全文获取类型
收费全文 | 6531篇 |
免费 | 318篇 |
国内免费 | 785篇 |
专业分类
林业 | 1373篇 |
农学 | 357篇 |
基础科学 | 1832篇 |
808篇 | |
综合类 | 2170篇 |
农作物 | 250篇 |
水产渔业 | 90篇 |
畜牧兽医 | 421篇 |
园艺 | 166篇 |
植物保护 | 167篇 |
出版年
2024年 | 36篇 |
2023年 | 166篇 |
2022年 | 270篇 |
2021年 | 264篇 |
2020年 | 271篇 |
2019年 | 373篇 |
2018年 | 196篇 |
2017年 | 323篇 |
2016年 | 434篇 |
2015年 | 332篇 |
2014年 | 360篇 |
2013年 | 339篇 |
2012年 | 519篇 |
2011年 | 488篇 |
2010年 | 341篇 |
2009年 | 360篇 |
2008年 | 286篇 |
2007年 | 302篇 |
2006年 | 291篇 |
2005年 | 217篇 |
2004年 | 199篇 |
2003年 | 152篇 |
2002年 | 127篇 |
2001年 | 153篇 |
2000年 | 131篇 |
1999年 | 88篇 |
1998年 | 78篇 |
1997年 | 77篇 |
1996年 | 76篇 |
1995年 | 51篇 |
1994年 | 61篇 |
1993年 | 47篇 |
1992年 | 41篇 |
1991年 | 46篇 |
1990年 | 36篇 |
1989年 | 28篇 |
1988年 | 27篇 |
1987年 | 17篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1962年 | 2篇 |
排序方式: 共有7634条查询结果,搜索用时 46 毫秒
21.
22.
Abstract. Usual residue-management options are to remove the residue, use it as mulch with or without undercutting or to incorporate it into the soil. While the role of surface mulch in evaporation has been widely studied, the information on the effect on evaporation of mulch with undercutting or residue incorporated into soil, particularly in relation to soil type and evaporativity (Eo) is lacking. We studied the effect of wheat straw used in various ways on the course of evaporation loss from soil columns with three soils at Ludhiana, India and one soil at Bushland, Texas, USA, under two Eo's Energy-limited evaporation rates under mulch (Eom) followed the soil-specific relation Eom/Eo= a e(bRes+cEo), where Res is residue rate t/ha and a, b and c are constants; Eo, is expressed in mm/d. In an effort to model the total evaporation (CE) during the energy-limited stage ‘U’ was obtained from appropriate CE versus time curves and (CE-U) was regressed over (t - ti)0.5 to obtain the slope ‘α’ (Ritchie 1972) for the soil-limited evaporation stage. The observed ‘U’ was independent of mulch rate and Eo but was strongly affected by soil type, Values of ‘α’ decreased with increase in mulch rate and decrease in Eo and coarseness of soil. The otherwise short lived benefit of evaporation reduction with mulch per se, which peaked after a few days was maintained when residue was mixed with soil at the stage when evaporation reduction reached a maximum; this benefit continued for several weeks. Cumulative evaporation values computed from ‘U’ and ‘α’ agreed closely with the observed values under straw mulch for loamy sand and clay loam soils and for ‘undercut’ and ‘residue mixed’ treatments on all soils regardless of Eo, and for all situations under small Eo. However, for sandy loam and silt loam soils under Eo of 10 mm/d, the modified square root of the time function of Jalota et al. (1988) gave a better fit. 相似文献
23.
对经营区边境伐区开设便道,还是开设手扶拖拉机道进行技术分析与经济分析,采用盈亏平衡分析法决策,并用实例论证其实用价值。 相似文献
24.
一种无土栽培新装置根区温湿度及对番茄根系生长的影响 总被引:1,自引:1,他引:0
以桶式Ⅱ型无土栽培装置为对照,式无土栽培新装置为处理.研究了新装置根区温湿度的变化以及根系生长状况。结果表明,在苗期和果实成熟期,两栽培装置中基质和气室温度的日变化随着温室气温的变化而变化,变化趋势总体上基本一致,新装置中基质和室的温度变化的幅度均低于对照。湿度的日变化趋势正好与温度的日变化趋势相反,先是缓慢下降而后又逐渐上升,变化的幅度整体上新装置低于对照。说明在新装置栽培下,基质和气室温湿度受外界光照剧烈变化影响的幅度小于对照,能够更好避免由于高温高湿造成的根系枯死。两种栽培装置的根系生长在苗期没有明显的差异,在果实成熟期差异显著,新装置高于对照。 相似文献
25.
