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   2880篇
  免费   287篇
  国内免费   1篇
林业   245篇
农学   125篇
基础科学   27篇
  625篇
综合类   96篇
农作物   165篇
水产渔业   433篇
畜牧兽医   1145篇
园艺   67篇
植物保护   240篇
  2024年   7篇
  2023年   40篇
  2022年   52篇
  2021年   127篇
  2020年   133篇
  2019年   160篇
  2018年   159篇
  2017年   172篇
  2016年   170篇
  2015年   128篇
  2014年   157篇
  2013年   179篇
  2012年   229篇
  2011年   238篇
  2010年   124篇
  2009年   114篇
  2008年   161篇
  2007年   139篇
  2006年   125篇
  2005年   86篇
  2004年   79篇
  2003年   68篇
  2002年   65篇
  2001年   49篇
  2000年   41篇
  1999年   24篇
  1998年   5篇
  1997年   16篇
  1996年   5篇
  1995年   10篇
  1994年   7篇
  1993年   3篇
  1992年   7篇
  1991年   10篇
  1990年   8篇
  1989年   14篇
  1988年   6篇
  1985年   10篇
  1984年   4篇
  1983年   5篇
  1978年   5篇
  1977年   2篇
  1974年   2篇
  1972年   2篇
  1971年   2篇
  1970年   4篇
  1934年   2篇
  1926年   1篇
  1925年   1篇
  1908年   1篇
排序方式: 共有3168条查询结果,搜索用时 15 毫秒
81.
The corneal endothelium is essential for the maintenance of the corneal transparency. The aim of this study was to examine the morphology of the endothelial surface and perform morphometric analysis of the normal corneal endothelial cells of the Magellanic penguin (Spheniscus magellanicus) using scanning electron microscopy. The present work demonstrates that the corneal endothelium of the Magellanic penguin is similar to those described in other vertebrates.  相似文献   
82.
Increased dietary protein consumption is thought to cause calciuresis, a negative calcium balance and increased bone loss that may result in skeletal deformities and fracture. To explore this hypothesis, 40 approximately 100-day-old meat-type Merino ram lambs were fed, for 6 months, diets with an increasing crude protein (CP) content (114, 142, 171 and 190 g/kg DM) but approximately on an iso-nutrient basis with regard to metabolisable energy, calcium and phosphorus. Increased protein consumption modestly (NS) enhanced calciuresis and resulted in significant (P < or = 0.01) limb skewness. This could not, however, be ascribed to osteopaenic bones, and compared with animals consuming lower protein rations, the bone mineral density (BMD) and vertebral trabecular bone volume of animals fed high protein diets were significantly increased: the BMD of thoracic vertebrae was positively related to the CP intake (r = 0.62; P < or = 0.001). In animals consuming higher protein diets, skeletal radiology and quantitative bone histology revealed no evidence of increased bone turnover as would be expected in animals that are in negative calcium balance. No relationship existed between limb skewness and the growth rate of lambs. However, the ratio of Ca:P in the forelimb (r = -0.98), vertebrae (r = -0.72) and rib (r = -0.42) was found to be inversely correlated with increased protein intake and resulted from an increase in the phosphorus content of bone, while the amount of bone calcium was unaffected. We conclude that qualitative micro-architectural abnormalities, and not mere bone loss, may underlie the skeletal deformities induced by increased protein consumption in sheep.  相似文献   
83.
1. Inclusion of raw faba bean (Vicia faba L., minor) in the diet of growing chickens was shown to affect the performance of the birds and to produce a significant increase in the relative weight of the pancreas. This was attributable to dietary trypsin inhibitors. 2. Trypsin inhibitors also produced degenerative changes in pancreatic acinar cells. These were observed by light and electron microscopy. 3. Progressive cytopathological changes were observed in the intestinal tract. The duodenum, jejunum and ileum were altered, with extensive erosion, shortening and atrophy of microvilli. 4. The results endorsed previous findings obtained using different legume seed lines (Phaseolus spp). Faba bean produced similar local reactions in the pancreas and the intestine. This may be caused by the presence of lectins in the seeds.  相似文献   
84.
The veterinary herd health and production control program for year-round calving herds, presented in this paper, comprises a basic system and a flexible system. The basic system is a uniform system of data recording, standard veterinary activities and problem detection for all farms. Record keeping by the farmer includes the updating of a farm diary and a fertility—health chart and the preparation of an examination list before each veterinary farm visit. Record keeping by the veterinarian comprises the updating of a general inventory and four index lists at each monthly visit. The index lists contain all relevant parameters or index figures needed to monitor the various aspects of the farm. These lists serve to detect unwanted situations or problems and to initiate problem analysis. The farm checklist, with time-related veterinary and agricultural attention points, is consulted at each farm visit. In this way, no aspect is omitted in the control program. Problem analysis is performed in the flexible system. This comprises subsystems adaptable to the specific demands on the farm at a given moment and with a given problem. It indicates to what extent action is needed to solve the problem. Agricultural activities must be coupled to veterinary activities in order to provide the farmer with optimal advice. The farm checklist can be considered as a link between the two disciplines: the veterinarian can enlist the agricultural officer at the right moment.The frame-work of the basic system is introduced with emphasis on record keeping by the farmer, veterinary farm visits and the farm checklist.  相似文献   
85.
Summary Salmonellae were isolated from 17 out of 550 pigs and 3 out of 299 calves killed in the Uplands (Kenya) slaughterhouse but none from 455 steers slaughtered at Nakuru. Follow up visits to the farms of origin revealed no salmonella problems.
