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   2920篇
  免费   113篇
  国内免费   127篇
林业   767篇
农学   186篇
基础科学   37篇
  91篇
综合类   1423篇
农作物   127篇
水产渔业   150篇
畜牧兽医   78篇
园艺   273篇
植物保护   28篇
  2024年   3篇
  2023年   20篇
  2022年   25篇
  2021年   46篇
  2020年   43篇
  2019年   59篇
  2018年   23篇
  2017年   84篇
  2016年   111篇
  2015年   74篇
  2014年   137篇
  2013年   133篇
  2012年   229篇
  2011年   276篇
  2010年   236篇
  2009年   231篇
  2008年   192篇
  2007年   183篇
  2006年   169篇
  2005年   151篇
  2004年   116篇
  2003年   89篇
  2002年   82篇
  2001年   71篇
  2000年   50篇
  1999年   40篇
  1998年   44篇
  1997年   31篇
  1996年   32篇
  1995年   30篇
  1994年   32篇
  1993年   17篇
  1992年   15篇
  1991年   13篇
  1990年   13篇
  1989年   23篇
  1988年   14篇
  1987年   5篇
  1986年   3篇
  1985年   3篇
  1984年   4篇
  1983年   1篇
  1982年   2篇
  1981年   2篇
  1980年   2篇
  1979年   1篇
排序方式: 共有3160条查询结果,搜索用时 15 毫秒
41.
孙永玉  李昆  陈晓鸣 《林业科学》2003,39(5):129-132
综述了紫胶虫优良寄主植物及久树繁殖技术的研究进展,特别是久树的种类、生物学、生理学和生态学的研究与进展,提出了寄主植物无性繁殖研究的思路和对策,展望了寄主植物的研究发展方向。  相似文献   
42.
以虎眼万年青的叶片为外植体,对不同激素浓度的愈伤组织和不定芽的诱导情况以及再生芽的无糖培养情况进行了研究.结果表明:适于愈伤组织诱导及不定芽分化的培养基为MS+BA1.0mg/L+NAA0.1mg/L,适宜的继代培养基为MS+BA0.5mg/L+NAA0.1mg/L;用无糖培养体系进行生根培养时,基质中NAA浓度为0.1mg/L时,再生芽的生根率达94%,种苗质量优于常规组培.  相似文献   
43.
研究了低产油茶树嫁接茶花后的亲和性及生长势,结果表明:杂交品系嫁接亲和性好,嫁接成活率达97%,红山茶种系次之,为91%,而云南山茶系列嫁接成活率为85%;在30个名优茶花品种中有16个品种长势好,11个品种长势较好,3个品种的生长势一般。大规格名优茶花快速繁育的技术关键是适宜品种选择,嫁接前复壮、嫁接中保湿促愈合、嫁接后整形修剪与肥水管理。  相似文献   
44.
天麻作为一种药材,同时又是一种理想的保健品,市场前景可观。巴东森林资源丰富,同时恩施辖区为我国第一个高硒区,在大力开发硒产品之际,巴东富硒天麻产业基地建设势在必行。它可使我县经济增长,农民增收,同时对巳东的产业结构大调整,山区资源大开发起着不可估量的作用。  相似文献   
45.
Effects of genotype, collection date, auxin treatment, crown position and artificial chilling on rooting and subsequent vegetative growth of Cupressus sempervirens L. softwood cuttings taken from 13-year-old plants were evaluated. Three different clones (318, 296 and 22) previously selected for resistance to cypress cortical cancer caused by Seiridium cardinale were used. In all these clones, both the IBA treated and the untreated cuttings showed seasonal periodicity of rooting. Untreated cuttings rooted best when collected in April (up to 49% for the best clone, i.e. 296) and rooted very poorly in July and October. Auxin treatments appeared unable to overcome this periodicity, as the cuttings taken in July and October did not respond to IBA stimulation. However, in January and April, IBA treatments enhanced adventitious root formation of poorly rooting clones (318 and 22), as well as of clone 296, which performed best (89%) when cuttings were treated in April with 1.5% IBA. Cuttings of each clone collected in the lower third of the crown of the donor trees showed a significantly higher rooting percentage, when compared with those from the upper third. A 4-week post-severance chilling treatment (4°C) significantly enhanced the rooting capacity of cuttings taken in January, while a longer chilling treatment (8 weeks) had a negative effect. The subsequent growth of the rooted cuttings was not affected by either the crown position of the severed cuttings, or the genotype.  相似文献   
46.
