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   1617篇
  免费   102篇
  国内免费   105篇
林业   226篇
农学   189篇
基础科学   88篇
  255篇
综合类   295篇
农作物   129篇
水产渔业   112篇
畜牧兽医   345篇
园艺   45篇
植物保护   140篇
  2024年   8篇
  2023年   19篇
  2022年   34篇
  2021年   74篇
  2020年   47篇
  2019年   41篇
  2018年   51篇
  2017年   65篇
  2016年   56篇
  2015年   63篇
  2014年   55篇
  2013年   100篇
  2012年   85篇
  2011年   96篇
  2010年   98篇
  2009年   83篇
  2008年   109篇
  2007年   103篇
  2006年   84篇
  2005年   77篇
  2004年   38篇
  2003年   38篇
  2002年   32篇
  2001年   32篇
  2000年   41篇
  1999年   43篇
  1998年   29篇
  1997年   34篇
  1996年   30篇
  1995年   30篇
  1994年   19篇
  1993年   27篇
  1992年   15篇
  1991年   13篇
  1990年   8篇
  1989年   8篇
  1988年   7篇
  1987年   4篇
  1986年   4篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1979年   2篇
  1978年   3篇
  1974年   1篇
  1969年   1篇
  1965年   2篇
  1964年   1篇
  1963年   3篇
  1944年   1篇
排序方式: 共有1824条查询结果,搜索用时 31 毫秒
91.
Three double low (erucic acid and glucosinolates) self-incompatible lines and 22 varieties from different origins were selected to produce 66 hybrids according to a NC II mating design. Field experiments for identification of hybrid performance and heterosis were conducted in two successive rapeseed growing seasons in Wuhan, China. After heterosis identifications, SI-1300 and Eagle were chosen to construct an F2 segregating population. One hundred and eighty four F2:3 lines were planted at Wuhan and Jingmen to test yield traits. F2 plants and the 25 parents were analyzed using simultaneously AFLP (amplified fragment length polymorphism) and SSR (simple sequence repeat) markers. A total of 270 and 718 polymorphic loci were detected in the F2 population and among the 25 parental lines, respectively. Of the 718 polymorphic loci, 178 were significantly correlated to yield traits. With the use of one-way ANOVA, 84 common QTLs were detected for 12 traits at two trial locations. Although the genetic distances based on general/specific heterozygosities and single-locus QTLs showed significant correlations with hybrid performance and heterosis for some yield traits, the determination coefficients were low. The results suggested that neither heterozygosities nor QTLs for yield traits were suitable to predict hybrid performance and heterosis in Brassica napus.  相似文献   
92.
TTCH定量测定辣椒种子的活力及活力丧失原因的探讨   总被引:2,自引:0,他引:2  
本文以辣椒种子为材料,测定了不同贮存年限的辣椒种子发芽率,用TTCH测定了其活力,结果表明活力指标与发芽率相关极显著,华椒1号的相关系数达0.8912,华椒17号的相关系数达0.9277。实验表明辣椒种子活力下降的内在因素是膜的破坏、活性物质减少及毒素积累等因素引起的。  相似文献   
93.
Genetic analysis of four self-incompatible lines in Brassica napus   总被引:3,自引:0,他引:3  
G. S. Yang    C. B. Chen    G. L. Zhou    C. N. Geng    C. Z. Ma    J. X. Tu  T. D. Fu 《Plant Breeding》2001,120(1):57-61
Reciprocal hybridization between four self-incompatible lines of Brassica napus: 271, 181, 184 and ‘White Flower’, revealed incompatibility. The reciprocal F1s obtained by bud pollination showed self-incompatible reactions, and no segregation for self-incompatibility was observed in all the reciprocal F2 populations, indicating that lines 271, 181, 184 and ‘White Flower’ were genetically identical with regard to self-incompatibility. Observations of self-incompatibility in 17 hybrids from crosses between line 271 and 17 varieties of B. napus showed 10 of the F1 hybrids to be self-compatible, while four were partially self-compatible and three were self-incompatible. Genetic analysis based on F2 and BC1 populations from five self-compatible F1 hybrids and two self-incompatible F1 hybrids suggested the existence of at least two loci controlling the self-incompatibility of line 271: one is the S locus, with dominant and recessive relationships between the S alleles, and the other is the suppressor (sp) of the S locus. The sp locus is genetically different from the S locus, and also shows dominant and recessive relationships between the sp alleles.  相似文献   
94.
