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   1208篇
  免费   83篇
林业   54篇
农学   13篇
基础科学   12篇
  129篇
综合类   187篇
农作物   48篇
水产渔业   46篇
畜牧兽医   673篇
园艺   14篇
植物保护   115篇
  2019年   20篇
  2018年   10篇
  2017年   18篇
  2016年   14篇
  2014年   11篇
  2013年   64篇
  2012年   33篇
  2011年   40篇
  2010年   30篇
  2009年   23篇
  2008年   36篇
  2007年   46篇
  2006年   32篇
  2005年   44篇
  2004年   37篇
  2003年   30篇
  2002年   44篇
  2001年   31篇
  2000年   46篇
  1999年   29篇
  1998年   18篇
  1997年   19篇
  1996年   15篇
  1995年   19篇
  1994年   10篇
  1993年   18篇
  1992年   26篇
  1991年   31篇
  1990年   28篇
  1989年   28篇
  1988年   23篇
  1987年   19篇
  1986年   13篇
  1985年   20篇
  1984年   13篇
  1983年   18篇
  1982年   15篇
  1981年   12篇
  1980年   10篇
  1979年   22篇
  1978年   13篇
  1976年   12篇
  1975年   11篇
  1974年   11篇
  1973年   14篇
  1972年   16篇
  1971年   15篇
  1970年   10篇
  1967年   15篇
  1938年   10篇
排序方式: 共有1291条查询结果,搜索用时 31 毫秒
51.
Staphylococcus intermedius (S. intermedius) was isolated from 88.6% and 49.4% of skin and ear samples, respectively, during the years 1992 through 1997, and frequency of isolation remained unchanged. More than 95% of all S. intermedius isolates were susceptible to cephalothin and oxacillin, providing support for empirical treatment of canine skin and ear infections with cephalexin. Pseudomonas aeruginosa (P. aeruginosa) was isolated from 7.5% and 27.8% of skin and ear samples, respectively. The frequency of isolation from skin samples increased over the study period. Because of multidrug-resistant profiles for P. aeruginosa isolates, especially for ear isolates, empirical treatment of P. aeruginosa infections is not advisable.  相似文献   
52.
53.
Ixodid ticks were collected from 104 wild carnivores belonging to 23 species in various nature reserves and on several farms in all nine provinces of South Africa. Seven feral cats in a nature reserve were also examined. Twenty-four tick species belonging to seven genera were recovered and identified. Amongst these ticks we consider the adults of Haemaphysalis leachi, Haemaphysalis spinulosa, Haemaphysalis zumpti, Ixodes rubicundus, Rhipicentor nuttalli, Rhipicephalus simus and Rhipicephalus turanicus to be true parasites of wild carnivores. Although numerous adult Rhipicephalus appendiculatus and Rhipicephalus zambeziensis were collected from some lions these were either sick or old animals. The immature stages of seven species regularly utilized wild carnivores as hosts on an opportunistic basis.  相似文献   
54.
Ergot alkaloids present in endophyte-infected tall fescue induce fescue toxicosis in livestock consuming the plant. The lysergic acid (LA) ring structure is a common moiety among the ergot alkaloids. Little is known about the bioavailability of LA because of limitations in available analytical protocols. Thus, a high-performance liquid chromatography procedure was developed to analyze biological matrices for LA. The biological matrices of interest were tall fescue straw and seed, and ruminant feces, urine, and ruminal fluid. Lysergic acid was added to each matrix at a high (150 ng/ml) or low (30 ng/ml) level. Using the high-level addition, the greatest recovery of LA was obtained from ruminal fluid, feces, and urine (P < 0.05), with an average 85.1% recovered. At the low level, a greater recovery of added LA was observed in the ruminal fluid, urine, and feces (82.1%; P < 0.05) than that in the other 2 matrices (62.6%). The limit of quantitation (LOQ) in ruminal fluid and urine was 5.5 and 18.4 ng/ml, respectively. Seed, straw, and feces had higher LOQ (24.2, 14.5, and 36.0 ng/g, respectively). Limit of detection (LOD) was 1.64, 10.80, 4.35, 5.52, and 7.26 ng/g for ruminal fluid, feces, urine, seed, and straw, respectively. To test the assay in vivo, samples of ruminal fluid and urine were collected from steers consuming a diet containing 400 ng of ergovaline/g and 30 ng of LA/g. All matrices sampled resulted in levels above the LOD and LOQ for the assay, indicating that this assay is sufficiently sensitive for use in assessing the bioavailability of LA.  相似文献   
55.
The effect of vulvar discharge syndrome (VDS) on sow and gilt fertility was studied on 26 farms. Of 824 animals inspected in 21 randomly selected and five VDS problem farms, 19 (2.3%) were afflicted with VDS. Altogether 542/799 of the examined animals (67.8%) farrowed thereafter. Nine of the 19 VDS animals (47.4%) and 533/780 non-VDS animals (68.3%) farrowed at the first chance after the examination (p = 0.05). None of the unmated gilts in this study had VDS. Environmental and individual factors likely to be associated with fertility and VDS were tested. In multivariate analysis, factors associated with farrowing were VDS, reproductive status, availability of roughage and confinement to individual stalls. None of the variables tested was associated with VDS. However, all of the VDS problem farms were overcrowded and had concrete, partly slatted floors with little or no bedding. The median value of haptoglobin (Hp) was 2.5 (range 1.3-3.1) g/l in VDS animals and 2.3 (0.5-4.3) g/l in controls (p = 0.6). The median C-reactive protein (CRP) in VDS animals was 30.3 (3.3-171.3) mg/l and in controls 25.9 (3.3-361.1) mg/l (p = 0.7). In conclusion, VDS decreased fertility of gilts and sows in the absence of a systemic acute-phase response, as indicated by stable concentrations of Hp and CRP.  相似文献   
56.
57.
Treating elderly pets and maximising your practice returns will be in focus at this year's AVA Annual Conference. The Scientific Organising Committee is delighted that such distinguished international and local speakers have agreed to give presentations in the Small Animal (Geriatric Medicine and Surgery) and Practice Management streams at the conference.
The AVA Conference will be at Hobart's Wrest Point Conference Centre from May 21–26, 2006. To see the full program and to register online visit www.ava.com.au/avaconference.  相似文献   
58.
The carboxyterminal processing protease of D1 protein (CtpA) is predicted to be an excellent target for the discovery of a general broad-spectrum herbicide. Directed and random screening of compounds against recombinant spinach CtpA (rCtpA) has led to the discovery of five different chemical classes of inhibitors. Lead compounds from each inhibitor class were investigated for their in vitro effects on the activities of both recombinant and native spinach CtpA. All of the lead compounds have Ki values of less than 50 μM when tested against rCtpA, and all except one showed competitive inhibition. Results from partially purified native CtpA from spinach were similar to those from the recombinant form of the enzyme, thus validating the use of rCtpA in the inhibitor screen. Compounds from three of the classes of CtpA inhibitors show in vivo herbicidal activity against Arabidopsis thaliana when applied either by addition to growth media or by spraying the leaves. Transgenic Arabidopsis plants which over-express CtpA showed greater resistance to the compounds than wild-type plants providing evidence that these inhibitors are directly acting against CtpA.  相似文献   
59.
Lambs sucking non-immunised ewes or ewes immunised 4-5 weeks before lambing with live attenuated, aromatic-dependent (aroA) Salmonella typhimurium (strain CS 332) were challenged orally at either 2, 4 or 7 days of age with virulent S. typhimurium (strain CS 94) at doses ranging from 109 to 1013 colony forming units. No lambs displayed signs of clinical salmonellosis and all survived challenge but those sucking immunised ewes had organisms of the challenge strain in their faeces for much shorter periods of time than lambs of the control ewes. High titres of specific antibodies were measured in colostrum and milk of immunised ewes in comparison with very low titres measured in samples from control ewes; these differences were reflected by the titres of antibodies in the sera of corresponding lambs. At 2 days after lambing, the major antibody isotype in the colostrum of immunised ewes and sera of their lambs was IgM whereas at 7 days IgG1 was the predominant isotype. While it was clear that vaccination of pregnant ewes with the live attenuated vaccination conferred protection against experimentally-induced salmonellosis in their lambs, considerable protection was observed in control lambs in spite of there being very low titres of antibodies in the mammary secretion of their dams. The latter observation could be related to the presence of contain non-antibody potent bactericidal factors previously described in colostrum and milk.

