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   14718篇
  免费   890篇
  国内免费   1672篇
林业   884篇
农学   840篇
基础科学   665篇
  1495篇
综合类   6984篇
农作物   1267篇
水产渔业   736篇
畜牧兽医   2471篇
园艺   1135篇
植物保护   803篇
  2024年   83篇
  2023年   319篇
  2022年   760篇
  2021年   694篇
  2020年   656篇
  2019年   668篇
  2018年   482篇
  2017年   755篇
  2016年   538篇
  2015年   742篇
  2014年   825篇
  2013年   984篇
  2012年   1251篇
  2011年   1383篇
  2010年   1231篇
  2009年   1006篇
  2008年   1134篇
  2007年   971篇
  2006年   776篇
  2005年   574篇
  2004年   412篇
  2003年   222篇
  2002年   222篇
  2001年   222篇
  2000年   220篇
  1999年   78篇
  1998年   7篇
  1997年   2篇
  1996年   3篇
  1995年   9篇
  1994年   3篇
  1993年   6篇
  1992年   5篇
  1991年   3篇
  1990年   2篇
  1988年   2篇
  1987年   6篇
  1986年   7篇
  1985年   1篇
  1983年   1篇
  1981年   4篇
  1962年   4篇
  1956年   2篇
  1955年   5篇
排序方式: 共有10000条查询结果,搜索用时 177 毫秒
951.
 根据GenBank上已发表的其他真菌α–微管蛋白基因序列中的保守区域设计简并引物,扩增出银耳α–微管蛋白基因的cDNA部分序列。分别利用SEFA-PCR方法和RACE技术,克隆了银耳α–微管蛋白基因的DNA和cDNA全长序列。银耳α–微管蛋白基因DNA全长1 962 bp,含有9个内含子,cDNA全长1 347 bp,编码448个氨基酸。生物信息学分析结果表明:银耳α–微管蛋白基因的cDNA序列与新型隐球酵母有80%相似性,编码的蛋白质属于Tubulin_FtsZ超家族中的α–微管蛋白亚家族,氨基酸序列中存在保守的GTP结合区域GGGTGSG,系统发育树显示银耳与新型隐球酵母距离最近。  相似文献   
952.
AIM: To investigate the protective role of heat-shock protein 70 (HSP70) in the pathogenesis of gastric mucosal damage in cirrhotic rats with portal hypertensive gastropathy (PHG).METHODS: The rat model of liver cirrhosis with PHG was established by injection with tetrachloride.The animals were divided into normal control group, PHG group, PHG+heat treatment group, PHG+BPI21 group and PHG+endotoxin groups.The endotoxin used in the experiment was at the dose of 3 mg/kg and endotoxin antagonist BPI21 was at the dose of 2 mg/kg.HSP70 was induced by pre-treating the animals with mild whole-body heating.The levels of HSP70 and tumor necrosis factor alpha (TNF-α) in the gastric mucosa were measured by ELISA.Furthermore, the pathological changes of the gastric mucosa were observed under microscope with HE staining.RESULTS: Compared with the normal control rats, the rats in PHG group showed obvious gastric pathological lesion, decrease in HSP70 production and increase in TNF-α level in the gastric mucosa, and increased endotoxin concentration in the plasma.Compared with PHG+endotoxin group, the gastric mucosal lesion in PHG+BPI21 group was significantly attenuated, accompanied by the increase in HSP70 production and decrease in TNF-α level in the gastric mucosa.Heat treatment increased HSP70 production and decreased TNF-α concentration in the PHG rats, thus attenuating the gastric mucosal damage.CONCLUSION: HSP70 alleviates the gastric mucosal lesion induced by endotoxin in cirrhotic rats with PHG and decreases the concentration of TNF-α in gastric mucosa, indicating a protective role of HSP70 in the pathogenesis of gastric mucosal damage in PHG.  相似文献   
953.
