全文获取类型
收费全文 | 5172篇 |
免费 | 287篇 |
国内免费 | 649篇 |
专业分类
林业 | 550篇 |
农学 | 320篇 |
基础科学 | 340篇 |
1524篇 | |
综合类 | 2150篇 |
农作物 | 146篇 |
水产渔业 | 230篇 |
畜牧兽医 | 513篇 |
园艺 | 145篇 |
植物保护 | 190篇 |
出版年
2024年 | 59篇 |
2023年 | 133篇 |
2022年 | 172篇 |
2021年 | 198篇 |
2020年 | 192篇 |
2019年 | 227篇 |
2018年 | 165篇 |
2017年 | 270篇 |
2016年 | 333篇 |
2015年 | 284篇 |
2014年 | 316篇 |
2013年 | 355篇 |
2012年 | 379篇 |
2011年 | 390篇 |
2010年 | 290篇 |
2009年 | 307篇 |
2008年 | 279篇 |
2007年 | 311篇 |
2006年 | 266篇 |
2005年 | 184篇 |
2004年 | 160篇 |
2003年 | 116篇 |
2002年 | 89篇 |
2001年 | 93篇 |
2000年 | 86篇 |
1999年 | 69篇 |
1998年 | 44篇 |
1997年 | 66篇 |
1996年 | 30篇 |
1995年 | 36篇 |
1994年 | 23篇 |
1993年 | 34篇 |
1992年 | 32篇 |
1991年 | 27篇 |
1990年 | 28篇 |
1989年 | 12篇 |
1988年 | 21篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有6108条查询结果,搜索用时 31 毫秒
11.
Growth and reproduction by powdery mildew pathogens is generally inhibited by decreasing relative humidity. With Erysiphe sp. on Rhododendron cv. Elizabeth, the initial stages of colony development were adversely affected by reducing the relative humidity from 100% to 70 and 85%. No significant effects on secondary or tertiary hyphal development were detected. Light intensity and photoperiod both had considerable effect on the induced resistance response of the host. Over the initial 5 days of colonization there were no significant differences between any of the treatments. After 13 days, however, expansion of fungal colonies at 180 photosynthetic active radiation (PAR) was limited solely to the area initially infested by primary hyphae. By comparison, in colonies grown at 80 PAR regardless of day length, secondary and tertiary hyphae had extended beyond the area first colonized. These effects resulted in differing morphologies, small colonies of densely packed hyphae formed at 180 PAR compared with open spreading colonies at 80 PAR. 相似文献
12.
亚硫酸氢钠处理减轻低温对温州蜜柑光合作用的影响 总被引:12,自引:0,他引:12
低温胁迫使温州蜜柑叶片的净光合速率(Pn)、光系统Ⅱ的光化学效率(Fv/Fm)及光合电子传递速率(ETR)下降,反映跨膜质子动力势的叶绿素毫秒延迟发光(ms-DIE)减弱,叶片中的ATP含量降低。低温胁迫前,用NaHSO3 5 mmol/L涂于叶片表面,可使处理植株叶片的Pn和Fv/Fm分别少下降了11.5%和11.6%,ETR和ATP含量几乎没有下降,ms-DLE的下降幅度减少。可见,在柑橘上施用NaHSO3能够减轻短期低温对光合机构及光合作用的影响。 相似文献
13.
14.
15.
本文就西吉县农用地膜的应用现状和污染现状进行了分析,并就这一现状提出了促进旱作农业可持续发展的对策措施。 相似文献
16.
水分条件对巴音布鲁克高寒湿地CO_2排放的影响 总被引:1,自引:0,他引:1
在新疆天山中部巴音布鲁克天鹅湖高寒湿地,以苔草(Carex tristachya)为主要建群种的样地为研究对象,利用英国PP-systems公司生产的便携式土壤呼吸测定系统(CIRAS-2-SRC)研究了不同地表水分条件对天鹅湖高寒湿地夏季土壤CO2排放的影响。结果表明,1)湿润区的生物量大于干燥区;干燥区土壤CO2排放高于湿润区,干燥区土壤CO2排放日变化曲线为单峰曲线,CO2排放最高点出现在当地14:00-16:00,最高值为1.185 0g CO2·m-2·h-1;湿润区土壤CO2排放日变化曲线为双峰曲线,两个峰值分别出现在12:00和16:00,最高值为1.024 0g CO2·m-2·h-1。2)不同水分条件下生物量中凋落物含量影响土壤CO2排放。土壤温度是CO2排放的主要限制因子,且地表干燥区CO2排放与土壤温度的相关性更显著(P0.01)。土壤湿度与CO2排放相关性不显著(P湿润区=0.997,P干燥区=0.409)。 相似文献
17.