Résumé

Des agneaux qui tètent des brebis non immunisées, ou bien immunisées, 4 à 5 semaines avant la mise bas avec un vaccin atténué constitué d'une souche de Salmonelle typhimurium dépendente pour sa croissance de la presence de composés aromatiques (souche aro A CS 332) ont reçu, à l'âge de 2, 4 ou 7 jours, par voie orale, des doses allant de 109 à 1013 Salmonella (souche virulente CS 94). Aucun agneau n'a présenté de signes cliniques et tous ont survécu à cette administration, mais les agneaux des brebis immunisées ont excrété la souche d'épreuve dans leur fécès pendent moins longtemps que les agneaux des brebis non vaccinées. Des titres plus élevés d'anticorps sont détectés dans le colostrum et le lait des brebis vaccinées et comparés aux brebis témoins. Cette différence est également notée pour les titres d'anticorps présents dans le sérum des agneaux issus de brebis vaccinées ou non. Deux jours après la mise bas, la classe des anticorps majoritaires, tant au niveau du colostrum des brebis vaccinées que du sérum de leurs agneaux, est la classe des IgM, alors qu'après 7 jours, les IgG1 prédominent. Bien qu'il soit clair que des brebis pleines vaccinées à l'aide d'un vaccin vivant atténué, apportent à leurs agneaux une protection vis à vis d'une Salmonella expérimentale, une réelle protection est également observée chez les agneaux témoins, malgré les titres faibles d'anticorps présente dans les sécrétions mammaires de leur mères. Cette dernière observation peut être mise en rapport avec la présence d'agents bactériodes ne contenant pas d'anticorps, déjà décrits dans le colostrum et le lait.  相似文献   

60.
Among the 57 monoclonal antibodies analyzed within the T-cell group of the Second International Swine CD Workshop, one mAb fell within cluster T14a that included the CD6 standard a38b2 (No. 175). The new mAb MIL8 (No. 082) and a38b2 both precipitated from activated T-cells a 150 kDa monomeric protein. Staining patterns on the various cell types were similar. There was no inhibition of binding of either mAb to peripheral blood T-cells with the opposite mAb. The new mAb, MIL8, reacts with a separate epitope on porcine wCD6.  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