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   10711篇
  免费   583篇
  国内免费   1046篇
林业   779篇
农学   1060篇
基础科学   177篇
  1382篇
综合类   4495篇
农作物   803篇
水产渔业   907篇
畜牧兽医   1440篇
园艺   423篇
植物保护   874篇
  2024年   22篇
  2023年   127篇
  2022年   200篇
  2021年   263篇
  2020年   249篇
  2019年   330篇
  2018年   220篇
  2017年   405篇
  2016年   514篇
  2015年   424篇
  2014年   372篇
  2013年   559篇
  2012年   868篇
  2011年   632篇
  2010年   599篇
  2009年   592篇
  2008年   624篇
  2007年   760篇
  2006年   698篇
  2005年   582篇
  2004年   477篇
  2003年   349篇
  2002年   296篇
  2001年   255篇
  2000年   227篇
  1999年   188篇
  1998年   187篇
  1997年   181篇
  1996年   144篇
  1995年   150篇
  1994年   96篇
  1993年   141篇
  1992年   131篇
  1991年   92篇
  1990年   82篇
  1989年   72篇
  1988年   56篇
  1987年   30篇
  1986年   69篇
  1985年   30篇
  1984年   14篇
  1983年   5篇
  1982年   4篇
  1981年   4篇
  1980年   4篇
  1979年   4篇
  1976年   2篇
  1975年   2篇
  1956年   2篇
  1955年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
报导了南瓜水溶性多糖的水提醇沉优化工艺。在单因素试验的基础上,选取南瓜水溶性多糖提取时间、提取温度和水料比3个因素进行Box-Benhnken中心组合设计,利用响应面分析法对其提取工艺参数进行优化研究。利用Design-Expert软件对南瓜水溶性多糖得率的二次多项数学模型解逆矩阵分析表明,在提取温度为72.41℃,提取时间为3.02h,水料比为33.48∶1时,南瓜水溶性多糖得率最高,最大得率预测值为2.463%,与实测值2.447%相符。利用优化工艺参数提取南瓜水溶性多糖时,具有最大的提取效果。  相似文献   
992.
药剂处理对瓜尔豆种子低温萌发和活力的影响   总被引:2,自引:0,他引:2  
用不同的药剂分别在20℃、15℃条件下浸泡瓜尔豆种子24h,放入15℃的发芽箱中发芽。结果表明:400ml/kg乙烯利、10mg/kgAMP、20mg/kg6-BAl5℃浸种显著或极显著的提高种子活力,促使种子低温萌发;而20℃浸种时对种子萌发没有显著影响。0.1%水杨酸钠在15℃条件下能显著提高种子的发芽率,较长时间的维持种子活力。0.1%甲醛处理完全杀死种子。20mg/kgIAA20℃浸种、30mg/kg2,4-D15℃浸种抑制种子的萌发。200ml/kgCCC、500mg/kgGA3、0.1mol/LKNO3、25ml/kg肌醇15℃或20℃浸种效果均不明显。  相似文献   
993.
7个籼型水稻细胞质雄性不育系异交性能的研究   总被引:3,自引:1,他引:3  
以7个籼型水稻细胞质雄性不育系D62A、D63A、D64A、D23A、G46A、金23A珍汕97A为材料,视珍汕97A为对照,在海南对它们的异交性能进行了研究.结果表明:7个细胞质雄性不育系的颖花开花率从高到低依次为D23A、D63A、D62A、D64A、珍汕97A、金23A、G46A;D62A等6个细胞质雄性不育系的柱头外露率均高于对照珍汕97A;除G46A、金23A外,其余4个的午前花率均比对照珍汕97A高;D62A、D63A、D64A等3个细胞质雄性不育系的平均张颖时间均比对照珍汕97A长,其余三个短于对照珍汕97A.柱头生活力系数大小依次是:对照珍汕97A、D62A、G46A、D63A、D23A、D64A、金23A.异交结实率从高到低的顺序是D62A、D63A、D23A、金23A、D64A、G46A、珍汕97A.  相似文献   
994.
G. Y. Lu    G. S. Yang  T. D. Fu 《Plant Breeding》2004,123(3):262-265
Rs1046AB is a genic male sterile two‐type line in rapeseed that has great potential for hybrid seed production. The sterility of this line is conditioned by the interaction of two genes, i.e. the dominant genic male sterility gene (Ms) and the suppressor gene (Rf). The present study was undertaken to identify DNA markers for the Ms locus in a BC1 population developed from a cross between a male‐sterile plant in Rs1046AB and the fertile canola‐type cultivar ‘Samourai’. Bulked segregant analysis was performed using the amplified fragment length polymorphism (AFLP) methodology. From the survey of 480 AFLP primer combinations, five AFLP markers (P10M13350, P13M8400, P6M6410, E7M1230 and E3M15100) tightly linked to the target gene were identified. Two of them, E3M15100 and P6M6410, located the closest, at either side of Ms at a distance of 3.7 and 5.9 cM, respectively. The Ms locus was subsequently mapped on linkage group LG10 in the map developed in this laboratory, adding two additional markers weakly linked to it. This suite of markers will be valuable in designing a marker‐assisted genic male sterility three‐line breeding programme.  相似文献   
995.
