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   19304篇
  免费   143篇
  国内免费   2篇
林业   3757篇
农学   1463篇
基础科学   142篇
  3236篇
综合类   924篇
农作物   2423篇
水产渔业   2000篇
畜牧兽医   2332篇
园艺   1155篇
植物保护   2017篇
  2023年   17篇
  2022年   52篇
  2021年   80篇
  2020年   51篇
  2019年   56篇
  2018年   2785篇
  2017年   2769篇
  2016年   1245篇
  2015年   162篇
  2014年   150篇
  2013年   195篇
  2012年   982篇
  2011年   2317篇
  2010年   2221篇
  2009年   1385篇
  2008年   1509篇
  2007年   1733篇
  2006年   224篇
  2005年   239篇
  2004年   238篇
  2003年   270篇
  2002年   165篇
  2001年   105篇
  2000年   106篇
  1999年   39篇
  1998年   17篇
  1997年   10篇
  1996年   11篇
  1995年   19篇
  1994年   7篇
  1993年   20篇
  1992年   31篇
  1991年   12篇
  1990年   22篇
  1989年   23篇
  1988年   24篇
  1987年   13篇
  1986年   6篇
  1985年   13篇
  1984年   10篇
  1983年   6篇
  1982年   6篇
  1981年   9篇
  1978年   6篇
  1977年   8篇
  1974年   8篇
  1973年   11篇
  1971年   4篇
  1968年   8篇
  1966年   4篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
For the evaluation of hormonal control of spermiation in fish, a method to quanify the spermiation response of mature Rhynchocypris oxycephalus (Sauvage and Dabry) to hormonal therapy is described. Spermatocrit was determined after 7 min centrifugation at 18,000 ± g and sperm density was estimated by a standard hemocytomer method. Sperm density can be predicted from spermatocrit since their relationship is linear as described by the regression equation, Y = 3.68X - 27.18 ( R 2 = 0.82, N = 50). where Y is spermatocrit and × is sperm density. Milt production by mature R. oxycephalus was highest at 24 h after injection of 1,000 IU human chorionic gonadotropin (HCG) and 50 μg luteinizing hormone-releasing hormone analogue (LHRHa) per kg body weight. Increased milt production coincided with low spermatocrit and sperm density levels. These results demonstrate that spermiation in mature R. oxycephalus can be reliably evaluated by a spermatocrit method and that HCG and LHRHa are effective in stimulating of spermiation in this species.  相似文献   
3.
Effective radiographic interpretation requires a veterinarian who is knowledgeable of equine limb anatomy and the various principles that affect the resulting image. The normal and its variations must be recognized and understood before the abnormal can be confidently identified as pathologic. Proper patient positioning and sound radiographic technique are mandatory if reliable diagnostic radiographs are to be produced. This review emphasizes equine foot radiographic variations of normal and pseudolesions that occur with commonly used radiographic views performed in equine practice.  相似文献   
4.
A complete radiographic examination of the equine foot consists of properly exposed, processed, and positioned radiographs. For radiographic interpretation, in addition to knowing radiographic signs of disease, a knowledge of normal radiographic anatomy and possible insignificant anatomic variations is necessary.  相似文献   
5.
Based on a simple model, the possible effects of certification of planting material on the occurrence of leek rust in a region can be derived from information on the proportion of infected fields (v) and the proportion of newly planted fields with infected planting material (i) in that region. Ifv i, certification of planting material will be highly effective.  相似文献   
6.
The knowledge of the biochemical mode of action of 1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea (diflubenzuron) is presented, explaining the insecticidal effect. Like its structural analog, 1-(2,6-dichlorobenzyl)-3-(3,4-dichlorophenyl)urea (Du 19111), it inhibits chitin synthesis in the cuticle of larvae. Virtually complete inhibition was demonstrable 15 min after the application of diflubenzuron. Neither diflubenzuron nor Du 19111 has any effect upon chitinase activity either in vivo or in vitro. The insecticidal effect upon the cuticle, therefore, must be explained as an inhibition of chitin synthesis and not as an activation of chitin degradation. In contrast to the action of Du 19111, no accumulation of N-acetylglucosamine occurs upon treatment of larvae with diflubenzuron. Similarities and differences in the mode of action of both compounds are discussed, together with other effects reported in the literature.  相似文献   
7.
