全文获取类型
收费全文 | 1349篇 |
免费 | 75篇 |
国内免费 | 114篇 |
专业分类
林业 | 124篇 |
农学 | 135篇 |
基础科学 | 35篇 |
244篇 | |
综合类 | 565篇 |
农作物 | 129篇 |
水产渔业 | 38篇 |
畜牧兽医 | 93篇 |
园艺 | 78篇 |
植物保护 | 97篇 |
出版年
2024年 | 12篇 |
2023年 | 19篇 |
2022年 | 33篇 |
2021年 | 34篇 |
2020年 | 42篇 |
2019年 | 46篇 |
2018年 | 27篇 |
2017年 | 42篇 |
2016年 | 58篇 |
2015年 | 52篇 |
2014年 | 68篇 |
2013年 | 69篇 |
2012年 | 75篇 |
2011年 | 69篇 |
2010年 | 63篇 |
2009年 | 67篇 |
2008年 | 58篇 |
2007年 | 69篇 |
2006年 | 75篇 |
2005年 | 63篇 |
2004年 | 52篇 |
2003年 | 43篇 |
2002年 | 41篇 |
2001年 | 27篇 |
2000年 | 39篇 |
1999年 | 38篇 |
1998年 | 32篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 22篇 |
1994年 | 26篇 |
1993年 | 16篇 |
1992年 | 23篇 |
1991年 | 28篇 |
1990年 | 19篇 |
1989年 | 18篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1956年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有1538条查询结果,搜索用时 15 毫秒
1.
花青素是由类黄酮合成途径产生的次生代谢产物,含量高时会使茶树新梢呈现红色或紫色。同时,花青素相比儿茶素等具有更明显的抗氧化、预防肿瘤等药理保健作用。文章就茶树花青素合成途径、转录及转录后调控等方面进行综述,以期更好地为高花青素茶树的育种研究提供理论依据。 相似文献
2.
浅谈人造薄木生产中单板的漂白 总被引:2,自引:0,他引:2
详细阐述了木材颜色的成因及漂白机理,重点介绍了人造薄木生产过程中单板漂白工艺。研究表明,经漂白处理的单板,颜色明显变浅,色调也比较均匀,而且还消除了板面污染,对单板的染色十分有利。 相似文献
3.
本文利用透射电镜研究了寄生于家鸭小肠上皮细胞的菲莱氏温扬球虫的受精和卵囊壁的形成过程。作者在感染后96 h 的样品中发现一例大、小配子已受精;小配子已进入大配子中,大配子胞质中有一根纵切的鞭毛,小配子的核呈流体状,位于大配子核附近。卵囊壁是由成囊颗粒内含物进入合子表面的膜之间沉积成层而形成。成囊颗粒Ⅰ形成外层卵囊壁,成囊颗粒Ⅱ形成内层卵囊壁。沉积于膜之间的成囊颗粒Ⅰ内含物逐渐浓缩,堆积成颗粒状,使卵囊壁外层外表面形成颗粒状突起。成熟的卵囊壁由三层组成:即薄的外周膜、外层和内层。其内的合子原生质还被两层单位膜包裹。 相似文献
4.
