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   2867篇
  免费   130篇
  国内免费   510篇
林业   136篇
农学   348篇
基础科学   158篇
  407篇
综合类   1411篇
农作物   21篇
水产渔业   7篇
畜牧兽医   106篇
园艺   540篇
植物保护   373篇
  2024年   35篇
  2023年   71篇
  2022年   105篇
  2021年   127篇
  2020年   129篇
  2019年   154篇
  2018年   116篇
  2017年   148篇
  2016年   171篇
  2015年   128篇
  2014年   145篇
  2013年   189篇
  2012年   258篇
  2011年   234篇
  2010年   181篇
  2009年   159篇
  2008年   107篇
  2007年   130篇
  2006年   115篇
  2005年   106篇
  2004年   85篇
  2003年   62篇
  2002年   49篇
  2001年   55篇
  2000年   64篇
  1999年   44篇
  1998年   45篇
  1997年   31篇
  1996年   28篇
  1995年   31篇
  1994年   29篇
  1993年   31篇
  1992年   30篇
  1991年   20篇
  1990年   21篇
  1989年   10篇
  1988年   11篇
  1987年   13篇
  1986年   7篇
  1985年   7篇
  1984年   3篇
  1983年   3篇
  1982年   3篇
  1981年   2篇
  1980年   3篇
  1979年   1篇
  1978年   2篇
  1976年   4篇
  1955年   5篇
排序方式: 共有3507条查询结果,搜索用时 15 毫秒
41.
通过光镜和透射电镜分别观察外源脱落酸(ABA)处理下楸子(Malus prunifolia)、平邑甜茶(M. hupehensis)和新疆野苹果(M. sieversii)叶片解剖结构及叶绿体超微结构的变化,利用扫描电镜和酶联免疫法分别研究ABA处理对叶片气孔特征及其内源激素含量的影响。结果表明:与对照相比,ABA处理下楸子、平邑甜茶和新疆野苹果的叶厚分别减少了7.93%、0.25%和0.81%,栅栏组织厚度分别减少了31.43%、8.53%和4.99%(P<0.05),海绵组织厚度分别增加了10.34%、6.14%和5.63%(P<0.05),叶肉组织结构疏松度(SR)分别增加了19.59%、6.55%和6.50%。ABA处理下楸子和平邑甜茶的栅栏组织/海绵组织厚度比值(P/S)及叶肉组织结构紧密度(CTR)较对照显著减少(P<0.05),其中,P/S值分别下降37.86%和13.82%,CTR分别下降25.46%和8.29%,而新疆野苹果的P/S值和CTR下降但不显著。此外,ABA处理下楸子和平邑甜茶的上表皮细胞厚度较对照分别增加了5.82%和6.43%,新疆野苹果的较对照减少了26.23%(P<0.05);楸子和新疆野苹果的下表皮细胞厚度较对照增加了12.09%和14.21%(P<0.05),平邑甜茶的较对照减少了12.56%。平邑甜茶和新疆野苹果叶片上下角质层厚度较对照显著增加(P<0.05),而楸子的变化不显著。在ABA诱导下,3种砧木的气孔密度、气孔大小(长度×宽度)及其开口度和开张比均不同程度地下降,其中,楸子的较对照分别下降了3.62%、7.12%×19.59%、67.60%和86.66%,平邑甜茶的分别下降了3.50%、4.99%×20.65%、32.42%和58.24%,新疆野苹果的分别下降了8.54%、0.92%×12.06%、20.37%和16.35%。ABA处理下3种砧木叶片细胞中叶绿体的数量变少,类囊体结构排列疏松,叶绿体上的淀粉粒趋于变小。外施ABA使3种砧木叶片内源ABA和玉米素核苷(ZR)的含量极显著增加(P<0.01),其中楸子ABA和ZR含量比对照分别增加30.83%和13.31%,平邑甜茶的分别增加62.40%和45.28%,而新疆野苹果的分别增加了37.07%和17.06%。楸子和新疆野苹果叶片的吲哚乙酸(IAA)和赤霉素(GA)含量无显著变化,而平邑甜茶叶片的IAA及GA含量比对照分别增加了62.62%和20.62%(P<0.01)。总之,在ABA处理下,3种苹果砧木的叶片组织解剖结构和气孔特征都发生旱生性结构变化,叶肉细胞中淀粉粒趋于变小,叶片内源ABA和ZR水平增加显著,而IAA和GA水平变化因基因型不同而存在差异。  相似文献   
42.
