全文获取类型
收费全文 | 1500篇 |
免费 | 53篇 |
国内免费 | 198篇 |
专业分类
林业 | 111篇 |
农学 | 103篇 |
基础科学 | 640篇 |
220篇 | |
综合类 | 567篇 |
农作物 | 11篇 |
水产渔业 | 33篇 |
畜牧兽医 | 44篇 |
园艺 | 7篇 |
植物保护 | 15篇 |
出版年
2024年 | 13篇 |
2023年 | 46篇 |
2022年 | 83篇 |
2021年 | 85篇 |
2020年 | 59篇 |
2019年 | 92篇 |
2018年 | 51篇 |
2017年 | 74篇 |
2016年 | 98篇 |
2015年 | 73篇 |
2014年 | 67篇 |
2013年 | 64篇 |
2012年 | 136篇 |
2011年 | 123篇 |
2010年 | 64篇 |
2009年 | 77篇 |
2008年 | 49篇 |
2007年 | 74篇 |
2006年 | 70篇 |
2005年 | 54篇 |
2004年 | 64篇 |
2003年 | 43篇 |
2002年 | 26篇 |
2001年 | 26篇 |
2000年 | 23篇 |
1999年 | 16篇 |
1998年 | 22篇 |
1997年 | 15篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 1篇 |
排序方式: 共有1751条查询结果,搜索用时 312 毫秒
11.
宽幅高效离心式双圆盘撒肥机设计与试验 总被引:3,自引:0,他引:3
为解决现有水旱田撒肥机械作业效率低、撒肥量调节技术落后、施肥均匀性稳定性差等实际问题,设计了一种同轴驱动的离心式双圆盘撒肥机。介绍了整机结构与工作参数,研究设计了撒肥传动系统、撒肥盘结构、排肥量液压调节装置等,并确定了关键结构和参数,同时进行了试验研究。试验结果显示,推肥板推肥角度-20°~30°可调,撒肥幅宽达到50m,总排肥量稳定性变异系数低于6%,施肥均匀性变异系数低于16%。研究结果表明,撒肥机工作性能稳定、撒肥量可控、抛撒均匀,整机设计满足水旱田宽幅高效撒肥作业要求。 相似文献
12.
13.
文章设计了基于单片机控制的送料机自动送料机控制系统,论述了单片机AT89C51在实现其生产过程控制的自动给料系统的设计方法。 相似文献
14.
In this paper the partial differential equation of coordinate transformation is computed by the finite difference formulations and some examples were computed and illustrated in pictures. 相似文献
15.
Tu Yaqing Li Zushu Huang Shanglian 《保鲜与加工》1993,(2):24-29
The idea for an expert system approach to the computer aided design of intelligent controllers (ESCAD1C) is discussed and the idea of two step modelling of an intelligent controller is presented on the basis of emulating human control behaviours to solve complex problems. The structure, functions and characteristics of ESCADTC system , and the design procedures of intelligent controllers are gived. The knowledge base and simulating functions for designing intelligent controllers are also described. 相似文献
16.
ZHANG Xin-yan 《保鲜与加工》2004,(5):54-56
While design the fuzzy controller, it is very important to determine the membership function of fuzzy variables.The data can be broadly classified as fuzzy sets by using the classification property of the BP neural network. The author selects a BP neural network with one hide layer and uses S function to the input and hide layer, and linear function to the output layer.Advanced BP algorithm isused to train the BP neural network in the environment of MATLAB . The nearer to the target values is the better the last output is.With the trained BP network , the membership values of the inputs can be got ten. This method has high rate and low error. 相似文献
17.
Hu Lide Yang Dan Wang Shilong 《保鲜与加工》1993,(6):58-64
After researching the function requirements of the planning and scheduling in manufacturing cells, the paper advanced a control structure with three phases, i. e. planning , scheduling and dispatching. The paper represented in detail the main purposes, requirements and scheduling actions in each phase. It suits to general machining FMSs. 相似文献
18.
Chen Ganping Xu Guoyu Qin Yihong 《保鲜与加工》1990,(1):43-48
A digital power system stabilizer ( DPSS ) and its design method are presented in this paper. The mathematical model of a single machine infinite bus power system is obtained using off-line parameter identifications, and on the base of the identified model the control system is synthesized by generalized minimum variance control principles. Through feedback combination of several signals this control system has double functions of damping low frequency oscillation and automatic voltage regulating. In order to avoid static errors the very effective way is to combine discrete generalized minimum variance control with continuous integral control. Besides the proposed control strategy is very simple in structures and very easy to realize. Simulation results under several cases have shown the correctness and effectiveness of the proposed control strategy. 相似文献
19.
In this paper, partial differential equations of vortex flow-stream function in boundary fitted coordinates and related ADI equations were listed. The flow around a cylinder in quadrilateral area by auto control boundary was computed. The diagram of distribution of speed arrow, constant lines of flow-stream function, vortex, two speed parts and pressure were studied. 相似文献
20.