全文获取类型
收费全文 | 5852篇 |
免费 | 264篇 |
国内免费 | 248篇 |
专业分类
林业 | 808篇 |
农学 | 370篇 |
基础科学 | 289篇 |
602篇 | |
综合类 | 2897篇 |
农作物 | 216篇 |
水产渔业 | 165篇 |
畜牧兽医 | 574篇 |
园艺 | 98篇 |
植物保护 | 345篇 |
出版年
2024年 | 32篇 |
2023年 | 59篇 |
2022年 | 116篇 |
2021年 | 167篇 |
2020年 | 151篇 |
2019年 | 216篇 |
2018年 | 92篇 |
2017年 | 186篇 |
2016年 | 225篇 |
2015年 | 206篇 |
2014年 | 363篇 |
2013年 | 335篇 |
2012年 | 424篇 |
2011年 | 471篇 |
2010年 | 329篇 |
2009年 | 337篇 |
2008年 | 348篇 |
2007年 | 311篇 |
2006年 | 302篇 |
2005年 | 225篇 |
2004年 | 169篇 |
2003年 | 140篇 |
2002年 | 147篇 |
2001年 | 138篇 |
2000年 | 111篇 |
1999年 | 94篇 |
1998年 | 98篇 |
1997年 | 75篇 |
1996年 | 64篇 |
1995年 | 73篇 |
1994年 | 71篇 |
1993年 | 46篇 |
1992年 | 75篇 |
1991年 | 39篇 |
1990年 | 46篇 |
1989年 | 40篇 |
1988年 | 27篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1980年 | 1篇 |
排序方式: 共有6364条查询结果,搜索用时 15 毫秒
81.
R. A. Daamen 《European journal of plant pathology / European Foundation for Plant Pathology》1989,95(2):85-105
Damage by mildew to winter wheat was studied in 11 field experiments in the Netherlands. Damage is described by the simple function: –0.013 (SE=0.003) kg are–1 per pustule-day of mildew per leaf, from second node stage to early dough at yield levels of 70 to 90 kg are–1, in diseasefree plots. No deviations from linearity at disease stresses from zero to two thousand pustuledays per leaf were observed. Years, cultivars or soil types did not affect the damage function significantly. The effects of mildew on some yield components were suggested.Mildew profiles in untreated plots could be described by the equation: CM=CLAb, in which CM and CLA are the cumulative pustule number and the cumulative leaf area, respectively, calculated both from top to bottom of the canopy, and totals standardized at unity. Estimates of the gradient parameter b aveaged 3.4 (SE=0.9). Observed differences in steepness of the profiles did not affect the damage function significantly.Samenvatting Opbrengstderving van wintertarwe door meeldauw werd bestudeerd in 11 veldproeven in Nederland. De schade bedroeg gemiddeld 0.013 (SE=0.003) kg are–1 per puistdag meeldauw per blad, vanaf het tweede-knoop stadium tot begin deegrijp bij opbrengstniveaus van 70 tot 90 kg are–1, in de blanco. Bij een ziektestress van 0 tot 2000 puistdagen meeldauw per blad werd geen afwijking van een rechtlijnig verband gevonden. De schaderelatie werd niet significant beïnvloed door de verschillende jaren, rassen of grondsoorten. Het effect van meeldauw op enkele opbrengstcomponenten werd aangetoond.Meeldauwprofielen in de onbehandelde veldjes konden worden beschreven met de vergelijking: CM=CLAb, waarin CM het cumulatieve aantal puistjes is en CLA het cumulatieve bladoppervlak, beide berekend van bovenin het bladerdek naar beneden, de totalen gestandaardiseerd op één. De gradiënt parameter b bedroeg gemiddeld 3.4 (SE=0.9). Waargenomen verschillen in steilte van de meeldauwprofielen beïnvloedde de schaderelatie niet aantoonbaar. 相似文献
82.
83.
迟爱民 《干旱区资源与环境》1994,8(1):110-115
本文通过对呼和浩特地区地面气象观测资料统计,分析了污染物的时空分布规律,从气象条件的角度说明了呼市大气污染往往是由局地环流形成的,并根据分析结果对呼市今后的污染治理提出了相应的建议。 相似文献
84.
