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   397篇
  免费   30篇
  国内免费   13篇
林业   22篇
农学   12篇
基础科学   4篇
  26篇
综合类   123篇
农作物   14篇
水产渔业   14篇
畜牧兽医   210篇
园艺   4篇
植物保护   11篇
  2024年   3篇
  2023年   9篇
  2022年   6篇
  2021年   12篇
  2020年   4篇
  2019年   8篇
  2018年   4篇
  2017年   13篇
  2016年   23篇
  2015年   17篇
  2014年   23篇
  2013年   23篇
  2012年   26篇
  2011年   28篇
  2010年   24篇
  2009年   24篇
  2008年   22篇
  2007年   18篇
  2006年   11篇
  2005年   17篇
  2004年   17篇
  2003年   13篇
  2002年   9篇
  2001年   9篇
  2000年   4篇
  1999年   5篇
  1998年   7篇
  1997年   3篇
  1996年   11篇
  1995年   2篇
  1994年   5篇
  1993年   1篇
  1992年   4篇
  1991年   5篇
  1990年   3篇
  1989年   3篇
  1988年   3篇
  1986年   3篇
  1985年   3篇
  1984年   2篇
  1981年   1篇
  1979年   1篇
  1978年   4篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1968年   1篇
  1954年   1篇
  1948年   1篇
排序方式: 共有440条查询结果,搜索用时 812 毫秒
1.
In May 1996 the Denver Zoological Gardens obtained two male and two female Pallas' cats (Otocolobus felis manul) that were wild-caught in the Ukraine. These animals were part of a group of 16 wild-caught adults (eight male and eight female) imported to the United States and Canada between 1995 and 1996. The Denver Zoological Gardens cats were quarantined at the zoo hospital for approximately I mo. During the quarantine period they were immobilized for physical examination, and sera were obtained from them to evaluate for exposure to Toxoplasma gondii. All cats were positive for T. gondii antibodies by latex agglutination (titers from 1:512 to 1:1,024). After being paired for breeding, one pair produced two litters, and another pair produced four litters, a total of 17 kittens between 1997 and 2001. Four kittens and two young adults died from a disseminated granulomatous and necrotizing inflammation consistent with toxoplasmosis. Toxoplasma gondii infection was confirmed in all six deceased cats by polymerase chain reaction performed on formalin-fixed tissues. An additional five kittens disappeared and were not available for necropsy. The fatality rate from toxoplasmosis was 35.3% (6/17) for cats that were available for necropsy and could have been as high as 64.7% (11/17) if it were assumed that the disappeared kittens were also affected. The Pallas' kitten survival rate at the Denver Zoological Gardens was 35.3%. This article describes the clinical and pathologic features of toxoplasmosis in a group of Pallas' cats at the Denver Zoological Gardens.  相似文献   
2.
3.
4.
卵泡从原始卵泡发育为成熟卵泡,直至排卵、黄体发育等过程都受到精密的调控,产生大量的优势卵泡是绵羊产多羔及实现快速扩繁的关键因素。研究发现,相关信号通路和转录因子通过影响绵羊卵泡中卵母细胞、颗粒细胞的生长,进而调控卵泡的发育成熟,对这些信号通路进行深入了解,有助于探索卵泡发育的调控机制,早日实现绵羊高效繁育。Notch是卵泡发育过程中发挥重要作用的高度保守信号通路,PI3K/AKT/mTOR信号通路各成员都是广泛存在于细胞内的信号转导分子,在卵泡发育早期发挥了主要作用,还有间隙连接(gap junction,GJ)和跨带突触(transzonal projections,TZPs)等物理连接方式,在细胞间的交流通讯起到重要作用。作者详细介绍了Notch信号通路、PI3K/AKT/mTOR信号通路、间隙连接及跨带突触的结构功能在绵羊卵泡发育中的调控作用,为进一步探明绵羊卵泡发育的调控机制提供参考。  相似文献   
5.
