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   16646篇
  免费   20篇
林业   3642篇
农学   1300篇
基础科学   144篇
  2800篇
综合类   715篇
农作物   2133篇
水产渔业   1813篇
畜牧兽医   1122篇
园艺   1118篇
植物保护   1879篇
  2023年   2篇
  2022年   11篇
  2021年   14篇
  2020年   13篇
  2019年   18篇
  2018年   2766篇
  2017年   2720篇
  2016年   1194篇
  2015年   70篇
  2014年   30篇
  2013年   26篇
  2012年   803篇
  2011年   2135篇
  2010年   2114篇
  2009年   1259篇
  2008年   1329篇
  2007年   1583篇
  2006年   35篇
  2005年   103篇
  2004年   109篇
  2003年   151篇
  2002年   63篇
  2001年   8篇
  2000年   44篇
  1998年   2篇
  1997年   4篇
  1996年   4篇
  1995年   1篇
  1994年   1篇
  1993年   12篇
  1992年   7篇
  1991年   1篇
  1990年   1篇
  1989年   6篇
  1988年   11篇
  1987年   1篇
  1985年   1篇
  1977年   5篇
  1974年   1篇
  1972年   1篇
  1969年   2篇
  1968年   4篇
  1967年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The experiment consisting of 7 days of digestibility and 90 days of feeding trial was conducted at Wogda (Ethiopia) to determine the effect of supplementation of graded levels of concentrate mix (CM) on feed intake, digestibility, and body weight (BW) change in hay-based feeding of Simada sheep. Twenty-yearling Simada sheep with a mean initial BW of 17.9 ± 0.81 kg (mean ± SD) were used in randomized complete block design arranged into five blocks of four animals. The four dietary treatments that consisted of hay alone (T1), hay +150 g dry matter (DM; T2, low), hay +250 g DM (T3, medium), and hay +350 g DM (T4, high) CM were randomly assigned to each sheep within a block. The CM consisted of wheat bran (WB), noug seed (Guizotia abyssinica) meal and safflower (Carthamus tinctorius) seed meal at the ratio of (2:1:1), respectively. Supplementation with T2 and T3 increased (P < 0.001) total DM and organic matter intake than the control treatment. Overall, supplementation improved (P < 0.001) crude protein intake, digestibility, feed conversion efficiency, BW gain, and profitability compared to the control, whereas sheep on the high than the low and medium level of supplementation performed better in these parameters among the supplemented treatments. From the results of this study, T4 is recommended as the best level of supplementation since it resulted in better nutrient utilization, animal performance, and profitability.  相似文献   
22.
The antigen detection enzyme immunoassay (AgELISA) in conjunction with parasitological examination of blood were used to study the enzootic situation of cameline trypanosomiasis in mid-Eastern Sudan. A one year survey showed that the infection is endemic among pastoral camels with a prevalence of 5.4% based on parasitological examination and 31.3% based on AgELISA. The infection rate was higher during the dry period (November to May) than the wet season. Young camels had a much lower infection rate as detected by parasitological techniques, but not with AgELISA. A lower prevalence of infection was detected by buffy coat technique (BCT) in herds of camels raised by nomads compared with those kept by agropastoralists and in camels located in the southern districts of mid-Eastern Sudan.  相似文献   
23.
The aim of the current investigation was to determine wild ostrich reproductive behaviour in Orbata Nature Reserve by observing 16 hens and 28 cocks over a seven-year period. Intense laying commenced in January, one month after the cessation of the rainy season, and 92% of the eggs were produced during the dry season (January to May, peaking in March). Over the seven years, 1,322 eggs were laid in 69 nests, which corresponded to an annual average production of 19.2 ± 9.1 eggs/nest and 11.8 eggs/hen. 24 nests (34.78%) were non-brooded, 17 nests (24.64%) were deserted in the course of incubation, and 28 nests (40.58%) possessed hatched eggs. All the non-incubated nests had egg losses equivalent to 46.6 ± 12.6%. Hatchability success of incubated eggs was 41.9 ± 12.0%. Ostriches tended to dig their nests adjacent to the reserve enclosure which had direct access by road and track, the latter subjecting them to human disturbance and predation. The systematic obstruction of these nests stimulated ostriches to build additional nests within the reserve perimeter. The authors discussed the results recorded in an ostrich flock in relation to the environmental factors (climatic factors, food disponibility and predation) and suggested possibilities for improved wildlife management.  相似文献   
24.
