全文获取类型
收费全文 | 3327篇 |
免费 | 189篇 |
国内免费 | 226篇 |
专业分类
林业 | 302篇 |
农学 | 342篇 |
基础科学 | 72篇 |
542篇 | |
综合类 | 1263篇 |
农作物 | 178篇 |
水产渔业 | 197篇 |
畜牧兽医 | 468篇 |
园艺 | 137篇 |
植物保护 | 241篇 |
出版年
2024年 | 13篇 |
2023年 | 37篇 |
2022年 | 55篇 |
2021年 | 82篇 |
2020年 | 82篇 |
2019年 | 106篇 |
2018年 | 76篇 |
2017年 | 132篇 |
2016年 | 126篇 |
2015年 | 134篇 |
2014年 | 167篇 |
2013年 | 185篇 |
2012年 | 261篇 |
2011年 | 280篇 |
2010年 | 218篇 |
2009年 | 245篇 |
2008年 | 211篇 |
2007年 | 198篇 |
2006年 | 189篇 |
2005年 | 122篇 |
2004年 | 99篇 |
2003年 | 83篇 |
2002年 | 68篇 |
2001年 | 60篇 |
2000年 | 69篇 |
1999年 | 72篇 |
1998年 | 37篇 |
1997年 | 37篇 |
1996年 | 38篇 |
1995年 | 40篇 |
1994年 | 43篇 |
1993年 | 29篇 |
1992年 | 29篇 |
1991年 | 25篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 18篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有3742条查询结果,搜索用时 15 毫秒
151.
Cowpea is an important legume in sub-Saharan Africa where its protein rich grains are consumed. Insect pests constitute a
major constraint to cowpea production. Flower bud thrips (FTh) is the first major pest of cowpea at the reproductive stage
and if not controlled with insecticides is capable of reducing grain yield significantly. Information on the inheritance of
resistance to FTh is required to facilitate breeding of resistant cultivars. The genetics of resistance was studied in crosses
of four cowpea lines. Maternal effect was implicated while frequency distributions of the F2 and backcross generations suggest quantitative inheritance. Additive, dominance and epistatic gene effects made large contributions
and since improved inbred lines are the desired product, selection should not be too severe in the early generations to allow
for desirable gene recombination. This study suggested that some of the genes involved in the control of resistance to FTh
are different in TVu1509 and Sanzi. Broad sense heritability ranged from 56% to 73%. Choice of maternal parent in a cross
will be critical to the success of resistance breeding. 相似文献
152.
不同中药对奶牛乳房炎病原菌抑菌效果的观察 总被引:1,自引:0,他引:1
本试验采用琼脂平板扩散法(打孔法),研究了黄芩等21种中药对从乳房炎奶牛乳汁中分离出的3种主要致病菌的体外抑菌情况。结果发现,大肠杆菌对黄芩高度敏感,对丹参、青翘属中度敏感;金黄色葡萄球菌对黄芩、青翘、丹参、地榆、红花、蒲公英高度敏感,对枳壳、忍冬藤、萹蓄、苦地丁、蟾酥、木通中度敏感;无乳链球对地榆、当归属高度敏感,对青翘、黄芩、蒲公英、丹参、苦地丁、红花、川芎、枳壳中度敏感。为防治奶牛乳房炎有效中药复方的筛选提供了理论依据。 相似文献
153.
60Coγ辐射对苹果属观赏海棠诱变效应的研究初报 总被引:3,自引:0,他引:3
摘 要:为探讨60Coγ射线辐射处理对苹果属观赏海棠的诱变效应,以观赏海棠品种绚丽(M. ‘Radiant’)和印第安魔力(M. ‘Indian Magic’)的一年生枝为试材,采用4个剂量的60Coγ射线辐射处理,观察与测试其被辐射枝条上芽体的成活率、成活后新梢的生长状况、新梢叶片形态的变化和对蚜虫的抗性。结果表明:60Coγ射线辐射处理降低被辐射枝条嫁接成活率,抑制其新梢和叶片的生长,使叶面积降低,厚度增加,叶色加深,新梢叶片蚜虫的感染率降低。分析认为:60Coγ射线辐射使观赏海棠嫁接后幼树的生长受到明显的抑制,使叶形态和功能得到改善,表现出明显的矮化征状,同时使植株抗虫性得到一定程度地提高。 相似文献
154.
以葛根为原料,以葛根黄酮的得率为指标,以料液比、提取电压、提取时间和提取次数为影响因素,采用正交试验优化其提取工艺,并对其保肝作用进行研究。结果表明,闪式提取法的最佳工艺条件为:提取次数2次,料液比1∶30(g/mL),提取电压160 V,提取时间80 s。该工艺条件下,葛根黄酮的得率为6.71%。动物实验表明,葛根黄酮能够明显降低小鼠血清中谷丙转氨酶(ALT)、谷草转氨酶(AST)活性和丙二醛(MDA)含量,提高小鼠肝组织中谷胱甘肽过氧化物酶(GSH-Px)、超氧化物歧化酶(SOD)活性,具有明显的保肝作用。本结果可为葛根黄酮的提取和应用研究提供参考。 相似文献
155.