为挖掘“商薯19”的增产潜力,以商洛市农户常用的竖插法为对照,采用单株水平扦插法、双株水平扦插法栽培“商薯19”。结果发现双株水平扦插法总产量最高(3 037.81 kg/667 m2),与竖插法产量(1 838.7 kg/667 m2)差异显著(P<0.05)。进一步统计不同扦插方式的大、中薯数量、产量及大、中薯率发现,双株水平扦插法主要通过增加大薯产量和中薯数量来达到增产效果。双株水平扦插法能够同时适应生产淀粉和鲜食的需求,有必要进一步试验、示范和推广。 相似文献
26.
Saila Holopainen Elina Rautala Liisa Lilja‐Maula Hannes Lohi Minna M. Rajamki Anu K. Lappalainen 《Veterinary radiology & ultrasound》2019,60(5):525-532
Canine idiopathic pulmonary fibrosis is a chronic, progressive interstitial lung disease particularly prevalent in West Highland White Terriers. In the present prospective pilot study, we evaluated the feasibility of modified VetMousetrap? device in high resolution CT to detect idiopathic pulmonary fibrosis in West Highland White Terriers. Twelve awake West Highland White Terriers with canine idiopathic pulmonary fibrosis and 24 clinically healthy West Highland White Terriers were scanned using a helical dual slice scanner utilizing VetMousetrap? device without or with minimal chemical restraint with butorphanol. Three evaluators blindly assessed the images for image quality and the presence of canine idiopathic pulmonary fibrosis related imaging findings such as ground glass opacity and reticular opacities. Additionally, the attenuation of the lung was quantified with ImageJ software using histogram analysis of density over the lung fields. Computed tomography was successfully completed and motion artifact ranked in statistical analysis barely noticeable to mild in all dogs. The agreement between imaging findings and clinical status was very good with overall κ value 0.91 and percentage of agreement of 94%. There was also very good intraobserver (κrange = 0.79‐0.91) and interobserver agreement (κ = 0.94). Moderate to severe ground glass opacity was present in all affected dogs. In the ImageJ analysis, a significant difference in lung attenuation between the study groups was observed. We conclude that modified VetMousetrap? device is applicable in diagnosing canine idiopathic pulmonary fibrosis in awake West Highland White Terriers avoiding anesthetic risk in these often severely hypoxic patients. 相似文献
27.
文章旨在探讨苜蓿干草切割长度对湖羊增重性能和营养物质表观消化率的影响。试验选择60只体重和日龄相近的断奶湖羊,随机分为4组,对照组日粮中的苜蓿干草为自然长度,其余3组分别饲喂切割长度为5、15和25 mm的苜蓿干草,预饲期为10 d,正试期为90 d,在饲喂试验结束前的最后10 d开展消化试验。试验结果表明,苜蓿干草切割长度对育肥羔羊的干物质采食量具有显著影响,育肥羔羊的干物质采食量随苜蓿干草切割长度的增加而降低。苜蓿干草切割长度对育肥羔羊的平均日增重具有显著影响,以苜蓿切割长度为15 mm具有最大日增重。育肥羔羊的营养物质表观率受苜蓿干草长度的影响显著,日粮营养物质的表观消化率随苜蓿干草切割长度的增加而增加。因此,在育肥羔羊饲料配制过程中,应考虑苜蓿干草的切割长度,本试验中以苜蓿干草切割长度为15 mm具有最佳生长性能。 相似文献
28.
P. H. M. Roseboom D. Peters 《European journal of plant pathology / European Foundation for Plant Pathology》1984,90(4):133-141
Beet yellows virus can be detected in leaf extracts of infected sugarbeet plants by ELISA. The use of discs was studied and proved to be a valuable and qualitatively reliable method. Leaf material could be stored at 4o or 22°C for at least six days without affecting the detection of this virus by ELISA. A dramatic decrease in ELISA values was found when leaf extracts were frozen.In an analysis of the distribution of virus over the plant it was found that young leaves present at the moment of infection and those which had still to develop after infection will contain virus. Symptoms produced by systemic virus invasion occur on the oldest leaves containing virus.Samenvatting Het bietevergelingsvirus kan op betrouwbare wijze met de ELISA methode in geïnfecteerde bieteplanten worden aangetoond. Een aanzienlijke vereenvoudiging van de procedure kan worden bereikt met de zogenaamde disc-method, waarbij intacte ponsstukjes in de putjes van de ELISA-plaat worden geïncubeerd. Hierbij komt voldoende virus uit de ponsstukjes voor ELISA vrij. Bladmateriaal kon op verschillende wijzen bewaard worden zonder dat de mogelijkheid om het virus aan te tonen achteruitging. Met bladextracten die ingevroren waren, werden echter slechte resultaten verkregen.In een analyse naar de verdeling van het virus over het loof bleek het virus voor te komen in de geïnoculeerde bladeren, in die bladeren die op het tijdstip van inoculatie minder dan de helft van hun uiteindelijke lengte bereikt hadden en in de bladeren die nog moesten verschijnen. De symptomen ontwikkelden zich op de oudste systemisch geïnfecteerde bladeren. 相似文献
29.
30.