A 7-year-old male neutered domestic shorthair outdoor cat was referred for chronic left forelimb lameness, which had been treated with intra-articular injections of triamcinolone acetonide. A soft tissue swelling around the elbow joint, extending from the distal humerus to the proximal ulna, was surgically explored and biopsy samples obtained. Mycobacterium bovis was cultured from samples from the soft tissue and bone. The mycobacteria from the media were killed and the DNA extracted and tested on a multiplex real-time PCR for the absence of specific genes and the presence of mycobacterial genus markers. The PCR revealed bacillus Calmette-Guérin Danish Strain 1331; this was also isolated from the prescapular lymph node, muscle and bone, obtained at post mortem examination. Badgers had been vaccinated with the bacillus Calmette-Guérin vaccine SSI (Statens Serum Institute) in the area where the cat lived, in the spring and autumn of the previous year. To the authors' knowledge, this is the first report of infection with M. bovis bacillus Calmette-Guérin Danish Strain 1331 in a domestic cat, potentially associated with annual vaccination of badgers in the proximity of the cat's home.  相似文献   
6.
用全产业链思维优化“粮改饲”生产力布局具有重要的现实意义和理论价值。本文以甘肃省为例,总结甘肃省“粮改饲”工作已取得的工作成效和不足,论述了“粮改饲”构建全产业链的必要性,初步探讨了甘肃省“粮改饲”全产业链模式和布局优化,并提出完善相关支持政策、培育壮大龙头企业、高度重视品牌建设和创新科技带动引领4条对策建议。 [关键词]全产业链|粮改饲|生产力布局|甘肃省  相似文献   
7.
8.
Bovine viral diarrhea virus (BVDV) affects cattle populations causing clinical signs that range from subclinical immunosuppression to severe reproductive and respiratory problems. Detection and removal of persistently infected (PI) calves is the single most important factor for control and eradication of BVDV. Current testing strategies to detect PI calves rely heavily on immunohistochemistry (IHC) and a commercially available antigen capture ELISA (ACE) assay. These viral assays depend on 1 or 2 monoclonal antibodies which target the E(rns) glycoprotein of BVDV. The sensitivity and specificity of these two tests have been reported previously. The purpose of this research was to characterize a strain of BVDV (AU501) that was undetectable using IHC and ACE based on a single monoclonal antibody, but was consistently detected in samples from a Holstein steer using virus isolation and PCR testing. Sequencing of this AU501 viral isolate revealed a unique mutation in the portion of the genome coding for the E(rns) glycoprotein. This unique field strain of BVDV demonstrates the risk of relying on a single monoclonal antibody for detection of BVDV. Multiple testing strategies, including polyclonal or pooled monoclonal antibodies that detect more than one viral glycoprotein may be necessary to detect all PI calves and facilitate eradication of BVDV.  相似文献   
9.
In a programme for developing systems which allow the transfer of foreign genes into apricot cultivars, we have tested cotyledons of immature embryos, somatic embryos and leaf discs. Apricot plants have been transformed, and then regenerated, with Agrobacterium tumefaciens strain LBA 4404 containing various binary plasmids: pBinGUSint, carrying the marker gene β-glucuronidase (GUS), and pBinPPVm, carrying the coat-protein gene of plum pox potyvirus (PPV). The marker gene GUS was used for visual evaluation of the efficiency of the transformation system. The coat-protein gene was used in the hope of introducing coat protein-mediated resistance to one of the most important stone-fruit pathogens in Europe and the Mediterranean area.  相似文献   
10.
Beef cattle from a herd in north Alabama were examined because of an outbreak of nonfatal skin disease characterized by discrete circumscribed areas of inflammation that developed on the skin from the neck to the hips. Areas of inflammation, which tended to be superficial, underwent necrosis and scabbed over. The scabs eventually dropped off leaving discrete, round, whitish, hairless lesions that were 1.2 to 2.5 cm diameter. Because clinical signs were consistent with those expected with pseudo-lumpy skin disease (PLSD) caused by bovine herpesvirus type 2 (BHV-2), samples from 16 representative animals were submitted for BHV-2 testing. All 16 animals were seropositive for BHV-2, but the virus could not be isolated from skin biopsy specimens or buffy coat samples. Results of a polymerase chain reaction assay incorporating primers designed to amplify 2 DNA sequences from BHV-2 were positive for 3 of the 10 cattle, suggesting that skin lesions in these cattle were a result of PLSD. Our findings suggest that PLSD may be more common and widespread in the United States than suggested by the frequency with which BHV-2 has been isolated from cattle with PLSD-like skin lesions.  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