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   22594篇
  免费   2644篇
  国内免费   1898篇
林业   2461篇
农学   1953篇
基础科学   1539篇
  4511篇
综合类   9442篇
农作物   1423篇
水产渔业   1333篇
畜牧兽医   2754篇
园艺   720篇
植物保护   1000篇
  2024年   31篇
  2023年   389篇
  2022年   693篇
  2021年   830篇
  2020年   826篇
  2019年   574篇
  2018年   534篇
  2017年   1104篇
  2016年   1283篇
  2015年   1050篇
  2014年   1356篇
  2013年   1418篇
  2012年   1899篇
  2011年   1933篇
  2010年   1463篇
  2009年   1487篇
  2008年   1303篇
  2007年   1423篇
  2006年   1194篇
  2005年   939篇
  2004年   737篇
  2003年   660篇
  2002年   496篇
  2001年   460篇
  2000年   395篇
  1999年   380篇
  1998年   328篇
  1997年   275篇
  1996年   236篇
  1995年   274篇
  1994年   246篇
  1993年   234篇
  1992年   171篇
  1991年   134篇
  1990年   108篇
  1989年   91篇
  1988年   70篇
  1987年   43篇
  1986年   28篇
  1985年   14篇
  1984年   4篇
  1982年   6篇
  1981年   2篇
  1979年   3篇
  1978年   1篇
  1977年   4篇
  1975年   1篇
  1963年   1篇
  1962年   2篇
  1956年   2篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
三七是我国特有的中药材,但连作障碍严重制约了其产业发展,轮作是生产上最常用且有效的缓解措施。本研究在三七收获后的土壤上轮作茴香,通过测定轮作土壤水浸液对三七存苗的影响来评价轮作对三七连作障碍的缓解效果,并从轮作对土壤细菌群落的影响方面深入阐释轮作缓解连作障碍的机制。结果表明,茴香轮作后的土壤水浸液可以显著提高三七的存苗率。土壤细菌分析表明,茴香轮作后土壤细菌群落发生了明显改变。细菌的丰富度增加,相对丰度>1%的优势菌门变形菌门Proteobacteria和放线菌门Actinobacteria的相对丰度呈增加趋势。属水平上,轮作茴香使66个属的相对丰度显著增加,其中相对丰度>0.2%的优势菌属有14个;30个属的相对丰度显著降低,其中优势菌属有8个,总体上看相对丰度显著增加的属多于显著降低的属。在相对丰度显著增加的优势菌属中包含常见的拮抗菌属假单胞菌属Pseudomonas和芽孢杆菌属Bacillus细菌。本研究也分离到2株假单胞菌和1株芽孢杆菌对三七根腐病菌腐皮镰刀菌Fusarium solaniMonographella cucumerina具有明显的拮抗活性。因此,轮作茴香可以改善三七连作土壤细菌群落结构,增加土壤中拮抗细菌的丰度,提高三七的存苗率。生产上利用茴香与三七轮作对缓解连作障碍具有一定潜力。  相似文献   
2.
为给内蒙古高原区、黄土高原区和西北荒漠绿洲区紫花苜蓿测土施肥奠定科学基础,采用零散实验数据整合法以及养分平衡-地力差减法,开展了三大自然区域紫花苜蓿土壤速效钾丰缺指标和推荐施钾量研究。结果表明,内蒙古高原区紫花苜蓿土壤速效钾第1~4级指标依次为≥342mg/kg、89~342mg/kg、24~89mg/kg和<24mg/kg,黄土高原区第1~6级指标依次为≥171mg/kg、96~171mg/kg、54~96mg/kg、30~54mg/kg、17~30mg/kg和<17mg/kg,西北荒漠绿洲区第1~4级指标依次为≥303mg/kg、140~303mg/kg、65~140mg/kg和<65mg/kg;当目标产量9~27t/hm2、钾肥利用率50%时,第1~6级土壤的推荐施钾量分别为0、54~162kg/hm2、108~324kg/hm2、162~486kg/hm2、216~648kg/hm2和270~810kg/hm2。  相似文献   
3.
The annual plant Impatiens glandulifera (Himalayan balsam) is the most widespread invasive non‐native weed in the British Isles. Manual control is widely used, but is costly and laborious. Recently, biological control using the rust fungus Puccinia komarovii var. glanduliferae has been trialled. We designed an experiment to assess the impact of these control methods on invertebrate communities in relation to unmanaged and uninvaded habitats, and to determine whether mycorrhizal inoculation aided post‐control recovery of these communities. Sixty invaded and twenty uninvaded field soil blocks were transplanted to the experiment site, where a mycorrhizal inoculum was added to half of all blocks. Biological and mechanical control treatments were applied to twenty invaded blocks independently; the twenty remaining invaded blocks were left intact. Above‐ and belowground invertebrate samples were collected from the blocks at the end of the growing season. Overall, aboveground invertebrate abundance increased with the removal of I. glandulifera, and several groups showed signs of recovery within one growing season. The effect of mechanical control was more variable in belowground invertebrates. Biological control did not affect aboveground invertebrate abundance but resulted in large increases in populations of belowground Collembola. Our experiment demonstrates that mechanical removal of I. glandulifera can cause rapid increases in invertebrate abundance and that its biological control with P. komarovii var. glanduliferae also has the potential to benefit native invertebrate communities.  相似文献   
4.
