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   59459篇
  免费   3355篇
  国内免费   37篇
林业   3159篇
农学   2271篇
基础科学   363篇
  7632篇
综合类   6849篇
农作物   2152篇
水产渔业   3234篇
畜牧兽医   33087篇
园艺   736篇
植物保护   3368篇
  2019年   515篇
  2018年   1000篇
  2017年   1084篇
  2016年   1042篇
  2015年   892篇
  2014年   1045篇
  2013年   2380篇
  2012年   1853篇
  2011年   2258篇
  2010年   1475篇
  2009年   1392篇
  2008年   2065篇
  2007年   2080篇
  2006年   1957篇
  2005年   1819篇
  2004年   1710篇
  2003年   1694篇
  2002年   1561篇
  2001年   2343篇
  2000年   2201篇
  1999年   1734篇
  1998年   687篇
  1997年   625篇
  1996年   603篇
  1995年   676篇
  1994年   574篇
  1993年   563篇
  1992年   1265篇
  1991年   1401篇
  1990年   1451篇
  1989年   1335篇
  1988年   1246篇
  1987年   1231篇
  1986年   1171篇
  1985年   1105篇
  1984年   922篇
  1983年   725篇
  1982年   528篇
  1979年   792篇
  1978年   617篇
  1977年   470篇
  1976年   525篇
  1975年   502篇
  1974年   624篇
  1973年   605篇
  1972年   634篇
  1971年   601篇
  1970年   588篇
  1969年   537篇
  1967年   497篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Summary A serological survey of cattle in Mali was carried out to determine the prevalence of antibody activity toBabesia bovis andB. bigemina. It was found that the level ofB. bovis infection as indicated by antibody activities was too low to be of immediate concern. However, the serological prevalence ofB. bigemina was high and this may indicate a potential disease problem. It was also found that when zebu and N'Dama cattle grazed together the N'Dama were twice as likely to have positive titres toBabesia as were the zebus.
Prevalencia Serologica De Babesiosis Bovina En Mali
Resumen Se llevó a cabo un análisis serológico en Malí, para detectar la prevalencia deBabesia bovis yBabesia bigemina. Se encontró, que la prevalencia serológica deB. bovis es baja para considerar la enfermedad una amenaza inmediata. Sinembargo, la prevalencia deB. bigemina fué alta, un problema potencial. Tambien se encontró, que cuando el ganado Cebu y N'Dama pastorea junto, el N'Dama presenta el doble de títulos serológicos deB. bigemina.

Frequence Serologique De La Babesiose Bovine Au Mali
Résumé Une enquête sérologique sur le bétail au Mali a été effectuée pour déterminer la fréquence de l'activité des anticorps àBabesia bovis etB. bigemina. On a trouvé que le degré d'infection àB. bovis tel qu'indiqué par les réactions anticorps était trop faible pour constituer un souci immédiat. Cependant la fréquence sérologique deB. bigemina était élevée, ce qui peut indiquer un problème pathologique potentiel. On a aussi noté que lorsque les zébus et les N'Dama broûtaient ensemble, les N'Dama avaient deux fois plus de chance d'avoir des titres positifs àBabesia que ne l'avaient les zébus.
  相似文献   
992.
A ten year old Hereford bull with Chediak-Higashi syndrome was examined at necropsy after a lifelong history of recurrent bacterial infections. Amyloidosis, which has not been previously reported in Chediak-Higashi, was identified in liver, spleen and kidney.  相似文献   
993.
A two year old Thoroughbred gelding, presented with guttural pouch hemorrhage, had the internal and external carotid arteries ligated. Guttural pouch mycosis was detected on endoscopic examination. After one month of topical antifungal therapy, the horse was returned and euthanized because of recurrent epistaxis. A bacterial infection of the guttural pouch with associated ulceration and hemorrhage from the maxillary artery was found at necropsy.

A two year old grade gelding had ulceration and hemorrhage from the external carotid artery. Utilizing balloon-tipped catheters and arterial ligation, hemestasis was achieved in the internal carotid artery and the external carotid artery and its branches. Mycotic ulceration of the internal carotid artery was detected endoscopically and treated with local antifungal therapy for one month. Thirty-three days postoperatively the horse returned, bleeding from a lesion in the maxillary artery. The rationale for surgical intervention to prevent epistaxis associated with guttural pouch mycosis and possible etiologies for postsurgical epistaxis are discussed.

