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   2114篇
  免费   107篇
  国内免费   154篇
林业   122篇
农学   117篇
基础科学   139篇
  153篇
综合类   1132篇
农作物   109篇
水产渔业   80篇
畜牧兽医   302篇
园艺   152篇
植物保护   69篇
  2024年   4篇
  2023年   18篇
  2022年   68篇
  2021年   69篇
  2020年   60篇
  2019年   59篇
  2018年   35篇
  2017年   66篇
  2016年   53篇
  2015年   73篇
  2014年   89篇
  2013年   123篇
  2012年   185篇
  2011年   177篇
  2010年   185篇
  2009年   188篇
  2008年   171篇
  2007年   181篇
  2006年   156篇
  2005年   135篇
  2004年   95篇
  2003年   38篇
  2002年   32篇
  2001年   47篇
  2000年   43篇
  1999年   13篇
  1998年   1篇
  1997年   1篇
  1995年   1篇
  1992年   2篇
  1989年   1篇
  1987年   1篇
  1960年   1篇
  1958年   1篇
  1956年   2篇
  1954年   1篇
排序方式: 共有2375条查询结果,搜索用时 109 毫秒
41.
以地被菊'映洁红菲'试管苗叶片为试材,采用组织培养法,研究了6-苄基腺嘌呤、萘乙酸激素浓度、蔗糖浓度、MS浓度、NO3-和NH+的浓度比、羧苄青霉素浓度及潮霉素浓度对不定芽分化的影响,以期建立'映洁红菲'高效的再生体系,为地被菊转基因体系奠定基础.结果 表明:在6-BA和NAA浓度分别为2.0、0.6 mg·L-1,蔗糖浓度为30 g·L-1,NO3-:NH4+为30∶30,基本培养基3/4MS中,'映洁红菲'叶片中愈伤组织诱导和不定芽分化率达到最高,平均每个叶盘分化3.22个不定芽,诱导率75.67%.在生根培养基中加入浓度为0.75 mg·L-1 IBA时,根系生长最好.'映洁红菲'遗传转化时,羧苄青霉素浓度为250mg· L-1,潮霉素浓度为2.0 mg·L-1,适合作为选择压.  相似文献   
42.
发酵豆粕的生产现状及产品质量评定研究   总被引:2,自引:0,他引:2  
介绍了国内主要发酵豆粕厂家的生产工艺流程、产品质量评定指标及鉴别方法。  相似文献   
43.
AIM: Toll-like receptor 4 (TLR4) was an important pathogen recognition receptor in the innate immune system. The aim of this study was to investigate the distribution of TLR4 polymorphisms in the general population of China. METHODS: Peripheral blood samples were collected from 191 unrelated healthy Chinese Cantonese individuals. The functional regions of TLR4 locus, including promoter region and all three exons with their surrounding intronic regions were amplified using polymerase chain reaction. After purified, the amplified products were directly sequenced on both strands. RESULTS: A total of eight single nucleotides polymorphisms (SNPs) were detected, five of which were novel. The most common SNP were -1607 C/T with the minor allele frequency of 0.283. Two nonsynonymous substitutions Asp299Gly and Thr399Ile, which were common in Caucasus, were not detected in Cantonese. Neutrality test revealed that TLR4 in Chinese Cantonese was not significantly deviated from the neutral model. CONCLUSION: This is the new finding on the distribution of TLR4 SNPs in the general population of China. It provides several ethnic specific SNPs for further disease association studies of TLR4 polymorphisms in Chinese populations.  相似文献   
44.
杂草稻对粳稻生长及产量的影响   总被引:4,自引:0,他引:4  
在同期播种情况下,和粳稻相比,杂草稻出苗时的叶片更肥长、营养生长期的植株更高、分蘖数多达4倍以上。不同生物型杂草稻的落粒性差异较大。杂草稻密度愈高对栽培粳稻的产量影响愈大。  相似文献   
45.
牛乳头状瘤的病理学观察及其病毒基因型分析   总被引:1,自引:0,他引:1  
为研究牛乳头状瘤病毒(BPV)在我国对牛的致病性及基因型,本研究选取某奶牛场发病的犊牛,通过对皮肤肿瘤样物进行临床观察、组织病理学及免疫组织化学检查,并应用DNA提取及PCR等技术对其进行鉴定.组织病理学结果显示牛乳头状瘤呈现角化过度和细胞空泡化现象;免疫组织化学结果显示胞浆棕染呈BPV阳性;应用PCR对其DNA进行扩增,检测出阳性样品,测序结果表明与BPV-1和BPV-2同源性达98%~99%.表明该奶牛场犊牛发病由BPV-1和BPV-2引起的.  相似文献   
46.