Resumen Se aisló salmonela de 17 de 550 cerdos y de 3 de 299 becerros sacrificados en el matadero de Uplands (Kenia). Pero no se encontró salmonela en 455 terneros sacrificados en otro matadero de Nakuru. Las visitas de inspección a los ranchos de donde provenian los animales no mostraron problema de salmonela.

Résumé Des Salmonelles ont été isolées chez 17 porcs sur un nombre total de 550 et chez 3 veaux sur un nombre total de 299, abattus à l'abattoir des Uplands (Kenya); aucune souche n'a été isolée à partir de 455 bouvillons abattus à Nakuru. A la suite de ces isolements, des visites effectuées dans les fermes d'origine ont montré qu'il n'existait aucun problème de Salmonellose.
  相似文献   
86.
87.
Ungulates are involved in the epidemiology of Borreliosis as maintenance hosts for vector tick species. We evaluated the prevalence of antibodies to Borrelia burgdorferi sensu lato in two different populations of southern chamois in Spain. Forty-six sera (40.4%) were positive at titres >/=1 : 64 using an indirect immunofluorescence assay (IFAT).  相似文献   
88.
Objective To evaluate the use of a combination of tiletamine/zolazepam and xylazine (TZX) in collared and white‐lipped peccaries and to compare its efficacy as an anesthetic technique with that of tiletamine/zolazepam and butorphanol (TZB). Study design Prospective experimental trial. Animals Seven white‐lipped peccaries (Tayassu pecari) (four females and three males) and four collared peccaries (Tayasu tajacu) (two males and two females). Methods Animal immobilization was attempted with TZX and TZB (IM) on two different occasions. Heart and respiratory rates (HR, RR), rectal temperature (RT), sedation, muscle relaxation, posture, auditory response and analgesia were evaluated every 15 minutes during immobilization. Induction, anesthesia, standing and walking time were determined after drug administration. Results Doses for white‐lipped peccaries were 1.23 ± 0.26 mg kg?1 (mean ± SD) of TZ and 1.23 ± 0.26 mg kg?1 of X, and 1.46 ± 0.09 mg kg?1 of TZ and 0.14 ± 0.008 mg kg?1 of B; doses for collared peccaries were 1.51 ± 0.29 mg kg?1 of TZ and 1.51 ± 0.29 mg kg?1 of X and 1.68 ± 0.02 mg kg?1 of TZ and 0.17 ± 0.002 mg kg?1 of B. In white‐lipped peccaries, both drug combinations provided a smooth induction and good immobilization for more than an hour. Anesthesia and standing times were significantly longer in animals given TZB, whereas walking time was significantly longer in animals given TZX. A significant decrease in HR was observed with both treatments. Respiratory rate decreased significantly with TZX, but the rate remained higher than with TZB. Induction and recovery quality in white‐lipped peccaries was better with TZB than with TZX. Neither protocol provided adequate immobilization in collared peccaries. Conclusion and clinical relevance At the doses described, TZB is effective in providing a long period of immobilization, whereas TZX is adequate for short to medium immobilization in white‐lipped peccaries. Neither drug combination was effective in collared peccaries at the doses given.  相似文献   
89.
OBJECTIVE: To determine duration and rates of recovery of Actinobacillus pleuropneumoniae and Haemophilus parasuis from 4 liquid media and 2 swab specimen transport systems and compare findings with those of Escherichia coli. SAMPLE POPULATION: One strain each of A pleuropneumoniae (biovar 1, serotype 1), H parasuis (serovar 5), and E coli (serotype O149:K91:H19). PROCEDURE: Strains were incubated in brain heart infusion broth supplemented with horse serum and other nutrients or in horse serum alone, with and without nicotinamide-adenine dinucleotide in both instances, for 150 days at 4 degrees C or room temperature (21 degrees C). Similarly, strains were tested in Stuart and Amies transport systems after storage at room temperature for 8 days. RESULTS: Colony counts greater than those of the initial inoculum were observed after incubation in horse serum for A pleuropneumoniae but not for H parasuis. Overall, incubation at 4 degrees C in the 4 liquid media resulted in longer recovery duration and higher rates than at room temperature. Culture of H parasuis resulted in lower recovery rates and shorter durations of recovery than culture of A pleuropneumoniae, except for culture in horse serum. Haemophilus parasuis survived longer than A pleuropneumoniae in the transport systems, and all organisms survived longer in the Amies system. CONCLUSIONS AND CLINICAL RELEVANCE: Survival of A pleuropneumoniae and H parasuis indicated that horse serum prolongs survivability, which may result in exposure of more animals during a prolonged period. The Amies system might be a good choice for collection of clinical samples from animals, especially for recovery of H parasuis.  相似文献   
90.
In this investigation, we determined the prevalence of the Ornithobacerium rhinotracheale (ORT) infection in broilers and broiler breeders in southern Brazil. We also correlated the presence of antibodies in broilers with performance. Sera from 1550 broilers from 50 flocks were collected during the slaughter time in nine companies with federal veterinary inspection of the state of Rio Grande do Sul. Sera from 480 meat-type breeders of 40 flocks from 14 companies in southern Brazil were also analyzed by enzyme-linked immunosorbent assay, and the prevalence of antibodies was determined. The prevalence of ORT antibodies in broiler flocks was 63.83%, but in each individual flock only 6.52% of the birds were positive. The prevalence in broiler breeder flocks was 100.00%, and in each individual flock 94.62% of the birds were positive. There was a positive correlation between the presence of antibodies to ORT and decreased body weight in broilers. There was no significant correlation between presence of antibodies to ORT and age, lineage, efficiency index, feed conversion, and mortality. There was a positive correlation between the presence of respiratory signs and antibodies to ORT, although the reverse correlation was not significant. These results confirm that ORT is present and widespread in broilers and broiler breeders in southern Brazil.  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