全文获取类型
收费全文 | 138292篇 |
免费 | 7866篇 |
国内免费 | 803篇 |
专业分类
林业 | 5920篇 |
农学 | 4582篇 |
基础科学 | 1075篇 |
16846篇 | |
综合类 | 25708篇 |
农作物 | 5151篇 |
水产渔业 | 6684篇 |
畜牧兽医 | 70416篇 |
园艺 | 1914篇 |
植物保护 | 8665篇 |
出版年
2019年 | 1417篇 |
2018年 | 2088篇 |
2017年 | 2361篇 |
2016年 | 2139篇 |
2015年 | 1983篇 |
2014年 | 2320篇 |
2013年 | 5042篇 |
2012年 | 4334篇 |
2011年 | 5279篇 |
2010年 | 3576篇 |
2009年 | 3488篇 |
2008年 | 5067篇 |
2007年 | 4710篇 |
2006年 | 4412篇 |
2005年 | 4176篇 |
2004年 | 3965篇 |
2003年 | 4019篇 |
2002年 | 3784篇 |
2001年 | 4279篇 |
2000年 | 4290篇 |
1999年 | 3427篇 |
1998年 | 1534篇 |
1997年 | 1387篇 |
1996年 | 1311篇 |
1995年 | 1448篇 |
1994年 | 1364篇 |
1993年 | 1293篇 |
1992年 | 2733篇 |
1991年 | 2932篇 |
1990年 | 2968篇 |
1989年 | 2802篇 |
1988年 | 2629篇 |
1987年 | 2612篇 |
1986年 | 2668篇 |
1985年 | 2488篇 |
1984年 | 2116篇 |
1983年 | 1879篇 |
1982年 | 1207篇 |
1979年 | 1882篇 |
1978年 | 1508篇 |
1977年 | 1300篇 |
1976年 | 1290篇 |
1975年 | 1360篇 |
1974年 | 1668篇 |
1973年 | 1686篇 |
1972年 | 1631篇 |
1971年 | 1521篇 |
1970年 | 1469篇 |
1969年 | 1447篇 |
1967年 | 1255篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
A total of 269 steers produced in a four-breed diallel mating design of Simmental, Limousin, Polled Hereford, and Brahman breeds were evaluated for the unadjusted and maintenance-adjusted total feed intake to total weight gain ratio. Time on feed ranged from 184 to 251 d. Covariate adjustments were made separately for age- and 12th rib fat-constant end points. Purebred, general combining ability, and maternal effects and heterosis were estimated. Effects of year, breed of dam, slaughter group, and days on feed accounted for most of the variation in feed conversion. Significantly higher unadjusted cumulative feed/gain ratios were found for steers from Brahman sires and for those from Simmental, Limousin, and Brahman dams. Adjustment to either fat- or age-constant values did not rerank breed groups, but a small reduction in the differences between these groups was detected for fat-constant efficiency. For maintenance-adjusted feed intake, progeny of Simmental and Limousin dams were less efficient than those of Polled Hereford and Brahman dams. Negative values for general combining ability, maternal effects, and heterosis would indicate less feed required per unit of weight gain. General combining ability for Polled Hereford crosses was negative and significant for cumulative feed/gain ratios, but no difference among dam breeds was found for the maintenance-adjusted ratio. Maternal effects for Limousin dams were positive and significant for all maintenance-adjusted ratios. Heterosis estimates for specific breed crosses were generally negative and ranged from -.87 to .22. 相似文献
982.
Effects of increasing photoperiod length on performance and health of broiler chickens 总被引:2,自引:0,他引:2
1. Broiler performance and health were compared from 0 to 42 d for lighting programmes consisting of near-continuous light 23L:1D (23L), a lighting programme where photoperiod gradually increased from 6 to 23 h between days 4 and 35 (INC) or an increasing-lighting programme with 1 h of light mid-way through the scotophase (INC + 1). 2. The increasing lighting programmes reduced growth rate and increased gain:food ratio from 0 to 21 d; INC + 1 growth rate was intermediate to the 23 L and INC treatments. From 0 to 42 d there were no differences in growth rate or gain:food ratio among lighting treatments. Males grew faster, ate more food and converted food more efficiently than females. 3. The increasing-lighting programmes (INC and INC + 1) resulted in less skeletal disease than the 23L control. The incidence of sudden death syndrome (SDS) and mortality other than SDS were numerically lower for the increasing lighting treatments. More males died as a result of SDS and were affected by skeletal defects than females. 4. In terms of health, increasing lighting programmes were superior to near-continuous light for broiler chickens. 相似文献
983.