灭幼脲三号对金纹细蛾和果园天敌的作用   总被引:4,自引:0,他引:4  
本研究结果表明,施药后30天,灭幼脲三号125mg/L、灭扫利100mg/L、水胺硫磷400mg/L对金纹细蛾的防治效果分别为99.1%、41.0%、52.1%,灭幼脲三号常用剂量对金纹细蛾跳小蜂成虫和蛹茧,以及异色瓢虫2龄纪虫无直接毒性,中天敌幼虫生长发育和变态,而灭扫利和水胺硫磷常用剂量对两种天敌直接杀伤作用很强。  相似文献   
43.
Xu 《Plant pathology》1999,48(4):462-471
A model developed to simulate epidemics of powdery mildew on vegetative shoots of apple generates two types of output. Firstly, it forecasts disease severity (percentage of host tissue infected) by incorporating effects on disease development of the amount of healthy susceptible tissue and current infectious (sporulating) disease, the level of initial inoculum (overwintered 'primary' mildew) and weather conditions. The effects of weather variables are considered on only two aspects of the fungal life cycle: initial spore germination and the subsequent development during the incubation period. Secondly, the model generates indices of the relative favourability of weather conditions on disease development by incorporating effects of weather on conidial production/dispersal and germination. On each day, forecasts of the (relative) severity of new infection and total current infectious disease are given for both types of output. The model was evaluated by comparing its predictions with the mildew epidemics observed in two unsprayed orchards over four years. In all the years, the temporal patterns of the predicted and the observed disease were generally similar. The pattern of the disease severity forecasts was marginally closer to the observed than that derived from two weather indices. Potential roles of the model in practical management of apple powdery mildew are discussed.  相似文献   
44.
黄色苹果新品种‘华月’   总被引:2,自引:0,他引:2  
‘华月’苹果是以‘金冠’为母本,‘华富’为父本杂交育成的新品种。果实圆柱形,平均单果质量230g;果皮黄色,阳面带红晕;果肉肉质,似‘富士’风味。晚熟,抗寒,高抗苹果早期落叶病、果实轮纹病。  相似文献   
45.
Red color plays a very important role when wax apple fruits are purchased. Temperature is one of the key factors among those influencing red color development. We evaluated the effects of temperature on color formation and other quality characteristics of ‘Pink’ wax apple fruit discs by using constant, slow-increase, fast-increase, transient shifting to high temperature, shifting to high temperature for different length of time and different day/night temperature regimes. The results show temperature has pronounced effects on quality attributes of wax apple fruit discs. Anthocyanin and total soluble solid (TSS) were greatest in the 20 °C treated discs under constant temperatures. In the slow-increase and fast-increase treatments, quality attributes in disc were better in treatments with a final temperature of 25 °C than of 30 °C. The concentration of soluble sugars (SS), starch, total phenolic compounds (TPC), free amino acids (FAA) and soluble protein (SP) all decreased with increasing temperature. Transient shifting to high temperature of 30 °C for 1-day had no effect on pigmentation but treatment periods from 3- to 5-days had a substantial adverse effect. At 30 °C for 5-days, exposed discs had the lightest weight and shortest diameter as well. Both SS and TPC decreased in the 3- and 5-day treatments. When temperature was shifted from 20 to 30 °C for 2 to 11 days, the widest and heaviest discs were found in the 5-day treatment. Anthocyanin and TSS concentration decreased following increased length of exposure to high temperature. Pigmentation of discs exposed to high temperature treatment was worse than in uncultured controls. Both protein and FAA concentrations decreased after culture. Among the 5 different day/night temperature combinations, discs under 25/20 °C had the highest anthocyanin and TSS concentrations, while those under 30/15 °C had the worst.  相似文献   
46.