旱作水稻水肥耦合模型及经济效应 总被引:1,自引:0,他引:1
为了探讨膜下滴灌旱作水稻水分、肥料与产量之间的关系,采用通用旋转组合设计试验方法,进行膜下滴灌旱作水稻水肥耦合模型试验,并对其应用前景进行了比较分析.在供试土壤膜下滴灌条件下,灌溉定额、氮、磷与水稻产量之间符合三元二次回归模型,其一次项、二次项及水氮交互项回归系数均达显著水平,三因素的增产作用从大到小依次为灌溉定额、施氮量、施磷量.采用此模型计算的预测产量与实际产量之间呈高度正相关,预测准确度达99%.由此计算得出最高产量灌溉定额及其施肥量、经济最佳灌溉定额及其施肥量.提出实现目标产量的水肥最优组合方案:若以9 300~9 600 kg/hm2为目标产量,则灌溉定额、氮、磷用量分别为9 730~10 500 m3/hm2,272~363 kg/hm2,136~147 kg/hm2;若同时考虑经济效益,则最佳的灌溉定额、氮、磷肥用量分别为8 500~9 015 m3/hm2,225~240 kg/hm2,90~120 kg/hm2.对比不同种植模式表明,膜下滴灌旱作水稻的产量与播后上水直播基本持平,其成本与育秧移栽种植持平,但水分生产效率(1.06 kg/m3)远远高于其他3种种植方式.与传统育秧移栽种植相比较,膜下滴灌旱作水稻节水50%,节约肥料30%以上. 相似文献
156.
This study used whole-farm management, nutrient budgeting/greenhouse gas (GHG) emissions and feed formulation computer tools to determine the production, environmental and financial implications of intensifying the beef production of typical New Zealand (NZ) sheep and beef farming systems. Two methods of intensification, feeding maize silage (MS) or applying nitrogen (N) fertiliser, were implemented on two farm types differing in the proportions of cultivatable land to hill land (25% vs. 75% hill). In addition, the consequences of intensification by incorporating a beef feedlot (FL) into each of the farm types were also examined.Feeding MS or applying N fertiliser substantially increased the amount of beef produced per ha. Intensifying production was also associated with increased total N leaching and GHG emissions although there were differences between the methods of intensification. Feeding MS resulted in lower environmental impacts than applying N even after taking into account the land to grow the maize for silage. Based on 2007/08 prices, typical NZ sheep and beef farms were making a financial loss and neither method of intensification increased profitability with the exception of small annual applications of N, especially to the 75% hill farm. These small annual additions of N fertiliser (<50 kg N/ha/yr applied in autumn and late winter) resulted in only small increases in annual N leaching (from 11 to 14 kg N/ha) and GHG emissions (from 3280 to 4000 kg CO2 equivalents/ha). Limited N applications were particularly beneficial to 75% hill farms because small increases in winter carrying capacity resulted in relatively large increases in the utilisation of pasture growth during spring and summer than the 25% hill farms. Intensification by incorporating a beef feedlot reduced environmental emissions per kg of beef produced but considerably decreased profitability due to higher capital, depreciation and labour costs. The lower land-use capability farm type (75% hill) was able to intensify beef production to a proportionally greater extent than the higher land-use capability farm (25% hill) because of greater potential to increase pasture utilisation associated with a lower initial farming intensity and inherent constraints in the pattern of pasture supply. 相似文献
157.
158.
根据我国北方冬季气温偏低、沼气池产气慢且少的特点,结合日照特点,设计了由太阳能温室和集热室两部分组成的太阳能双效增温沼气系统。利用传热学的基本理论,建立了沼气系统的热平衡方程,并通过理论计算,分析了太阳能双效增温沼气系统内各部分的热利用效率。 相似文献
159.
随着新一轮的中职学校德育课课程改革的深入开展和中职学生主体意识的增强,传统的德育课教学有许多方面需要进一步改进和完善.在中职学校德育课教学中实施高效良性的师生互动,能提高德育课的教学实效和学生的思想道德素质,为学生职业生涯发展奠定基础. 相似文献
160.
Elin Enfors Jennie Barron Hodson MakuriraJohan Rockström Siza Tumbo 《Agricultural Water Management》2011,98(11):1687-1695
Yield levels in smallholder farming systems in semi-arid sub-Saharan Africa are generally low. Water shortage in the root zone during critical crop development stages is a fundamental constraining factor. While there is ample evidence to show that conservation tillage can promote soil health, it has recently been suggested that the main benefit in semi-arid farming systems may in fact be an in situ water harvesting effect. In this paper we present the result from an on-farm conservation tillage experiment (combining ripping with mulch and manure application) that was carried out in North Eastern Tanzania from 2005 to 2008. Special attention was given to the effects of the tested treatment on the capacity of the soil to retain moisture. The tested conservation treatment only had a clear yield increasing effect during one of the six experimental seasons (maize grain yields increased by 41%, and biomass by 65%), and this was a season that received exceptional amounts of rainfall (549 mm). While the other seasons provided mixed results, there seemed to be an increasing yield gap between the conservation tillage treatment and the control towards the end of the experiment, and cumulatively the yield increased with 17%. Regarding soil system changes, small but significant effects on chemical and microbiological properties, but not on physical properties, were observed. This raises questions about the suggested water harvesting effect and its potential to contribute to stabilized yield levels under semi-arid conditions. We conclude that, at least in a shorter time perspective, the tested type of conservation tillage seems to boost productivity during already good seasons, rather than stabilize harvests during poor rainfall seasons. Highlighting the challenges involved in upgrading these farming systems, we discuss the potential contribution of conservation tillage towards improved water availability in the crop root zone in a longer term perspective. 相似文献