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   709篇
  免费   35篇
  国内免费   54篇
林业   64篇
农学   60篇
基础科学   52篇
  101篇
综合类   232篇
农作物   31篇
水产渔业   28篇
畜牧兽医   116篇
园艺   88篇
植物保护   26篇
  2024年   4篇
  2023年   14篇
  2022年   28篇
  2021年   34篇
  2020年   27篇
  2019年   40篇
  2018年   30篇
  2017年   34篇
  2016年   43篇
  2015年   33篇
  2014年   40篇
  2013年   44篇
  2012年   40篇
  2011年   42篇
  2010年   43篇
  2009年   36篇
  2008年   31篇
  2007年   37篇
  2006年   37篇
  2005年   22篇
  2004年   28篇
  2003年   19篇
  2002年   12篇
  2001年   11篇
  2000年   9篇
  1999年   10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   2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798条查询结果,搜索用时 735 毫秒
151.
AIM: To investigate the possible signaling pathway that promotes epithelial-mesenchymal transition (EMT) of the lung cancer A549 cells stimulated with muscarinic receptor 3 (M3R) agonist carbachol. METHODS: The lung cancer cells A549 were treated with 400 μmol/L carbachol. The morphological changes of the cells were observed under inverted phase contrast microscope. The migration and invasion abilites were measured by Wound healing and Transwell assays. qPCR was used to detect the mRNA level of vimentin and E-cadherin. The protein levels of p-AKT, vimentin and E-cadherin were determined by Western blot. RESULTS: After treatment with carbachol, the A549 cells showed loss of the close connection and the cell morphology was transformed from irregular polygon to spindle-like cells. The results of Wound healing and Transwell assays showed that the migration and invasion abilites of the A549 cells were enhanced. Carbachol increased the vimentin expression and decreased the E-cadherin expression at mRNA and protein level (P<0.05). The phosphorylation of AKT in the A549 cells was up-regulated (P<0.05). These changes was inhibited by M3R antagonist 4-DAMP. CONCLUSION: Carbachol promotes EMT in the human lung cancer A549 cells by activating PI3K/AKT signaling pathway.  相似文献   
152.
AIM: To investigate the effect of toosendanin (TSN) on invasion and migration abilities of human ovarian cancer cells and the related mechanism. METHODS: The human ovarian cancer cell lines CAVO-3 and SKVO-3 were treated with TSN at different concentrations. The cell viabilty at 12, 24, 48, 72 and 96 h after TSN treatment was measured by CCK-8 assay. Scratch wound healing assay and Transwell assay were employed to measure the invasion and migration abilities of CAVO-3 cells. The protein expression of nuclear factor-κB (NF-κB) p65, E-cadherin, N-cadherin, vimentin and Snail was determined by Western blot. RESULTS: TSN significantly inhibited the viability of CAVO-3 and SKVO-3 cells (P<0.05). Compared with control group, the migration and invasion abilities of CAVO-3 cells in TSN group decreased significantly (P<0.05). In addition, the expression of NF-κB p65 and E-cadherin protein increased notably, followed with N-cadherin, vimentin and Snail protein decreased significantly (P<0.05). However, the inhibitor of NF-κB BAY11-7082 reversed the impact above. Compared with TSN group, the migration and invasion abilities in TSN+BAY11-7082 group increased significantly (P<0.05). The protein expression of E-cadherin also decreased notably, followed with the protein expression of N-cadherin, vimentin and Snail increased significantly (P<0.05). CONCLUSION: TSN inhibits the invasion and migration abilities of human ovarian cancer cells, which is related to the inhibition of epithelial-mesenchymal transition process mediated by NF-κB/Snail signaling pathway.  相似文献   
153.
本试验旨在探究过瘤胃葡萄糖对围产期奶牛空肠微生物群落和黏膜代谢及免疫相关基因表达的影响。选择10头围产期荷斯坦奶牛[4~5岁、体重(515±42)kg]随机分为2组,每组5头。对照组和过瘤胃葡萄糖组奶牛饲喂相同的基础饲粮,同时对照组每头每日给予90 g过瘤胃脂肪,过瘤胃葡萄糖组每头每日给予200 g过瘤胃葡萄糖。预试期14 d(产前第21天到产前第8天),正试期21d(产前第7天到产后第14天)。正式期结束后,将所有奶牛(10头)屠宰并取空肠食糜样品,测定其中挥发性脂肪酸的含量和微生物群落;同时取空肠黏膜样品,进行代谢及免疫相关基因表达分析。结果显示:与对照组相比,添加过瘤胃葡萄糖有降低空肠食糜中总挥发性脂肪酸含量的趋势(P=0.094)。与对照组相比,添加过瘤胃葡萄糖有上调空肠黏膜中葡萄糖转运蛋白4(GLUT4)表达量的趋势(P=0.063),有下调Toll样受体4(TLR4)(P=0.063)、白细胞介素-17A(IL 17A)(P=0.063)和白细胞介素-26(IL 26)(P=0.063)表达量的趋势,同时显著性地上调了丙酮酸羧化酶(PC)(P=0.016)、闭合蛋白(occludin)(P=0.016)和胰岛素生长因子结合蛋白5(IGFBP5)(P=0.032)的表达量,显著性地下调了白细胞介素-22(IL 22)(P=0.016)、基质金属蛋白酶1(MMP1)(P=0.016)和基质金属蛋白酶9(MMP9)(P=0.032)的表达量。此外,与对照组相比,添加过瘤胃葡萄糖显著性地增加了空肠食糜中梭菌属ⅪⅤ子集的数量(P=0.036)。由此可见,围产期奶牛饲粮中添加过瘤胃葡萄糖可以改善葡萄糖在机体的代谢以及提高免疫力,同时促进免疫相关有益菌梭菌属ⅪⅤ子集的定植,从而缓解围产期能量负平衡导致的不良影响。  相似文献   
154.
