全文获取类型
收费全文 | 601篇 |
免费 | 24篇 |
国内免费 | 24篇 |
专业分类
林业 | 51篇 |
农学 | 17篇 |
基础科学 | 177篇 |
67篇 | |
综合类 | 238篇 |
农作物 | 34篇 |
水产渔业 | 7篇 |
畜牧兽医 | 39篇 |
园艺 | 14篇 |
植物保护 | 5篇 |
出版年
2024年 | 9篇 |
2023年 | 20篇 |
2022年 | 13篇 |
2021年 | 15篇 |
2020年 | 10篇 |
2019年 | 19篇 |
2018年 | 9篇 |
2017年 | 15篇 |
2016年 | 19篇 |
2015年 | 36篇 |
2014年 | 38篇 |
2013年 | 34篇 |
2012年 | 42篇 |
2011年 | 46篇 |
2010年 | 31篇 |
2009年 | 38篇 |
2008年 | 36篇 |
2007年 | 26篇 |
2006年 | 28篇 |
2005年 | 31篇 |
2004年 | 20篇 |
2003年 | 31篇 |
2002年 | 3篇 |
2001年 | 6篇 |
2000年 | 11篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
排序方式: 共有649条查询结果,搜索用时 15 毫秒
1.
小麦植株感染条锈病后叶片花青素含量会发生明显变化。为了在地块尺度上利用冬小麦花青素值实现条锈病害的直观、快速监测,通过监测叶片花青素含量评估小麦条锈病严重程度,2021年获取感染条锈病的小麦田块的无人机RGB影像和采集地面病害区域的花青素含量数据,利用影像提取采样点感兴趣区的光谱特征参数和基于灰度共生矩阵的纹理特征参数,采用连续投影算法(SPA)结合相关性分析优选特征参数,分别采用单一光谱特征参数和组合参数,结合主成分回归(PCR)、拉索回归(LR)、随机森林回归(RFR)、梯度提升回归(GBR)和误差反向传播神经网络(BPNN)等方法构建了小麦花青素含量估算模型,并利用最优模型反演了田块的花青素含量。结果表明,图像光谱特征结合纹理特征后,花青素估算模型的R2增大,RMSE减小,模型精度显著提升。基于组合特征参数构建的随机森林模型精度最高,验证集R2、RMSE和MAE分别为0.801、0.026、0.021。该模型具有良好的花青素含量估算能力,得到的花青素值分布图与条锈病的空间分布具有一致性,能够定量化、可视化地反映病害严重程度。 相似文献
2.
《The Journal of Applied Poultry Research》2015,24(2):233-239
Formal systems of inquiry are of limited value when working with rural communities in developing countries. The current research used alternative systems of inquiry and learning that involved applying participatory epidemiology (PE) techniques to collect veterinary information about Newcastle disease (ND) in rural areas. Results indicated that poultry constituted the largest proportion (42.4%) of livestock species kept, and the poultry diseases that local farmers callbingiri, ciwon-sufe,dankanoman-kaji, dangari, andgurdumu are consistent with modern veterinary knowledge of Newcastle disease, respiratory disease, coccidiosis, fowl pox, and ectoparasitism, respectively.Tsuwen zaki (lion's testicle;Cucumuis pustulatus) andgarafuni (balsam pear;Momordica balsamina) are traditional remedies used to prevent Newcastle disease. Local farmers are knowledgeable about common disease that affect their poultry; they have good diagnostic abilities and can recognize clinical signs. There should be improved veterinary outreach to share some of this information via active community participation, and PE should be incorporated into state and national disease surveillance systems. 相似文献
3.
4.
