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   188篇
  免费   9篇
  国内免费   6篇
林业   5篇
农学   41篇
基础科学   6篇
  25篇
综合类   31篇
农作物   22篇
水产渔业   3篇
畜牧兽医   21篇
园艺   2篇
植物保护   47篇
  2024年   1篇
  2023年   1篇
  2022年   4篇
  2021年   4篇
  2020年   8篇
  2019年   7篇
  2018年   4篇
  2017年   5篇
  2016年   8篇
  2015年   5篇
  2014年   3篇
  2013年   9篇
  2012年   8篇
  2011年   6篇
  2010年   13篇
  2009年   10篇
  2008年   5篇
  2007年   5篇
  2006年   7篇
  2005年   10篇
  2004年   3篇
  2003年   6篇
  2002年   5篇
  2000年   9篇
  1999年   7篇
  1998年   3篇
  1997年   3篇
  1996年   4篇
  1995年   4篇
  1994年   5篇
  1993年   9篇
  1992年   2篇
  1991年   2篇
  1990年   3篇
  1989年   5篇
  1987年   6篇
  1986年   1篇
  1985年   1篇
  1983年   1篇
  1976年   1篇
排序方式: 共有203条查询结果,搜索用时 31 毫秒
91.
A probabilistic production costing method for multistates and multiblocks of units is presented in this paper. The mixtures of normal distributions are used to represent the power of the system and the load. The energy, reliability and production costs are calculated directly from the analytical formulae. Numeral examples demonstrate that the algorithm presented in the paper is accurate and efficient.  相似文献   
92.
低温等离子体净化汽车尾气中NO的实验研究   总被引:1,自引:0,他引:1  
研制了一套高压脉冲电源和介质阻挡放电反应器,通过在常压下放电产生低温等离子体。结合模拟汽车排气试验,对NO的去除率随放电管的放电电压、NO的初始浓度以及气体流量的改变而变化的规律进行研究。研究表明,利用介质阻挡放电产生低温等离子体净化尾气,是一种具有发展前景的排气后处理技术,对汽车尾气的净化具有明显的净化效果。  相似文献   
93.
试验旨在研究不同比例的甜高粱(SS)与苜蓿(AF)混合青贮对卡拉库尔羊消化道pH和消化酶活性的影响。选择4月龄卡拉库尔羊30只,随机分为5组,每组3个重复,每个重复2只,在甜高粱与苜蓿比为100:0(SS100)、80:20(SS80)、60:40(SS60)、40:60(SS40)、20:80(SS20)的基础上补饲40%的精料,3个月的饲养试验结束后,每组选择3只进行屠宰采样,测定胃肠道pH及消化酶活性。结果表明:消化道pH随甜高粱比例的减少而下降,甜高粱占比20%时,pH最低,但均无显著性差异;随甜高粱比例的减少,复胃中蛋白水解酶、氨基肽酶、内切葡聚糖酶、纤维素酶及木聚糖酶活性呈升高趋势,SS40组酶活性最高;SS40组显著增强了小肠黏膜上糜蛋白酶、胰蛋白酶、α-淀粉酶及脂肪酶活性;空肠内容物中糜蛋白酶、α-淀粉酶及回肠内容物中胰蛋白酶活性呈线性升高趋势,回肠内容物中脂肪酶呈先升高后降低二次曲线趋势,且SS40组酶活性最佳。结果提示,甜高粱与苜蓿混贮时甜高粱比例的减少可显著提高卡拉库尔羊消化道内消化酶活性,甜高粱与苜蓿比为40:60时卡拉库尔羊消化道酶活性较高。  相似文献   
94.
In the alpine region of the Qinghai-Tibetan Plateau four indigenous perennial grass species Bromus inermis (BI), Elymus sibiricus (ES), Elymus nutans (EN) and Agropyron cristatum (AC) were cultivated as three mixtures with different compositions and seeding rates, BI + EN, BI + ES + AC and BI + ES + EN + AC. From 1998 to 2001 there were three different weeding treatments: never weeded (CK); weeded on three occasions in the first year (1-y) and weeded on three occasions in both the first and second year (2-y) and their effect of grass combination and interactions on sward productivity and persistence was measured. Intense competitive interference by weedy annuals reduced dry matter (DM) yield of the swards. Grass combination significantly affected sward DM yields, leaf area index (LAI) and foliar canopy cover and also species composition DM and LAI, and species plant cover. Interaction between weeding treatments and grass combination was significant for sward DM yield, LAI and canopy cover, but not on species composition for DM, LAI or species plant cover. Grass mixture BI + ES + EN + AC gave the highest sward DM yield and LAI for both weeding and non-weeding treatments. Species ES and EN were competitively superior to the others. Annual weedy forbs must be controlled to obtain productive and stable mixtures of perennial grasses, and germination/emergence is the most important time for removal. Weeding three times (late May, late June and mid-July) in the establishment year is enough to maintain the production and persistence of perennial grass mixtures in the following growing seasons. Extra weeding three times in the second growing year makes only a slight improvement in productivity.  相似文献   
95.