肉用西门塔尔牛改良云南黄牛的效果初报 总被引:2,自引:0,他引:2
对云南黄牛、西门塔尔与云南黄牛的杂交牛(西本杂)体尺体重进行了测定,结果西本牛与本地牛体尺体重都有了显著提高(P<0.01)。西本杂牛的初生、6、12、18、24月龄体重比同龄本地牛分别高出82%、18%、69%、50%、78%。 相似文献
85.
86.
教育对经济增长具有很强的促进作用。文章采用计量经济学方法,测算重庆市教育对重庆市经济增长的贡献率,并把计算结果同京、津、沪、川的数据作了对比。发现重庆市的教育贡献率上升,但是高等教育贡献率非常低。当前,重庆市实施“科教兴渝”战略,一方面应注重持续发展基础教育,实现重庆教育均衡发展;另一方面注重协调发展高等教育,进一步改善教育体系,同时创新留住人才的机制。 相似文献
87.
88.
生态灌木蒙古莸的生物生态学特性及其经济价值评价 总被引:7,自引:0,他引:7
本文对饲料型优良生态灌木—蒙古莸的分布与生物学和林学特性,以及其快繁技术、饲用与药用价值等进行了研究和评价。从生态建设与经济发展角度,提出了蒙古莸资源的保护、开发与利用的途径。 相似文献
89.
European policies and instruments such as the Common Agricultural Policy (CAP) and many instruments for nature and landscape
conservation in Europe have for some decades been dominated by centralisation and standardisation. This paper shows that this
has led to the neglect of contextual and place-related approaches and an unnecessarily high degree of over-simplification.
Recently, as a reaction to this over-simplification, diversity and specific character has been particularly stressed in many
European and national strategies for rural landscapes and conservation, but the processes of simplification still continue.
Using examples from mixed agriculture and forestry landscapes in Portugal, Slovenia and Sweden, this paper aims to contribute
to understanding the gap between centrally defined strategies for rural landscapes and awareness and management practices
at local level. The three countries are situated at the outer fringes of Europe, and are complementary with their different
degrees of urbanisation, forest distribution and tree-richness in the agricultural landscapes. Furthermore, the aim is to
show how local landscape management is driven and to identify factors contributing to a better use of public policies through
a participatory process with visions for the future. Systems of landscape classifications such as landscape character assessment
often recognise the specific character of these landscapes, but have so far achieved very little for the preservation of their
locally specific values, nor have they contributed to the development and the creation of new visions for future management.
Such systems could contribute much more if they could be opened to adaptation on a more local scale in communication-led management
planning. 相似文献
90.
While several studies have demonstrated that roads can act as barriers to small mammal movement, the relationship between
road density and small mammal abundance has not yet been investigated. In southeastern Ontario, Peromyscus leucopus (white-footed mice) suffer high over-winter mortality rates, resulting in small springtime populations and frequent local
extinctions. Peromyscus leucopus movement is known to be inhibited by roads, which should result in lower rates of immigration into and recolonization of
habitats in landscapes with high road density. We tested two predictions: (1) Forest sites situated in landscapes with high
road densities have a higher chance of P. leucopus being absent during the early spring than forest sites situated in landscapes with low road densities and (2) P. leucopus populations during the summer are smaller in forest sites situated in landscapes with high road densities than in landscapes
with low road densities. We sampled P. leucopus in focal patches within nineteen landscapes (7 rural, low-road-density landscapes; 7 rural, high-road-density landscapes;
5 urban landscapes). There was no significant relationship between road density and the presence/absence of P. leucopus during the early spring. We found a significant positive effect of road density on P. leucopus relative abundance during the summer, even when we excluded the urban landscapes and based the analysis on only the 14 rural
landscapes. Our results suggest that any negative effect of roads on P. leucopus populations, created by their inhibition to moving across roads, is far outweighed by some positive effect of roads on P. leucopus abundance. We suggest that the two most likely explanations are that roads are positively correlated with an important as-yet-undetermined
component of habitat quality, or that roads positively affect P. leucopus by negatively affecting their predators. 相似文献