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   730篇
  免费   27篇
  国内免费   21篇
林业   101篇
农学   34篇
基础科学   4篇
  41篇
综合类   395篇
农作物   76篇
水产渔业   7篇
畜牧兽医   30篇
园艺   53篇
植物保护   37篇
  2024年   2篇
  2023年   8篇
  2022年   9篇
  2021年   10篇
  2020年   19篇
  2019年   21篇
  2018年   14篇
  2017年   22篇
  2016年   47篇
  2015年   29篇
  2014年   25篇
  2013年   41篇
  2012年   75篇
  2011年   71篇
  2010年   58篇
  2009年   49篇
  2008年   44篇
  2007年   42篇
  2006年   43篇
  2005年   42篇
  2004年   22篇
  2003年   8篇
  2002年   8篇
  2001年   5篇
  2000年   6篇
  1999年   6篇
  1998年   9篇
  1997年   8篇
  1996年   4篇
  1995年   5篇
  1994年   7篇
  1993年   1篇
  1992年   4篇
  1991年   2篇
  1990年   2篇
  1989年   4篇
  1988年   6篇
排序方式: 共有778条查询结果,搜索用时 15 毫秒
1.
紫苏是延边地区的重要经济作物之一.但目前随着种植年限的延续,开始大量发生虫害、病害以及草害等,从而导致减产、降效,严重影响苏子生产.研究结果表明,延边紫苏地适宜土壤处理的除草剂为敌草胺与扑草净的混剂,使用剂量为3kg/hm^2 5kg/hm^2,一年生杂草除草效果可达到90%以上;茎叶处理除草剂为拿捕净(12.5%,1.0kg/hm^2)、稳杀得(35%,1.0kg/hm^2)、精禾草克(5%,1.0kg/hm^2);紫苏的主要病害为锈病,对紫苏叶片质量影响较大;主要食粒虫害(待定)对产量的影响较大.  相似文献   
2.
不同的施肥方式对剑麻施肥区域土壤微生物类群的影响   总被引:5,自引:0,他引:5  
研究不同的施肥方式对剑麻施肥区域土壤微生物类群产生的影响。结果表明,不同施肥方式下土壤微生物总量各有差异,在总体数量上以细菌为主,真菌次之,再其次是放线茵,特殊生理类群是解磷茵居多,纤维素分解茵次之,固氮茵最少;但从土壤微生物多样性指数来看,则表现为土壤中主要微生物类群多样性指数是施肥点的土壤高于附近的土壤,而土壤中特殊生理微生物多样性指数则无此变化趋势,即微生物总数高的土壤,其多样性指数不一定高。因此评价土壤生物多样性应将二者结合起来。  相似文献   
3.
Agave tequilana is the raw material for the production of the alcoholic beverage tequila. A bacterial disease has affected the A. tequilana crop in recent years. Previous reports based on colony and cell morphology, Gram stain and potato rot indicated that Erwinia sp. is the main pathogen. We isolated a several bacterial isolates capable of producing soft-rot symptoms in greenhouse pathogenicity assays. An extensive characterisation involving pathogenicity tests, fatty acid profile, metabolic and physiological properties, ribosomal DNA sequence and intergenic transcribed spacer amplification (ITS-PCR) and restriction banding pattern (ITS-RFLP) was made of each isolate. Three different species: Erwinia cacticida, Pantoea agglomerans and Pseudomonas sp. were identified. Fatty acid and metabolic profiles gave low similarity values of identification but 16S rDNA sequence, ITS-PCR and ITS-RFLP confirmed the identification of E. cacticida. In the phylogenetic tree, E. cacticida from blue agave was grouped neither with E. cacticida type strains nor with Erwinia carotovora. This is the first report that associates E. cacticida with A. tequilana soft-rot symptoms.  相似文献   
4.
以玄武岩发育而成酸性粘土、龙舌兰麻H.11648幼苗为试材,以施用充足化肥为对照,施用有机肥、碱性物质(碳酸钙、白云石粉)作为其他处理,测量各处理对龙舌兰麻H.11648幼苗株高、叶宽、叶片数影响,为龙舌兰麻H.11648合理施用有机肥和碱性物质提供依据。结果如下: 1、用碱性物质碳酸钙或白云石粉调节的土壤pH值6.0、6.5处理的龙舌兰麻H.11648幼苗株高、叶宽、叶片数增长率与对照(pH5.5)没有显著差异,龙舌兰麻H.11648幼苗在玄武岩发育土壤上生长酸害阈值为pH值5.5;2、有机肥处理对龙舌兰麻H.11648幼苗株高、叶片数增长率没有显著影响,但4%、8%有机肥显著增加了叶宽(增长率分别比对照提高62.7%、76.7%),有机肥显著促进了龙舌兰麻H.11648幼苗生长。  相似文献   
5.
