat middlings (WM) and flaxseed (FS) on net absorption of fluid and solutes during ETEC challenge. Products were generated by incubating WM and FS with a blend of carbohydrase enzymes to produce 2 products: 80% ethanol-soluble (ES) and 80% ethanol-insoluble (EI) which were studied in 2 experiments in which 2 factors were investigated: products (EI vs. ES) and time of ETEC challenge (before vs. after perfusion). Pairs of small-intestine segments, one non-challenged and the other ETEC-challenged were perfused with products for 7.5 h. ETEC reduced fluid absorption by more than 380 µL/cm2 in saline (control) perfused segments, whereas this reduction was significantly ( P  < 0.05) less for the WM and FS products. Interaction ( P  > 0.05) between product and time of challenge was not observed. For WM, products effects on ETEC-challenged segments were such that perfusion of ES resulted in higher total solute (measured as osmolality) absorption than EI (138 vs. 103 µOsmol/cm2). In conclusion, hydrolysis products from WM and FS were beneficial in maintaining fluid balance during ETEC challenge, suggesting potential in controlling ETEC induced diarrhea in piglets.  相似文献   
64.
The aim of the work was to determine the concentration of 234U and 238U and calculate the values of the 234U/238U activity ratio in samples of living organisms, bottom water, surface and interstitial water and also sediments from the various regions of southern Baltic Sea. The knowledge of 234U/238U activity ratio in ecosystem allows getting know about the mechanisms and processes of uranium transport and origin.The activities of the analyzed uranium radionuclides in samples were measured using alpha spectrometry. The results of researches revealed diversified concentrations of uranium in the sediments of the southern Baltic Sea (sea and coastal waters) and increase of uranium with sediment depth, suggesting the diffusion of uranium from sediments to water through interstitial water and diagenesis processes in sediment material. The nuclides of uranium 234U and 238U were radioactive state equilibrium in most of the sediments. The values of the 234U/238U activity ratio oscillate around one. In bottom, surface, interstitial water and living organisms mean values of the 234U/238U activity ratio are between 1.12 and 1.15. Higher uranium concentration was observed in samples of sediments and seawater after flood in 1997 and torrential rainfalls in 2000–2001. River waters are characterized by higher 234U/238U activity ratio. The values of the 234U/238U activity ratio equal 1.27 in sediments and 1.34–1.38 in seawater indicate the influence of fresh waters.  相似文献   
65.
66.
Summary Using potato parental lines homozygous at a locus or loci controlling resistance to potato leafroll virus (PLRV) can give advantages in the selection of resistant forms. In order to identify homozygous diploid clones their test-cross families were evaluated. All the clones that were test-crossed expressed resistance in primarily- and secondarily-infected plants and etiolated sprouts, and were derived from mating genotypes highly resistant to PLRV. Genotypes from test-cross families varied in resistance to PLRV, and one family was found which had only resistant genotypes, suggesting that the resistant parent of this progeny was homozygous at resistance loci. Evidence was gathered that resistance in some diploid clones may result from resistance to virus multiplication as well as restricted virus transport from leaves to tubers.  相似文献   
67.
Inflammatory processes were provoked in 35 rats by subcutaneous implantation of sterile cotton-wool pads and treated five days by means of various antiphlogistic substances. The action of sodium salicylate (administered alone or in conjunction with gamma-globulin or with glucose) proved similar to that of prednisolone which was given as control substance. Human gamma-globulin exhibited neither anti-inflammatory nor pro-inflammatory effects. Experiments with twelve rabbits revealed that the pyretogenic potential of sodium nucleinate, one per cent (0.01 g/kg body weight) was stronger than that of animal charcoal or peptone. Yet, the two latter substances may be used, as well. The antipyretic effect of sodium salicylate was not as intensive but just as reliable as that of aminophenazone, when both preparations were applied to rabbits with induced fever. Concomitant administration of glucose is recommended to prevent development of undesired side-effects, such as giddiness or ataxia.  相似文献   
68.
We examined the year-round viable seed dispersal by European bison (Bison bonasus L.) subject to three population management systems (captive, semi-wild, wild) in Bia?owie?a Primeval Forest. The forest is inhabited by the world's largest free-roaming population of European bison (>450 head). Dung samples were collected approximately fortnightly from September 2005 to September 2006 in each of the management systems. Emergent seedlings were counted for 24 months in greenhouse conditions. A total of 10,807 seedlings, which included 178 plant taxa, emerged from 74 bison dung samples. Species richness and seedling abundance/sample were greatest during August and September, the months of the highest fructification season, and were lowest in May. Twenty-two percent of recorded species were forest plants. The captive bison population had the greatest mean seedling abundance (236 ± 61/sample), the greatest species diversity (144), and the highest percentage of synanthropic species (29.2%). The gradient of these characteristics decreased with a decrease in management intensity of the bison populations. The results of the regression analysis indicated that in the semi-wild managed system, the number of plant species found in dung samples collected during winter was significantly negatively correlated with snow depth. Number of seedlings and number of plant species dispersed depended on plant phenology and intensity of supplementary feeding. The mean number of seeds/sample dispersed by European bison was 5–15 times lower, and the mean number of species/sample was 2–3 times lower than those published for cattle or horses. In contrast, the total number of plant species dispersed by bison was approximately 2–3 times higher than for wild or domestic large ungulates. These results indicate that European bison are an important dispersal agent of seeds in forest ecosystems. The high percentage of synanthropic species dispersed by bison demonstrated that seeds in the fodder help maintain native and non-native plant diversity of ecosystems. Managers of animal populations must pay proper attention to fodder origin and quality.  相似文献   
69.
70.
Unconscious motivation in humans is often inferred but rarely demonstrated empirically. We imaged motivational processes, implemented in a paradigm that varied the amount and reportability of monetary rewards for which subjects exerted physical effort. We show that, even when subjects cannot report how much money is at stake, they nevertheless deploy more force for higher amounts. Such a motivational effect is underpinned by engagement of a specific basal forebrain region. Our findings thus reveal this region as a key node in brain circuitry that enables expected rewards to energize behavior, without the need for the subjects;awareness.  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