基于中国南方过渡带气候区的特点,依据高尔夫球场对草坪草种选择的基本要求和各草坪草种(品种)的生物学特性,选择过渡带气候区长沙为试验点,以10个常用的草坪草品种(系)为研究对象,按照美国USGA标准建立试验坪床进行草坪建植,采用3个一级质量指标和10个二级指标,利用模糊综合评价法对10个草坪草品种建植的草坪进行草坪质量的综合评价。研究结果表明:在过渡带长沙地区,海滨雀稗‘Salam’、‘天堂草328’、‘老鹰草’和‘运动百慕大’等草坪草品种的草坪综合质量等级为V级,表现优秀,适合用于对草坪质量要求高的果岭区域;海滨雀稗‘海浪’和‘09-1’的草坪综合质量为IV级,表现良好,适用于对草坪质量要求较高的球道;综合评价等级相对较低的为结缕草和匍匐剪股颖,其不适合在湖南地区的高尔夫球场使用。  相似文献   
155.
AIM: To investigate the expression of poly(ADP-ribose) polymerase-1(PARP-1) in the epithelial ovarian cancer(EOC) and its relationship with epithelial-mesenchymal transition(EMT). METHODS: The expression of PARP-1, E-cadherin, vimentin and Snail was detected in the EOC and benign ovarian tumor tissues by immunohistochemical method and real-time PCR. The expression of PARP-1, E-cadherin, vimentin and Snail proteins in the SKOV3 cells treated with efficient PARP-1 inhibitor PJ34 was determined by Western blotting. RESULTS: The positive expression rates of PARP-1, vimentin and Snail were significantly higher in the EOC than that in the benign ovarian tumor tissues, whereas the positive expression rate of E-cadherin was the opposite(P<0.05). The expression of PARP-1, E-cadherin, vimentin and Snail in the EOC was associated with the histological grade, clinical stage and lymphatic metastasis(P<0.05), but no relationship with age and pathological types was observed. The expression of E-cadherin in the EOC was negatively co-related to that of PARP-1. In contrast, the expression of vimentin and Snail in the EOC was positively co-related to that of PARP-1. The relative mRNA expression of PARP-1, vimentin and Snail in the EOC was significantly higher than that in the benign ovarian tumor tissues(P<0.05), while the mRNA expression of E-cadherin in the EOC was remarkably lower than that in the benign ovarian tumor tissues(P<0.05). The protein expression of PARP-1, vimentin and Snail in the SKOV3 cells was significantly decreased(P<0.05), while E-cadherin protein was increased after treated with PJ34(P<0.05). CONCLUSION: PARP-1 may contribute to the onset of EMT in the EOC by regulating the expression of E-cadherin, vimentin and Snail. The role of PARP-1, which is relevant to EMT, might be important in the development of ovarian cancer.  相似文献   
156.
Transition proteins (TNPs) are essential in chromatin condensation during spermiogenesis, and hence, they are the candidate genes for identifying sperm motility markers. Coding and in silico predicted promoter regions of these genes were investigated in crossbred and purebred cattle, and also, their mRNA quantification was done to explore its use as a diagnostic tool of infertility. PCR‐SSCP analysis revealed two band patterns in fragment III of TNP1 and fragment II of TNP2 gene. Sequence analysis revealed a deletion of “G” nucleotide in 3′UTR region of TNP1 and C>T SNP in intronic region of TNP2 gene. Least square analysis of variance did not reveal any significant influence of nucleotide deletion on any sperm motility parameters in both crossbred and purebred cattle. However, C>T SNP had a significant effect on initial progressive motility (p < 0.05) in purebred cattle and post‐thaw motility in overall cattle population. RT‐qPCR analysis did not reveal any significant variation in TNP1 and TNP2 gene expression among poorly motile and good quality spermatozoa of Vrindavani bulls.  相似文献   
157.