Essential oils of peppermint Mentha piperita L. (Lamiaceae), which are used in flavors, fragrances, and pharmaceuticals, were investigated for their antimicrobial properties against 21 human and plant pathogenic microorganisms. The bioactivity of the oils menthol and menthone was compared using the combination of in vitro techniques such as microdilution, agar diffusion, and bioautography. It was shown that all of the peppermint oils screened strongly inhibited plant pathogenic microorganisms, whereas human pathogens were only moderately inhibited. Chemical compositions of the oils were analyzed by GC and GC/MS. Using the bioautography assay, menthol was found to be responsible for the antimicrobial activity of these oils.  相似文献   
95.
以竹炭粉、陶土为主要原料,经混合、成型、干燥和煅烧等工艺制得竹炭陶土复合材料(以下称竹炭陶),采用扫描电子显微镜(SEM)、X射线衍射(XRD)仪、拉曼光谱测试仪(Raman)、傅里叶变换红外光谱(FTIR)和比表面积测试仪等仪器,对竹炭陶的微晶构造、孔隙结构、吸附和红外辐射性能等进行表征。结果表明:竹炭微粒镶嵌在陶土基体中,保留原有以中孔为主的孔隙结构和类石墨化晶体结构,获得的竹炭陶具有较大的比表面积和中孔为主的孔隙结构,能有效地吸附甲醛、苯等有害气体。加入一定量的竹炭能提高竹炭陶的远红外发射率,其红外发射率均高于陶土和竹炭,结合红外吸收光谱谱图分析,竹炭陶具有高红外发射率的本质在于具有倍频吸收、分子基团振动、转动及晶格振动。  相似文献   
96.
Zosima absinthifolia (ZA) extracts and the coumarins (+)-columbianadin and (-)-deltoin were evaluated for their potential hepatoprotective and antiinflamatory effects in a CCl(4)-induced hepatotoxicity assay in rats and by the inhibition of TNF-α production on LPS-stimulated THP-1 macrophages, respectively. Both the ZA extracts and the coumarins showed hepatoprotective activity confirmed by monitoring the ALT/AST levels and by histopathological examination. The antiinflamatory activity, proved by the inhibition of TNF-α production, was found to be higher for the n-hexane root extract than for coumarins, suggesting synergic potential of the extract. The concentration of (-)-deltoin and (+)-columbianadin in extracts was determined by HPLC analysis.  相似文献   
97.
为了使森林资源资产评估过程更加科学,评估结果更加客观,通过多种方法计算比较分析验证发现,林业上的传统成本法与其它行业的不一样,未考虑经营合理利润,其评估值只是投资的价值,而不是投资价值。结果表明:森林资源资产评估中的成本法的折现率应该使用项目内部收益率,而不是待业基准收益率,通过这样的修正,使用一套指标,分别运用成本法...  相似文献   
98.
本文叙述了我国黄土地区主要类型土壤中天然放射性元素的含量水平、迁移积聚和剖面分布情况。研究结果表明,本地区土壤放射性元素的含量、比值和离散程度均接近其黄土母质,但各土类间仍表现出一定的分异,在弱碱性的土壤环境里,以(UO2)^2+存在的铀比较活跃。碳酸盐能促使铀的淋滤,而有机质的存在却有利于铀的积聚。钍和镭集中积蓄在富含粘粒的土层中,但在林地土壤中钍有淋移的迹象。从各核素的剖面分布看,土壤在发育过  相似文献   
99.
鼎湖山南亚热带常绿阔叶林凋落物的特征   总被引:45,自引:0,他引:45       下载免费PDF全文
  相似文献   
100.
The roots of Angelica sinensis (Danggui), a traditional Chinese medicine, have been used for invigorating blood circulation for over 2000 years in China. Three common species of Angelica roots are found in Asia: A. sinensis from China, A. acutiloba from Japan, and A. gigas from Korea. By using a molecular genetic approach, the 5S-rRNA spacer domains of the three species of Angelica were amplified, and their nucleotide sequences were determined. Diversity in DNA sequences among various species was found in their 5S-rRNA spacer domains, which could serve as markers for authentic identification of Angelica roots. In chemical analyses, the main constituents of Angelica roots including ferulic acid and Z-ligustilide were determined by HPLC; roots of A. sinensis were clearly distinct in that they contained approximately 10-fold higher levels of ferulic acid and Z-ligustilide as compared to roots of A. acutiloba and A. gigas. In addition, the amounts of main constituents in roots of A. sinensis varied according to different regions of cultivation and different methods of preservation. The chemical profile determined by HPLC therefore could serve as a fingerprint for quality control of Angelica roots.  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