桉树扦插育苗技术简述   总被引:2,自引:0,他引:2  
本文阐述了扦插的生物学机理、桉树扦插育苗技术和插后管理。  相似文献   
47.
日本野漆树嫁接繁育技术初探   总被引:2,自引:4,他引:2  
对日本野漆树进行了3年的嫁接试验,探索出日本野漆树引种在我国最佳的嫁接时间和方法,试验结果显示:夏季采用切腹嫁接法,成活率达46%,秋季采用切腹嫁接,成活率达87%,高于日本文献介绍的同期成活率值(30%~40%),可见在我国南方秋季采用切腹嫁接可大大提高日本野漆树嫁接成活率。  相似文献   
48.
Immature female gametophytes and enclosed zygotic embryos of slash pine (Pinus elliottii Engelm.) collected at various developmental stages were cultured either on eight initiation media supplemented with different plant growth regulator (PGR) combinations or on LPM medium solidified with two brands of agar. Embryonal-suspensor cell masses extruded from gametophyte explants infrequently produced white or translucent mucilaginous embryogenic cultures. Variation in extrusion frequency was observed across seed sources (families), explant collection dates, agar types and culture media. Increased explant maturity (as related to collection dates) reduced cell extrusion rates. Four types of extrusions were grouped according to their morphology. One type of extrusion produced the greatest number of established and long-surviving embryogenic cultures. This extrusion type (type I) was associated with an extrusion condition termed empty in which the entirety of the embryonal-suspensor mass was extruded out of the gametophyte. Three other extrusion types (types II, III and IV) showed less culture establishment and survival.  相似文献   
49.
Rooting of baldcypress cuttings   总被引:6,自引:0,他引:6  
A test of the rooting performance and growth of cuttings from 1-year-old and 25-to 50-year old baldcypress (Taxodium distichum L.) branch tips is reported. Rooting of cuttings from one-year-old trees averaged 75% (0.1% IBA treatment) and 88% (control), cuttings from 25 to 50-year-old trees averaged 12% in both the IBA treatment and the control treatment. Indole-3-butyric acid at a 0.1% concentration did not enhance rooting, but resulted in a significant increase in shoot dry weight on cuttings from one-year-old trees. The results of this experiment suggest that cuttings from mature baldcypres trees have the potential to root, thereby, additional rooting techniques such as girdling and stump sprouts is worthy of pursuing.  相似文献   
50.
Ficus species are multipurpose trees well known by rural populations in Sahelian and Sudanian zones of Africa. Their uses are well documented but their amenability for vegetative propagation has not been extensively studied. This paper compares the rooting ability of stem and aerial root cuttings from thirteen Ficus species found in West Africa. It highlights the differences between species belonging to the sub-genera Sycomorus and Urostigma. The former show no capacity to propagate from cuttings whereas the latter, with epiphytic development, can be propagated by cuttings, although this capacity varies among species. Thus, F. thonningii, F. leprieurii and F. ovata are easily propagated, while F. platyphylla and F. elasticoides are propagated with difficulty. The rooting capacity also varies depending on the cutting material used. It decreases in the following order: long leafless hardwood cuttings (pole) > nodal cuttings > apical cuttings. Rooting potential increases when the cuttings are harvested towards the end of the dry season(March to May). Aerial root can be used for cuttings in all species of the sub-genus Urostigma. The capacity of root cuttings to regenerate is greatest when cuttings are collected at the beginning of the dry season (November). In this case, wound-induced adventitious roots arise at the basal end of the cutting while de novo buds are developed from the cambium at the distal end. The subsequent morphological development is identical to that of a stem cutting. These results clarify and allow the optimal use of the knowledge and methods developed by the indigenous people of the Sahel and could assist and promote fig tree (Ficus sp.) domestication in the dry tropics.This revised version was published online in November 2005 with corrections to the Cover Date.  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