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   293篇
  免费   24篇
  国内免费   7篇
林业   16篇
农学   16篇
基础科学   1篇
  26篇
综合类   65篇
农作物   11篇
水产渔业   7篇
畜牧兽医   131篇
园艺   18篇
植物保护   33篇
  2024年   1篇
  2023年   2篇
  2022年   5篇
  2021年   8篇
  2020年   7篇
  2019年   16篇
  2018年   8篇
  2017年   5篇
  2016年   21篇
  2015年   13篇
  2014年   12篇
  2013年   10篇
  2012年   15篇
  2011年   12篇
  2010年   10篇
  2009年   21篇
  2008年   15篇
  2007年   16篇
  2006年   12篇
  2005年   13篇
  2004年   10篇
  2003年   10篇
  2002年   5篇
  2001年   14篇
  2000年   8篇
  1999年   7篇
  1998年   4篇
  1997年   5篇
  1996年   4篇
  1995年   9篇
  1994年   3篇
  1993年   3篇
  1992年   3篇
  1991年   3篇
  1990年   4篇
  1989年   4篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1978年   1篇
  1975年   1篇
  1974年   1篇
排序方式: 共有324条查询结果,搜索用时 15 毫秒
21.
取发生不同程度菌种退化的相同来源的金针菇(Flammulina velutipes)工厂化袋栽菌株和栽培菌包,观察其在PDA平板上的分纯情况和形态特征;采用LBL液体培养基检测不同菌株对培养基的脱色情况。实验结果表明:这些退化菌株经过分离可以得到不同菌落形态的分离菌株,而且对LBL液体培养基表现不同的脱色能力,退化严重的菌株脱色能力最差,说明LBL液体培养基的脱色反应结合菌种纯度的检测可以在一定程度上排除生产上的退化菌株。  相似文献   
22.
研究结果表明,无论是香菇生料菌砖栽培,还是金针菇熟料袋栽,菌种世代的多少对产量均无明显的影响,这可能是由于菌种通过无性繁殖,遗传性变异甚小之故;研究结果还表明,金针菇菌丝生长的速度似乎有随着菌种工代的增多而加快的趋势,这窨是由于低代菌种自琼脂培养基移接天以杂本屑,棉籽壳等为主要原料的粗质培养基上的时间较短,适应酶的活性较弱,分解,利用高分子化合物的能力较差,故菌丝生长速度较为缓慢?还是由于其他原因  相似文献   
23.
The vertebral columns of 327 clinically normal, 12 to 18 months old dachshunds, were x-rayed. This sample represented 16.1% of all dachshunds registered with the Norwegian Kennel Club in the period 1986-1988. Calcified intervertebral discs were identified in 79 (24.2%) of the dogs and the number of calcified discs in each individual varied from 1 to 11 with a mean of 2.3. Calcified discs were estimated to occur in 23.5% of Norwegian dachshunds. The occurrence of calcified discs in standard-sized dachshunds was higher in the wirehaired variety (27.1%) than in the smoothcoated (16.4%) or longhaired (9.1%) varieties. However, within the longhaired variety the occurrence was higher in dwarfs and kaninchens (36.0%) than in standard-sized dachshunds (9.1%). Calcification was identified in all cervical, thoracic and lumbar intervertebral discs other than T1-2, and was found to be most frequent in the caudal thoracic vertebral column.  相似文献   
24.
Objective To describe a slowly progressive retinopathy (SPR) in Shetland Sheepdogs. Animals Forty adult Shetlands Sheepdogs with ophthalmoscopic signs of SPR and six normal Shetland Sheepdogs were included in the study. Procedure Ophthalmic examination including slit‐lamp biomicroscopy and ophthalmoscopy was performed in all dogs. Electroretinograms and obstacle course‐test were performed in 13 affected and 6 normal dogs. The SPR dogs were subdivided into two groups according to their dark‐adapted b‐wave amplitudes. SPR1‐dogs had ophthalmoscopic signs of SPR, but normal dark‐adapted b‐wave amplitudes. Dogs with both ophthalmoscopic signs and subnormal, dark‐adapted b‐wave amplitudes were assigned to group SPR2. Eyes from two SPR2 dogs were obtained for microscopic examination. Results The ophthalmoscopic changes included bilateral, symmetrical, greyish discoloration in the peripheral tapetal fundus with normal or marginally attenuated vessels. Repeated examination showed that the ophthalmoscopic changes slowly spread across the central parts of the tapetal fundus, but did not progress to obvious neuroretinal thinning presenting as tapetal hyper‐reflectivity. The dogs did not appear seriously visually impaired. SPR2 showed significantly reduced b‐wave amplitudes throughout dark‐adaptation. Microscopy showed thinning of the outer nuclear layer and abnormal appearance of rod and cone outer segments. Testing for the progressive rod–cone degeneration ( prcd )‐mutation in three dogs with SPR was negative. Conclusion Slowly progressive retinopathy is a generalized rod–cone degeneration that on ophthalmoscopy looks similar to early stages of progressive retinal atrophy. The ophthalmoscopic findings are slowly progressive without tapetal hyper‐reflectivity. Visual impairment is not obvious and the electroretinogram is more subtly altered than in progressive retinal atrophy. The etiology remains unclear. SPR is not caused by the prcd‐mutation.  相似文献   
25.
从理论与实践分析BT型、滇型粳稻不育系具有高度的遗传稳定性,发生混杂退化的主要原因在于:①繁殖过程中保持系的机械混杂;②杂交稻或恢复基因的迁移、扩散;③一般常规品种不育基因迁移及其连锁反应.针对BT型不育系混杂退化原因,提出“人工回交株系循环法“不育系原种繁种程序.  相似文献   
26.
