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   456篇
  免费   21篇
林业   6篇
农学   2篇
  35篇
综合类   40篇
农作物   50篇
水产渔业   29篇
畜牧兽医   296篇
园艺   4篇
植物保护   15篇
  2023年   3篇
  2021年   5篇
  2020年   8篇
  2019年   11篇
  2018年   12篇
  2017年   5篇
  2016年   4篇
  2015年   9篇
  2014年   6篇
  2013年   19篇
  2012年   22篇
  2011年   27篇
  2010年   13篇
  2009年   14篇
  2008年   18篇
  2007年   15篇
  2006年   23篇
  2005年   21篇
  2004年   13篇
  2003年   17篇
  2002年   13篇
  2001年   20篇
  2000年   12篇
  1999年   9篇
  1997年   3篇
  1996年   5篇
  1995年   3篇
  1992年   9篇
  1991年   5篇
  1990年   15篇
  1989年   8篇
  1988年   6篇
  1987年   12篇
  1986年   7篇
  1985年   6篇
  1983年   3篇
  1980年   2篇
  1979年   4篇
  1973年   2篇
  1972年   2篇
  1971年   4篇
  1970年   4篇
  1969年   3篇
  1966年   2篇
  1947年   4篇
  1946年   8篇
  1945年   7篇
  1944年   6篇
  1943年   6篇
  1941年   3篇
排序方式: 共有477条查询结果,搜索用时 15 毫秒
51.
Neospora caninum, an obligate intracellular protozoan parasite, is the causative agent of bovine neosporosis, an important disease affecting the reproductive performance of cattle worldwide. Currently there is no effective vaccine available to prevent N. caninum infection in cattle. In this study, we examined the feasibility of developing a live, recombinant N. caninum vaccine using Brucella abortus vaccine strain RB51 as the expression and delivery vector. We generated two recombinant RB51 strains each expressing SRS2 (RB51/SRS2) or GRA7 (RB51/GRA7) antigens of N. caninum. BALB/c mice immunized by single intraperitoneal inoculation of the recombinant RB51 strains developed IgG antibodies specific to the respective N. caninum antigen. In vitro stimulation of splenocytes from the vaccinated mice with specific antigen resulted in the production of interferon-gamma, but not IL-5 or IL-10, suggesting the development of a Th1 type immune response. Upon challenge with N. caninum tachyzoites, mice vaccinated with strain RB51/SRS2, but not RB51/GRA7, showed significant resistance to cerebral infection when compared to the RB51 vaccinated mice, as determined by the tissue parasite load using a real-time quantitative TaqMan assay. Interestingly, mice vaccinated with either strain RB51 or RB51/GRA7 also contained significantly lower parasite burden in their brains compared to those inoculated with saline. Mice vaccinated with strain RB51/SRS2 or RB51/GRA7 were protected to the same extent as the strain RB51 vaccinated mice against challenge with B. abortus virulent strain 2308. These results suggest that a recombinant RB51 strain expressing an appropriate protective antigen(s), such as SRS2 of N. caninum, can confer protection against both neosporosis and brucellosis.  相似文献   
52.
OBJECTIVE: To determine complications and neurologic outcomes associated with dexamethasone administration to dogs with surgically treated thoracolumbar intervertebral disk herniation, compared with dogs not receiving dexamethasone. DESIGN: Retrospective case series. ANIMALS: 161 dogs with surgically confirmed thoracolumbar disk herniation. PROCEDURES: Medical records from 2 hospitals were used to identify dogs that had received dexamethasone < 48 hours prior to admission (dexamethasone group dogs), dogs that received glucocorticoids other than dexamethasone < 48 hours prior to admission (other-glucocorticoid group dogs), and dogs that received no glucocorticoids (nontreatment group dogs). Signalment, neurologic injury grade, laboratory data, and complications were extracted from medical records. RESULTS: Dexamethasone group dogs were 3.4 times as likely to have a complication, compared with other-glucocorticoid or nontreatment group dogs. Dexamethasone group dogs were 11.4 times as likely to have a urinary tract infection and 3.5 times as likely to have diarrhea, compared with other-glucocorticoid or nontreatment group dogs. No differences in neurologic function at discharge or recheck evaluation were detected among groups. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that treatment with dexamethasone before surgery is associated with more adverse effects, compared with treatment with glucocorticoids other than dexamethasone or no treatment with glucocorticoids, in dogs with thoracolumbar intervertebral disk herniation. In this study population, no difference in outcome was found among groups. These findings suggest that the value of dexamethasone administration before surgery in dogs with thoracolumbar disk herniation should be reconsidered.  相似文献   
53.
Neospora caninum, Sarcocystis spp, and Toxoplasma gondii are related coccidian parasites that can cause abortion and neonatal mortality in animals. In addition, T gondii and certain species of Sarcocystis are zoonotic. This article reviews information on the etiology, diagnosis, control, and prevention of these diseases.  相似文献   
54.