Brachiaria decumbens is an extremely productive tropical grass due to its aggressive growth habit and its adaptation to a varied range of soil types and environments. As a result of the vast availability, treated B. decumbens demonstrates as a promising local material that could be utilised as an improved diet for sheep and goats. Despite the fact that the grass significantly increases weight gains in grazing farm animals, there were many reports of general ill-thrift and sporadic outbreaks of photosensitivity in livestock due to the toxic compound of steroidal saponin found in B. decumbens. Ensiling and haymaking were found to be effective in removing toxin and undesirable compounds in the grass. Biological treatments using urea, activated charcoal, polyethylene glycol, and effective microorganisms were found to be useful in anti-nutritional factor deactivation and improving the nutritive values of feedstuffs. Besides, oral administration of phenobarbitone showed some degree of protection in sheep that fed on B. decumbens pasture. In this review, we aim to determine the effect of B. decumbens toxicity and possible treatment methods on the grass to be used as an improved diet for small ruminant.  相似文献   
8.
Papillomaviruses are non-enveloped, DNA viruses that infect skin and mucosa of a wide variety of vertebrates, causing neoplasias or simply persisting asymptomatically. Avian papillomaviruses, with six fully sequenced genomes, are the second most studied group after mammalian papillomaviruses. In this study, we describe the first oral avian papillomavirus, detected in the tongue of a dead Yorkshire canary (Serinus canaria) and in oral swabs of the same bird and other two live canaries from an aviary in Madrid, Spain. Its genome is 8,071 bp and presents the canonical papillomavirus architecture with six early (E6, E7, E1, E9, E2, E4) and two late open reading frames (L1 and L2) and a long control region between L1 and E6. This new avian papillomavirus L1 gene shares a 64% pairwise identity with FcPV1 L1, so it has been classified as a new species (ScPV1) within the Ethapapillomavirus genus. Although the canary died after showing breathing problems, there is no evidence that the papillomavirus caused those symptoms so it could be part of the oral microbiota of the birds. Hence, future investigations are needed to evaluate the clinical relevance of the virus.  相似文献   
9.
A cross-sectional study was done from March 2013 to May 2014 to assess knowledge, attitudes, and practices towards cystic echinococcosis (CE) or hydatidosis among selected pastoral and agro-pastoral communities in Uganda. A structured questionnaire was administered to 381 respondents. Multivariate logistic regression analysis was done to find the relationship between knowledge about CE and factors such as age, sex, and level of education across all regions. The odds ratio and confidence interval were used to determine the difference in responses across regions. It was shown that age above 36 years was significantly (p < 0.001) associated with awareness about CE in livestock. Likewise, uneducated (p < 0.0001) and agro-pastoralists (p = 0.01) were significantly less knowledgeable than the educated and pastoralists across all regions. The overall knowledge towards CE in livestock was low 17.8% (95% CI = 14.0–21.6). Dog ownership was high and they never dewormed their freely roaming dogs. Dogs shared water with livestock. In conclusion, knowledge about CE in livestock was low across all regions. Therefore, public health education and formulation of policies towards its control by the relevant stakeholders should be done. Also, the true prevalence of CE in livestock needs to be done so that the magnitude and its public health significance are elucidated.  相似文献   
10.
BackgroundProliferative enteritis caused by Lawsonia intracellularis undermines the economic stability of the swine industry worldwide. The development of cost-effective animal models to study the pathophysiology of the disease will help develop strategies to counter this bacterium.ObjectivesThis study focused on establishing a model of gastrointestinal (GI) infection of L. intracellularis in C57BL/6 mice to evaluate the disease progression and lesions of proliferative enteropathy (PE) in murine GI tissue.MethodsWe assessed the murine mucosal and cell-mediated immune responses generated in response to inoculation with L. intracellularis.ResultsThe mice developed characteristic lesions of the disease and shed L. intracellularis in the feces following oral inoculation with 5 × l07 bacteria. An increase in L. intracellularis 16s rRNA and groEL copies in the intestine of infected mice indicated intestinal dissemination of the bacteria. The C57BL/6 mice appeared capable of modulating humoral and cell-mediated immune responses to L. intracellularis infection. Notably, the expression of genes for the vitamin B12 receptor and for secreted and membrane-bound mucins were downregulated in L. intracellularis -infected mice. Furthermore, L. intracellularis colonization of the mouse intestine was confirmed by the immunohistochemistry and western blot analyses.ConclusionsThis is the first study demonstrating the contributions of bacterial chaperonin and host nutrient genes to PE using an immunocompetent mouse model. This mouse infection model may serve as a platform from which to study L. intracellularis infection and develop potential vaccination and therapeutic strategies to treat PE.  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