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   1253篇
  免费   128篇
  国内免费   152篇
林业   10篇
农学   55篇
基础科学   13篇
  44篇
综合类   417篇
农作物   14篇
水产渔业   81篇
畜牧兽医   868篇
园艺   17篇
植物保护   14篇
  2024年   4篇
  2023年   17篇
  2022年   25篇
  2021年   54篇
  2020年   52篇
  2019年   59篇
  2018年   32篇
  2017年   76篇
  2016年   64篇
  2015年   69篇
  2014年   65篇
  2013年   73篇
  2012年   99篇
  2011年   109篇
  2010年   89篇
  2009年   79篇
  2008年   60篇
  2007年   79篇
  2006年   60篇
  2005年   54篇
  2004年   40篇
  2003年   28篇
  2002年   25篇
  2001年   21篇
  2000年   20篇
  1999年   28篇
  1998年   15篇
  1997年   20篇
  1996年   14篇
  1995年   14篇
  1994年   17篇
  1993年   11篇
  1992年   11篇
  1991年   14篇
  1990年   5篇
  1989年   7篇
  1988年   5篇
  1987年   5篇
  1986年   3篇
  1985年   1篇
  1984年   2篇
  1982年   1篇
  1981年   1篇
  1979年   1篇
  1975年   1篇
  1956年   4篇
排序方式: 共有1533条查询结果,搜索用时 15 毫秒
141.
将WGA-HRP注入75~90日龄鸡肾上腺内,追踪支配鸡肾上腺传出神经元的胞体。结果显示,鸡肾上腺接受交感性节前和节后神经元的支配,以节后神经元支配占主导;迷走神经的传出神经元也支配鸡肾上腺,但处于次要地位  相似文献   
142.
Development of transferred xenogeneic vole embryos in mouse uteri   总被引:1,自引:0,他引:1  
An experimental model to study interspecific pregnancy using voles, Microtus arvalis, and green fluorescent protein gene‐induced transgenic mice is presented. Xenogeneic blastocysts from the vole were transferred into the uteri of pseudopregnant mice along with allogeneic blastocysts from green fluorescent protein gene‐induced transgenic mice. The uteri containing xeno‐allo combined transfers were examined from day 6 to 13 of gestation. Although the vole embryos implanted, the uteri containing vole embryos were smaller compared with those having allogeneic mouse embryos. On day 8, the uteri containing vole embryos hemorrhaged internally and no vole embryo was found in the pregnant uterus after day 11. Allogeneic mouse embryos developed normally despite the presence and abortion of the vole embryos. In uteri implanted with vole embryos, decidua were formed and numerous blood vessels were distributed around the embryo. Maternal blood cells infiltrated into the celomic cavity of the vole embryo through the discontinuous region of trophoblast. Periodic acid‐Schiff‐positive granulated metrial gland cells were remarkably increased in the decidual sites. These findings suggest that a disorder of embryo–maternal interaction might induce the appearance of numerous granulated metrial gland cells and rejection of the embryos.  相似文献   
143.
对秋季中华蜜蜂工蜂有分泌活性舌腺(9日龄)和无分泌活性的舌腺(采集蜂)的超微结构进行了观察和比较,发现二者的舌腺细胞的超微结构存在着差异。9日龄工蜂舌腺处在分泌活性状态。细胞核发达,多突起;粗面内质网发达,成平行状排列;胞内管、胞外管中都充满电子致密度均匀的物质,即王浆物质;有大量的分泌块;线粒体内嵴排列紧密,呈板层状。而采集蜂舌腺处在无分泌活性状态。核周边异染色质增多;粗面内质网不太发达,多呈泡状;胞内管中物质为一些不均匀的电子致密度大的粗颗粒物质;胞外管中只有少量水样物质;线粒体内嵴间隙相对变大,多发现内嵴间隙呈管泡状。  相似文献   
144.
用光镜和电镜观察了补饲吉林麦饭石鸡的甲状腺和肝脏组织结构。结果:实验组鸡甲状腺呈现一系列功能旺盛的结构象,肝细胞中肝糖元数量增加。此外,讨论了造成这些结构变化的原因。  相似文献   
145.
Hypothyroidism was diagnosed in a dog which had undergone unilateral thyroid lobectomy and external beam irradiation (48 Gy in 3 Gy fractions) for a functional cystic thyroid adenocarcinoma. Hypothyroidism became biochemically apparent within 4 months of completion of radiation therapy, and clinically apparent within 7 months. Clinical signs resolved after thyroid hormone supplementation. The potential for alterations in thyroid function should be considered in any animal undergoing radiation therapy in which the thyroid gland is included in the radiation field. This potential may be greater if surgery and radiation are combined.  相似文献   
146.