Oxidative stress can induce apoptosis of granulosa cells and lead to follicular atresia, thereby reducing the number of pigs giving birth. The aim of this study was to investigate the protective effect of Periplaneta americana peptide (PAP) on the apoptosis of the granulosa cells of pig ovaries (PGCs) induced by hydrogen peroxide (H2O2) via FoxO1. PGCs were treated with H2O2 to establish a cell apoptosis model. Cell viability was measured using the cell counting kit-8 (CCK-8) assay, and cell apoptosis was detected using flow cytometry. The malondialdehyde (MDA) level and nitric oxide (NO) content were detected to reflect the oxidative stress. Western blotting, qRT-PCR and overexpression were undertaken to determine the expression of FoxO1 and caspase-3, and immunofluorescence was used to detect FoxO1 in the nucleus and cytoplasm. PGCs were treated with 100 μM H2O2 for 6 hr, which resulted in oxidative damage and apoptosis and an apoptosis rate for PGCs of 32.95%. Next, PGCs were treated with 400 μg/ml PAP for 24 hr to repair the apoptosis induced by H2O2. PAP improved cell viability in H2O2-stimulated PGCs, the increased MDA level and NO content caused by H2O2 stimulation were reversed and the apoptotic rate of PGCs was reduced. The qRT-PCR and Western blotting results indicated that PAP decreased the H2O2-induced apoptosis and the expression of FoxO1 and caspase-3 in PGCs. The effect of PAP was the same following FoxO1 overexpression. FoxO1 was expressed in the nucleus when stimulated by H2O2 or overexpression; however, it migrated to the cytoplasm following PAP treatment. PAP decreased the apoptosis of PGCs induced by H2O2 by regulating FoxO1 expression and nuclear translocation.  相似文献   
6.
1994-2003年在黄土高原半干旱区的陕西吴旗县、安塞县进行中国沙棘优良类型和俄罗斯优良沙棘品种引种试验,采用家系选择法初步筛选出5个中国沙棘生态经济型优良单株,对3个俄罗斯良种沙棘的生长适应性经济性状进行了评价。前者生长迅速、树冠好、根系发达、郁闭快、水土保持效益好,果实较大、单株产量较高、Vc和含油量较高,适于在黄土丘陵区种植;后者经济性状较好,果实大、无刺或少刺,但适应性较中国沙棘差。  相似文献   
7.
首先对18个胡麻(Linum usitatissimum Linn.)品系的5个产量构成性状及产量进行相关分析,指出单株粒数和分枝长与产量之间的相关性达显著水平,并且各性状之间还存在着相互作用、相互制约和相互促进的关系。因此对吉林省胡麻产量及其构成性状的关系须采用通径分析方法进行分析,以估算每一个性状对产量的直接作用,以及一个性状通过另一个性状对产量的间接作用。通径分析结果表明,在吉林省提高胡麻产量,可主要通过提高单株粒数和增加分枝数来实现;返青将致使胡麻减产。  相似文献   
8.
分别用3种不同浓度的乙醇水溶液进行热回流浸提,制备地胆头原液.然后用醇溶液调pH值法除去鞣质以及乙醚脱脂、活性炭脱色等方法进行除杂脱色,制备地胆头有效部位注射液.对地胆头注射液进行了质量和安全性检查及体外药效试验.结果表明,制备的地胆头注射液对金黄色葡萄球菌、肺炎双球菌、大肠埃希氏杆菌和肠炎沙门氏菌均有明显的抑制作用,其中用65%乙醇提取制备的地胆头注射液效果最好,3种注射液都具有很好的澄明度和安全性.  相似文献   
9.
杀虫剂对2种麦蚜的敏感性和选择性测定   总被引:1,自引:0,他引:1  
用浸叶法测定了麦长管蚜和黍缢管蚜对几种杀虫剂的敏感性和选择性。结果表明 ,麦长管蚜对几种杀虫剂的敏感性呈以下规律 :辛硫磷<毒死蜱<吡虫啉<抗蚜威<啶虫咪<氧化乐果<甲基对硫磷 ;致死中浓度 (LC50)按以下次序增大 :啶虫脒 ,辛硫磷 ,毒死蜱 ,抗蚜威 ,甲基对硫磷 ,吡虫啉 ,氧化乐果。黍缢管蚜对几种杀虫剂敏感性呈以下规律 :吡虫啉<毒死蜱<啶虫脒<抗蚜威<甲基对硫磷<氧化乐果 ,致死中浓度 (LC50)按以下次序增大 :啶虫脒 ,毒死蜱 ,吡虫啉 ,抗蚜威 ,甲基对硫磷 ,氧化乐果。麦长管蚜和黍缢管蚜对几种杀虫剂的选择性依次为 :啶虫咪<甲基对硫磷<抗蚜威<毒死蜱<氧化乐果<吡虫啉  相似文献   
10.
To investigate the action of dinotefuran (MTI-446, 1-methyl-2-nitro-3-(tetrahydro-3-furylmethyl)guanidine), a recently developed insecticide, on insect nicotinic acetylcholine receptors (nAChRs), we determined the potencies of the compound and 15 analogues in inhibiting the specific binding of [3H]epibatidine (EPI), a nAChR agonist, and [3H]alpha-bungarotoxin (alpha-BGT), a competitive nAChR antagonist, to the nerve cord membranes of American cockroaches (Periplaneta americana). Racemic dinotefuran inhibited [3H]EPI binding with an IC50 of 890 nM and [3H]alpha-BGT binding with an IC50 of 36.1 microM. Scatchard analysis indicated that the dinotefuran inhibition of [3H]EPI binding was a competitive one. Slight structural modification caused a drastic reduction in potency; only four analogues were found to be equipotent to or more potent than dinotefuran. Chloropyridinyl and chlorothiazolyl neonicotinoid insecticides displayed two or three orders of magnitude higher potency than dinotefuran. There was a good correlation between the IC50 values of tested compounds obtained with [3H]EPI and those obtained with [3H]alpha-BGT. A better correlation was observed between 3-h knockdown activities (KD50) against German cockroaches (Blattella germanica) and IC50 values obtained from [3H]EPI assays than between 24-h lethal activities (LD50) and IC50 values. While the results indicate that dinotefuran and its analogues interact with the ACh-binding site in cockroach nAChRs, it remains to be elucidated why they displayed lower potencies than those expected based on their insecticidal activities.  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