L J Myers 《Veterinary Clinics of North America: Small Animal Practice》1991,21(2):389-389
The need to evaluate sensory function in the dog is discussed. A group of techniques that use innate behaviors (species-typical behaviors) and are effective in the evaluation of sensory function of domestic animals are described. Techniques to measure olfactory, gustatory, auditory, and visual function are included. 相似文献
984.
K E Brennan P J Ihrke 《Journal of the American Veterinary Medical Association》1983,182(11):1201-1204
A retrospective study of 182 cases of grass awn migration in dogs and cats seen during a 1-year period was performed. The 182 cases comprised 61% of all foreign body-related cases during that year. Compared with the total hospital population, there was an increased prevalence of grass awn problems in the Springer Spaniel, Golden Retriever, Brittany Spaniel, and Airedale Terrier, but a decreased prevalence in German Shepherd Dogs, Miniature Poodles, and Dachshunds. The most common site of grass awn localization was the external ear canal, involving 51% of grass awn cases. Other common sites of grass awn localization included the interdigital webs, eye, nose, lumbar area, and thoracic cavity. Only 8 of the 182 animals were cats and 7 of the 8 had ocular involvement. 相似文献
985.
Cerebellar degeneration in dairy calves: clinical, pathologic, and serologic features of an epizootic caused by bovine viral diarrhea virus 总被引:1,自引:0,他引:1
T M Wilson A deLahunta L Confer 《Journal of the American Veterinary Medical Association》1983,183(5):544-547
Three of nine dairy calves born in the spring/summer wee severely ataxic at birth. Necropsy of the 3 affected calves revealed severe cerebellar degeneration (hypoplasia). Clinical signs were inapparent in the adult cows. Serum neutralization titers of the cows and calves indicated high bovine viral diarrhea titers. 相似文献
986.
The Effects of Cesarean Section Anesthesia on Heat Loss and Heat Production in the Newborn Rabbit 下载免费PDF全文
The newborn of some smaller animals rely upon heat produced by nonshivering thermogenesis in the brown fat to prevent a fall in body temperature after birth. Because of their pharmacological properties, some drugs may affect nonshivering thermogenesis. Therefore, in this study, the ability of newborn rabbits delivered under Innovar-Vet, ketamine hydrochloride, methoxyflurane and epidural anesthesia to maintain the rectal, subcutaneous interscapular and lumbar temperature was investigated at an ambient temperature of 35°C or 22°C and the results compared with control newborns delivered without anesthesia. When the newborns were exposed to 35°C, the anesthetics studied had no effect on the ability of the newborn to maintain the rectal temperature and the subcutaneous temperature over the interscapular fat pad was similar to the lumbar subcutaneous temperature thereby indicating that nonshivering thermogenesis was not activated. However, at an ambient temperature of 22°C Innovar-Vet or methoxyflurane reduced the temperature difference between interscapular and lumbar temperatures to 1.6°C compared to 2.5°C in controls and the difference between core temperature and ambient temperature to 3.5°C greater compared to 7.5°C in controls. Ketamine hydrochloride or lidocaine hydrochloride plus meperidine has less effect because these compounds lack adrenergic blocking properties. These data suggest that newborns delivered under anesthetics or tranquillizers that have adrenergic blocking properties require a warm (35°C) environment to prevent a fall in core temperature. 相似文献
987.
Detecting anti-Treponema hyodysenteriae antibodies in swine serum using immunofluorometry. 下载免费PDF全文
An indirect fluorescent antibody test was adapted for measuring serum anti-Treponema hyodysenteriae antibodies with a fluorometer. The immunofluorescence was recorded as fluorescent signal units. Cultures of T. hyodysenteriae and Treponema innocens were used as antigen. There was a significant (P less than 0.01) correlation between the immunofluorescence recorded with the fluorometer and that evaluated visually with a microscope. The swine exposed orally to swine dysentery infective inoculum and subsequently hyperimmunized by the intravenous inoculation of live cultures of T. hyodysenteriae had the highest average fluorescent signal unit, which was 104.5. There was a significant (P less than 0.01) correlation between the level of anti-T. hyodysenteriae antibody and the interval length between the last day of diarrhea and the day of bleeding. However, in measuring fluorescent signal units in serum from swine infected with nonpathogenic large spirochetes, (T. innocens), there was also a significant (P less than 0.01) correlation between T. hyodysenteriae and T. innocens as antigen. The coefficient of variation of the average fluorescent signal unit for a highly positive serum and a highly negative serum between 16 runs of assays were 5.7% and 19% respectively; the coefficient of variation of the average fluorescent signal unit for duplicate samples on 358 serum samples tested was 5.8%. 相似文献
988.
