全文获取类型
收费全文 | 1003篇 |
免费 | 46篇 |
国内免费 | 134篇 |
专业分类
林业 | 121篇 |
农学 | 134篇 |
基础科学 | 98篇 |
111篇 | |
综合类 | 401篇 |
农作物 | 86篇 |
水产渔业 | 66篇 |
畜牧兽医 | 75篇 |
园艺 | 70篇 |
植物保护 | 21篇 |
出版年
2024年 | 5篇 |
2023年 | 18篇 |
2022年 | 24篇 |
2021年 | 45篇 |
2020年 | 36篇 |
2019年 | 36篇 |
2018年 | 27篇 |
2017年 | 32篇 |
2016年 | 44篇 |
2015年 | 32篇 |
2014年 | 48篇 |
2013年 | 50篇 |
2012年 | 66篇 |
2011年 | 91篇 |
2010年 | 63篇 |
2009年 | 75篇 |
2008年 | 59篇 |
2007年 | 62篇 |
2006年 | 62篇 |
2005年 | 38篇 |
2004年 | 36篇 |
2003年 | 18篇 |
2002年 | 27篇 |
2001年 | 24篇 |
2000年 | 28篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 18篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1183条查询结果,搜索用时 203 毫秒
71.
2012-2013年在大田种植条件下,以短季棉常规品种百棉2号和中棉所50及杂交棉品种百棉3号为材料,在麦后直播和种植密度为15万株/hm2条件下,研究不同品种产量和株型对棉太金的响应。结果表明,3个品种子棉产量对棉太金的响应及同一品种子棉产量在不同年份对棉太金的响应不一致。棉太金显著减低了3个品种的株高和果枝长度,但抑制程度之间存在明显差异,百棉3号的株高受抑制程度最低;棉太金对3个品种的1~3台和4~6台果枝长度抑制效果显著,对百棉2号和中棉所50的≥7台果枝长度影响效果不显著,但显著降低了百棉3号的≥7台果枝长度;棉太金对3个品种的果枝台数、果节数和果枝始节节位影响效果不显著。 相似文献
72.
作者结合多年工程施工实践,论述了水稳砂砾层的施工工艺及在施工中应注意的问题。对从事实际施工技术人员具有一定的指导意义。 相似文献
73.
Summary About 13,000 somaclones of 17 cultivars and clones of potato were obtained from in vitro callus cultures and individually
planted in a greenhouse, followed by tuber generations grown in the field. These plants were subjected to the multistage selection
procedure commonly used in potato breeding. Over a period of five years and three field generations the tuber number, size,
shape, eye depth, starch content, starch yield and tuber appearance of these somaclones were assessed and compared with that
of the controls. These characters varied depending on donor genotype and trait. The frequency of variants was assessed and
there were acceptable proportions of desirable abberrants and invariants among the somaclones. Depending on trait the average
gain rate for all donor genotypes ranged between 0.2 and 2.3% for-deviants, between 12.2 and 15.5% for invariants and between
0.1–1.4% for +deviants.
It is concluded that this technique should be used into potato breeding programmes to improve commercially important characteristics
of specific cultivars and breeding clones. 相似文献
74.
From progeny lists of 30 Dutch Warmblood sires, 586 3-year-old females by these stallions were randomly selected, each progeny group aimed at 20 animals for statistical reasons. The front feet of the sires and female progeny were examined radiographically using lateromedial and dorsopalmar upright pedal projections. The radiological features associated with navicular disease were classified 0–4 using a standardised classification, grades 3 and 4 representing the more severe changes. The shape of the proximal articular border of the navicular bone outlined on the dorsopalmar view was classified 1–4: l=concave; 2=undulating; 3=straight; 4=convex. A significant shape-grade association was found, the highest grades 3 and 4 incidence associated with shape 1 and the lowest grades 3 and 4 incidence demonstrated by shape 4. In shapes 1 and 2, navicular bones grades 3 and 4 features were mainly characterised by inverted flask-shaped channels. In shape 3, navicular bones grades 3 and 4 were dominated by enthesiophytes. These findings indicate an apparent shape predisposition to radiological changes associated with navicular disease. The shape of the navicular bone in the offspring was on average the same as the sire, indicating an hereditary element in navicular bone shape. 相似文献
75.
研究了3个正常叶型材料与鸡脚叶型材料杂交得到的杂种2代结果表明,选用适当亲本组配的杂交组合,不仅F_1能获得高产,F_2也有一定利用价值,其中尤以鄂棉15×鸡-2最好。对几个农艺性状与产量的相关分析表明,在条裂叶型、正常叶型材料中,果枝数、果节数与皮棉产量达显著正相关,条裂叶型F_2的纤维长度高于正常叶型。以合理正常叶植株与条裂叶植株的比例和适当的栽培措施改善农艺性状,便能提高F_2的产量和纤维品质。 相似文献
76.
根据玉米种子的籽粒和幼芽的品种性状不同,提出了单交玉米Sc7004杂交率的室内鉴定方法。 相似文献
77.
人工鱼礁开口比和迎流面形状对流场效应影响的双因素方差分析 总被引:2,自引:0,他引:2
采用基于计算流体动力学模型的方法对人工鱼礁流场效应进行数值模拟,选取单体人工鱼礁模拟近岸海域的鱼礁流场,对其附近流场进行三维数值模拟,在此基础上应用双因素方差分析法分析了人工鱼礁开口比和迎流面形状对流场效应的影响。结果表明:人工鱼礁开口比是鱼礁流场效应的主要影响因素,开口比越小,水流受鱼礁阻隔程度越大,礁前上升流流速越大,背涡流紊流区域越明显,背涡流区域就越长;鱼礁迎流面形状对流场效应的影响次之。 相似文献
78.
79.
Leaf shapes are not only the useful indicators in plant taxonomy,but also the important factors affecting energy and material exchange in leaves.In this paper,we collected and scanned the leaves of Nitraria tangutorum in Dengkou of Inner Mongolia Autonomous Region(the mean annual precipitation 145 mm) and Minqin of Gansu Province (the mean annual precipitation 115 mm) and N. sphaerocarpa in Dunhuang,and then analyzed leaf shape parameters with Image - Pro Plus6.0 image processing software and leafδ13C values in the isotope laboratory of the Chinese Academy of Forestry.The result showed that:1) as leaf area increased with increasing water availability the increases in the leaf length and width were asynchronously;2) with the same leaf width,the 1 eaves of N.tangutorum and N.sphaerocarpa were significantly longer in high water available conditions;and 3) although there were significantly differences in water availability between Dengkou and Minqin,as well as between the bottom and middle of the alluvial fan near the East Lake in Dunhuang,the leafδ13C values of N.tangutorum or N.sphaerocarpa were similar in different water conditions(P>0.05).Our results suggested that the ratio of leaf perimeter to area would be an important factor which linked leaf shape to plant water physiology.During growing procedure of leaf area,leaf length increase was prior to its width to alleviate the reduction in ratio of perimeter to area and maintain water use efficiency of the plant. 相似文献
80.