八棱海棠耐盐碱性评价   总被引:1,自引:1,他引:1  
为探明八棱海棠的耐盐碱性种质资源价值,以实生苗为试材,采用水培的方法评价了八棱海棠耐盐性和耐碱性.结果表明:1)0.4% NaCI处理30 d时,八棱海棠的盐害指数为51.1,根据耐盐性评价标准判定为中等耐盐型树种;其实生个体间存在广泛的抗性分离现象,极强、强、中、弱和极弱耐盐型植株分别占群体总数的20.6%、23.9%、37.0%、12.0%和6.5%.2)pH9.5碱处理(Na2CO3)30 d时,八棱海棠的碱害指数为16.3,根据耐碱性评价标准判定为极强耐碱型树种;其实生个体间存在广泛的抗性分离现象,极强、强、中、弱和极弱耐碱型植株分别占群体总数的79.1%、15.3%、4.2%、1.4%和0%.八棱海棠中存在极强耐盐型和极强耐碱型植株,是优异的耐盐/碱型种质资源树种.  相似文献   
47.
用等离子发射光谱仪测定了公路两侧苹果中的Pb含量。结果表明,汽车尾气对苹果造成的Pb污染,在公路两侧30 m范围内较高,5 m和30 m处果实果皮中的Pb含量分别为0.292m g/kg和0.291 m g/kg,是无公害苹果生产标准(0.2 m g/kg)的1.46和1.45倍。随着偏离公路距离的增加,苹果中Pb含量逐渐降低。在距离150 m处降至当地的背景值。对苹果套袋能够有效地降低果实中的Pb含量,最高可降低80%左右。  相似文献   
48.
The vertical distribution pattern and seasonal dynamics of fine root parameters for the apple trees of different ages (3, 10, 15, and 20 years old) on the Loess Plateau of China were studied. Soil coring method was used to determine the vertical distribution and seasonal dynamics of fine roots at different root radial distances (1.0, 1.5, and 2.0 m from the main tree trunk). The fine root biomass density (FRD), fine root length density (RLD), and specific root length (SRL), as well as soil water content and soil temperature were also measured. The FRD and RLD for the 10, 15, and 20 years old trees reached peak values in the 20-30 cm soil layer. For the 3 years old tree, the highest FRD and RLD were observed in the 10-20 cm soil layer. The FRD and RLD decreased with increased soil depth from the 10-20 or 20-30 cm soil layer for all age apple trees. The SRL declined with the increase of tree age. The FRD at the 1.0 m radial distance from the main tree trunk was higher than that at other radial distances in the 3 and 10 years old orchard. However, in the 15 and 20 years old orchards, especially the 20 years old orchard, the FRD at the 2.0 m radial distance was nearly equal to or higher than that at the 1.0 and 1.5 m radial distances. For all the root radiuses or the tree ages, the FRD, RLD, and SRL were the highest in spring and the lowest in autumn. The age of an apple tree does not affect the vertical distribution pattern but the biomass of fine roots and the SRL. Radial distance affects the root horizontal distribution of 3 and 10 years old trees but the 15 and 20 years old trees. Additionally, effects of soil temperature and soil moisture on fine root distribution or seasonal dynamics are not significant.  相似文献   
49.
基于高光谱和数码照相技术的苹果花期光谱特征研究   总被引:2,自引:1,他引:2  
 【目的】旨在探索苹果花期的光谱特征和敏感波段。【方法】以栖霞市为研究区,利用苹果花期数码照片监督分类,提取苹果花树比和花叶比指标信息,通过与同步高光谱探测数据的相关分析,研究苹果树花期光谱特性,确定其敏感的光谱波段。【结果】苹果树花期光谱特征主要表现为对蓝光和红光的吸收、对绿光的反射,和对750~1 300 nm近红外的强烈反射。其光谱特征变化与花叶比和花树比指标呈现较好的相关性,敏感波段范围为400~530 nm的蓝青光和570~700 nm的橙红光,以及中等花树比果树760~1 350 nm的近红外。【结论】该研究提出了高光谱遥感与数码照相技术相结合的有效方法,初步探明了苹果树花期的光谱特征,为苹果园地信息提取、营养诊断和苹果生产管理的实时性与信息化提供了理论依据和技术支撑。  相似文献   
50.
41%草甘膦异丙胺盐水剂防除北方苹果园杂草药效试验结果表明,该药剂可有效防除北方苹果园的一生杂草及多年生杂草,且对果树安全,推荐使用剂量为1230-2460g a.i./hm^2。于苹果园杂草旺盛生长期进行茎叶喷雾处理。  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