18.
The environmental impact of crop production is mainly related to fossil fuels consumption and to fertilisers application. Emissions arising from the spreading of organic and mineral fertilisers are important contributors for impact categories such as eutrophication and acidification. The choice of the fertilisers and of the spreading techniques as well as the crop residues management can deeply affect the environmental impact related to crop cultivation.In this study, seven scenarios describing fertilising schemes characterised by different organic and mineral fertilisers and by different mechanisation were compared. The aim is to evaluate, using the Life Cycle Assessment (LCA) method, how the environmental performances of grain maize production were affected by these different fertilisers schemes. The study was carried out considering a cradle to farm gate perspective and 1 t grain maize was selected as functional unit. Inventory data were collected on a farm located in Po Valley (Northern Italy) during year 2013 and were processed using the composite method recommended by the International Reference Life Cycle Data System (ILCD). The compared scenarios involved organic and mineral fertiliser distribution and were: pig slurry incorporation after >3 days after spreading (BS), fast pig slurry incorporation within 2 h from spreading (AS1), direct soil injection of pig slurry (AS2), pig slurry incorporation (after >3 days) with straw collection (AS3), digestate spreading instead of pig slurry (after >3 days) (AS4), only mineral fertilisers (i.e. urea and superphosphate) distribution (AS5) and only mineral fertilisers (i.e. calcium ammonium nitrate and superphosphate) distribution (AS6).The results were not univocal, since climate and soil conditions as well as physical and chemical fertiliser characteristics differently affected the environmental load, especially for particulate matter formation, terrestrial acidification and terrestrial eutrophication impact categories. AS1 and AS2 showed the most beneficial results for these impact categories (between ↙67% and ↙73% respect to worst scenario). AS6, on the opposite, showed the highest environmental impact for those impact categories mainly affected by energy and fossil fuel consumption (climate change, ozone depletion, human toxicity with carcinogenic effect, particulate matter, freshwater eutrophication, freshwater ecotoxicity and mineral, fossil and renewable resources depletion), categories on which AS3 and AS4 were the best solutions. AS3 was the most impacting for terrestrial acidification and eutrophicationA sensitivity analysis was carried out varying grain maize yield (mostly affected: marine eutrophication) and ammonia volatilisation losses due to organic fertilisers (mainly affected: terrestrial acidification and eutrophication).The achieved results can be useful for the development of ⬓spreading rules⬽ that drive the application of organic fertilisers in agricultural areas where there is an intense livestock activity. 相似文献
19.
本试验以1株饲用益生菌解淀粉芽孢杆菌B7(Bacillus amyloliquefaciens B7,B.amyloliquefaciens B7)为研究对象,为了增强其在液态条件下的发酵水平,提高其芽孢发酵工艺优化效率,拟采用测定芽孢吡啶二羧酸(dipicolonic acid,DPA)浓度的方法来代替传统的平板芽孢计数法,以探讨此测定方法在芽孢发酵优化工艺中的可行性。首先,通过单因素试验筛选出对菌株产孢有显著促进作用的因子,进一步通过正交优化试验确定蛋白胨、玉米粉、大米蛋白粉和Mn2+组合的最优水平。结果表明,发酵液中的芽孢浓度与测定的DPA荧光强度呈线性相关,在蛋白胨20 g/L、玉米粉10 g/L、大米蛋白粉20 g/L、Mn2+1.0 mmol/L时发酵48 h,检测到DPA荧光强度达到最大,其相应的芽孢浓度达到7.0×109 CFU/mL。与实验室常用的LB培养基相比,芽孢浓度提高了3.3倍;与工业生产用培养基相比,芽孢浓度提高了2.2倍。本研究为芽孢杆菌发酵过程中芽孢浓度测定提供了一种快速方法,为工业菌株B.amyloliquefaciens B7的发酵提供了一种成分简单且高产芽孢的培养基。 相似文献
20.
池永亮 《林业机械与木工设备》2015,(3):19-21,26
分别采用GB 18580标准中的干燥器法和穿孔萃取法检测中密度纤维板的甲醛释放量,并根据两种方法检测出的结果分析其相关性。结果表明,两种检测方法呈显著线性相关。 相似文献