Reducing methane emission from ruminant animals has implications not only for global environmental protection but also for efficient animal production. Tea saponins (TS) extracted from seeds, leaves or roots of tea plant are pentacyclic triterpenes. They have a lasting antiprotozoal effect, but little effect on the methanogen population in sheep. There was no significant correlation between the protozoa counts and methanogens. The TS decreased methanogen activity. It seems that TS influenced the activity of the methanogens indirectly via the depressed ciliate protozoal population. The TS addition decreased fungal population in the medium containing rumen liquor in in vitro fermentation, but no such effect was observed in the rumen liquor of sheep fed TS. Tea saponins had a minor effect on the pattern of rumen fermentation and hence on nutrient digestion. When added at 3 g/day in diets, TS could improve daily weight gain and feed efficiency in goats. No positive associative effect existed between TS and disodium fumarate or soybean oil on methane suppression. Inclusion of TS in diets may be an effective way for improving feed efficiency in ruminants.  相似文献   
25.
26.
Summary A pilot health monitoring system was started in 1990 to develop statistically valid data for use in estimating the disease frequencies in dairy cattle and buffaloes. This paper presents the design of the monitoring programme and frequencies of selected diseases. Eighty herds were selected with typical livestock management practices of the farmers in the area. Veterinary assistants visited the farms once a month for 12 months to collect livestock inventory, production, disease and preventive treatment data. The incidence density method was used as a measure of disease frequency.In adults, breeding problems, mastitis and gastro-intestinal problems were the highest reported conditions. Respiratory problems were the commonest in young stock. The calves of both species frequently had gastro-intestinal and respiratory disease conditions. Most of the calf crop of both species were lost within the first 3 months of life.
Monitoreo De Problemas De Salud Bovina En Hatos Lecheros Pequenos En El Territorio Capital De Islamabad
Resumen Se inició un sistema de monitoreo piloto en 1990, con el propósito de desarrollar datos estadísticos válidos para estimar la frecuencia de enfermedades en ganado lechero y en búfalos. Este artículo presenta el diseño del programa de monitoreo y la frecuencia de las enfermedades seleccionadas. Se seleccionaron ochenta hatos con el manejo típico de los ganaderos del área. Los veterinarios visitaron las fincas una vez al mes durante 12 meses para colectar información. El método de densidad en la incidencia fue usado para medir la frecuencia de enfermedades.En adultos, las condiciones más frecuentemente encontradas fueron problemas de fertilidad, mastitis y problemas gastrointestinales. Las afecciones respiratorias fueron el común denominador en jóvenes. Los terneros de ambas especies se encontraron frecuentemente con problemas gastrointestinales y respiratorios, conjuntamente, siendo la mortalidad extremadamente alta en los 3 primeros meses de vida para ambas especies.

Gestion Des Problemes De Sante Bovine De Petits Troupeaux Laitiers Sur Le Territoire De Islamabad: Schema, Donnees Et Frequences De La Maladie
Résumé Un système pilote de gestion de la santé a débuté en 1990 pour développer des données statistiquement valables pour être utilisées dans l'estimation de la fréquence des maladies de bovins laitiers et de buffles. Cet article présente le schéma du programme de gestion et les fréquences des maladies sélectionnées. Quatre vingt troupeaux ont été choisis; leur élevage était conduit selon la méthode propre aux fermiers de la région. Des assistants vétérinaires ont visité les fermes une fois par mois durant 12 mois pour relever les données sur l'inventaire du bétail, la production, les maladies et les traitements préventifs. L'importance de l'incidence a été utilisée comme méthode pour mesurer la fréquence des maladies. Chez les adultes, les problèmes prédominants dans les conditions indiquées concernaient la reproduction, les mammites et des troubles gastrointestinaux. Les problèmes respiratoires étaient les plus communs chez le jeune bétail. Les veaux des deux espèces présentaient fréquemment des troubles respiratoires et gastrointestinaux. La majorité de la production de veaux des deux espèces étaient perdue dans les trois premiers mois de vie.
  相似文献   
27.
Ornithobacterium rhinotracheale is a gram negative bacterial pathogen causing respiratory tract infections in poultry. Tracheal, lung and serum samples were obtained from 21 broiler flocks of 8 farms from a slaughterhouse located in south-eastern of Iran. Among 630 tracheal and lung samples from samples resulting from 315 chickens, 11 (3.5%) ORT isolates were identified using biochemical tests. The isolates originated from 9 (42.9%) flocks out of 4 farms. All of the isolates were recovered from tracheal swabs and showed an API 20NE identification biocode 0-2-2-0-0-0-4. Of the 420 serum samples examined by ELISA, 134 (31.9%) sera from 17 (81.0%) flocks were positive for ORT antibodies. These results indicate that ORT is present in most broiler flocks with respiratory disorders in southeast Iran.  相似文献   
28.