  相似文献   
994.
Forty-seven healthy, owned dogs were vaccinated with Madivak and 85 with Rabisin. Geometric mean titres of 17.40 and 1.03 IU/ml were measured by the rapid immunofluorescent focus inhibition test 30–40 and 350–370 days, respectively, after a single injection. Four out of 130 (3.1%) and 18 out of 106 (17% ) dogs had a titre of less than 0.5 IU/ml in serum 30–40 and 350–370 days after vaccination. Twenty-one dogs (19.8%) had a titre of 0.5 IU/ml 350–370 days after vaccinaton. There was no significant difference in antibody levels between animals vaccinated with Rabisin or Madivak. Our results indicate that a booster is always necessary after a single injection to ensure that all dogs have a lasting antibody titre.  相似文献   
995.
Thromboembolic meningoencephalitis (TEME) caused by Huemophilus somnus infection was diagnosed for the first time in New Zealand in an eight month old bull calf. Clinical signs included pyrexia, excessive salivation, recumbency, opisthotonus and rigidity of the front legs. Multiple red, malacic foci (1-10 mm in diameter) were visible grossly on the surface of the cerebrum and cerebellum, and were scattered throughout the brain parenchyma. Histologically these lesions consisted of focal haemorrhage, necrosis and neutrophilic infiltration. Fibrin thrombi and colonies of gram negative bacteria were present in many small blood vessels within necrotic foci. An organism with the morphological and biochemical characteristics of Haemophilus somnus was cultured from the brain. Although TEME is an important disease of feedlot cattle in North America and Europe it is relatively uncommon in cattle grazing pasture and is therefore unlikely to become a major problem in New Zealand.  相似文献   
996.
Rickets was diagnosed in a group of 80 yearling Angus steers wintered for three months on a crop of swedes (Brassica napus) in the Kimbolton area. Growth rate was poor and several steers developed lameness during the final three weeks on the crop. Five animals were euthanased after developing bone fractures. Necropsy of two animals revealed soft ribs, enlarged costochondral junctions and irregularly thickened growth plates in long bones. Histologically there were islands of hypertrophic cartilage within metaphyses and disruption of metaphyseal trabeculae. Thickened, irregular, trabeculae were sometimes lined by wide osteoid seams. Phosphorus deficiency was considered to be the most likely aetiology of the osteodystrophy. The dry matter content of the swedes was only six percent, and in order to satisfy their phosphorus requirements each steer would have had to ingest approximately 330 kg of swedes per day. Rickets is an uncommon disease of grazing animals in New Zealand and to our knowledge this is the first report of its occurrence in cattle.  相似文献   
997.
Weakness, lethargy, ataxia, lateral recumbency, limb paddling, tremors, salivation, and diarrhea were observed in newborn pigs on a commercial swine farm. Many pigs became moribund and died. All had been treated with an aerosol wound spray containing 2.5% chlorpyrifos. A controlled study was undertaken to determine whether the aerosol spray was the cause of these clinical signs. Pigs exposed to aerosol spray containing 2.5% chlorpyrifos at 3 hours (n = 4) and 6 hours (n = 3) after birth developed clinical signs similar to those on the farm; none survived. Pigs exposed at 24 hours (n = 5) after birth developed clinical signs consistent with those that had developed in pigs on the farm; 3 died and 2 survived. Of 3 pigs exposed to the same spray at 36 hours after birth, 1 developed tremors 7.5 hours later and diarrhea 9 hours later, then returned to normal.  相似文献   
998.
Effects of protein concentration on responses to dietary lysine by chicks   总被引:2,自引:0,他引:2  
Chicks were fed on diets varying in crude protein (CP) content (140 to 280 g/kg diet) in either 8 steps, experiment 1, or 6 steps, experiment 2. Protein composition was held constant in each experiment. At each protein concentration, 5 (experiment 1) or 6 (experiment 2) concentrations of lysine were tested, ranging from 40 to 60 g/kg CP. Growth rate and efficiency of food utilisation to 21 d of age responded to increasing dietary protein contents up to about 230 g CP/kg. An estimate of lysine requirement at each protein concentration was obtained by fitting a quadratic curve to the response data and calculating the dose of lysine (g/kg CP) needed to maximise either growth rate or gain/food ratio. Although no growth response to dietary protein was obtained between 240 and 280 g CP/kg, the amount of lysine needed to maximise growth and gain/food ratio over this range increased systematically when expressed as g/kg diet, but remained constant if expressed as g/kg CP. The regression of lysine required (g/kg diet) for maximum performance (growth or food efficiency) on CP (g/kg diet) was strictly linear for both responses in both experiments throughout the entire range studied (140 g CP/kg to 280 g CP/kg). The estimated lysine requirement was 0.053 of the CP in experiment 1 and 0.055 of the CP in experiment 2. It is concluded that a fixed ratio of lysine to protein should be specified in practical diet formulation, rather than a minimum dietary concentration of lysine. This would ensure that, if the dietary protein content rises above a prescribed minimum value in least-cost formulation, an appropriate adjustment will automatically be made to the lysine content of the solution.  相似文献   
999.
An equation was developed that describes the probability of eliminating egg-borne Mycoplasma meleagridis (MM) of turkeys by egg treatment. Probability (P) of MM elimination was described in terms of four parameters: pretreatment prevalence of MM, alpha; treatment failure rate, beta; number of eggs treated, n; and hatching rate, h. The eradication equation, based on the Poisson probability distribution, was P(0) = e-n alpha beta h. Probabilities derived from 12 hypothetical MM-eradication situations showed that increasing the size of any or all of the parameters decreased the likelihood of eradication. Use of the predictive equation as a planning tool in a successful MM-eradication program is demonstrated.  相似文献   
1000.
The productivity of sheep and goats was examined under three management systems. A regime by which each animal received five doses of fenbendazole in a year gave similar results in terms of survival and liveweight gain to monthly dosing. Sheep kept by traditional methods without anthelmintic treatment survived and grew less well than goats. In contrast goats grew better and produced more young under traditional management although they were in general lighter than sheep.  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