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   115篇
  免费   7篇
林业   7篇
农学   4篇
基础科学   2篇
  22篇
综合类   6篇
农作物   11篇
水产渔业   9篇
畜牧兽医   51篇
园艺   1篇
植物保护   9篇
  2023年   3篇
  2022年   4篇
  2021年   8篇
  2020年   5篇
  2019年   5篇
  2018年   6篇
  2017年   4篇
  2016年   9篇
  2015年   3篇
  2014年   5篇
  2013年   2篇
  2012年   10篇
  2011年   12篇
  2010年   4篇
  2009年   7篇
  2008年   5篇
  2007年   9篇
  2006年   9篇
  2005年   5篇
  2004年   3篇
  2003年   3篇
  1993年   1篇
排序方式: 共有122条查询结果,搜索用时 15 毫秒
21.
A 22‐year‐old Arabian mare was examined for evaluation of haematuria of 2 months' duration. Complete blood cell count and chemistry revealed anaemia of chronic disease (i.e. normocytic, normochromic) and hypoproteinaemia. Cystoscopy revealed a haemorrhagic mass protruding into the lumen of the urinary bladder in the apical region. The mass was surgically removed by partial cystectomy performed through a caudal ventral midline laparotomy. Histological examination of the mass confirmed the diagnosis of squamous cell carcinoma. Tumours of the equine urinary bladder are rare, and when a partial cystectomy is indicated, a caudal ventral midline laparotomy may provide adequate surgical exposure even in adult horses.  相似文献   
22.
Three experimental diets were used to investigate the digestion of carbohydrates and utilization of energy in sows fed diets with different levels and physicochemical properties of dietary fiber (DF). The low-fiber diet (LF; DF, 16%; soluble DF, 4.8%) was based on wheat and barley. The high-fiber 1 diet (HF1; DF, 41%; soluble DF, 11%) was based on wheat and barley supplemented with the coproducts: sugar beet pulp, potato pulp, and pectin residue, and the high-fiber 2 diet (HF2; DF, 44%; soluble DF, 7.3%) was based on wheat and barley supplemented with approximately 1/3 of the coproducts used in diet HF1 and 2/3 of brewers spent grain, seed residue, and pea hull (1:1:1, respectively). The diets were studied in 2 series of experiments. In Exp. 1, the digestibility and ileal and fecal flow of nutrients were studied in 6 ileal-cannulated sows placed in metabolic cages designed as a repeated 3 x 3 Latin square design. In Exp. 2, energy metabolism was measured in respiration chambers using 6 sows in a repeated 3 x 3 Latin square design. The DF level influenced the ileal flow of most nutrients, in particular carbohydrates, which increased from 190 g/d when feeding the LF diet to 538 to 539 g/d when feeding the HF diets; this was also reflected in the digestibility of OM and carbohydrates (P < 0.05). The ranking of total excretion of fecal materials was HF2 > > HF1 > LF, which also was reflected in the digestibility of OM, protein, and carbohydrates. Feeding HF diets resulted in greater CH(4) production, which was related to the amount of carbohydrates (r = 0.79) and OM (r = 0.72) fermented in the large intestine, but with no difference in heat production (12.2 to 13.1 MJ/kg of DM). Retained energy (MJ/kg of DM) was decreased when feeding HF1 compared with LF and negative when feeding HF2. Feeding sows HF1 reduced the activity of animals (5.1 h/24 h) compared with LF (6.1 h/24 h; P = 0.045).  相似文献   
23.
Improving water use efficiency is a key element of water management in irrigated viticulture, especially in arid or semi-arid areas. In this study, the micrometeorological technique “Eddy Covariance” was used to directly quantify the crop evapotranspiration (ET) and to analyze the complex relationships between evapotranspiration, energy fluxes, and meteorological conditions. Both observed Direct measurements (DIR) of latent heat flux (LE) and observed from the residual of the energy balance (REB) equation were used for crop evapotranspiration calculations. Observed crop coefficients (K cms) were then determined using the standardized reference evapotranspiration (ETo) equation for short canopies. In addition, linear approximations from observations were used to model the seasonal trend lines for crop coefficients and K cs values were parameterized by first identifying the beginning and end of each growth stage. The modeled K cs values were used to predict daily ET from ETo measurements and compared with values from literature. The daily observed DIR ET values (ETdo) were lower than REB ET (ETro) during periods with precipitation, but they were similar during dry periods, which implies that energy balance closure is better when the surface is drier. Comparisons between modeled ET and crop ET estimated using K c values from best agreement was observed between the modeled REB and FAO 56 and the local K c values provided by the Regional Agency ARPAS showed good agreement with observed ET (from DIR and REB data) than the FAO 56 ones. The study confirmed that the availability of locally driven K c could be relevant to quantify the crop water requirement and represents the starting point for a sustainable management of water resources.  相似文献   
24.
The hexavalent state, considered to be the highest oxidation level accessible for iron, has previously been found only in the tetrahedral ferrate dianion, FeO4(2-). We report the photochemical synthesis of another Fe(VI) compound, an octahedrally coordinated dication bearing a terminal nitrido ligand. M?ssbauer and x-ray absorption spectra, supported by density functional theory, are consistent with the octahedral structure having an FeN triple bond of 1.57 angstroms and a singlet d2(xy) ground electronic configuration. The compound is stable at 77 kelvin and yields a high-spin Fe(III) species upon warming.  相似文献   
25.
