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   520篇
  免费   22篇
  国内免费   1篇
林业   94篇
农学   19篇
基础科学   6篇
  66篇
综合类   55篇
农作物   12篇
水产渔业   37篇
畜牧兽医   219篇
园艺   18篇
植物保护   17篇
  2023年   5篇
  2021年   7篇
  2020年   4篇
  2019年   7篇
  2018年   5篇
  2017年   6篇
  2016年   11篇
  2015年   10篇
  2014年   14篇
  2013年   14篇
  2012年   14篇
  2011年   27篇
  2010年   14篇
  2009年   16篇
  2008年   23篇
  2007年   23篇
  2006年   24篇
  2005年   19篇
  2004年   18篇
  2003年   16篇
  2002年   17篇
  2001年   5篇
  2000年   12篇
  1999年   7篇
  1998年   5篇
  1993年   9篇
  1992年   5篇
  1991年   4篇
  1990年   5篇
  1989年   7篇
  1987年   10篇
  1986年   5篇
  1985年   8篇
  1984年   5篇
  1981年   5篇
  1978年   5篇
  1977年   6篇
  1975年   7篇
  1973年   11篇
  1971年   8篇
  1970年   5篇
  1968年   6篇
  1965年   7篇
  1938年   7篇
  1936年   8篇
  1935年   4篇
  1934年   4篇
  1931年   7篇
  1930年   3篇
  1928年   3篇
排序方式: 共有543条查询结果,搜索用时 156 毫秒
81.
The objective of this study was to establish a technique for radiographic examination of the coxofemoral joint and adjacent bony structures in standing cattle. Left (or right) 30° dorsal-right (or left) ventral radiographic views of the coxofemoral joint region of standing cattle (n = 10) with hind limb lameness were evaluated retrospectively. In addition, an experimental study of oblique laterolateral views of the coxofemoral joint region of a bovine skeleton at angles of 15-45° was carried out to determine the optimal position for visualization of the hip region. In the 10 clinical patients, the bodies of the ilium and ischium, the acetabulum and proximal third of the femur could be assessed. Six of these cattle had fractures of the body of the ilium and body of the ischium, five with and one without involvement of the acetabulum, two had craniodorsal and one caudoventral luxation of the femur and one had a femoral neck fracture. The described laterodorsal-lateroventral radiographs of the hip region in standing cattle were suitable for assessing the coxofemoral joint, the proximal aspect of the femur and parts of the ischium, ilium and pubis. After testing the optimal angle on the skeleton, it was seen that distortion and superimposition were minimized by positioning the X-ray beam at an angle of 25° to the horizontal plane. It can be concluded that the described technique improves the evaluation of injuries of the coxofemoral region in cattle. With the appropriate angle, the technique can also be applied in recumbent cattle.  相似文献   
82.
萧友 《猪业科学》2005,22(6):60-61
猪育种专家和生产者可做的工作决不仅仅是给猪称重,而是从较大窝重中选择后备母猪和选择生长最快的猪或有价值的猪。分子图谱(DNA)分析对猪遗传育种专家如何选择目前商品猪群中遗传的差异具有划时代的影响。过去10年中,猪遗传育种专家第一次直接研究了猪的染色体图谱,包括自由遗传标记和已经知道的基因。就像交通地图一样,在这些图谱上,研究者可以分析和找到影响猪主要经济性状的染色体区域和主要的基因。这些研究已经以遗传检测(DNA)的形式产生了真正的成果,该检测对个体生产者和育种公司改善种群具有重要作用。在养猪行业中,可以采用大…  相似文献   
83.
