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   1137篇
  免费   32篇
  国内免费   81篇
林业   77篇
农学   113篇
基础科学   8篇
  91篇
综合类   356篇
农作物   92篇
水产渔业   29篇
畜牧兽医   295篇
园艺   169篇
植物保护   20篇
  2024年   2篇
  2023年   6篇
  2022年   15篇
  2021年   24篇
  2020年   18篇
  2019年   16篇
  2018年   9篇
  2017年   15篇
  2016年   26篇
  2015年   22篇
  2014年   35篇
  2013年   47篇
  2012年   61篇
  2011年   79篇
  2010年   54篇
  2009年   117篇
  2008年   79篇
  2007年   110篇
  2006年   93篇
  2005年   85篇
  2004年   51篇
  2003年   47篇
  2002年   31篇
  2001年   25篇
  2000年   33篇
  1999年   18篇
  1998年   19篇
  1997年   14篇
  1996年   21篇
  1995年   15篇
  1994年   14篇
  1993年   9篇
  1992年   10篇
  1991年   3篇
  1990年   11篇
  1989年   6篇
  1988年   5篇
  1987年   2篇
  1986年   2篇
  1983年   1篇
排序方式: 共有1250条查询结果,搜索用时 31 毫秒
131.
2005年12月~2006年8月,采用瞬时扫描取样法和全事件取样法,对云南野生动物园内5只孟加拉虎行为进行了初步观察。结果表明,在观察期内,笼养孟加拉虎白昼行为时间分配上两性存在一定差异,即雌性的睡眠和卧息多于雄性的睡眠和卧息;雌性的走动和其它行为少于雄性的走动和其它行为。在活动节律上,两性有极大的相似性,只是雌虎在下午的卧息高峰值比雄虎晚约1h。  相似文献   
132.
植物类受体蛋白激酶在植物的生长发育和信号转导中起到重要作用。以香蕉果实cDNA噬菌体文库为材料,通过原位杂交方法获得1个长度为1 689 bp的香蕉果实类受体蛋白激酶基因,编码563个氨基酸序列,包含1个高度保守的蛋白激酶家族结构域。Southern杂交分析结果表明,该基因在香蕉基因组中不止有1个拷贝。构建了该基因的RNAi干扰载体,为该基因功能研究打下基础。  相似文献   
133.
Abstract

The aim of this study was to evaluate the effect of Mentha piperita L. (MP) dried leaves on the in vitro rumen methanogenesis and fermentation. It was found that after 24 hours of incubations, addition of 16.34 and 23.35 mg of MP to the 233.3 mg of substrate significantly decreased methane emission by 41.52 and 15.51%, respectively. Simultaneously, the MP supplementation exerted no effect on the dry matter digestibility and volatile fatty acid profile. Addition of MP to the ruminants' diet inhibits the methane production without altering the basic parameters of rumen fermentation.  相似文献   
134.
Abstract

Twist in wood, being closely related to spiral grain, may cause serious problems in building structures, furniture and joinery. It is therefore of great interest to sort out, at an early stage in the manufacturing process, trees, logs and boards that have an excess of spiral grain. The spiral grain pattern is described by a helical deviation of the fibre direction in relation to the longitudinal direction of a living tree or a log and seems to be an indicator for other defects such as compression wood. Remote microwave sensing of spiral grain has received a lot of interest during the past two decades. Its development has been impeded by the large variation with moisture content of the microwave properties of wood and by the complexity in modelling the electromagnetic field in a log with spiral grain. A review is presented of a direct method with no requirement for information on moisture content for boards. This procedure has recently been generalized to cylindrical logs and trees having a constant slope of the grain. A further generalization is presented here to allow for the normal spiral grain pattern with radially changing slope of grain in wood under bark. Based on this theory, a measurement procedure is proposed for the detection of wood grain angle with radial dependence, requiring no information on moisture content in the sapwood, which is also applicable to completely or partially frozen wood. A suitable application would be an instrument to use in the forest for measurements on living trees or logs.  相似文献   
135.
Broccoli (Brassica oleracea var. italica) is an important nutritionally rich vegetable cole crop grown in the world. Environmental stress, pests, and diseases cause enormous yield losses because of a limited gene pool. Genetic manipulation is becoming an important method for broccoli improvement. The objective of present study was to evaluate the potency of thidiazuron (TDZ) as a plant growth regulator in evoking morphogenic responses in leaf and petiole explants of broccoli. An efficient, reproducible, and high frequency plant regeneration protocol has been standardized in broccoli cv. Solan green head. Leaf and petiole explants were cultured on Murashige-Skoog (MS) medium, supplemented with a wide range of TDZ concentrations. The following treatments were designed for efficient in vitro shoot regeneration: TDZ alone, TDZ with adenine, TDZ with naphthalene acetic acid (NAA), and TDZ with indole acetic acid (IAA). Among the 36 combinations of growth regulators used, the highest percentage of leaf explants producing shoot (89.25%) was recorded on MS medium containing 1.0 μM TDZ and 0.107 μM NAA. The multiple shoot regeneration response of petiole explant producing shoots (91.55%) was obtained on MS medium containing 2.0 μM TDZ and 0.107 μM NAA. Shoot multiplication and elongation were obtained on the same medium. For root regeneration in in vitro regenerated shoots, different concentrations of NAA were applied. High frequency (100%) root regeneration response with healthy and vigorous roots was observed on MS medium supplemented with 0.54 μM NAA. The regenerated plantlets with well-developed shoots and root system were transferred to pots containing cocopeat and successfully acclimatized. We recommend 1.0 μM TDZ with 0.107 μM NAA and 2.0 μM TDZ and 0.107 μM NAA combinations for adventitious shoot regeneration from leaf and petiole explants in broccoli cv. Solan green head respectively. This is the first report on high frequency organogenesis from leaf and petiole explants of broccoli cv. Solan green head using thidiazuron.  相似文献   
136.
