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
51.
实验通过台盼蓝染色、MTT、细胞流式等方法研究高温(40℃/41℃)对乳腺细胞活性、细胞周期及凋亡的影响。结果表明,高温可以抑制乳腺细胞的增殖,使细胞产生S、G2期阻滞,诱导乳腺细胞凋亡,并随高温强度的增加而作用增强。试验提示高温可诱导乳腺细胞周期阻滞,抑制细胞增殖。  相似文献   
52.
Ultrasonographic images were acquired of the mammary glands of 40 bitches with physiologically lactating (n = 20) or inflamed glands (n = 20). Echogenicity, structure, homogeneity, thickness, and distinguishability of each tissue layer were assessed. Additionally, overall echogenicity was noted. In the normal lactating gland, different tissues could be differentiated easily. The parenchyma was, without exception, separated from adjacent tissues and was visible as medium echogenic tissue with a coarse-grained structure. The tissue always had some echogenic lines and anechoic areas and was slightly heterogeneous. The loss of distinct layering of the tissue was characteristic of an inflamed mammary gland and inflamed regions had reduced echogenicity. Additionally in five bitches with mastitis, the ultrasound examination was repeated five times for documentation of the progress of the illness and associated changes, supplemented with a color Doppler sonogram to assess changes in blood vessel density. Information from the examinations carried out via B-mode did not allow treatment success to be predicted. Two bitches with reduced blood vessel density centrally had a poor outcome whereas three bitches with increased blood vessel density had a good outcome. Thus, Doppler sonography might be a useful tool to obtain information of the prognosis in acute canine mastitis.  相似文献   
53.
Objective: To describe a case of atrioventricular block and syncope secondary to systemic hypertension in a dog with malignant pheochromocytoma. Case Summary: A 13‐year‐old spayed female mixed‐breed dog presented following an acute onset of collapse. The dog was hypertensive and had paradoxical high‐grade second‐degree atrioventricular block with concurrent syncope. Initial emergent therapy included a nitroprusside infusion for the systemic hypertension and vagolytic therapy for the bradyarrhythmia. A left adrenal mass was seen on abdominal ultrasound and was further characterized by MRI. Following medical stabilization with phenoxybenzamine and propantheline, a left adrenalectomy was performed. Histological diagnosis was consistent with a malignant pheochromocytoma. Following tumor removal there has been no further hypertension, atrioventricular block or syncope. Unique information provided: This is the first documented case of a malignant pheochromocytoma presenting as syncope secondary to hypertension induced atrioventricular block.  相似文献   
54.
A fibroadenoma was diagnosed in the left udder of a 3-month-old female Chios lamb. No recurrence was observed after surgery. Grossly, the tumor had a whitish-gray lobular appearance, and the lobules were interlaced with thin septa. Microscopically, the tumor was composed of proliferating fibroepithelial tissue, including differentiated ducts lined by whorls and interlacing bundles of abundant loose fibrovascular stroma. Immunohistochemistry revealed the ductal epithelium to be positive for pancytokeratin (AE1/AE3) and loose fibrovascular stroma was positive for vimentin and basal cells covering the ductal epithelium of alpha-smooth-muscle actin. Immunostaining for the estrogen and progesterone receptors was negative. A diagnosis of mammary fibroadenoma was made based on the histological and immunohistochemical findings.  相似文献   
55.
The objective of this study was to determine whether an association could be demonstrated between survival and the expression of the adhesion molecule E‐cadherin by the neoplastic cells in a group of dogs with anal sac gland carcinomas (ASGCs). Archived formalin‐fixed, paraffin wax‐embedded primary tumour specimens were obtained for 36 cases of canine ASGC with known clinical management and survival data. Immunohistochemical methods were used to evaluate E‐cadherin expression by the neoplastic cells and data were evaluated for an association between E‐cadherin expression and survival. On univariate analysis, the median survival time for cases with tumours expressing E‐cadherin in more than 75% of cells was significantly greater than that for cases with tumours expressing E‐cadherin in fewer than 75% of cells (1168 versus 448 days, P = 0.0246). Both E‐cadherin expression and presence or absence of distant metastases were significantly associated with survival on multivariate analysis. This study demonstrates that expression of E‐cadherin at the cytoplasmic membrane in canine ASGCs is variable and potentially predictive of survival.  相似文献   
56.
不同物种的乳腺分泌物中含有的细胞成分被称为体细胞,其中包括淋巴细胞、白细胞、巨噬细胞和上皮细胞。物种、乳腺感染情况、不同生理阶段和饲养管理条件等因素均会影响乳中的体细胞数量和细胞类型。近年来,乳中体细胞得到了人们的关注和深入研究,显示出广阔的应用前景。人们利用从初乳和常乳中得到的乳腺上皮细胞已经成功进行了乳腺细胞的原代培养和建立了乳腺细胞系,为乳生成、被动免疫转移和乳腺癌的研究提供了良好平台。体细胞中提取的RNA代表了乳腺组织的基因表达,因此为研究乳腺组织的基因表达提供了方便、良好的来源。  相似文献   
57.