成年母鸡松果腺组织结构的研究   总被引:1,自引:0,他引:1  
用透射与扫描电镜和荧光显微镜对25只成年母鸡的松果腺进行了系统观察。松果腺主要由松果体细胞组成,其间夹杂有少量胶质细胞。松果体细胞的核呈圆形或椭圆形,而胶质细胞的核多呈不规则形。松果体细胞具有突起,线粒体丰富,高尔基复合体发达,胞质中散布有核糖体,并见有粗面和滑面内质网、微管、溶酶体、脂滴以及少量致密核芯小体和板层小体。胶质细胞的结构特征为胞质中含有微丝。毛细血管内皮不含窗孔。本研究结果表明,鸡松果体细胞具有内分泌细胞的结构特征,因而认为鸡的松果腺是一个内分泌腺。  相似文献   
147.
周乃明  吴载德 《蚕业科学》1989,15(3):167-169
本试验采用组织化学方法和聚丙烯酰胺凝胶圆盘电泳,分析了家蚕食道下腺细胞RNA的变化,以及分泌颗粒的化学性质和分泌去向。试验表明,龄初时细胞中RNA含量极低,至催眠期,细胞中RNA明显增多。分泌颗粒对Millon试剂和酸性快绿均呈阳性反应。而电泳结果表明,食道下腺分泌3种蛋白,脂肪体分泌6种蛋白,从迁移率角度分析,这9种蛋白分别和血液中的蛋白十分相似。  相似文献   
148.
Using a simple in vitro test it was demonstrated that staphylococci, Streptococcus agalactiae, and micrococci, the species of bacteria which are commonly isolated from udder infections, adhered to mammary gland epithelial cells readily and in large numbers. Some strains of organisms which are associated with sporadic outbreaks or occur less commonly, like Str. dysgalactiae and Str. uberis, adhered moderately. Escherichia coli, Klebsiella spp., Corynebacterium pyogenes, C. bovis, Str. bovis, and Str. faecalis, species which are isolated occasionally, adhered poorly. From these studies, it appears that selective adherence of bacteria to the epithelial cells is a factor contributing to the ability of organisms to infect the mammary gland and may, therefore, be considered an important stage in the pathogenesis of bovine mastitis.  相似文献   
149.
BACKGROUND: The cytologic diagnosis of ear canal tumors is difficult or impossible by swab alone because cell exfoliation may be poor and neoplastic cells may be masked by associated inflammation. Fine-needle biopsy (FNB) can be used to obtain a higher yield of cells for diagnosis. OBJECTIVE: The purpose of this study was to assess the efficacy and diagnostic value of FNB and cytologic examination in providing an accurate diagnosis of masses growing in the external ear canal of cats. METHODS: Cytologic specimens from masses in the external ear canal, taken under inhaled, general anesthesia, were classified into 4 groups: 1) ceruminous gland hyperplasia or adenoma, 2) ceruminous gland adenocarcinoma, 3) inflammatory polyps, and 4) other neoplastic and non-neoplastic masses. Cytopathologic diagnoses were compared with the final histopathologic diagnoses, and indices of diagnostic test accuracy (sensitivity, specificity, likelihood ratios, diagnostic-odds ratios) were calculated. RESULTS: Twenty-seven masses (from 25 cats, including 2 cats affected bilaterally) were included in the study. The results showed good correspondence between cytologic and histologic diagnoses with an overall agreement index (kappa) of .74, a diagnostic odds ratio of 22, and 100% (27/27) agreement in the diagnosis of inflammatory polyps versus neoplasia (both benign and malignant). CONCLUSIONS: FNB cytopathology of external ear masses in the cat was sufficiently accurate for distinguishing inflammatory polyps from neoplasia. For differentiation of benign proliferation and malignant neoplasia, however, histopathologic confirmation is recommended.  相似文献   
150.
Lipids are a kind of substance which can store and provide energy for animals. A large number of studies have confirmed that the change of lipids in diets can alter the expression of microRNAs (miRNAs) and thus affect the biological activities of the bodies. This review mainly summarizes the regulation of fatty acids on the expression of miRNAs in mammary gland of dairy cows, from the aspects of bovine mammary miRNAs expression characteristics, miRNAs that regulate milk fat synthesis, and the changed bovine mammary miRNAs in response to exogenous addition of fatty acids. All these works may be beneficial for the establishment of the connection between nutrients and mammary function, and provide information for the related research in the future.  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