R. P. Baayen D. M. Elgersma 《European journal of plant pathology / European Foundation for Plant Pathology》1985,91(3):119-135
Stems of the susceptible Early Sam and resistant Novada carnations were inoculated with a conidial suspension ofFusarium oxysporum f. sp.dianthi. Stem segments of either cultivar were sampled regularly and used for determination of fungal growth and for microscopical investigation.Early Sam showed typicalFusarium wilt symptoms and its stems were colonized intensively. The observed vascular browning appeared to be caused by discolouration of primary walls of infected vessels and surrounding cells. Vessels were rarely occluded with gel. Cell wall degradation led to the formation of stem cavities. Hyperplasia of xylem parenchyma was not seen.In Novada, fungal colonization remained low throughout the experiment. Macroscopic symptoms were absent except for longitudinal bursts in the stem, which appeared to be caused by hyperplasia of xylem parenchyma bordering infection. Vascular gelation occurred in the infected tissues, causing some vascular browning also. Xylem vessel regeneration was observed in the hyperplastic layer. Cavities were not formed, and wall discolouration was rare. Vascular gelation is considered part of theFusarium wilt resistance mechanism. It is followed by xylem vessel regeneration, which expresses a general plant response to vascular dysfunction rather than being part of the resistance mechanism.Although of different origin, vascular browning as such occurs in both susceptible and resistant interactions. In breeding for resistance, care should hence be taken with the current use of browning as an indication of disease.Samenvatting Anjers van de vatbare cultivar Early Sam en de resistente cultivar Novada werden geïnoculeerd met een conidiënsuspensie vanFusarium oxysporum f. sp.dianthi. Van beide cultivars werden regelmatig stengeldelen geoogst om deze microscopisch te onderzoeken en om de schimmelgroei te bepalen.Early Sam vertoonde de voor deze verwelkingsziekte kenmerkende symptomen en werd intensief gekoloniseerd. Aan het vaatweefsel waargenomen bruinkleuring bleek veroorzaakt te worden door verkleuring van de primaire wanden van geïnfecteerde vaten en de hen omringende cellen. Zelden trad er in de vaten gomvorming op. Celwandafbraak veroorzaakte de vorming van holten in de stengel. Hyperplasie van het houtparenchym werd niet waargenomen.In Novada bleef de schimmelgroei gedurende het hele experiment beperkt. Macroscopisch waren er enkel lengtescheuren in de stengel te zien, die veroorzaakt bleken te worden door hyperplasie van aan de infectie grenzend houtparenchym. In het geïnfecteerde vaatweefsel optredende gomvorming veroorzaakte ook enige bruinkleuring. In het hyperplastische weefsel werd regeneratie van houtvaten waargenomen. In de stengel werden geen holten gevormd, en verkleuring van de celwanden kwam weinig voor. De vorming van gommen in de houtvaten maakt waarschijnlijk deel uit van het resistentiemechanisme. De daarop volgende houtvatregeneratie is eerder een algemene reactie van de plant op vaatverstopping dan een deel van het resistentiemechanisme.Vaatverbruining, zij het van verschillende oorsprong, komt voor in zowel vatbare als resistente interacties. Om die reden moet men in de resistentieveredeling bij de anjer voorzichtig zijn met het gebruik van bruinkleuring als ziekteïndicatie. 相似文献
5.
Aleš Lebeda Ida Blok 《European journal of plant pathology / European Foundation for Plant Pathology》1990,96(1):51-54
Results are given on the occurrence of sexual compatibility types of seven isolates ofBremia lactucae originating fromLactuca serriola (prickly lettuce). It is concluded that the isolates studied are heterothallic. Both compatibility types (B1 en B2) were determined, but type B2 was prevalent. Sexual recombination ofB. lactucae isolates originating from wild and cultivated lettuce may occur.Samenvatting Zeven isolaten vanBremia lactucae, afkomstig vanLactuca serriola in Tsjechoslowakije, zijn onderzocht op hun sexuele compatibiliteitstype door ze te combineren met Nederlandse fysio's vanB. lactucae, afkomstig van cultuursla (L. sativa), waarvan het compatibiliteitstype (B1 of B2) bekend is. Alle isolaten vanL. serriola bleken heterothallisch te zijn, waarbij type B2 meer werd aangetroffen dan type B1. Sexuele recombinatie vanBremia-isolaten van wildeLactuca-soorten en cultuursla blijkt goed mogelijk te zijn. 相似文献
6.
7.
8.