At least three species of Sarcocystis (S. neurona, S. falcatula, S. speeri) have recently been shown to use opossums of the genus Didelphis as their definitive host. In order to evaluate the evolutionary relationships among Sarcocystis spp. isolates from the Americas, and to determine whether organisms representing the same parasite lineages are transmitted north and south of the Panamanian isthmus, we inferred the phylogenetic relationships from nucleotide sequence variation in parasites isolated from three opossum species (D. virginiana, D. albiventris, D. marsupialis). In particular, we used variation in the 25/396 marker to compare several isolates from Brazil, Argentina, and the United States to each other and to cloned S. neurona and S. falcatula whose morphology and host affinities have been defined in the laboratory. S. neurona was identified from a Brazilian D. albiventris, as well as from North American D. virginiana. Parasites resembling the Cornell isolate of S. falcatula are transmitted both south and north of the Panamanian isthmus by D. albiventris and D. virginiana, respectively. Distinct attributes at two genetic loci differentiated a Brazilian isolate of S. falcatula from all other known parasite lineages. We confirm S. neurona as the causative agent of recently reported neurologic disease in Southern sea otters, Enhydra lutris nereis. And we found that S. speeri could not be compared to the other opossum-derived Sarcocystis isolates on the basis of nucleotide variation at the 25/396 locus. The widespread distribution of certain species of Sarcocystis may derive from their ability to parasitize migratory bird hosts in their intermediate stage.  相似文献   
55.
Infrared spectra of material captured from comet 81P/Wild 2 by the Stardust spacecraft reveal indigenous aliphatic hydrocarbons similar to those in interplanetary dust particles thought to be derived from comets, but with longer chain lengths than those observed in the diffuse interstellar medium. Similarly, the Stardust samples contain abundant amorphous silicates in addition to crystalline silicates such as olivine and pyroxene. The presence of crystalline silicates in Wild 2 is consistent with mixing of solar system and interstellar matter. No hydrous silicates or carbonate minerals were detected, which suggests a lack of aqueous processing of Wild 2 dust.  相似文献   
56.
The objective of this study was to assess the effects of in‐feed chlortetracycline (CTC) as a measure of preventing or minimizing infectious problems of reproductive failure in gilts and sows. In a farm of 400 Large White × Landrace gilts and sows with a clinical history of porcine respiratory and reproductive syndrome (PRRS) virus, the animals were treated with CTC. Treatment consisted of 10 g CTC sow/day for 15 days every 3 months. It improved the health status of sows by decreasing post‐farrowing clinical mastitis and vaginal discharges, abortions, return‐to‐oestrus and irregular return‐to‐oestrus rates. These beneficial effects had a positive impact on the performance of the litter. More piglets were born live and weaned. These positive effects improved with repeated use of CTC. The serological evidence of PRRS virus, Leptospira spp. and Chlamydia spp. and the subsequent beneficial use of the antimicrobial agent indicate that reproductive failure, possibly resulting from the bacterial agents can be controlled with in‐feed use of broad spectrum antimicrobials.  相似文献   
57.
The laryngeal muscles of 18 horses were examined histologically. The neurogenic changes found in each muscle were scored by four reviewers and the results evaluated statistically. Fifteen of these horses had endoscopic evidence of abnormal laryngeal function, three of which were defined as having adductor paralysis. Measurement of muscle fibre area in two horses with idiopathic laryngeal hemiplegia (ILH) was performed. In the quantitative study of neurogenic change, the adductor muscles were more significantly affected than the abductor muscle. This was also true in the clinical cases of ILH where measurement of muscle fibre area demonstrated that the lateral cricoarytenoid (adductor) muscles showed a wider range of pathological changes than the dorsal cricoarytenoid muscle (abductor). Those horses with the most severe muscle pathology also had the most abnormal endoscopic findings. The propensity for denervation of the adductor muscles should provide clues as to the pathogenesis and natural history of horses with sub-clinical laryngeal disease and ILH.  相似文献   
58.
Lesions in fetal pigs with transplacentally-induced toxoplasmosis   总被引:1,自引:0,他引:1  
Two sows (Nos. 1, 2) were each fed 1,000 Toxoplasma gondii oocysts. Sow No. 1 was fed oocysts at 60 day of gestation and was euthanatized 49 days later. Sow No. 2 was fed oocysts at day 45 of gestation and euthanatized 62 days later. Sow No. 1 had eight dead fetuses of which one was mummified and unsuitable for histologic study. Sow No. 2 had 11 fetuses, of which four fetuses were mummified and unsuitable for histologic examination, two fetuses were dead and five were live. Lesions and Toxoplasma parasites were identified in seven fetuses from sow No. 1 and three fetuses from sow No. 2. No lesions were found in four fetuses from sow No. 2. Toxoplasma gondii was present in trophoblasts and produced areas of necrosis of the chorioallantois with focal placental separation. The predominant lesions were necrotizing placentitis, non-suppurative encephalomyelitis, and myocardial degeneration, necrosis and mineralization. Numerous tachyzoites were seen in trophoblast cells lining areolae in placenta.  相似文献   
59.
60.
Coccidiosis in swine   总被引:1,自引:0,他引:1  
It is clear that although the clinical history, pathologic lesions, and endogenous stage life cycle of I. suis are well understood, the epidemiology of this parasite is not understood or is misunderstood. Consequently, treatment of individual piglets and prophylactic use of coccidiostats in sows have not been consistently rewarding. The best control at present is achieved through use of extensive sanitation, particularly steam cleaning. The incidence of clinical coccidiosis in piglets continues to be a major component (approximately 20 per cent) in the differential etiology of scours in baby pigs.  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