范恩普  崔德祥 《种子》1995,(2):15-17
1989~1993年对F1代西瓜亲本在相同条件下进行了连继世代选择和不加选择的加代繁殖两种处理,结果表明:F1代亲本的连续选择能不断提高株系的亲和力,产量比未加选择的增产25.88%。经选择后,母本x-4株系可溶性固形物从10.11%增至11.43%,增长13.06%.父本N-2株系的可溶性固形物含量从7.3%增至8.8%,增长21.92%。F1代炭疽病的发病率和病情指数从89.44%,33.23下降到61.17%和11.63。F1代西瓜亲本连续选择可增加商品率和品质,防止亲本连年自交衰竭和F1代种子退化,并可延长双亲和F1的使用年限,增加单位面积产量,增强抗病性。  相似文献   
27.
Two 12-week-old Tippler pigeons were evaluated for ocular abnormalities associated with congenital blindness. The pigeons were emaciated and blind. Biomicroscopy and direct and indirect ophthalmoscopy findings of the Tippler pigeons were normal with the exception of partially dilated pupils at rest. Scotopic (blue stimuli) and photopic monocular electroretinograms were extinguished in the blind Tippler pigeons. Histological and electron microscopy studies revealed reduced numbers of rods and cones, and an absence of the double cone complex. The photoreceptor cells' outer segments were absent, and the inner segments were short and broad. The number of cell nuclei in the outer and inner nuclear layers was decreased, and the internal and external plexiform layers were reduced in width. Photoreceptor cell endfeet with developing synaptic ribbons were present in the external plexiform layer. Inflammatory cell and subretinal debris was not seen. The electroretinographic, histopathological, and ultrastructural findings of the blind Tippler pigeons support the diagnosis of a photoreceptor cell dysplasia.  相似文献   
28.
烤烟叶片成熟过程与衰老是烟草发育的重要阶段,是一个复杂和高度调控的过程,涉及衰老相关基因的调控表达和叶绿体的分解,也是烟草质量和品质形成的关键时期,因此其成为烟草生产和研究的重要时段。介绍了烟叶衰老过程相关基因的表达变化和叶绿素分解的过程,为从分子水平定义烟叶的成熟度提供理论依据。  相似文献   
29.
Purpose To describe the clinical, histological, and immunohistochemical manifestations of canine necrotizing scleritis. Methods A retrospective examination of the clinical records and samples of ocular tissues from five dogs with a histological diagnosis ‘necrotizing scleritis’ was completed. Archived, formalin‐fixed, paraffin‐embedded samples and two control globes were stained with hematoxylin and eosin, Gram, periodic acid–Schiff (PAS) and Masson trichrome stains, and they were immunohistochemically labeled for CD3, CD18, and CD20. Results Of the five cases reviewed, only two could be confirmed as idiopathic necrotizing scleritis. The other three cases were retrospectively diagnosed as unilateral focal, non‐necrotizing scleritis, one as episcleritis and the third was scleritis secondary to a proptosed globe based on our retrospective clinical, histological, and immunohistochemical evaluations. In these two cases, idiopathic necrotizing scleritis manifested as a bilateral, progressive, inflammatory disease of the sclera and cornea that induces significant uveitis. Light microscopic examination confirmed collagen degeneration and granulomatous inflammation. There was no evidence for an infectious etiology based on Gram’s and PAS stainings. Immunohistochemical labeling revealed a predominance of B cells in idiopathic, bilateral necrotizing scleritis. Tinctorial staining abnormalities with Masson’s trichrome stain were present in scleral collagen of the two cases with idiopathic necrotizing scleritis as well as a case of secondary traumatic scleritis. Conclusions Based on a limited number of cases, idiopathic canine necrotizing scleritis shares similar histopathological features with non‐necrotizing scleritis and episcleritis; however, necrotizing scleritis is B‐cell‐dominated and bilateral, and significant collagen alterations manifest with Masson’s trichrome stain.  相似文献   
30.
The first joint Japanese Society of Toxicologic Pathology (JSTP) and National Toxicology Program (NTP) Satellite Symposium, entitled “Pathology Potpourri,” was held on January 29th at Okura Frontier Hotel in Tsukuba, Ibaraki, Japan, in advance of the JSTP’s 29th Annual Meeting. The goal of this Symposium was to present current diagnostic pathology or nomenclature issues to the toxicologic pathology community. This article presents summaries of the speakers’ presentations, including diagnostic or nomenclature issues that were presented, select images that were used for audience voting or discussion, and the voting results. Some lesions and topics covered during the symposium include: treatment-related atypical hepatocellular foci of cellular alteration in B6C3F1 mice; purulent ventriculoencephalitis in a young BALB/c mouse; a subcutaneous malignant schwannoma in a RccHan:WIST rat; spontaneous nasal septum hyalinosis/eosinophilic substance in B6C3F1 mice; a rare pancreatic ductal cell adenoma in a young Lewis rat; eosinophilic crystalline pneumonia in a transgenic mouse model; hyaline glomerulopathy in two female ddY mice; treatment-related intrahepatic erythrocytes in B6C3F1 mice; treatment-related subendothelial hepatocytes in B6C3F1 mice; spontaneous thyroid follicular cell vacuolar degeneration in a cynomolgus monkey; congenital hepatic fibrosis in a 1-year-old cat; a spontaneous adenocarcinoma of the middle ear in a young Crl:CD(SD) rat; and finally a series of cases illustrating some differences between cholangiofibrosis and cholangiocarcinoma in Sprague Dawley and F344 rats.  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