为了解金属硫酸盐浸种对水稻种子萌发和秧苗吸收Cd等元素的影响,以水稻品种五丰优286为试验材料,选择多种浓度的硫酸亚铁(FeSO4)、硫酸锌(ZnSO4)和硫酸锰(MnSO4)作为浸种剂进行室内催芽和水培试验,测定水稻胚根长、胚芽长、发芽率,以及秧苗中的Cd、Mg、B、P、K含量。结果显示,FeSO4和MnSO4浸种均可提高水稻的发芽率,促进胚根和胚芽生长,且能有效降低秧苗中的Cd含量;而ZnSO4浸种对水稻胚根和胚芽的生长表现出明显的抑制作用,且会增加秧苗中的Cd含量。FeSO4和MnSO4浸种对水稻秧苗Mg、B、P、K的吸收无明显抑制作用,且FeSO4浸种对秧苗B的吸收有促进作用。总的来看,FeSO4和MnSO4浸种具有较好的降低水稻Cd吸收的应用潜力,值得进一步深入研究。  相似文献   
5.
戴炜  唐宇翀  喻娜  陈垚 《园艺与种苗》2021,(4):52-53,64
[目的]为丰富四川地区宿根花卉品种,从云南引进马利筋至四川地区,研究其引种栽培繁殖方法。[方法]采用扦插、播种、分根等繁殖技术,比较马利筋引种扩繁的成活率。[结果]从云南引种的马利筋能够在四川种植并进行繁殖。在秋季对马利筋进行扦插繁殖,成活率为100%;在春季对马利筋进行播种繁殖,成活率高达91%;冬末春初时,对马利筋进行分根繁殖,成活率为88%。通过这些不同的繁殖方式可以迅速增加马利筋的繁殖数量。[结论]研究为马利筋引种繁殖提供了理论支撑,为其规模化种植提供了数量基础。  相似文献   
6.
Yield performance in cereal and legume intercropping is related to nutrient management, however, the yield response of companion crops to nitrogen (N) input is inconclusive and only limited efforts have focused on rationed phosphorous (P) fertilization. In this study, two multi-year field experiments were implemented from 2014–2019 under identical conditions. Two factors in a randomized complete block design were adopted in both experiments. In field experiment 1, the two factors included three planting patterns (mono-cropped wheat (MW), mono-cropped faba bean (MF), and wheat and faba bean intercropping (W//F)) and four N application rates (N0, 0 kg N ha–1; N1, 90 and 45 kg N ha–1 for wheat and faba beans, respectively; N2, 180 and 90 kg N ha–1 for wheat and faba beans, respectively; and N3, 270 and 135 kg N ha–1 for wheat and faba beans, respectively). In field experiment 2, the two factors included three P application rates (P0, 0 kg P2O5 ha–1; P1, 45 kg P2O5 ha–1; and P2, 90 kg P2O5 ha–1) and the same three planting patterns (MW, MF, and W//F). The yield performances of inter- and mono-cropped wheat and faba beans under different N and P application rates were analyzed and the optimal N and P rates for intercropped wheat (IW) and MW were estimated. The results revealed that intercropping favored wheat yield and was adverse to faba bean yield. Wheat yield increased by 18–26%, but faba bean yield decreased by 5–21% in W//F compared to MW and MF, respectively. The stimulated IW yield drove the yield advantage in W//F with an average land equivalent ratio (LER) of 1.12. N and P fertilization benefited IW yield, but reduced intercropped faba bean (IF) yield. Nevertheless, the partial LER of wheat (pLERwheat) decreased with increasing N application rates, and the partial LER of faba bean (pLERfaba bean) decreased with increasing P application rates. Thus, LER decreased as N input increased and tended to decline as P rates increased. IW maintained a similar yield as MW, even under reduced 40–50% N fertilizer and 30–40% P fertilizer conditions. The estimated optimum N application rates for IW and MW were 150 and 168 kg ha–1, respectively, and 63 and 62 kg ha–1 for P2O5, respectively. In conclusion, W//F exhibited yield advantages due to stimulated IW yield, but the intercropping yield benefit decreased as N and P inputs increased. Thus, it was concluded that modulated N and P rates could maximize the economic and ecological functions of intercropping. Based on the results, rates of 150 kg Nha–1 and 60 kg P2O5 ha–1 are recommended for IW production in southwestern China and places with similar conditions.  相似文献   
7.