植物病害生物防治与微生态学   总被引:11,自引:0,他引:11  
在概述植物病害生物防治生态学意义的基础上,从植物微生态学的角度阐述了植物根围菌及内生菌作为生防菌的依据和意义。特别是内生菌是植物体内的正常菌群,对植物病害生物防治具有重要的生态学实践意义。  相似文献   
47.
AIM: To observe the inhibition effects of 10-23 deoxyribozyme (DNAzyme) specific to human proliferating cell nuclear antigen (PCNA) gene on the proliferation of human umbilical artery smooth muscle cells (HUASMC) in vitro. METHODS: Using lipofectamine (Lip)-mediated method, the DNAzyme specific to PCNA was introduced into HUASMC. [3H]-TdR incorporation was determined. The cell proliferation was examined by MTT assay and cell cycle was detected by flow cytometry. RESULTS: [3H]-TdR incorporation in 1.0 μmol/L DNAzyme group was lower than that in control group (P<0.05) at 2 days after transfection. Compared with control group, the A value of MTT cholorimetric analysis decreased in 1.0 μmol/L DNAzyme group and antisense oligodeoxynucleotide (ASODN) group, at 2, 3 and 5 days after transfection significantly (P<0.01). The decrease in A value showed a dose-dependent manner within the experimental range at 5 days. After 2 days, the percentage of quiescence cells (G0/G1) was 73.8%, 54.7% and 41.1% in DNAzyme, ASODN and control groups, respectively. CONCLUSION: The DNAzyme specific to PCNA suppresses the proliferation of HUASMC effectively in vitro.  相似文献   
48.
新疆石河子农耕区鼠类群落结构及其危害状况   总被引:1,自引:0,他引:1  
2001年6~9月,在石河子农耕区依不同生境类型选择9个样地,以夹夜法布夹11 300夹次,共捕获鼠417只,鼠种由小家鼠、灰仓鼠、红尾沙鼠、褐家鼠等10种组成.采用聚类分析方法将鼠类群落划分为3种类型:农田-林地鼠类群落(小家鼠 灰仓鼠 根田鼠)、荒漠-沙地鼠类群落(子午沙鼠 红尾沙鼠 大沙鼠)和城市居民点鼠类群落(褐家鼠 小家鼠 灰仓鼠).其中,农田-林地鼠类群落的Shannon-Wiener多样性指数较高.根据鼠类群落结构特征,并结合鼠害发生状况将垦区鼠类危害型划分为4种类型.  相似文献   
49.
结果表明:5%锐劲特悬浮剂对水稻三化螟有较好的防治效果,60ml/667m2、50ml/667m2、40ml/667m23个剂量防效分别达到88.70%,81.16%和76.96%,明显高于目前常用农药18%杀虫双水剂250ml/667m2;建议在生产上推广应用,防治白穗用药应掌握在水稻破口抽穗期  相似文献   
50.
AIM: To evaluate the immunogenicity of a novel orthopedics materials (graded zirconia-hydroxyapatite composite) in vitro by using peripheral blood mononuclear cells (PBMCs) from healthy young people, and simple zirconia-hydroxyapatite composited material was used as control materials. METHODS: Proliferation of PBMCs cultured in different liquid after 5 days was measured by MTT methods. ELISA was used to detect TNF-α and IL-6 concentration in the supernatant of PBMCs cultured in the extracts after 24 hours. Flow cytometery was used to measure CD69 and CD25 in activated PBMCs cultured in the extracts of the two kinds of materials after 24 hours. RESULTS: The proliferation rate of the simple composite group was significantly lower than that in negative group (P<0.05), but there was no difference between the graded composited group and negative group. After 24 hours culture with LPS, the concentrations of TNF-α and IL-6 in the simple composited group were significantly higher than that in graded composited group, respectively (P<0.05). Cultured with PHA for 24 hours, the ratio of CD69 and CD25 positive PBMCs in the simple composited group was all significantly higher than that in graded composited material group (P<0.01). CONCLUSION: The number of PBMCs activated by the graded composited material is less than the simple composited material and the immunogenicity of the graded composited material is lower than the simple composited material.  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