AIM: To observe the effect of cyclosporine A on intima hyperplasia of rat abdominal aortas injured by balloon.METHODS: Thirty-six healthy adult male SD rats were randomly divided into 3 groups: sham group (n=12), balloon-injured group (n=12) and cyclosporine A treatment group (n=12).From the 3rd day before injury to the 30th day after injury, the rats in cyclosporine A treatment group were treated with cyclosporine A at a dose of 12.5 mg/kg everyday, while the rats in sham group and balloon-injured group were fed with the same volume of water.On the 30th day after injury, the specimens were obtained from the rats.HE staining and immunohistochemistry were used to measure the expression level of calcineurin (CaN) in arterial wall.Pathological changes of the arterial wall were observed under light microscope.The expression of CaN and nuclear factor 3 of activated T-cells(NFATc3) in the abdominal aortas was detected by the technique of real-time PCR.RESULTS: Intimal hyperplasia was observed in balloon-injured rats.The neointima was not uniform in thickness on the 30th day.The thickness of the intimal layers and the ratio of the intimal to the medial layers in cyclosporine A group were obviously lower than those in balloon group(P<0.05).Immunohistochemistry revealed that calcineurin expression increased after balloon injury, but the expression of calcineurin in cyclosporine A group was obviously decreased as compared with balloon group (P<0.05).The results of real-time PCR showed that the mRNA expression of calcineurin and NFATc3 in cyclosporine A group was significantly lower than that in balloon-injured group (P<0.05).CONCLUSION: Cyclosporine A attenuates restenosis by suppressing the CaN-NFATc signaling pathway.  相似文献   
954.
AIM: To study the expression of prostate-specific membrane antigen (PSMA) on the level of phospho-ERK, cell growth and migration of prostate cancer LNCaP cells.METHODS: The method of silencing PSMA was established by lentivirus-mediated RNAi in our early experiment. The cells were divided into 3 groups.In experimental group, the expression of PSMA in LNCaP cells was stably blocked by lentivirus-mediated RNAi. In negative control group, the cells were transfected with lentivirus-mediated control RNAi (without any interference to PSMA).The normal LNCaP cells served as blank control. The cells in these 3 groups were cultured in both 2 environments: normal medium and medium with PD98059 (an inhibitor of ERK phosphorylation). The phospho-ERK was detected by Western blotting and immunocytochemistry. Furthermore, the growth and migration of the cells were evaluated by MTT and transwell assays,respectively.RESULTS: In normal medium, the expression of phospho-ERK was attenuated in experimental group (P<0.05) and the quantity of "positive" cells was less than those in other 2 groups (P<0.05). Furthermore, the growth curves of the cells showed that the growth ability in experimental group was significantly decreased (P<0.05, after 48 h) and the migration ability in experimental group was reduced (P<0.05). In the inhibitory medium, the cells in all 3 groups expressed phospho-ERK at a lower level. Moreover, the abilities of growth and migration in these 3 groups were poorly displayed. These inhibitory effects on phosphorylation of ERK were similar to the cells in experimental group cultured in normal medium.CONCLUSION: PSMA may play a role in up-regulation of phospho-ERK and it may take an advantage in growth and migration of prostate cancer LNCaP cells.  相似文献   
955.
AIM: To establish and evaluate a rat model of heart ischemia-reperfusion injury in vivo. METHODS: Seventy-two male Sprague-Dawley rats weighing(250±50)g were randomly divided into sham operation group(sham), ischemia-reperfusion group(I/R) and normal group. The animals were anesthetized and heparinized. Myocardial ischemia-reperfusion was induced by ligating the left anterior descending coronary artery with "U-shape tube" for 35 min followed by 120 min or 240 min reperfusion in vivo. The heart infarct size was measured by triphenyltetrazolium chloride(TTC) staining. The myocardial cell apoptotic index was determined by the method of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling(TUNEL). Immunohistochemical method was used to detect the expression of Bcl-2 and Bax in rat ischemia myocardium. The blood level of MB isoenzyme of creatine kinase(CK-MB),cardiac troponin I(cTnI),nitric oxide(NO),malondialdehyde(MDA), total superoxide dismutase(T-SOD)and glutathione peroxidase(GSH-Px) were detected after reperfusion for 2 h and 4 h. RESULTS: Compared with normal group and sham group, there were obvious changes of ST-T segment and Q wave in the electrocardiogram of I/R group. The blood level of CK-MB, cTnI, NO, MDA and GSH-Px in I/R group increased(P<0.05,P<0.01) after reperfusion for 2 h and 4 h, and the blood level of T-SOD in I/R group after reperfusion for 2 h and 4 h also increased(P<0.05). The heart infarct size in I/R group was the largest as compared to other groups. Among these groups, the apoptotic index of I/R group was the highest and the Bcl-2/Bax ratio in I/R group decreased(P<0.01).CONCLUSION: The rat model of heart ischemia-reperfusion injury in vivo can be successfully established with the "U-shape tube". There are obviously changes of heart infarct size, blood level of CK-MB, cTnI, NO, MDA, T-SOD and GSH-Px, myocardial apoptotic index and Bcl-2/Bax ratio between I/R rats and control animals.  相似文献   
956.