为了进行抗蜱和蜱传病疫苗的研究,本实验对亚洲璃眼蜱雌蜱吸血前后唾液腺消减文库中获取的一个全长编码基因P18进行了研究。该基因全长519bp,共编码170个氨基酸,分子量为18.36Ku,等电点为4.28。BLAST分析表明,该基因预测的氨基酸与肩突硬蜱、篦子硬蜱唾液腺的抗凝血小肽有30%~40%低度同源性。将该基因亚克隆到pET-32a( )表达载体,转化BL21(DE3)宿主菌,经IPTG诱导,重组融合蛋白以可溶性形式高效表达。将可溶性重组蛋白免疫小鼠后获得的抗血清。经免疫印迹分析表明,该重组蛋白抗体可特异性的识别半饱雌蜱唾液腺中的天然蛋白抗原,而未吸血雌蜱唾液腺中则不显现特异条带。RT-PCR结果进一步证实,该基因在蜱吸血后的唾液腺中差异表达。  相似文献   
58.
In a previous study, it was found that there are sex differences in goats with respect to the levels of cortisol secretion induced by transportation stress. We also found that treatment of castrated male goats with dihydrotestosterone (DHT) suppressed the increase in plasma cortisol concentration following transportation, but did not suppress the secretion of adrenocorticotropic hormone (ACTH). This suggests that androgen might block ACTH ‐ induced cortisol secretion. In order to examine this hypothesis, the effects of androgen on ACTH‐induced cortisol secretion in goats were investigated. First, castrated male goats were treated with testosterone (T), DHT or cholesterol (cho) for 21–25 days. Cho was used as a control for T and DHT treatment. Then, plasma cortisol concentrations were compared among the hormonal treatments after ACTH injection. Subsequently, the distribution of androgen receptors in the caprine adrenal gland was investigated. There were no differences in the basal cortisol concentrations among the hormonal treatments. However, plasma cortisol concentrations after ACTH injection were significantly lower in T ‐ and DHT ‐ treated goats than in cho ‐ treated goats. Androgen receptors were present in 60% of the cells in the zonae fasciculata and reticularis of the adrenal cortex, the regions that secrete glucocorticoids. These results suggest that androgen may act directly on the adrenal cortex to suppress cortisol secretion induced by ACTH.  相似文献   
59.
以华盛顿脐橙为试验材料,研究了采前喷钙和套袋对果皮病变的影响。结果表明,华盛顿脐橙果皮油胞凹陷和油胞破裂等田间果皮病变高达30%以上;果皮病变与果园管理水平、植株和果皮钙含量密切相关,采前喷钙和套袋处理提高了果实硬度,增加果皮钙含量,降低采后果皮病变率40%~50%,达显著和极显著水平;同时钙处理促进果实着色,显著增加果皮红色度和光泽度。采前喷钙和套袋对提高华脐果实的外观品质和商品性具有很好的作用。  相似文献   
60.
用组织块培养法获得山羊乳腺细胞原代培养物。根据山羊乳腺成纤维细胞与上皮细胞对胰蛋白酶的敏感性不同将二者分离纯化,对细胞生长特性进行了光镜观察。结果如下:细胞可形成闭合型细胞群和开放型细胞群。乳腺上皮细胞与成纤维细胞混生时,细胞之间形成许多腔状结构。纯化的乳腺上皮细胞通过单细胞悬浮后传代,部分细胞形成岛屿状聚集,部分细胞以贴壁的自由单个细胞散在形式存在。上皮细胞增殖可形成圆顶型结构,呈乳头状,称之为乳球体;可产生乳腺上皮细胞并分泌乳汁。山羊乳腺上皮细胞含不同的细胞类型.大多数上皮细胞呈短梭形或多角形。细胞之间紧密相靠。互相衔接。连接成片,呈蜂窝状;细胞核呈圆形或椭圆形.核仁2~4枚;部分细胞呈圆饼状,体积较大;出现部分长形细胞;接触抑制的上皮细胞形态不均一。纯化的山羊乳腺上皮细胞传代至第15代时其生长仍正常,经透射电镜观察发现细胞表面微绒毛极为发达,细胞质中线粒体和粗面内质网丰富,细胞质内有大量脂滴及小泡,表明第15代山羊乳腺上皮细胞增殖活力旺盛。染色体数目分析表明.该细胞系稳定,在离体培养条件下细胞不发生转化。山羊乳腺上皮细胞系的细胞染色体数目为60.染色体组型为2n=60。  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