全文获取类型
收费全文 | 4130篇 |
免费 | 157篇 |
国内免费 | 845篇 |
专业分类
林业 | 336篇 |
农学 | 173篇 |
基础科学 | 2107篇 |
880篇 | |
综合类 | 1242篇 |
农作物 | 126篇 |
水产渔业 | 73篇 |
畜牧兽医 | 109篇 |
园艺 | 18篇 |
植物保护 | 68篇 |
出版年
2024年 | 66篇 |
2023年 | 174篇 |
2022年 | 253篇 |
2021年 | 226篇 |
2020年 | 181篇 |
2019年 | 293篇 |
2018年 | 136篇 |
2017年 | 272篇 |
2016年 | 304篇 |
2015年 | 239篇 |
2014年 | 256篇 |
2013年 | 195篇 |
2012年 | 347篇 |
2011年 | 274篇 |
2010年 | 203篇 |
2009年 | 265篇 |
2008年 | 162篇 |
2007年 | 229篇 |
2006年 | 208篇 |
2005年 | 177篇 |
2004年 | 137篇 |
2003年 | 80篇 |
2002年 | 72篇 |
2001年 | 65篇 |
2000年 | 55篇 |
1999年 | 39篇 |
1998年 | 41篇 |
1997年 | 39篇 |
1996年 | 28篇 |
1995年 | 20篇 |
1994年 | 19篇 |
1993年 | 21篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1986年 | 3篇 |
排序方式: 共有5132条查询结果,搜索用时 15 毫秒
31.
Operational Deflection Shapes of large scale electromechanical system can be ex-tracted directly from multipoints response of the operating system by using of the modal shape analy-sis method. Thev can be used for engineers evaluating the practical dynamic beavior of the largescale elecltromechanical system,checking the existence of local reso,iance of the Stibsystem. and in-dentifying the wcakened positions of the rigidity of structure, In this paper the method of measuringand extracting the operational deflection shal1e of the electromecha nical system is given and theavailability of operational deflection shape is proved by analyzing the actual vibration of a large ex-haust fan system as an example. 相似文献
32.
33.
Wang Bingle Song Liquan 《保鲜与加工》1988,(2)
This paper presents a new method by using mass and acceleration parameters for balancing inertial force of mechanism. Compared with other balance methods, this one is simple, clear and superior in regularity when the balancing equation of complex mechanism is established, and its solving procedure is also easy. The new methcd is convenient to learn and use as well as convenient to program. 相似文献
34.
It is difficult to measure the geometric quantity of small parts in finishing, assembling and measuring, because it's easy to break the workpieces' surface and alter their position by means of traditional contact measuring methods.There are some non contact measurers, such as,light feeler pin and interference microscope etc., because of it's high price and strict working conditions,so it's difficult to promote them in widely use. Precision measurement system based on machine vision has the advantages of non contact measuring as well as high performance and low price. Some problems, such as light source, algorithm of edge fitting, auto focusing,are discussed. 相似文献
35.
36.
Tu Zhiying Yu Chuzhong 《保鲜与加工》1988,(1)
In this paper, the machine( physical) parameters of the alternator system are on-line estimated on the basis of the derived system continuous-tims model, using Recursive Least-squares Estimation and Inverse Calculation Method proposed by Authors. Therefore, the estimated machine parameters can effectively track the changes of their true values and accomplish the fault detection for the alternator system. This paper gives a new way for machne parameter estimation and fault detection of the alternator systems. 相似文献
37.
A vision system based on the service robot is involved. In the system, picture signal is acquired by the picture sensor OV7635. Frame memory AL422B is used as data buffer memory, while CPLD controlled the time order DSP performed. In the software system of image processing, to accomplish color image segmentation and recognition, the threshold vector judgment and improved seed-fill algorithm is introduced, and the image geometric moment is calculated during the segmenting. In order to achieve a vision servo system which composed of image-based feedback and adaptive compensation, the deduced matrix-based Jacobian from the image moment is taken as image feature. Adopted the TFT LCD is adopted to straightly disolav the result of vision recognition and vision tracing. 相似文献
38.
39.
针对小水电站年发电量序列的特点,将最小二乘支持向量机(least squares support vector machine,LS-SVM)回归模型引入年发电量预测领域,并给出了相应的过程和算法。与常规基于人工神经网络(artificial neural net-works,ANN)的智能预测方法比较,该模型优点是明显的:①将神经网络迭代学习问题转化为直接求解多元线性方程;②整个训练过程中有且仅有一个全局极值点,确定了预测的稳定性。最后,一个实际的预测例子表明:该模型实现容易、预测准确,适用于小水电站预测。 相似文献
40.