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   5818篇
  免费   121篇
  国内免费   215篇
林业   410篇
农学   228篇
基础科学   212篇
  375篇
综合类   2322篇
农作物   240篇
水产渔业   217篇
畜牧兽医   1793篇
园艺   243篇
植物保护   114篇
  2024年   39篇
  2023年   117篇
  2022年   150篇
  2021年   176篇
  2020年   141篇
  2019年   169篇
  2018年   182篇
  2017年   86篇
  2016年   118篇
  2015年   112篇
  2014年   187篇
  2013年   190篇
  2012年   276篇
  2011年   337篇
  2010年   191篇
  2009年   199篇
  2008年   263篇
  2007年   309篇
  2006年   297篇
  2005年   271篇
  2004年   219篇
  2003年   212篇
  2002年   196篇
  2001年   175篇
  2000年   180篇
  1999年   86篇
  1998年   63篇
  1997年   87篇
  1996年   64篇
  1995年   58篇
  1994年   89篇
  1993年   56篇
  1992年   66篇
  1991年   64篇
  1990年   63篇
  1989年   51篇
  1988年   22篇
  1987年   26篇
  1986年   23篇
  1985年   25篇
  1984年   25篇
  1983年   20篇
  1982年   21篇
  1957年   12篇
  1956年   14篇
  1922年   19篇
  1921年   26篇
  1920年   23篇
  1919年   16篇
  1896年   12篇
排序方式: 共有6154条查询结果,搜索用时 0 毫秒
991.
为了明确小麦籽粒性状的遗传控制基础,以γ射线诱变结合花药培养创制的大粒、高蛋白小麦新种质H307及生产上主栽品种郑麦9023创建的含有310个株系的重组自交系为实验材料,利用QTL-ICIMapping V3.3软件构建了包含133对SSR标记的遗传连锁图谱,对千粒重、粒长、粒宽、籽粒面积、周长、粗蛋白和淀粉含量进行QTL分析,结果在两年环境条件下共检测到47个加性QTL和10个QTL富集区,其中6个千粒重QTL,分别位于1D、2B、3D、6D和7A染色体上,单个QTL可解释4.54%~13.14%的表型变异;31个粒形QTL,位于1B、1D、2B、3B、3D、5A、5D、6B、6D、7A和7D染色体上,单个QTL可解释2.90%~15.86%的表型变异;10个粗蛋白和淀粉含量QTL,分别位于1A、1B、4B和6A染色体上,单个QTL可解释3.64%~12.19%的表型变异。2B染色体上检测到1个贡献率较大且能稳定表达的重要染色体区段,该区段包含控制小麦千粒重、粒长、粒宽、籽粒面积和周长的10个QTL。1BL染色体上检测到1个控制籽粒粗蛋白含量的微效QTL,对表型的贡献率为3.64%,与连锁分子标记gwm818的遗传距离为0.22cM,该位点是一个不同于前人研究结果的新位点。  相似文献   
992.
气候条件与茶园管理关键技术   总被引:4,自引:1,他引:4  
本文在研究分析了气温、降水和冻土等主要气候条件的基础上,结合山东茶区的茶叶生产实践经验,提出了营造防护林网、蓄水灌溉或茶园行间铺草、茶树修剪与鲜叶采摘、施肥、病虫害防治和越冬管理技术等北方茶园管理关键技术。  相似文献   
993.
旱优540是上海市农业生物基因中心用沪旱5A作母本,以旱恢840作父本配组育成的籼型高产优质节水抗旱杂交水稻新组合,具有节水抗旱、优质、高产、适应性广等优点,2019年通过上海市农作物品种审定委员会审定.  相似文献   
994.
The gammaherpesvirus bovine herpesvirus-4 (BHV-4) has been isolated from a wide variety of animals, including lions and domestic cats. Although BHV-4 antibodies have been detected in normal cats and cats with urinary disorders, the epidemiology and pathogenic role of BHV-4 in cats is unknown. The purpose of this study was to determine the prevalence of BHV-4 antibodies and viral nucleic acid in a population of free-roaming cats. Plasma and peripheral blood leukocyte samples were collected from 52 male and 52 female free-roaming cats impounded at a regional animal control facility in Central Michigan. Plasma concentrations of BHV-4 antibodies were measured with an indirect fluorescent antibody test. Peripheral blood leukocyte DNA was isolated, and a 2-stage polymerase chain reaction with heminested primers delineating a conserved portion of the BHV-4 glycoprotein B gene homologue was used to amplify BHV-4-specific DNA sequences. BHV-4 antibodies were detected in 38 (73%) male and 23 (44%) female cats. Seropositive cats were significantly more likely to be male than female (odds ratio = 3.22; P = .007). Cell-associated viremia was detected in 17 (33%) male and 11 (21%) female cats. Of the 61 seropositive cats, 23 (38%) had a detectable viremia; only 5 (12%) seronegative cats had detectable viremia. Seropositive cats were significantly more likely to be viremic than seronegative cats (OR = 4.30: P = .009). Our results suggest that BHV-4 infection may be more widespread in certain cat populations than previously reported. Furthermore, many cats seropositive for BHV-4 antibodies have a concurrent cell-associated viremia.  相似文献   
995.
