全文获取类型
收费全文 | 3308篇 |
免费 | 130篇 |
国内免费 | 327篇 |
专业分类
林业 | 223篇 |
农学 | 344篇 |
基础科学 | 350篇 |
567篇 | |
综合类 | 1064篇 |
农作物 | 103篇 |
水产渔业 | 140篇 |
畜牧兽医 | 536篇 |
园艺 | 78篇 |
植物保护 | 360篇 |
出版年
2024年 | 18篇 |
2023年 | 69篇 |
2022年 | 125篇 |
2021年 | 137篇 |
2020年 | 164篇 |
2019年 | 180篇 |
2018年 | 120篇 |
2017年 | 147篇 |
2016年 | 191篇 |
2015年 | 149篇 |
2014年 | 167篇 |
2013年 | 206篇 |
2012年 | 237篇 |
2011年 | 243篇 |
2010年 | 189篇 |
2009年 | 186篇 |
2008年 | 145篇 |
2007年 | 149篇 |
2006年 | 151篇 |
2005年 | 121篇 |
2004年 | 90篇 |
2003年 | 78篇 |
2002年 | 66篇 |
2001年 | 55篇 |
2000年 | 37篇 |
1999年 | 39篇 |
1998年 | 47篇 |
1997年 | 30篇 |
1996年 | 48篇 |
1995年 | 31篇 |
1994年 | 24篇 |
1993年 | 19篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 21篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1962年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有3765条查询结果,搜索用时 15 毫秒
61.
可视化编程技术在发动机外特性曲线绘制中的应用 总被引:1,自引:0,他引:1
通过对汽车发动机外特性的理论分析,在处理汽车发动机外特性曲线时,建立了一种适合处理发动机外特性曲线的三次样条函数拟合的数学模型,在C Builder可视化开发平台上,编制了汽车发动机外特性曲线绘制程序.利用三次样条函数插值法对实验数据进行拟合,实现了发动机外特性曲线绘制的自动化. 相似文献
62.
对某铝合金活塞在机械疲劳试验机上做的疲劳试验进行有限元分析,为活塞的改进设计提供依据。采用装有活塞销的三维整体活塞有限元模型,应用接触单元模拟实际情况,对活塞在交变机械载荷作用下的应力和应变进行了计算,找出了危险点部位,计算结果与试验吻合。 相似文献
63.
64.
综述了国内外拖拉机液压提升能力试验的几种加载方案,并就其优缺点进行了探讨,给出了一种适于基层单位进行液压提升器检测维修的经济型方案。 相似文献
65.
电力负荷中期预测是指未来3~5年的负荷预测,是制定电力系统发展规划的基础,也是规划工作的重要组成部分,其目的是为合理地安排电源和电网建设进度提供宏观决策的依据,使电力建设满足国民经济增长和人民生活水平提高的需要。为此,通过对各种预测方法及特点的分析比较,得出用灰色模型预测方法作为农网电力负荷中期预测的方法,且该方法所需原始数据少、误差小、精度高。 相似文献
66.
Cyprodinil is a representative of the new class of broad-spectrum anilinopyrimidine fungicides. The effect of cyprodinil on mycelial growth of Botryotinia fuckeliana on solid agar medium depends on the composition of the medium and on the age of the mycelium to be used for the bioassay. An in-vitro method was developed to study the sensitivity distribution to cyprodinil in two wild-type populations of B. fuckeliana from fruits of strawberry with grey mould. To validate the applicability of the method, sensitivities to cyprodinil, mepanipyrim and pyrimethanil were monitored in populations of B. fuckeliana from grapes with grey mould from different vineyards, including one trial vineyard where reduced performance of cyprodinil had been encountered. The monitoring procedure was based on the inhibition of the mycelial growth on a synthetic medium containing L -asparagine (asp-agar) amended with the active ingredients. The mycelium was grown on asp-agar discs, starting from a spore suspension, for 17 h prior to the beginning of the test. This procedure proved to be efficient. The two wild-type populations from different sampling sites showed similar distributions of the sensitivity to cyprodinil. Some isolates from the trial site with reduced performance of anilinopyrimidines showed reduced sensitivities to cyprodinil, mepanipyrim and pyrimethanil, demonstrating cross-resistance between these anilinopyrimidines. 相似文献
67.