线粒体膜通透性变化与细胞凋亡的关系   总被引:4,自引:2,他引:2  
线粒体膜通透性转换孔是一种位于线粒体内膜的非选择性孔道,它的开放引起线粒体膜通透性改变,导致细胞色素C、凋亡诱导因子和Ca2+及膜间隙中的胱冬肽酶原等凋亡因子释放到细胞质中,致使细胞整体结构破坏、功能紊乱,发生凋亡。以前普遍认为线粒体膜通透性改变(mitochondrial permeability transition,MPT)是导致细胞凋亡的关键点,但一些新的研究结果表明,MPT与细胞凋亡并不存在必然的联系。作者结合细胞凋亡方面的研究着重就线粒体膜通透性转换的生物学功能和腺嘌呤核苷酸转位子、环孢素A 结合蛋白D及Bcl-2家族蛋白定位、转位在通透性转换中的作用及其与细胞凋亡的关系进行概括性论述与分析。  相似文献   
158.
This paper examines changes in broom snakeweed populations (Gutierrezia sarothrae [Pursh] Britt. & Rusby) from 1979 to 2014 at three prairie grassland sites in New Mexico. Data gathered each fall were used to study broom snakeweed population dynamics and to estimate the probability that the relatively short-lived subshrub will die off or invade blue grama (Bouteloua gracilis [H.B.K. Lag]) rangelands. Annual broom snakeweed standing crop data were used to categorize populations as None (< 100 kg ha? 1), Light (< 300), Moderate (< 750), or Heavy (≥ 750). Ordered logit regression was then used to estimate the frequency of transition between these categories over time depending on environmental and site factors. Significant variables found to influence annual variation in broom snakeweed included the broom snakeweed standing crop and density observed the previous period (+ effect for continued broom snakeweed); grass standing crop the previous period (?); rainfall received from April to June (+); and average temperatures during April (+) and June (?). The probability of broom snakeweed invading an area that is currently without the plant ranges from about 1% to > 40% depending on environmental conditions and the amount of grass standing crop present. Transition probability estimates were also used in a Monte Carlo simulation model to evaluate the economics of broom snakeweed control. The economics of chemical broom snakeweed control were most strongly related to the rate of snakeweed reinvasion on treated areas and to the probability of natural die-off if infested areas were not sprayed.  相似文献   
159.
Woody plant encroachment is widespread throughout drylands of the world, but rates and patterns of encroachment at the regional scale can be mediated by soil and climate. Climoedaphic properties may therefore help to explain patterns of woody plant dominance. In the Caldenal region of central Argentina, which is experiencing widespread woody plant encroachment, we used stratified and targeted inventory of vegetation and soils alongside climate data to classify vegetation states and then identify factors indicating resistance to woody plant encroachment. We found that three climoedaphic contexts differed in the degree of woody plant dominance. Sandsheet landforms had the lowest likelihood of a shrub thicket state. Within loamy soils, sites with deep soil carbonates in warmer and wetter climates were less likely to feature a shrub thicket state than sites with shallow carbonates in cooler and drier climates. These contexts serve as a basis for recognizing different ecological sites to assist mapping and prioritization of management interventions in the Caldenal region. Simple inventory-based approaches can be helpful for designing land management recommendations in other ecosystems.  相似文献   
160.
AIM: To investigate the effect of Eph receptor A2 (EphA2) on drug resistance of colorectal carcinoma cells and its possible mechanisms. METHODS: Real-time PCR and Western blot were used to detect the expression of EphA2 at mRNA and protein levels in LoVo and LoVo/5-FU cells. EphA2 siRNA was transfected to down-regulate the EphA2 expression in LoVo/5-FU cells, and the drug sensitivity was calculated by CCK-8 assay. Meanwhile, cell migration and invasion were measured by wound healing assay and Transwell assay, and the protein levels of E-cadherin, β-catenin, N-cadherin, vimentin, Notch and Snail were determined by Western blot. RESULTS: The expression of EphA2 at both mRNA and protein levels was significantly up-regulated in LoVo/5-FU cells (P<0.05). Knockdown of EphA2 suppressed the cell viability, and migration and invasion abilities, but promoted drug sensitivity of LoVo/5-FU cells. Up-regulation of E-cadherin and β-catenin, and down-regulation of N-cadherin and vimentin were observed, indicating that the epithelial-mesenchymal transition (EMT) process was suppressed. Knockdown of EphA2 decreased the expression levels of Notch and Snail. CONCLUSION: Down-regulation of EphA2 partly reverses drug resistance of LoVo/5-FU cells. The mechanism may be related to suppressing cell growth, migration, invasion and EMT process via Notch/Snail signaling pathway.  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