137.
小麦茎生长点转化研究初报   总被引:7,自引:2,他引:5  
为了躲避转基因技术对组织培养的过分依赖,本研究以小麦为材料尝试了一种对生长点直接进行转化的方法,并初步证明了这一方法的可行性。具体做法是:将种子萌芽,然后剥去胚芽鞘暴露出生长点,再用玻璃纤维制作的小刷子将生长点刺伤,最后用带有外源基因的农杆菌进行侵染处理。用携带hph-GUS基因的LBA4404农杆菌,侵染处理1~11日龄幼苗(生长点),共培养7d后检测新生芽中GUS的瞬时表达情况;侵染1~2日龄幼苗(生长点),取长成植株的2~3朵小花进行GUS稳定表达检测。又用携带BADH和npt Ⅱ基因的AGL1农杆菌菌株侵染1日龄的幼苗(生长点),在含:100mg/L卡那霉素的蛭石中进行选择。结果表明,GUS的瞬时表达率随被处理幼苗的日龄增加而降低,以2日龄幼苗为最高(10.7%)。用花序检测GUS的稳定表达,被侵染受体为1日龄幼苗时的表达率高于2日龄的幼苗。蔗糖的存在并不提高GUS基因在花序中表达的频率。不过花序表现为GUS阳性的植株后代,经PCR检测后并没有证实GUS基因存在。用AGL1菌株进行转化,获得了13.6%的抗卡那霉素的绿色植株,但只有3株呈现PCR阳性,且只有1株结了实。  相似文献   
138.
Prolific and rapid in vitro plant organogenesis via direct regeneration has been obtained from axenic seedling-derived petiole and leaf explants of Ficus religiosa in Murashige and Skoog (MS) medium containing different concentrations of cytokinins in combination with indole-3-butyric acid (IBA). MS medium with 1.5 mg/l 6-benzylaminopurine plus 0.15 mg/l IBA produced the highest shoot induction frequency with an average of 6.26 and 10.13 shoots per leaf and petiole explants, respectively. After 4 weeks, the highest root formation frequency (96.7%), root number (5.73), and root length (4.76 cm) were with MS medium containing 2.0 mg/l IBA plus 0.1 mg/l α-naphthalene acetic acid. In addition, the effect of four sodium nitroprusside (SNP) treatments on acclimatization was also studied. Highest morphological traits such as survival rates, fresh and dry root weights as well as antioxidant enzymatic activities such as superoxide dismutase, peroxidase, and catalase was achieved with 125 ppm SNP. The α-amino acid, proline, content was highest with this treatment while the highest H2O2 (hydrogen peroxide) was in the controls. This study introduces a cost-effective, prolific, and efficient in vitro multiplication system to supply pharmaceutical and ornamental needs. It is the first report of an in vitro organogenesis protocol for F. religiosa by direct regeneration through axenic seedling-derived petiole and leaf explants, which can be efficiently employed for the utilization of active biomolecules.  相似文献   
139.
为了研究茬次和一天内不同收获时间对紫花苜蓿青贮饲料品质的影响,并进一步评价其饲用价值,本试验采用双因素设计,两茬紫花苜蓿于现蕾期同一天08:00(AM),13:00(M)和18:00(PM)刈割并调制青贮饲料,室温下保存45 d后,取样分析并采用体外发酵法评价其饲用价值。结果表明,第1茬紫花苜蓿青贮饲料的相对饲喂价值(relative feed value,RFV),干物质体外消化率(in vitro dry matter digestibility,IVDMD)及体外发酵挥发性脂肪酸(volatile fatty acids,VFA)、产气量均显著高于第2茬(P<0.05)。下午收获的紫花苜蓿青贮饲料有更高的干物质(dry matter,DM)含量及IVDMD (P<0.05)。因此,在实践生产中,要抓好第1茬的苜蓿生产,推迟刈割时间至中午或下午,可获得更高品质的紫花苜蓿青贮饲料。  相似文献   
140.
We describe a simple technique for obtaining endophytic microorganisms from field-collected roots. Roots of plant species were surfaced-sterilized, cut into pieces, and then each root piece was transferred to drops of Gel-Gro medium. The number of segments with bacteria and fungi was quantified and those with bacteria and dark septate endophytic (DSE) fungi were plated onto tryptic soy agar (TSA) and malt extract agar (MEA), respectively. When arbuscular mycorrhizal fungi (AMF) grew from root segments, they were inoculated into Ri T-DNA-transformed carrot root cultures. Eight different species of bacteria and five dark septate endophytes were isolated. Thirty AMF isolates were identified and continuous pure cultures established. This easy and inexpensive approach allowed us to culture various endophytic microorganisms in an in vitro system saving time and space.  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