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   723篇
  免费   48篇
  国内免费   57篇
林业   65篇
农学   64篇
基础科学   56篇
  107篇
综合类   246篇
农作物   31篇
水产渔业   28篇
畜牧兽医   118篇
园艺   88篇
植物保护   25篇
  2024年   2篇
  2023年   17篇
  2022年   32篇
  2021年   37篇
  2020年   28篇
  2019年   41篇
  2018年   32篇
  2017年   34篇
  2016年   45篇
  2015年   35篇
  2014年   41篇
  2013年   46篇
  2012年   41篇
  2011年   43篇
  2010年   46篇
  2009年   37篇
  2008年   31篇
  2007年   40篇
  2006年   37篇
  2005年   23篇
  2004年   29篇
  2003年   19篇
  2002年   12篇
  2001年   11篇
  2000年   9篇
  1999年   9篇
  1998年   7篇
  1997年   6篇
  1996年   6篇
  1995年   4篇
  1994年   4篇
  1993年   5篇
  1992年   3篇
  1991年   3篇
  1990年   3篇
  1989年   4篇
  1988年   3篇
  1987年   2篇
  1986年   1篇
排序方式: 共有828条查询结果,搜索用时 15 毫秒
11.
拟在动态平衡的视角下对现代足球阵型的演变历程进行梳理与整合,希望对阵型之间的关联及其对足球运动发展的影响提供见解,对阵型演变的不同阶段进行探讨,探寻足球攻守平衡与不同阵型的嬗变关系,同时也为推动未来足球阵型演变对战术打法的影响研究提供参考依据。采用文献资料、系统分析、专家访谈和逻辑分析等方法,对现有的足球阵型发展的概况进行分析之后,认为现代足球阵型的演变历程不断交替出现攻守的平衡与不平衡,正是交替出现的状况促进了阵型的改变,进而影响了阵型的发展。当阵型的发展过程中出现攻守平衡时,就有其它后来者对该阵型进行学习、模仿、改进、提高。当阵型的发展过程中出现攻守不平衡,攻强于守或者守强于攻时,就会促进阵型的演变向攻守平衡的方向发展,因此就会出现阵型的发展处于不平衡-平衡-不平衡-再到平衡的态势,从而形成比赛阵型发展本身的稳定与不稳定状态交替出现。研究认为,世界足球阵型演变的过程是一种动态的、不断发展的、维持某种平衡与稳定的、平衡和不平衡交替运动的情况,即动态平衡的状态。提出将现代足球阵型演变的过程分为不同的阶段,每一个阶段内,都分别出现攻守平衡与攻守不平衡的状态,而这种平衡与不平衡的存在与区别、斗争与转化正是足球阵型演变与发展的规律。  相似文献   
12.
AIM: To investigate the effects of chronic hypoxia on the aggressiveness of MCF-7, a human breast cancer cell line, and the underlying mechanisms.METHODS: MCF-7 cells were cultured under hypoxia (1% O2, 5% CO2 and 94% N2) or control (95% O2 and 5% CO2) condition. The viability, proliferation, and invasion and migration abilities of the MCF-7 cells were determined by MTT assay, CCK-8 assay, cell counting, and cell invasion and migration assays. Anchorage-independent growth and the alteration of cellular polarization of the MCF-7 cells were tested by soft agar colony formation assay and Matrigel-3D culture assay, respectively. The effects of chronic hypoxia on the growth and metastasis of MCF-7 cells in vivo were investigated by xenograft in nude mice. The morphological changes of the MCF-7 cells were observed under an inverted microscope. Hypoxia-induced alterations in the levels of hypoxia inducible factor-1 (HIF-1) and phosphorylated glycogen synthase kinase-3β (p-GSK-3β) as well as epithelial-mesenchymal transition (EMT) molecules, such as E-cadherin, N-cadherin, vimentin, matrix metalloproteinase (MMP)-3 and MMP-9, were determined by Western blot.RESULTS: Chronic hypoxia significantly increased the viability, proliferation, and invasion and migration abilities of MCF-7 cells in vitro, enhanced the anchorage-independent growth, facilitated cellular polarization alteration in Matrigel-3D culture, and promoted cancer metastasis in vivo. Hypoxia up-regulated HIF-1, activated GSK-3β, down-regulated E-cadherin and increased the protein levels of N-cadherin, vimentin, MMP-3 and MMP-9. CONCLUSION: Chronic hypoxia enhances the aggressiveness of breast cancer cells probably through EMT.  相似文献   
13.