Throughout the developing world, it is a well-documented fact that women farmers tend to get lower yields than their male counterparts. Typically this is attributed to disproportionate access to high-quality inputs and labor, with some even arguing there could be a skills-gap stemming from unbalanced access to training and education. This article examines the gender-based yield gap in the context of Zambian maize producers. In addition to the usual drivers, we argue that Zambia’s patriarchal and multi-tiered land distribution system could disfavor women with respect to accessing quality soils. We are uniquely able to control for soil characteristics using farm data from a sample of 1573 fields with accompanying soil analysis. We find an expected difference in yields, but no evidence of a gap in unobserved characteristics, like skill, after controlling for access to inputs, especially quality soil, suggesting women are indeed disproportionately disadvantaged. We discuss how our findings could be used to develop self-targeting policy interventions that could empower women and would be consistent with the government’s stated equity goals.  相似文献   
26.
LC-MS4 has been used to detect and characterize in green coffee beans 15 quantitatively minor p-coumaric acid-containing chlorogenic acids not previously reported in nature. These comprise 3,4-di-p-coumaroylquinic acid, 3,5-di-p-coumaroylquinic acid, and 4,5-di-p-coumaroylquinic acid (Mr 484); 3-p-coumaroyl-4-caffeoylquinic acid, 3-p-coumaroyl-5-caffeoylquinic acid, 4-p-coumaroyl-5-caffeoylquinic acid, 3-caffeoyl-4-p-coumaroyl-quinic acid, 3-caffeoyl-5-p-coumaroyl-quinic acid; and 4-caffeoyl-5-p-coumaroyl-quinic acid (Mr 500); 3-p-coumaroyl-4-feruloylquinic acid, 3-p-coumaroyl-5-feruloylquinic acid and 4-p-coumaroyl-5-feruloylquinic acid (Mr 514); and 4-dimethoxycinnamoyl-5-p-coumaroylquinic acid and two isomers (Mr 528) for which identities could not be assigned unequivocally. Structures have been assigned on the basis of LC-MS4 patterns of fragmentation. Forty-five chlorogenic acids have now been characterized in green Robusta coffee beans.  相似文献   
27.
The use of transgenic plants as delivery system for antigenic proteins is attractive for its simplicity and increases likelihood for local immune response at sites of infection. The aim of this study was to evaluate the protective effect of oral administration of tobacco seeds, expressing the FedA, the major protein of the F18 adhesive fimbriae, and B subunit of verocytotoxin, against verocytotoxin-producing E. coli (VTEC) strain in piglets. Forty-three early weaned piglets, were randomly divided into 4 experimental groups: 3 test groups and a control. Treatment groups orally received a bolus, with different dose of tobacco seeds on 0, 1, 2, 14 days post primary administration. After challenge, with 1*1010 CFU of O138 Escherichia coli strain, piglets showed clinical scores significantly higher in the control group compared to orally immunized groups (P?<?0.05) and the latter showed a faster recovery than in CG. In conclusion, oral administration of recombinant tobacco seeds expressing antigenic proteins against VTEC strains can induce a protective effect against challenger strain in piglets.  相似文献   
28.
In the last decades, the marine environment was discovered as a huge reservoir of novel bioactive compounds, useful for medicinal treatments improving human health and well-being. Among several marine organisms exhibiting biotechnological potential, sponges were highlighted as one of the most interesting phyla according to a wide literature describing new molecules every year. Not surprisingly, the first marine drugs approved for medical purposes were isolated from a marine sponge and are now used as anti-cancer and anti-viral agents. In most cases, experimental evidence reported that very often associated and/or symbiotic communities produced these bioactive compounds for a mutual benefit. Nowadays, beauty treatments are formulated taking advantage of the beneficial properties exerted by marine novel compounds. In fact, several biological activities suitable for cosmetic treatments were recorded, such as anti-oxidant, anti-aging, skin whitening, and emulsifying activities, among others. Here, we collected and discussed several scientific contributions reporting the cosmeceutical potential of marine sponge symbionts, which were exclusively represented by fungi and bacteria. Bioactive compounds specifically indicated as products of the sponge metabolism were also included. However, the origin of sponge metabolites is dubious, and the role of the associated biota cannot be excluded, considering that the isolation of symbionts represents a hard challenge due to their uncultivable features.  相似文献   
29.
4′-Geranyloxyferulic (GOFA) and boropinic acid have been discovered during the last decade as interesting phytochemicals having valuable pharmacological effects as cancer chemopreventive, anti-inflammatory, neuroprotective, and anti-Helicobacter pylori agents. A reverse-phase HPLC-UV/Vis method for the separation and quantification of the title oxyprenylated ferulic acid derivatives in extracts obtained from peels of nine edible Citrus and Fortunella fruits was successfully applied. Concentration values showed a great variation between the different species, being orange (C. sinensis) the fruit richest in GOFA (0.141?±?0.011 mg/g of exocarp fresh weight) and kumquat (Fortunella japonica) the one in which boropinic acid was recorded as the most abundant phytochemical (0.206?±?0.002 mg/g of exocarp fresh weight). Both secondary metabolites were not detected only in three species. The set-up methodology showed limits of quantification (LOQ) values, that were able to selectively quantify both GOFA and boropinic acid. Results described herein depict a potential chemopreventive dietary feeding role for the Rutaceae spp. under investigation.  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