Isolation of Pasteurella haemolytica and correlation with serum antibody response in clinically normal beef calves 总被引:1,自引:0,他引:1
Bacteria from the nasal cavity and trachea were cultured, and serum antibody titers determined for Pasteurella haemolytica serotype 1 in 164 beef calves obtained from a closed herd on range pasture. At the first sampling, P. haemolytica serotype 1 was cultured from 16.4% of the calves. Antibody titers were determined by a quantitative fluorimetric method and the mean titer was 9.5 +/- 5.8. Fifty-seven randomly selected calves were used to study the correlation of serum antibody response and positive culture of P. haemolytica under natural conditions. Clinical signs of respiratory disease were not observed in those calves. During the observation periods, there was a two-fold increase in the percentage of calves that were culture positive. There was no significant difference between mean serum antibody titers or frequency distribution of antibody titers from the two samplings. Comparisons between serum antibody titers, rise in titers, and P. haemolytica isolation failed to reveal any significant correlation. Of the 9 calves that had a decline in antibody titer to P. haemolytica, none was culture positive. Seroconversion to respiratory viruses did not correlate with P. haemolytica related variables. 相似文献
5.
提出了基于数学模型的幼苗外观特征自动检测方法,检测项目包括生长状态、子叶参数和胚轴参数。首先经过图像预处理提取幼苗二值图,利用行像素统计图确定特征参数基准点位置。然后以标定胚轴最小矩形倾斜度和宽度判定弯曲状态;子叶跨度通过两子叶端点距离确定,子叶展开角通过两子叶底端平展位置拟合线夹角判定;胚轴弯曲度通过胚轴中心线上曲率最大的位置为分界点分别判断两段斜度而求得,胚轴长、轴径结合斜度补偿求得。与手工测量数据对比,轴长、轴径和子叶跨度的相关系数分别为0.935 1、0.899 9和0.903 4,相对误差分别小于7%、5%和7%,绝对误差分别小于4 mm、0.2 mm和6 mm。 相似文献
6.
7.
机器视觉技术在禽蛋品质和孵化成活性检测中的应用 总被引:1,自引:0,他引:1
本文论述了利用机器视觉技术进行禽蛋品质检测分级及种蛋孵化成活性检测的意义,从禽蛋外形、表面缺陷、内部缺陷检测及种蛋孵化成活性检测等方面阐述了国内外研究现状,从硬件和软件两方面分析了在研究和应用中存在的不足,指出了目前尚需解决的难点问题。 相似文献
8.
Land use changes threaten agricultural land. If agricultural land is going to be preserved, the social and economic causes
of conversion must be understood. However, analyzing the causes of agricultural conversion is complex because trends need
to be documented before analyzing the causes. One of the leading uses of agricultural land is for residential purposes. This
paper projects residential development in a Hudson River Valley watershed within Dutchess County in New York State using an
integrated modeling framework consisting of an econometric model, a geographic information system (GIS), and Monte Carlo simulation.
The econometric model is used to project residential development, providing parcel-specific probabilities of residential development.
The GIS is employed to extract socio-economic and county-level tax parcel data to be used in conjunction with bio-geophysical
attributes, such as slope, soil, and location, to calculate and project growth trends on a residential level for undeveloped
land parcels. Monte Carlo simulation is used to distribute these projections into the GIS to display outcomes of scenario
analyses to provide policy-makers a demonstration of how policies would likely affect the agricultural landscape of the watershed.
John M. Polimeni is an Assistant Professor of Economics in the Department of Humanities and Social Sciences at the Albany College of Pharmacy
in Albany, New York. Dr. Polimeni received a PhD in Ecological Economics and a BS in Mathematics at Rensselaer Polytechnic
Institute. His professional interests include: quantitative economics, spatial and regional economics, land use change, economic
development, and graduate education in Ecological Economics. He is currently working on linking ecological economics with
the laws of thermodynamics and neuroeconomics into one unified model. 相似文献
9.
基于改进Hough变换的农田作物行快速检测算法 总被引:5,自引:0,他引:5
选取苗期农田作为研究对象,采集了包含行栽作物和土壤背景的农田图像,针对现有作物行定位方法易受外界干扰和处理速度较慢的不足,提出将投影法和直接Hough变换法相结合检测作物行的算法.采用2G-R-B 法和OTSU法将图像二值化,通过快速中值滤波算法去除噪声,再利用垂直直方图投影将图像进行水平条划分获取作物垄平均定位点,最后通过Hough变换检测垄定位点,得到作物行中心线.试验结果表明:基于垂直直方图投影的Hough变换检测作物行中心线的算法在保证高定位精度的同时,算法处理速度比直接Hough变换检测法提高了3倍,得到的定位基准线能代表作物行走向. 相似文献
10.