分别采用微生物培养的方法、16S rDNA PCR-RFLP方法和phl D基因PCR-RFLP方法研究了嫁接对西瓜根际微生物种群数量、细菌群落结构及拮抗菌(2, 4-DAPG产生菌)群落结构的影响。结果表明:① 嫁接西瓜根际细菌和真菌数量有所提高,而放线菌数量则有所减少。② 嫁接西瓜与自根西瓜具有1个相同的主要根际细菌基因型;不同砧木嫁接的西瓜与自根西瓜也分别具有不同基因型的细菌。③ 嫁接西瓜具有与自根西瓜不同的主要根际拮抗菌基因型。  相似文献   
957.
李春静  董大伟 《湖南农机》2011,38(7):245-246
钻孔灌注桩是指在工程现场通过机械钻孔、钢管挤土或人力挖掘等手段在地基土中形成桩孔,并在其内放置钢筋笼、灌注混凝土而做成的桩.文章介绍了钻孔灌注桩在施工中遇到的一些质量问题,提出一些可行的预防措施与解决办法,减少财产损失以及对整个工程质量的影响.  相似文献   
958.
河南省是我国的第一农业大省,其粮食生产情况对我国粮食安全有着举足轻重的作用.鉴于粮食生产系统的影响因素很多,选择了12个粮食生产中的基本影响因素,通过主成分分析,确定出影响河南省粮食产量的主要因子为农业机械总动力、化肥施用折纯量、农用塑料薄膜使用量、农田有效灌溉面积和年底常用耕地面积5个主要影响因素.并对影响河南省粮食...  相似文献   
959.
研究了全硝(100%NO-3)、铵硝配施(75%NO-3: 25%NH+4)及全铵(100%NH+4)营养对樱桃番茄果实有机酸含量的影响,测定了与有机酸合成相关的磷酸烯醇式丙酮酸羧化酶(PEPC)、柠檬酸合成酶(CS)、苹果酸脱氢酶(MDH)活性变化,并利用RT-PCR检测了相应的基因在转录水平上的表达差异。结果表明, 1)全硝和铵硝配施处理下果实柠檬酸含量在整个生育期均显著高于全铵处理,而铵硝配施处理下果实中柠檬酸和苹果酸含量在成熟期均显著低于全硝处理。2)不同形态氮素及配施处理下,果实中柠檬酸含量与CS活性的变化趋势均呈单峰型,但到达峰值的时间不同。全铵处理下果实苹果酸含量与PEPC活性呈显著正相关,全硝、铵硝配施处理下果实苹果酸和柠檬酸含量都与MDH活性呈显著正相关。3)在膨大期和成熟期,全硝处理和铵硝配施处理下PEPC基因(PPC1、PPC2)表达显著高于全铵处理; 线粒体苹果酸脱氢酶(mMDH)的表达对果实苹果酸脱氢酶活性和苹果酸积累起主要作用,表明适当比例的铵硝配施可能通过影响果实中PEPC和MDH的活性和基因表达从而显著降低成熟果实有机酸的含量。  相似文献   
960.
外源NO对缺铁胁迫下花生生理特性的影响   总被引:2,自引:1,他引:1  
为探讨外源NO对缺铁胁迫下花生生理特性的影响,采用溶液培养方法,研究了营养液中Fe(Ⅲ)-EDTA 浓度分别为0、10、100 mol/L 条件下,外施250 mol/L硝普钠(SNP, 一种NO 供体)对花生生理特性以及矿质元素含量的影响。结果表明,在相同供铁水平下,外施NO可促进花生幼苗的生长,提高根系活力、净光合速率、蒸腾速率、气孔导度和叶片抗氧化酶活性,降低胞间CO2 浓度和MDA 含量,抑制花生对P 的吸收;在Fe(Ⅲ)-EDTA 浓度分别为0、10 mol/L 条件下综合效果更显著。在0、10、100 mol/L Fe(Ⅲ)-EDTA 中施加SNP 处理20d 后,叶片活性铁含量分别比未施加SNP处理提高了130.7%、136.4%、56.1%,差异显著;同时植株全铁含量及地上部吸铁量占植株总量的百分率也显著提高。说明外源NO可促进铁从根部向植株地上部的运输以及植株体内铁的有效性,提高了铁的运输和利用效率,有效缓解缺铁胁迫的抑制。同时,外施NO还可提高花生叶片叶绿素、类胡萝卜素含量和叶绿素a/b值。在Fe(Ⅲ)-EDTA 浓度分别为0、10 mol/L 条件下,添加SNP 可以明显降低生长介质的pH,比较 1d 内生长介质中pH 变化看出,花生在14h左右分泌H+ 的能力最强。  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