两种深度养殖池塘水质和浮游藻类多样性分析   总被引:1,自引:0,他引:1  
本试验研究了珠海市之山水产养殖基地的3个浅水池塘(1.3±0.1) m和3个深水池塘(2.2±0.1) m中的浮游藻类的种类组成、分布和群落结构特点以及理化指标的变化,以探讨两种不同深度池塘的水质和浮游藻类多样性之间的差异,为传统池塘挖深改造提供理论依据。结果显示,浮游藻类密度、藻类组成及藻类优势种群在两种不同深度池塘中存在明显的差异,深水池塘的藻类密度、丰度指数、多样性指数和均匀度指数均显著低于浅水池塘(P<0.05)。总磷(TP)和总氮(TN)浓度在两种不同深度池塘中也存在着明显的差异,深水池塘中的总磷(TP)和总氮(TN)浓度显著高于浅水池塘(P<0.05)。深水池塘中的藻类密度与TN和TP之间存在着显著的相关性,但浅水池塘的藻类密度和TN、TP相关性不显著。  相似文献   
996.
通过试验研究凋亡因子Caspase-9在肉用绵羊主要生殖器官中的表达,并探讨其生理意义.利用免疫组织化学的方法对Caspase-9在肉用绵羊主要生殖器官中的表达进行研究.研究结果显示,Caspase-9只在细胞质中表达,其在卵巢中主要分布于原始卵泡、初级卵泡及颗粒性黄体细胞,而卵泡膜性黄体细胞中未见表达;黄体期,主要表达于子宫的浅层腺体腺上皮细胞、子宫内膜上皮细胞、子宫颈黏膜固有层的淋巴小结、输卵管黏膜上皮分泌细胞和纤毛细胞、峡部的浆液性腺的腺上皮细胞;卵泡期,子宫和输卵管各个部位阳性反应不明显.在正常生理情况下,Caspase-9参与了肉用绵羊主要生殖器官周期性变化的调控和子宫黏膜免疫,对生殖器官功能的稳定发挥起着重要作用.  相似文献   
997.
Campylobacter jejuni and Campylobacter coli strains were isolated from feces of dairy cattle at farms with no known problem due to campylobacteria. Farms were located in the northeast, desert southwest, and Pacific west. Twenty isolates were identified by ribotyping with a RiboPrinter. The ability of these bovine isolates to colonize the ceca of chicks was determined by challenge inoculation and reisolation of the challenge strain from the ceca at 1 and 2 wk after challenge. Isolates recovered from chick ceca were examined by ribotyping to assure they matched the challenge strain. One hundred percent of the bovine-derived challenge strains were capable of colonizing chicks. These results indicate that dairy cattle may be asymptomatic Campylobacter carriers and potential sources of campylobacteria contamination of poultry facilities.  相似文献   
998.
OBJECTIVE: To describe the localization of immunoreactive transforming growth factor (TGF)-beta1 in both normal skin and full-thickness dermal wounds of the limb and the thorax of the horse. STUDY DESIGN: Six full-thickness excisional wounds were created on the lateral aspect of one metacarpal region and on the midthoracic area of each horse. Sequentially collected tissue specimens from wound margins were assessed for TGF-beta1 expression by immunohistochemistry. ANIMALS: Four horses (2 to 4 years of age). METHODS: A neutralizing monoclonal anti-human TGF-beta1 antibody was used to detect the spatial expression of TGF-beta1 protein by immunohistochemical localization in biopsies obtained before wounding and at 12 and 24 hours, and 5, 10, and 14 days. RESULTS: No differences in localization of immunoreactive TGF-beta1 were detected between limb and thorax, for either intact skin or wounds. Unwounded epidermis stained moderately for TGF-beta1 protein throughout all layers, whereas the dermis was relatively devoid of immunoreactivity. During the acute stage of repair, migrating epithelium lost its stain, whereas cells of epidermal appendages remained strongly immunoreactive. The epithelium recovered its TGF-beta1 immunoreactivity during wound remodeling, although cells of the stratum corneum remained negative. Macrophages of the inflammatory exudate had positive cytoplasmic staining that diminished with time. Immunoreactivity of granulation tissue fibroblasts was evident early on and increased throughout the repair process. CONCLUSIONS: TGF-beta1 is constitutively expressed in normal, unwounded equine epithelium. Its expression is upregulated within the skin on injury and is associated with the cells involved in wound repair. CLINICAL RELEVANCE: A more precise understanding of the temporal and spatial expression of TGF-beta1 during wound repair in horses should provide the groundwork for possible future manipulations of both normal and aberrant tissue repair.  相似文献   
999.
水葫芦对加州鲈池塘水质及底泥净化作用研究   总被引:1,自引:0,他引:1  
水葫芦具有良好的净水能力,但并未作为水质改良的途径进行推广。在模拟加州鲈养殖生态的池塘中施放密度为10株/m2的水葫芦,与不作处理的池塘作对比,处理8…d后,通过测定模拟池塘水体pH、氨氮、亚硝酸盐、总氮及总磷浓度等水质指标,底泥有机物及全磷含量等指标及池塘浮游生物量,评价水葫芦对加州鲈高密度精养池塘水体的净化作用。结果表明,水葫芦对水体pH无明显影响,水体中氨氮最大去除率达60.9%,总氮最大去除率达59%。水葫芦处理后,底泥有机物的最大去除率达65.6%,全磷的最大去除率达46.9%。水葫芦对浮游生物总量影响不明显,但显著降低了绿藻、蓝藻生物量,在一定程度上控制了浮游植物种群结构。  相似文献   
1000.
为更好保护地方猪种质资源,利用超低温冷冻精液长期保存公猪精液,具有重大的现实意义。根据全国畜牧总站、中国饲料工业协会《关于开展玉山黑猪品种遗传资源生物保种项目的计划通知》要求,2018年~2019年,笔者对玉山黑猪进行了超低温细管冷冻精液制作,冻后活力质量均在35%以上,符合冷冻精液人工授精要求。本文从鲜精采集运输、检测离心、稀释平衡、冷冻制作等方面详细阐述玉山黑猪遗传物质制作过程。  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