The present experiment was designed to study the pharmacokinetics of levofloxacin in six healthy cross bred female cow calves (4 to 6 months age) weighing between 40 to 80 kg. Plasma from blood was separated by centrifugation at 10,000 rpm. Quantitative estimation of levofloxacin was done by UV-VIS spectrophotometer at 286 nm. The mean maximum plasma concentration (Cpmax ) of levofloxacin in febrile calves (5.28?±?0.32 µg/ml) did not differ significantly as compared with healthy calves (4.50?±?0.22 µg/ml) after single dose (20 mg/kg) oral administration. The mean therapeutic plasma concentration ( Cpther ) of levofloxacin was maintained for longer period in febrile calves (10 h) as compared to healthy calves ( 8 h). The mean maximum urine concentration (Cumax) in febrile (40.86?±?2.19 µg/ml) also did not differ significantly as compared with healthy calves (39.38?±?2.43 µg/ml). No significant difference in various pharmacokinetic parameters of plasma was observed in healthy calves ( β?=?0.23?±?0.01/h ; t1/2 β?=?3.00?±?0.17 h and MRT?=?4.66?±?0.14 h ) and febrile calves ( β?=?0.23?±?0.01/ h; t1/2 β?=?3.05?±?0.16 h and MRT?=?5.04?±?0.14 h ) . The mean value of β, and t ½ β calculated in urine also did not differ between healthy and febrile calves. However, the value of MRT(3.79?±?0.07 h) and ClB(1.65?±?0.09 ml/kg/min) calculated in urine of febrile calves significantly(p?B?=?2.09?±?0.13 ml/kg/min). Based on kinetic profile levofloxacin may be given orally at the dose rate of 1.49 mg/kg B.W.at 8 h intervals in febrile calves.  相似文献   
29.
Data from post-mortem and field studies were obtained that discussed poisoning in ostriches following ingestion of toxic plants. From the notes, all plants studied caused death in ostriches and there was systemic organ damage. Poisoning from Sarcostemma viminale (Melktou) resulted in beak patting, muscular tremors and head flopping, followed by collapse and violent kicking before death. Ingestion of Combretum oatesii (Red wings) seeds from plants in free grazing pastures resulted in vomiting, restlessness, eyelid flicking, collapse and kicking movements. Dichapetalum cymosum (Gifblaar) killed an ostrich after episodes of shaking legs, rapid respiration and bradycardia and hyperaemia of the lungs, liver and kidneys. Poisoning from Senecio sceleratus (Ragwort) caused skin haemorrhages and bleeding in tracheal mucous membranes, the pericardium, diaphragm and interperitoneal membrane. Consumption of drupes from Melia azedarach (Syringa berry) caused muscle tremors, kicking movements and respiratory distress. Lantana camara (Cherry pie) poisoning resulted in extremely inflamed eyes with copious yellow exudates extending down their beaks and onto their necks. Bentonite was administered by gavage at a dose of 5 g/kg. Poisoning in these cases is usually associated with the farmer allowing his/her birds to roam free-range in paddocks in which toxic plants are growing. Toxic plants should be removed from grass cut for hay. The author is willing to send photographs of all poisonous plants if requested by a reader.  相似文献   
30.
The irrational use of antibiotics in humans and animals is highly related to the emergence and increase of antibiotic-resistant bacteria worldwide. A cross-sectional survey aimed at evaluating the current level of practices regarding antibiotic use in farm animals in Rwanda was carried out countrywide. Interviews were conducted on 229 farmers rearing different types of animals. The study has revealed that almost all respondent farmers could name at least one antibiotic used in farm animals and peni-streptomycin was named by most of them (95.6%). The use of antibiotics in farm animals was observed in the majority of respondents (97.4%). It was found that 44.4 and 26.5% of respondents reported that they used antibiotics for disease prevention and growth promotion, respectively. The use of non-prescribed antibiotics in animals was also reported by more than the half of respondent farmers (55.6%). The majority of farmers had a moderate level of practices regarding antibiotic use in farm animals (73.5%), very few had a high level (26%) and only one respondent had a low level. The high level of practices in regard to antibiotic use in animals was associated with the location of the farm, the type of reared animals, and the rearing system. The results of this study give an insight into antibiotics usage practices in farm animals in Rwanda. The generated information can guide sensitizations and promotions of the prudent use of antibiotics among farmers in order to limit the increase of antibiotic resistance in the country.  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