农业专业镇是广东省农村经济发展的重要推动力。如今农业专业镇的发展面临着结构调整、产业升级和增长方式转变的巨大挑战,服务平台发展的战略选择对农业专业镇发展至关重要。专业镇的中小微企业服务平台建设发展呈现出以创新为核心、产学研紧密结合的趋势:加快中小微企业服务平台发展,在战略上必须以政府为主导,市场化配合运作,将载体建设与功能培育协同运作,将产学研合作与联盟服务协同运作,将品牌建设与重点扶持紧密结合,形成协同运作体系网。  相似文献   
14.
AIM: To observe the influence of gold nanoparticles combined with Endostar (AuNPs-Endostar) on the melanoma lung metastasis of mice and the underlying mechanism. METHODS: C57BL/6 mice (n=24) were selected for constructing the model of spontaneous lung metastasis of melanoma B16-F10 cells. Subsequently, the mice were randomly divided into Endostar group, AuNPs group, AuNPs-Endostar group and model group. After the formation of melanoma, the mice in each group were injected with different drugs through tail vein for 0.1 mL daily. After 9 d, the mice were narcotized for cutting the tumors in situ. After the operation, they were raised for 2 weeks before killed for obtaining the lung tissues to observe the situation of the metastasis. HE staining was utilized for observing the necrosis status of the tumors in situ, while immunostaining was applied for testing the expression of CD31, carbonic anhydrase-IX (CA-IX), vimentin and zonula occludens-1 (ZO-1) in the tumors. RESULTS: Compared with model group, the pulmonary metastasis in the groups with medical treatment was obviously reduced. In AuNPs-Endostar group, the metastasis inhibition rate was the highest, and the tumor necrosis was also decreased obviously, with the significant reduction of CD31, CA-IX and vimentin expression in the tumors and significant increase in ZO-1 expression. CONCLUSION: Compared with using Endostar or AuNPs alone, the combination of AuNPs with Endostar significantly improves the curative effect of inhibiting the pulmonary metastasis of melanoma in the mice. The mechanism may be related to reducing the tumor angiogenesis, norma-lizing the blood vessels and improving tumor hypoxia, thus inhibiting the tumor epithelial-mesenchymal transition, increasing the tight junctions between tumor cells and decreasing the invasiveness.  相似文献   
15.
过渡乳是初乳向常乳过渡的乳汁。目前国内对于过渡乳的概念还没有深刻的认识。根据调研,目前在犊牛灌服初乳后,为了节省人力、节约成本,牧场对于过渡乳的使用并不充分,有的完全废弃,有的违规操作进行售卖,而采用代乳粉、常乳等代替过渡乳对犊牛进行饲喂。针对这一问题,本文从过渡乳的定义、营养价值和对犊牛生产性能的影响三个方面进行综述,以为过渡乳的使用以及犊牛7日龄内饲喂方案的制定提供参考。  相似文献   
16.
17.
Fair-trade and organic products are often sold at price premiums justified by smaller production volumes that are associated with greater social and environmental responsibility. The consumption of these products confers on the consumer a greater sense of morality – and usually a claim to better taste. This paper tells the story of attempts to promote organic/fair-trade rice production by de facto organic Cambodian farmers for export to North American and European markets in order to assist poor farmers to trade their way out of poverty. It demonstrates that instead of promoting sustainable agriculture and fair trade between developed and developing markets, organic/fair-trade projects may impose First World consumer ideals and tastes that are out of step with the larger realities of agrarian transition in Cambodia and the wider region of developing Southeast Asia.  相似文献   
18.
19.
AIM: To investigate the role of voltage-dependent anion channel (VDAC) in H9c2 cardiomyocytes subjected to anoxia/reoxygenation (A/R).METHODS: The shRNAs targeting VDAC1 mRNA were inserted into pSUPER plasmid.H9c2 cells were randomly divided into 5 groups as follows: control group, A/R group, anoxia preconditioning (APC) group, pSUPER-VDAC1-A/R group and pSUPER-A/R group. The expression of VDAC1 was detected by Western blotting. Cellular injury was evaluated by measuring the cell viability and the release of lactate dehydrogenase (LDH) and creatine phosphokinase (CPK). The mitochondria membrane potential was determined by flow cytometry.RESULTS: VDAC1 expression was up-regulated in A/R group and was inhibited in APC group. Similarly, down-regulation of VDAC1 expression by shRNA protected H9c2 cells from A/R injury. Moreover, we found that, with silencing VDAC1 expression, mitochondrial membrane potential was well preserved in H9c2 cells subjected to A/R.CONCLUSION: Down-regulation of VDAC1 protects H9c2 cells against A/R injury and its possible mechanism appears to be related to the regulation of mitochondial permeability transition pore opening.  相似文献   
20.
本文就大气保护制冷行业的关系并从保护臭氧层、大气变暖的角度,论述了空调制冷行业与环保的关系。  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