全文获取类型
| 收费全文 | 3876篇 |
| 免费 | 576篇 |
| 国内免费 | 177篇 |
专业分类
| 林业 | 1496篇 |
| 农学 | 461篇 |
| 基础科学 | 105篇 |
| 126篇 | |
| 综合类 | 1688篇 |
| 农作物 | 147篇 |
| 水产渔业 | 84篇 |
| 畜牧兽医 | 306篇 |
| 园艺 | 82篇 |
| 植物保护 | 134篇 |
出版年
| 2024年 | 16篇 |
| 2023年 | 43篇 |
| 2022年 | 76篇 |
| 2021年 | 108篇 |
| 2020年 | 143篇 |
| 2019年 | 127篇 |
| 2018年 | 55篇 |
| 2017年 | 104篇 |
| 2016年 | 163篇 |
| 2015年 | 80篇 |
| 2014年 | 151篇 |
| 2013年 | 268篇 |
| 2012年 | 357篇 |
| 2011年 | 357篇 |
| 2010年 | 283篇 |
| 2009年 | 308篇 |
| 2008年 | 317篇 |
| 2007年 | 294篇 |
| 2006年 | 272篇 |
| 2005年 | 219篇 |
| 2004年 | 171篇 |
| 2003年 | 100篇 |
| 2002年 | 57篇 |
| 2001年 | 48篇 |
| 2000年 | 64篇 |
| 1999年 | 44篇 |
| 1998年 | 45篇 |
| 1997年 | 61篇 |
| 1996年 | 20篇 |
| 1995年 | 23篇 |
| 1994年 | 40篇 |
| 1993年 | 21篇 |
| 1992年 | 31篇 |
| 1991年 | 28篇 |
| 1990年 | 20篇 |
| 1989年 | 32篇 |
| 1988年 | 67篇 |
| 1987年 | 2篇 |
| 1986年 | 11篇 |
| 1985年 | 2篇 |
| 1984年 | 1篇 |
排序方式： 共有4629条查询结果，搜索用时 125 毫秒
71.
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
72.
The structural defects of the heart are often reflected in the sounds that heart produces. Because of the non-stationary of the PCG signal, it is important to maintain its time-frequency character. We discuss the Short-Time Fourier Transform (STFT) method and the wavelet method. Some normal and abnormal heart sounds were analyzed by these methods. We can see the advantage and disadvantage of them obviously from the examples. 相似文献
73.
He Zefu Wu Yunjian 《保鲜与加工》1988,(4)
The effect of small amounts of gallium on the intergranular segregation of phosphorus in carbon steels is discussed, with the help of the impact test, fracture morphology and micro-structure analyses, combined with composition analysis on the fracture surfaces by Auger electronspectrometer. The results show that gallium in the steel with a content of gallium more than ten thou-sandth can suppress, to some extent, the intergranular segregation of phosphorus and retard the tempering process. As a result, the temper embrittlement of the steel disappears and the embrittlement transition temperature declines. 相似文献
74.
The feasible control problem is presented for the day-operation of the Three-Gorge Caseade Hydropower Station. The significance of the problem is explained. Basic propetties ofthe problem and the approaches to study it are discussed. Two methfods are given for solving theproblem. which are calculus of variation and linear programming. In the former. the Euler equationwith time-lag and the generalised two-point boundary conditions are obtained and the correspondingpractical implication is interpreted. In the latter. the rationality for the discrete model is exptainedand the computalional details are given for the implement software. some questions which should bepaid much attentfon and the corresponding propeels are prasented based on the numerical results andtheoretical analysis 相似文献
75.
Ren Yuanzhi 《保鲜与加工》1994,(1)
The condition when forces are applied to load mechnical mornent limiter of tow-er cranes is analysed and disctissed in this paper.A lifting performance curve adapted for the me-chanical load moment limiter is also obtained.And finally,the curve drawing method is explainedthrough the practical example. 相似文献
77.
This paper presents the end-effect factor of Synchronous motor with cylindricalsolid rotor offered by analysing the 3-D electromagnetic field and using the Poynting vector.To ap-ply it in an actual calculation,the end-effect factor is proved correct and applicable. 相似文献
78.
79.
80.
Electromagnetic potentials and gauge transformation are derived for non-cloSedexterior differential forms with the help of relevant homology.Since de Rham ccahomology is sure-ly a relavant homology. potentials for both closed and non-closed forms and the gauge transforma-tion ean be unified in terms of relavent homology. 相似文献