68.
采用菌丝生长速率法,测定了11种杀菌剂对杨梅褐斑病菌的离体抑菌活性,结果表明,嘧菌酯的抑制活性最强,EC50值为0.96 mg/L;百菌清的活性最弱,EC50值为69.24 mg/L;其余药剂的抑制活性依次为吡唑醚菌酯>氟硅唑>腈菌唑>抑霉唑>戊唑醇>咪鲜胺>喹啉铜>代森锰锌>多菌灵,EC50值在3.25~68.73 mg/L之间。林间试验结果表明,嘧菌酯对杨梅褐斑病具有很好的控制效果,其防效显著优于喹啉铜和多菌灵。进一步的研究结果表明,供试100株杨梅褐斑病菌对嘧菌酯的EC50值在0.15~2.17 mg/L之间,呈近似正态的连续分布,其平均EC50值为0.97?.22 mg/L,可作为该病菌对嘧菌酯的敏感性基线,用于田间抗药性监测。 相似文献
69.
针对电力负荷中期预测比较困难并且存在较大误差的问题,提出了基于径向基核函数与基于平衡策略的Sequential minimal optimization(SMO)改进算法相结合的负荷中期预测方法,结合EUNITE网络提供的实际数据,研究了日最大负荷的前后期关系、日最大负荷与节假日的关系和当日与对应星期数的相关性,建立了相应的电力负荷中期预测模型。并对预测结果进行了分析。算例表明,该算法具有运算速度快、精度较高的优点。 相似文献
70.
Effects of sediment load on the abrasion of soil aggregate and hydraulic parameters in experimental overland flow 下载免费PDF全文
The breakdown of soil aggregates under rainfall and their abrasion in overland flow are important processes in water erosion due to the production of more fine and transportable particles and, the subsequent significant effect on the erosion intensity. Currently, little is known about the effects of sediment load on the soil aggregate abrasion and the relationship of this abrasion with some related hydraulic parameters. Here, the potential effects of sediment load on soil aggregate abrasion and hydraulic parameters in overland flow were investigated through a series of experiments in a 3.8-m-long hydraulic flume at the slope gradients of 8.7 and 26.8%, unit flow discharges from 2×10~(–3) to 6×10~(–3) m~2 s~(-1), and the sediment concentration from 0 to 110 kg m~(–3). All the aggregates from Ultisols developed Quaternary red clay, Central China. The results indicated that discharge had the most significant(P0.01) effect on the aggregates abrasion with the contributions of 58.76 and 60.34%, followed by sediment feed rate, with contributions of 39.66 and 34.12% at the slope gradients of 8.7 and 26.8%, respectively. The abrasion degree of aggregates was found to increase as a power function of the sediment concentration. Meanwhile, the flow depth, friction factor, and shear stress increased as a power function along with the increase of sediment concentration at different slope gradients and discharges. Reynolds number was obviously affected by sediment concentration and it decreased as sediment concentration increased. The ratio of the residual weight to the initial weight of soil aggregates(Wr/Wi) was found to increase as the linear function with an increasing flow depth(P=0.008) or Reynolds number(P=0.002) in the sediment-laden flow. The Wr/Wi values followed a power function decrease with increasing friction factor or shear stress in the sediment-laden flow, indicating that friction factor is the best hydraulic parameter for prediction of soil aggregate abrasion under different sediment load conditions. The information regarding the soil aggregate abrasion under various sediment load conditions can facilitate soil process-based erosion modeling. 相似文献