Isolated rat brain synaptosomes were used to evaluate the action of pyrethroid mixtures on Ca2+ influx and subsequent glutamate release under depolarizing conditions. In equipotent binary mixtures at their respective and/or estimated EC50s with deltamethrin always as one of the two components, cismethrin, λ-cyhalothrin, cypermethrin, esfenvalerate and permethrin were additive and S-bioallethrin, fenpropathrin and tefluthrin were less-than-additive on Ca2+ influx. In binary mixtures with deltamethrin always as one of the two components, esfenvalerate, permethrin and tefluthrin were additive and λ-cyhalothrin was less-than-additive on glutamate release. Binary mixture of S-bioallethrin and cismethrin was additive for both Ca2+ influx and glutamate release. Only a subset of pyrethroids (S-bioallethrin, cismethrin, cypermethrin, and fenpropathrin) in binary mixtures with deltamethrin caused a more-than-additive effect on glutamate release. These binary mixtures were, however, only additive (cismethrin and cypermethrin) or less-than-additive (S-bioallethrin and fenpropathrin) on Ca2+ influx. Therefore, increased glutamate release evoked by this subset of pyrethroids in binary mixture with deltamethrin is not entirely occurring by Ca2+-dependent mechanisms via their action at voltage-sensitive calcium channels. These results suggest that pyrethroids do not share a common mode of toxicity at presynaptic nerve terminals from rat brain and appear to affect multiple target sites, including voltage-sensitive calcium, chloride and sodium channels.  相似文献   
96.
通过对集流面材料理论分析及现场运行验证表明:①聚丙烯纤维是最为理想的混凝土外加剂,可以显著提高混凝土强度等级,增强集流面承压能力和抗冻性能;②在改性混凝土方案下,确保经济、安全的集流面厚度为3.0cm。该厚度可以确保集流面承压强度及抗冻指标,有效降低集流面建造成本;③推荐C15+聚丙烯纤维以及C20为理想的新型混凝土集...  相似文献   
97.
用I_2、KI、CuSO_4、FeSO_4及其不同组成的混合物代替传统松花蛋配方中的PbO制作鹌鹑松花蛋,与铅法和锌法作对照,筛选出碘混合物配方较好,并用正交试验确定其最佳工艺条件为NaOH4.0%、碘混合物0.2%、温度20℃。形成鹌鹑松花蛋的关键是NaOH浓度,其次为碘混合物百分含量。成品用食品级涂料涂膜保鲜,室温下存放2个月其失重<4.3%,杂菌数<30个/g。  相似文献   
98.
在紫花苜蓿混播草地放牧利用过程中,由于家畜行为对分区位置和放牧阶段的适应机制尚不清晰,制约了混播草地的科学利用和高效转化。本文研究了苜蓿混播草地分区位置和放牧阶段对绵羊活动距离和活动时间的影响。结果表明:放牧分区位置距离饮水点和休息区的距离每增加100 m,绵羊的活动距离增加2.42 km·d-1,活动时间增加46.74 min·d-1。不同放牧阶段草地质量差异明显,绵羊的活动距离和活动时间随着放牧阶段,即进入放牧分区后的天数增加而显著增加。绵羊通过改变活动距离和活动时间适应放牧分区位置和放牧阶段草地质量的变化,增加活动速率来适应草地质量的降低。苜蓿混播草地集约化放牧育肥时,饮水点和休息区距离放牧分区最远端的距离不宜超过198 m,每个分区放牧时间不宜超过4 d。研究结果可为苜蓿混播草地肉羊高效放牧育肥提供技术支撑。  相似文献   
99.
Uptake and translocation of the fungicide cymoxanil was studied using tomato and potato plants infected with Phytophthora infestans and grape plants infected with Plasmopara viticola. Translocation of cymoxanil was mainly translaminar and acropetal from roots and stems to leaves to an extent similar to that of the phenylamide fungicide oxadixyl. Basipetal translocation from upper to lower leaves, as well as lateral movement, was also observed but to a lesser extent. Plant parts that grew after application were protected against P. infestans and P. viticola because of systemic activity up to 7 days by cymoxanil alone and up to 14 days when cymoxanil was used as part of a three-way mixture with oxadixyl and mancozeb. Drench application of cymoxanil and a simultaneous spray application of mancozeb against P. infestans and P. viticola resulted in a significant synergistic interaction. The spray application of the three-way mixture oxadixyl/mancozeb/cymoxanil was more effective against both sensitive and phenylamide-resistant strains of P. infestans and P. viticola than the individual components alone, representing significant levels of synergistic interactions. Synergy ratios were higher for resistant than for sensitive strains of both pathogens.  相似文献   
100.
几种复配剂对稻飞虱的防治效果比较   总被引:1,自引:0,他引:1  
比较了6种复配剂对稻飞虱的防效,结果表明:噻嗪异丙威、吡蚜噻嗪酮、丙威毒死蜱的防效优异,吡虫乙酰甲、吡虫仲丁威的防效较好,以上5种复配剂均显著优于吡虫杀虫单,因此噻嗪异丙威、吡蚜噻嗪酮、丙威毒死蜱可作为防治稻飞虱的常规品种,吡虫乙酰甲、吡虫仲丁威作为替换品种,在防治过程中注意经常轮换药剂品种。  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