Atmospheric CO2 enrichment affects C3 crops both directly via increased carbon gain and improved water use efficiency and indirectly via higher temperatures and more frequent climatic extremes. Here we investigated the response of spring wheat (Triticum aestivum L. cv. Triso) to CO2 enrichment (550 vs. 380 µmol/mol) and heat, applied as a constant +4°C increase or a typical heat wave either before or after anthesis, or as two typical heat waves before and after anthesis. We applied a climate chamber approach closely mimicking ambient conditions. CO2 enrichment increased above‐ground biomass and yield by c. 7 and 10%, but was not able to compensate for adverse heat stress effects, neither before nor after anthesis, with few exceptions only. Yield depression due to heat stress was most severe when two heat waves were applied (?19%). This adverse effect was, however, compensated by CO2 enrichment. Applying heat stress before or after anthesis did not exert different effects on yield for both +4°C warming and heat wave application. However, +4°C depressed yield more than a heat wave at ambient CO2, but not so at elevated CO2. Thus, the interactive effects were complex and prediction of future wheat yield under CO2 enrichment and climate extremes deserves more attention.  相似文献   
84.
We investigated the feasibility of bacteriophage therapy to combat canine and feline Escherichia coli urinary tract infections (UTIs) by testing the in vitro lytic ability of 40 naturally occurring bacteriophages on 53 uropathogenic E. coli (UPEC). The mean number of UPEC strains lysed by an individual bacteriophage was 21/53 (40%, range 17-72%). In total, 50/53 (94%) of the UPEC strains were killed by one or more of the bacteriophages. Ten bacteriophages lysed 51% of UPEC strains individually and 92% of UPEC strains as a group. Electron microscopy and DNA sequencing of 5 'promising' bacteriophages revealed that 4 bacteriophages belonged to the lytic T4-like genus, while one displayed morphologic similarity to temperate P2-like bacteriophages. Overall, these results indicate that the majority of UPEC are susceptible to lysis by naturally occurring bacteriophages. Thus, bacteriophages show promise as therapeutic agents for treatment of canine and feline E. coli UTIs.  相似文献   
85.
The clinical findings and treatment of 3 calves with bleeding attributable to severe thrombocytopenia (1000 to 5000 platelets/microl) are described. The calves responded to treatment with whole blood transfusion, dexamethasone and other drugs. One calf was subsequently diagnosed with persistent bovine viral diarrhoea virus infection and was euthanased despite a favourable response to treatment. The other two calves were discharged after platelet counts had normalised and bleeding had stopped.  相似文献   
86.
87.
88.
89.
PTK787/ZK 222584 is an inhibitor of the vascular endothelial growth factor (VEGF) receptor tyrosine kinases. In this study, the effectiveness of PTK787/ZK 222584 and radiation on canine oral melanoma xenografts was assessed. Xenografts were treated with radiotherapy (4x6Gy), or with PTK787/ZK 222584, or with a combination of both. Treatment efficacy was assessed using a tumour growth delay assay, serial power Doppler and pO(2) measurements during and after therapy. There was a significant growth delay for the group treated with radiation alone and for the combined treatment group. However, tumour growth delay was similar in both groups. Tumours were hypoxic before irradiation and no significant re-oxygenation occurred during therapy. In all tumours, vascularity and perfusion were significantly lower at the end of the study but no significant differences in perfusion, vascularity and oxygenation status were observed between and within treatment groups. The combination of PTK787/ZK 222584 and radiotherapy did not perform better than radiotherapy alone in this model.  相似文献   
90.
Samples from moribund lumpfish were collected in a marine hatchery in Scotland in 2015. Black nodules were noted on the skin, and gills and fungal hyphae were extensively distributed in musculature and internal organs. Multifocal chronic inflammatory lesions displaced structures in all affected organs. Mortalities commenced on completion of spawning in May and were evenly distributed over the second year in the temperature range 11–15°C. The main systemic infection causing agent was initially identified based on morphological characteristics as an Exophiala species. Ribosomal DNA (rDNA) ITS regions of the isolates were subsequently sequenced confirming the isolates belonged to Exophiala genus. All isolates fell in a single phylogenetic cluster, which is represented by Exophiala angulospora. Fish were treated with either formalin or Bronopol or a combination of both, but there was no effect on the pattern or numbers of mortalities. Isolates were also tested against three different concentrations of Latrunculin A, Amphotericin B and Itraconazole with no success. It is of utmost importance to increase the knowledge on pathogen–host interactions to successfully develop sustainable control methods.  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