全文获取类型
收费全文 | 724篇 |
免费 | 37篇 |
国内免费 | 130篇 |
专业分类
林业 | 46篇 |
农学 | 125篇 |
基础科学 | 156篇 |
173篇 | |
综合类 | 332篇 |
农作物 | 27篇 |
水产渔业 | 4篇 |
畜牧兽医 | 10篇 |
园艺 | 3篇 |
植物保护 | 15篇 |
出版年
2024年 | 4篇 |
2023年 | 16篇 |
2022年 | 13篇 |
2021年 | 21篇 |
2020年 | 27篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2017年 | 42篇 |
2016年 | 36篇 |
2015年 | 40篇 |
2014年 | 39篇 |
2013年 | 39篇 |
2012年 | 61篇 |
2011年 | 51篇 |
2010年 | 53篇 |
2009年 | 54篇 |
2008年 | 50篇 |
2007年 | 59篇 |
2006年 | 38篇 |
2005年 | 43篇 |
2004年 | 37篇 |
2003年 | 30篇 |
2002年 | 26篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1988年 | 2篇 |
1986年 | 1篇 |
排序方式: 共有891条查询结果,搜索用时 15 毫秒
201.
天津农学院为了培养学生准确掌握和使用先进分析仪器的能力,开设了仪器分析课程。以傅里叶红外光谱仪教学为例,探讨了改革傅里叶红外光谱仪的实验教学内容、教学模式、教学方法,使学生的实验技能得到提高,培养学生良好的实验素质和严谨的科研作风。 相似文献
202.
203.
针对复杂红外背景下单一跟踪算法难以准确定位运动目标的问题,提出了基于尺度无迹卡尔曼滤波(SUKF,scale unscented Kalman filter)与尺度不变特征变换(SIFT,scale invariant featuretransform)相结合的红外运动目标跟踪方法。首先,通过SUKF算法对状态空间进行滤波估计,确定运动目标的初步位置,并以此建立局部SIFT特征检测域。其次,SIFT算法在该局部检测域内对运动目标进行特征提取与匹配,最终实现对目标的准确定位;同时,利用定位结果更新并校正SUKF的状态模型。实验结果表明,本文提出的基于SUKF-SIFT的跟踪策略与相关算法相比,体现出较好的跟踪效果与实时性能。 相似文献
204.
一种改进的小波阈值去噪方法 总被引:1,自引:0,他引:1
为了改进滤波效果,提高去噪质量,在分析目前被广泛应用的软、硬阈值去噪方法的基础上,提出了一种改进的阈值去噪方法.该方法既兼顾了软、硬阈值函数的优点,同时又在一定程度上弥补了它们在图像去噪中的缺陷.有效克服了硬阈值法去噪信号失真的和软阈值法细节模糊现象.仿真结果表明:该方法可以有效地去除白噪声干扰,无论在视觉效果上还是在信噪比定量指标上均明显优于传统的软、硬阈值算法,达到良好的去噪效果. 相似文献
205.
206.
For consumers, fresh-cut fruits and vegetables are a convenient product and a healthy source of fresh food that has nutritional and sensory characteristics similar to those of intact products. In this paper, a non-destructive method for analyzing fresh-cut fruit and vegetables is described. The biospeckle laser technique is based on the optical phenomenon of interference generated by a coherent light interacting with biological materials or dynamical systems. Although many publications on this technique's biological applications have reported that biospeckle activity corresponds to the activity of biological samples, there is some difficulty in determining the correlation between a particular phenomenon and the activity observed. In this study, we evaluated the use of biospeckle data for measuring the physiological properties of fresh-cut carrots stored at two temperatures (0 and 10 °C). In conjunction with the biospeckle activity, the moisture content, respiration rate, water activity, and mass loss changes were monitored using traditional analytical methods to evaluate the possible correlation of the biospeckle data with any of these phenomena with or without the use of frequency signatures. The results showed that the manifestation of water in the monitored activity was isolated only by removing these high frequencies, thus allowing the activity manifested in the material to be linked to a specific phenomenon, such as respiration. Therefore, we were able to monitor the respiration process in fresh-cut carrots and assign a spectral signature to their water content and respiration. 相似文献
207.
We propose an approach to texture characterization and comparison that directly uses the information of digital images of
the earth surface without requesting a prior distinction of structural ‘patches’. Digital images are partitioned into square
‘windows’ that define the scale of the analysis and which are submitted to the two-dimensional Fourier transform for extraction
of a simplified textural characterization (in terms of coarseness) via the computation of a ‘radial’ power spectrum. Spectra computed from many images of the same size are systematically compared
by means of a principal component analysis (PCA), which provides an ordination along a limited number of coarseness vs. fineness
gradients. As an illustration, we applied this approach to digitized panchromatic air photos depicting various types of land
cover in a semiarid landscape of northern Cameroon. We performed ‘textural ordinations’ at several scales by using square
windows with sides ranging from 120 m to 1 km. At all scales, we found two coarseness gradients (PCA axes) based on the relative
importance in the spectrum of large (> 50 km−1), intermediate (30–50 km−1), small (10–25 km−1) and very small (<10 km−1) spatial frequencies. Textural ordination based on Fourier spectra provides a powerful and consistent framework to identifying
prominent scales of landscape patterns and to compare scaling properties across landscapes. 相似文献
208.
209.
A method of realizing wavelet transform with linear analog filter is proposed. It shows another new way of obtaining fast wavelet transform. It has also given out a procedure of constructing such a filter network and verified by the Mexican hat Wavelet. 相似文献
210.
This paper illustrates the methods of extracting characteristic parameters and deformation recognition using wavelet transfor,which applied in low voltage impulse(LVI) method on the transformer winding deformation detection.The results show that it is effective to eliminate the noise using wavelet transform,meanwhile,it can also make measurement has repetitivity and has a property on model recognition on defomation. 相似文献