The present study was conducted to investigate the effects of methyl jasmonate (MeJA) dipping treatment on mitochondrial energy metabolism and quality parameters of Nanguo pears during room temperature storage. The results showed that MeJA treatment suppressed the respiration rate and weight loss, and maintained the flesh firmness of Nanguo pears. MeJA also effectively maintained the content of ascorbic acid and titratable acidity in the fruit. Furthermore, the activities of H+-ATPase, Ca2+-ATPase, succinate dehydrogenase (SDH) and cytochrome C oxidase (CCO) of the MeJA-treated fruit were significantly higher than those of the untreated fruit. The contents of adenosine triphosphate (ATP) and adenosine diphosphate (ADP) and the energy charge were also enhanced by MeJA treatment. These results suggest that postharvest MeJA treatment could maintain the quality of Nanguo pears, in part by modulating mitochondrial energy metabolism during room temperature storage.  相似文献   
8.
思政教育是高职院校教学的重点内容,对学生的思想、行为会产生直接影响,同时与工匠精神存在紧密关系,需要对其予以融合。为了提升高职机械类专业教学的质量,引入思政教育极为重要,其在推动学生全面发展方面也发挥出了重要作用。基于此,主要以机械基础类专业教学为例,分析了高职机械类专业课程与思政教育的联系为切入点。同时,通过调整教学思路与路径,结合机械发展史展开思政教育,引入大国重器实际研发案例,落实全面评价这些思政教育的融入策略。  相似文献   
9.
【目的】探明机插条件下减穴稳苗配置对杂交籼稻群体冠层质量的影响,为西南弱光稻区杂交籼稻机插栽培技术的推广应用提供理论支撑。【方法】2016—2017年采用两因素随机区组田间试验,因素1,2年均为不同田间配置,设常规配置(30 cm×12 cm)和减穴稳苗(30 cm×23 cm);因素2,2016年为不同株型水稻品种(F优498,中后期株叶型松散;宜香优2115,中后期株叶型上紧下披),2017年为不同基本苗(42×104/hm2和63×104/hm2);研究了不同田间配置对机插杂交籼稻群体冠层结构、光合特性和微环境(冠层温度、湿度和透光率)的影响。【结果】(1)减穴稳苗齐穗期能维持与常规配置相当的单茎绿叶面积、粒叶比和上三叶比叶重,其中2017年倒二叶与倒三叶比叶重显著增大;齐穗期剑叶光合速率、气孔导度、蒸腾速率分别较常规配置显著提高23.84%、23.53%和13.79%。(2)较常规配置,减穴稳苗显著增大各时期冠层幅度,提高冠层透光率,降低收敛指数,群体通透性更好;减穴稳苗处理提高了2016年F优498孕穗期和齐穗期的一次分蘖角度,而宜香优2115的一次分蘖角度2年均表现为减穴稳苗小于常规配置。(3)相关分析表明,孕穗期冠层日均温、昼夜温差和昼夜湿差与齐穗期剑叶和倒二叶比叶重呈显著或极显著正相关,与齐穗期收敛指数呈显著负相关;此外,孕穗期冠层日均温和昼夜湿差还与齐穗期冠层幅度呈显著正相关;齐穗期冠层日均温和昼夜温差与分蘖盛期、拔节期及齐穗后20 d的一次分蘖角度呈显著或极显著负相关,日均相对湿度则相反。减穴稳苗有效地改善了植株冠层结构,从而显著提高孕穗期和齐穗期的冠层温度和昼夜温差,提高孕穗期、齐穗期和齐穗后20 d的昼夜湿差,并显著降低日均相对湿度。【结论】减穴稳苗田间配置优化了机插杂交稻的群体冠层结构和光分布,增大了群体内部昼夜温差和湿差,降低了相对湿度,提高了群体质量和光合速率,为高产稳产奠定了基础,是西南弱光稻区进一步推进机插秧发展的重要技术途径。  相似文献   
10.
檫木在东南沿海地区常规造林成活率偏低,对檫木裸根苗进行截干造林试验,结果表明:造林前两年檫木截干与未截干造林在成活率和地径、树高、抽高等生长量指标除了在第二年树高差异为显著水平外,其他指标在年度、性状间均为极显著差异;截干造林明显提高檫木造林成活率,造林第一年成活率100%,第二年成活率98%,两年生时截干造林成活率比未截干造林提高30.15%;明显促进地径生长,地径年生长量29%以上;大幅度提高抽梢生长量,第一年增幅222.78%,第二年增幅94.49%,檫木截干造林在东南沿海地区效果明显,是值得推广的造林方法。  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