Barber SM McLaughlin BG Fretz PB 《The Canadian veterinary journal. La revue veterinaire canadienne》1983,24(2):46-49
A one month old Quarterhorse colt was presented after a week history of bilateral nasal discharge and respiratory difficulty. The cervical esophagus was greatly dilated, tortuous and filled with diluted milk. A nasogastric tube could not be passed beyond the base of the heart. An aspiration pneumonia was found at postmortem examination and the esophageal segment from the pharynx to the base of the heart was dilated, thin-walled, had degenerative muscular changes, and a reduction in size and number of ganglion cells of the myenteric plexus. Muscular hypertrophy of the terminal esophagus had reduced its lumen size. Some similarities and disparities of this condition to achalasia of man and megaesophagus of dogs are discussed. 相似文献
989.
Genetic diversity,anti‐microbial resistance,plasmid profile and frequency of the Vi antigen in Salmonella Dublin strains isolated in Brazil 下载免费PDF全文
F. P. Vilela M. R. Frazão D. P. Rodrigues R. G. Costa M. R. T. Casas S. A. Fernandes J. P. Falcão F. Campioni 《Zoonoses and public health》2018,65(1):e34-e43
Salmonella Dublin is strongly adapted to cattle causing enteritis and/or systemic disease with high rates of mortality. However, it can be sporadically isolated from humans, usually causing serious disease, especially in patients with underlying chronic diseases. The aim of this study was to molecularly type S. Dublin strains isolated from humans and animals in Brazil to verify the diversity of these strains as well as to ascertain possible differences between strains isolated from humans and animals. Moreover, the presence of the capsular antigen Vi and the plasmid profile was characterized in addition to the anti‐microbial resistance against 15 drugs. For this reason, 113 S. Dublin strains isolated between 1983 and 2016 from humans (83) and animals (30) in Brazil were typed by PFGE and MLVA. The presence of the capsular antigen Vi was verified by PCR, and the phenotypic expression of the capsular antigen was determined serologically. Also, a plasmid analysis for each strain was carried out. The strains studied were divided into 35 different PFGE types and 89 MLVA‐types with a similarity of ≥80% and ≥17.5%, respectively. The plasmid sizes found ranged from 2 to >150 kb and none of the strains studied presented the capsular antigen Vi. Resistance or intermediate resistance was found in 23 strains (20.3%) that were resistant to ampicillin, ciprofloxacin, chloramphenicol, imipenem, nalidixic acid, piperacillin, streptomycin and/or tetracycline. The majority of the S. Dublin strains studied and isolated over a 33‐year period may descend from a common subtype that has been contaminating humans and animals in Brazil and able to cause invasive disease even in the absence of the capsular antigen. The higher diversity of resistance phenotypes in human isolates, as compared with animal strains, may be a reflection of the different anti‐microbial treatments used to control S. Dublin infections in humans in Brazil. 相似文献
990.
I. Hajek F. Kettner V. Simerdova C. Rusbridge P. Wang B. A. Minassian V. Palus 《The Journal of small animal practice》2016,57(11):650-652
Lafora disease is a fatal genetic disorder characterised by neurotoxic deposits of malformed insoluble glycogen. In humans it is caused by mutation in the EPM2A or NHLRC1 genes. There is a known mutation in miniature wirehaired dachshunds which has not been documented in other dog breeds, including beagles, in which the disease is relatively commonly reported. This case report describes the causative defect in two affected beagles, namely the same massive expansion as in miniature wirehaired dachshunds of a 12‐nucleotide repeat sequence that is unique to the canine NHLRC1 gene. This is the first mutation described in beagles with Lafora disease, and so far the only Lafora disease genetic variant in dogs. 相似文献