A range of agricultural practices influence soil microbial communities, such as tillage and organic C inputs, however such effects are largely unknown at the initial stage of soil formation. Using an eight-year field experiment established on exposed parent material (PM) of a Mollisol, our objectives were to: (1) to determine the effects of field management and soil depth on soil microbial community structure; (2) to elucidate shifts in microbial community structure in relation to PM, compared to an arable Mollisol (MO) without organic amendment; and (3) to identify the controlling factors of such changes in microbial community structure. The treatments included two no-tilled soils supporting perennial crops, and four tilled soils under the same cropping system, with or without chemical fertilization and crop residue amendment. Principal component (PC) analysis of phospholipid fatty acid (PLFA) profiles demonstrated that microbial community structures were affected by tillage and/or organic and inorganic inputs via PC1 and by land use and/or soil depth via PC2. All the field treatments were separated by PM into two groups via PC1, the tilled and the no-tilled soils, with the tilled soils more developed towards MO. The tilled soils were separated with respect to MO via PC1 associated with the differences in mineral fertilization and the quality of organic amendments, with the soils without organic amendment being more similar to MO. The separations via PC1 were principally driven by bacteria and associated with soil pH and soil C, N and P. The separations via PC2 were driven by fungi, actinomycetes and Gram (−) bacteria, and associated with soil bulk density. The separations via both PC1 and PC2 were associated with soil aggregate stability and exchangeable K, indicating the effects of weathering and soil aggregation. The results suggest that in spite of the importance of mineral fertilization and organic amendments, tillage and land-use type play a significant role in determining the nature of the development of associated soil microbial community structures at the initial stages of soil formation. 相似文献
9.
P. Taranet G. Kirchhof R. Fujinuma N. Menzies 《Journal of Agronomy and Crop Science》2018,204(3):313-324
Large mounds amended with plant residues are a common cultivation method for sweetpotato (Ipomoea batatas) in the western parts of the Papua New Guinea highlands, with a suggested benefit of elevated root zone temperature (RZT) from decomposition. This study aimed to evaluate whether RZT affects the formation and growth of sweetpotato storage roots. Experiments evaluated the effects of a constant elevated RZT on the Beauregard cultivar and of a short‐term increase in RZT on the Beauregard and Northern Star cultivars. Plants were grown in 18‐L pots divided into a control compartment (constant RZT at 20°C) and a treated compartment (RZT at 30, 40 or 50°C). Constant elevated RZT was maintained until harvest, while short‐term increase in RZT occurred in weeks 2 and 3 only. Constant elevated RZT did not affect the total number of storage roots, but RZT of 30°C and above reduced the dry‐biomass of storage roots. The short‐term increase in RZT did not alter the total number or dry‐biomass of storage roots in Beauregard, while both of these attributes were reduced at RZT of 40°C or above in Northern Star. Elevated RZT inhibited dry‐biomass accumulation of storage root, with a more pronounced impact at constant elevated RZT. These results demonstrate that any benefits of the mound culture on sweetpotato yield production do not arise through the influence of temperature elevation. 相似文献
10.
魏俊峰 《上海交通大学学报(农业科学版)》2015,(5):47-50
拟在动态平衡的视角下对现代足球阵型的演变历程进行梳理与整合,希望对阵型之间的关联及其对足球运动发展的影响提供见解,对阵型演变的不同阶段进行探讨,探寻足球攻守平衡与不同阵型的嬗变关系,同时也为推动未来足球阵型演变对战术打法的影响研究提供参考依据。采用文献资料、系统分析、专家访谈和逻辑分析等方法,对现有的足球阵型发展的概况进行分析之后,认为现代足球阵型的演变历程不断交替出现攻守的平衡与不平衡,正是交替出现的状况促进了阵型的改变,进而影响了阵型的发展。当阵型的发展过程中出现攻守平衡时,就有其它后来者对该阵型进行学习、模仿、改进、提高。当阵型的发展过程中出现攻守不平衡,攻强于守或者守强于攻时,就会促进阵型的演变向攻守平衡的方向发展,因此就会出现阵型的发展处于不平衡-平衡-不平衡-再到平衡的态势,从而形成比赛阵型发展本身的稳定与不稳定状态交替出现。研究认为,世界足球阵型演变的过程是一种动态的、不断发展的、维持某种平衡与稳定的、平衡和不平衡交替运动的情况,即动态平衡的状态。提出将现代足球阵型演变的过程分为不同的阶段,每一个阶段内,都分别出现攻守平衡与攻守不平衡的状态,而这种平衡与不平衡的存在与区别、斗争与转化正是足球阵型演变与发展的规律。 相似文献