全文获取类型
收费全文 | 6455篇 |
免费 | 372篇 |
国内免费 | 902篇 |
专业分类
林业 | 467篇 |
农学 | 492篇 |
基础科学 | 1721篇 |
1750篇 | |
综合类 | 2016篇 |
农作物 | 145篇 |
水产渔业 | 310篇 |
畜牧兽医 | 478篇 |
园艺 | 78篇 |
植物保护 | 272篇 |
出版年
2024年 | 47篇 |
2023年 | 131篇 |
2022年 | 225篇 |
2021年 | 254篇 |
2020年 | 239篇 |
2019年 | 277篇 |
2018年 | 203篇 |
2017年 | 295篇 |
2016年 | 361篇 |
2015年 | 281篇 |
2014年 | 335篇 |
2013年 | 369篇 |
2012年 | 491篇 |
2011年 | 475篇 |
2010年 | 404篇 |
2009年 | 347篇 |
2008年 | 345篇 |
2007年 | 374篇 |
2006年 | 336篇 |
2005年 | 262篇 |
2004年 | 224篇 |
2003年 | 195篇 |
2002年 | 178篇 |
2001年 | 164篇 |
2000年 | 154篇 |
1999年 | 119篇 |
1998年 | 82篇 |
1997年 | 100篇 |
1996年 | 76篇 |
1995年 | 75篇 |
1994年 | 75篇 |
1993年 | 50篇 |
1992年 | 46篇 |
1991年 | 43篇 |
1990年 | 27篇 |
1989年 | 31篇 |
1988年 | 24篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1974年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有7729条查询结果,搜索用时 625 毫秒
51.
Zhao Tingchao Huang Shanglian Chen Weimin 《保鲜与加工》1997,(5):104-109
The paper discuss the concept of fiberoptic smart civil structure,and analysis the principle of non destructive evaluation of civil structure with the help of embeded fiberoptic sensor in sensing the inner state and integrity of the structure.The typical experiment and development of fiberoptic sensing system in the health monitoring of dam,highway,bridge and buildings are overriewed. 相似文献
52.
With interconnecting and developing of power system, the problem of power flow computation on dispersed data resource need to be solved. A new distributed computation method of power flow based on Ward equivalent is presented. According to master-slaver splitting principle, multi-area interconnected power system is divided into master-slaver areas. Boundary buses in different areas are defined as different bus-types. Neighborhood areas are equivalent by Ward equivalent principle, and the equivalent injection power and equivalent impedance are worked out. Power flows from master area to slaver areas are solved by Newton method, and the equivalent injection power and equivalent impedance on the boundary are modified by their solutions. The process above repeats until to convergence. The proposed distributed power flow method takes full advantage of the information of power, voltage, network configuration in neighborhood areas, so it is better on convergence and quality of solution. The proposed algorithm is testified by IEEE 14-bus system and a practical 181-bus system. 相似文献
53.
Chen HuaZhou Jiaqi 《保鲜与加工》1990,(4):1-6
Based on the maximum flow principle about networks, a network flow approach to reliability evaluation in large scale netwerks ty mixing inereasing flow with decreasing flow is proposed in this paper.This approach gets the initial flow of each branch in a r.etwork associated with a state of the retwork by decreasing flows of some branches correlative to another state of the network.As a result, the number of flow compute required can be reduced enormously.The numerical example shows that the approach is powerful. The comparison of this approach with the minimal cutset one is also given in this paper. 相似文献
54.
The authors analyze the influence in vector controlled induction machine caused by parameter variation and main flux saturation affects speed estimation of adaptive state observer. According to simulation of the modified scheme with saturated induction motor model, it is proved that when the vector control scheme operates in field weakening region, the main flux saturation will obviously influence precision of speed observer and bring great error of speed estimation. Thereby, the main flux saturation should be compensated to improve performance of the vector control system. 相似文献
55.
Wang Yuanliang Li Shiqi 《保鲜与加工》1992,(2):116-121
Several aspects of the conditional equation derived from the accumulative equation are discussed in detail. The results indicate that the conditional equation not only is well consistent with the principles of electronegativity and absolute hardness equalization, but also satisfies the bonding of a full -prerequisite condition, e. g. two like electronic charge species repel and unlike attract each other'. In addition these principles are in the accumulative state. Mathematically, some other aspects of the conditional equation are worth studying based on the generalization of this equation. 相似文献
56.
57.
In accordance with the special characteristics of state medium-sized construction enterprises and their reform objects of "having a free hand and enlivening", the suitable objective model, the stock cooperative system for state medium-sized construction enterprises has been put forward in this paper by analyzing the system mechanism of stock cooperative system enterprises. Then the causes for it were expounded. 相似文献
58.
Using gained experimental data to develop the models of stable flow stresses at high temperature plastic deformation by statistical methods for alloy materials, precision of the models is poor and at the same time the processes of modeling are complicated with great workload. On the basis of the data obtained on Gleeble-1500 Thermal Simulator,the predicting models for the relation between stable flow stress during high temperature plastic deformation and deformation strain, strain rate and temperature for 1420 Al-Li alloy have been developed with BP Artificial Neural Network method. The results show that the model on basis of BPNN is practical and it reflects the real feature of the deforming process. It states that the difference between the real value and the output of the model is in order of 5 percent. 相似文献
59.
60.
Xu Jiang Xian Xuefu Du Yungui Zhang Guangyang 《保鲜与加工》1993,(5):42-47