Summary Ninety Chinese rice landraces were examined with special reference to the indica-japonica differentiation in terms of traditional criteria, isozyme analysis and PCR analysis of the chloroplast DNA (cpDNA). Cultivars were separated into indica and japonica defined by a discriminant function (Z) based on key characters, as well as by isozyme genotypes. Most indica landraces had chloroplast DNAs with a deletion at the Pst-12 fragment, while most japonica landraces had cpDNAs without the deletion. Two traditionally recognized varietal groups in China, keng and hsien, corresponded largely to the respective japonica and indica revealed in our study. The results obtained in this study showed good agreement for classification of indica and japonica types by the three methods: discriminant analysis by Z value, isozyme analysis, and PCR analysis for cpDNA.  相似文献   
996.
Keuls  M.  Garretsen  Frida 《Euphytica》1982,31(1):51-64
Summary In the first part of this paper some experimental conditions necessary for a valid statistical analysis of differences in growth curves are discussed.Next the multivariate character of growth curves is considered. Data on the growth curves of three genotypes of an experiment with tomatoes of the IVT are used for illustrating the computational procedure and some aspects of interpretation.The growth curves of log dry leaf weight for each plot could be described by a quadratic function of time and were characterised by three components: mean level m, slope 1 (linear component) and curvature q (quadratic component).Univariate analyses of variance (ANOVA) showed significant differences between cultivars for each growth component: however, this is only part of the information as the correlation between the components is not involved. From a multivariate analysis of variance (MANOVA) it appeared that in this experiment the differences in growth between the cultivars were best expressed by using mean level m only.An estimate of the final (reduced) statistical model underlying the tomato example is derived.It is advised to split up growth into different phases of development each with its own analysis. At least four harvest dates for every phase seem desirable.  相似文献   
997.
小麦花粉植株中保卫细胞长度的分布   总被引:5,自引:0,他引:5  
本文对小麦植株叶片保卫细胞长度进行了测量.研究结果,472丛小麦花粉植株叶片中保卫细胞长度的分布在36—84μ之间,453株普通六倍体小麦叶片保卫细胞长度分布在57.6—81.6μ之间,二者分布有交叉重迭.经分析检验,花粉植株中叶片保卫细胞长度达65.0μ以上的,可以认为该植株已自然加倍了.经应用于花粉植株的倍数鉴定,准确率达93—94%.  相似文献   
998.
为发掘和利用荆州黑麦所携抗梭条花叶病基因,综合利用分子细胞遗传学与分子标记技术结合多年抗性鉴定,从高感梭条花叶病小麦地方品种辉县红与荆州黑麦杂交后代(F7~F9)中选育出二体异附加系5个(分别添加1R、2R、R3、5R和R7)、5RS端二体异附加系1个和多重异附加代换系2个(染色体组成分别为20’’+2R(2D)’’+4R’’和19’’+1R(1B)’’+2R(2B)’’+4R’’)。鉴定表明,双二倍体荆辉1号高抗梭条花叶病,表明黑麦抗性基因可在小麦背景中稳定表达,2R、R7二体异附加系及2个含2R的多重异附加代换系均表现高抗,推测2R和R7上可能携带抗病基因。这些材料是研究荆州黑麦抗性基因遗传及小麦抗病育种的新种质。  相似文献   
999.
水稻抽穗期控制候选基因的SNP/InDel多态性分析   总被引:2,自引:0,他引:2  
抽穗期是水稻的一种重要农艺性状,但其遗传控制机理还不清楚。本文利用数据库搜索的方法,搜索并分析了30个与拟南芥光周期调控途径花期控制基因同源的水稻基因。利用水稻多态性数据库,得到了发生在这些基因以及Hd6、Ehd1、OsSOCl上的820个SNP及191个InDel位点。分析表明,这些位点不是平均分布到每个基因上。SNP/InDel含量较高的基因存在SNP/InDel的热点片段。14.1%的SNP位点,及7%的InDel位点分布在基因的编码区。本文也分析了侯选基因侧翼5Kb范围内的SNP/InDel多态性位点。按照侧翼多态性位点数目的分布可以将侯选基因分成4种类型,即两侧保守型、两侧热点型、单侧热点型、一侧热点一侧保守型。  相似文献   
1000.
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   
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