全文获取类型
收费全文 | 3261篇 |
免费 | 166篇 |
国内免费 | 285篇 |
专业分类
林业 | 373篇 |
农学 | 230篇 |
基础科学 | 510篇 |
639篇 | |
综合类 | 1326篇 |
农作物 | 60篇 |
水产渔业 | 207篇 |
畜牧兽医 | 170篇 |
园艺 | 46篇 |
植物保护 | 151篇 |
出版年
2024年 | 14篇 |
2023年 | 54篇 |
2022年 | 74篇 |
2021年 | 101篇 |
2020年 | 104篇 |
2019年 | 122篇 |
2018年 | 88篇 |
2017年 | 129篇 |
2016年 | 179篇 |
2015年 | 161篇 |
2014年 | 212篇 |
2013年 | 222篇 |
2012年 | 260篇 |
2011年 | 287篇 |
2010年 | 194篇 |
2009年 | 240篇 |
2008年 | 179篇 |
2007年 | 226篇 |
2006年 | 172篇 |
2005年 | 124篇 |
2004年 | 111篇 |
2003年 | 78篇 |
2002年 | 56篇 |
2001年 | 50篇 |
2000年 | 50篇 |
1999年 | 25篇 |
1998年 | 29篇 |
1997年 | 18篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 24篇 |
1993年 | 21篇 |
1992年 | 9篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1984年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有3712条查询结果,搜索用时 15 毫秒
41.
By analyzing the pressure distribution between gears and sealing blocks in compound gear pump with three idlers,the resultant hydraulic forces acting on seal blocks are obtained.The conclusion is the unbalanced resultant hydraulic forces are relatively small in magnitude.In the pump,the inner sealing edges are long and so it s Sealing effect is good,but the outer sealing effect is relatively poor because of its short sealing edges.The little unbalanced force pushes the sealing block to te pumping chamber,therefore it is advantageous to meliorating the pump's sealing effect,thereby to improving it's volumetric efficiency as well. 相似文献
42.
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
43.
The analysis of vibration response of structure with TMD is carried out under earthquake ,considering the ground-structure interaction. The varying rule of square difference of displacement of structure with the TMD on or off by changing the first inherent frequency is also presented .It has been proved by comparing and analyzing that a TMDstructure with optimum parameters can efficiently reduce the vibration of structure under strong wind and earthquake,when the main frequency of the ground motion is within the range of TMD vibration reducing frequency. 相似文献
44.
A new type of inorganic anchoring material is developed as a substitution for anchoring adhesive to overcome some imperfections in the process of planting reinforcing steel bar.The mix proportion of the anchoring material is determined by experiments.The compressive strength,adhesive force to concrete,volume stability and anchoring force with steel bar are studied.The early strength of the anchoring inorganic material is quite high: for 1d up to 38.5MPa and 3d up to 60MPa.It is a good adhesive to concrete and the adhesive strength of 28d is about 2MPa.The anchoring material will have tiny volume expansion with the age,which is beneficial to enhancing the anchoring force.The essential component of the inorganic anchoring material is cement-based material,so some defects of the organic macromolecular material can be avoided,such as poor stability and requirement for vigorous construction conditions.Its characteristics in early strength,adhesive force to concrete and volume expansion can satisfy the requirement of the construction to the planting reinforcing steel bar and the loading force,thus it can be used as a substituting material for anchoring adhesive. 相似文献
45.
46.
He Zonglu Duan Yurong 《保鲜与加工》1990,(5):98-105
The productive forces distribution model with entropy constraint is established. it satisfies both the demand with minimization of total cosls and the other demands with optimum distribution at a certain level. The model's regular optimal solution is a gravity molel.. 相似文献
47.
Based on the data of dynamic tests of small single-storey steel frames,the suitability of simplified hi-linear restoring force model in earthquake response analysis is discussed, and the Maximum displacement response MD, the sum of squares of the displacements in the whole vibrating history SSD, and the total dissipated energy EI are considered respectively as equivalent object. 相似文献
48.
49.
Liu Jianglong Liu Chao 《保鲜与加工》1993,(5):109-114
Melt flow in the course of laser alloying is considered on the basis of mechanics. The findings show that the melt flow in laser alloying pool is mainly controlled by two action forces,i. e. the surface tension force on alloying pool.surface,caused by the temperature difference on the pool surface and the buoyancy force in alloying pool caused by the temperature difference in the horizontal direction in the melt pool. These two forces differ in their acting areas. The analysis of the Bond dimensionless number used for laser alloying shows that the two force actions are in the same order,and almost equal under the certain condition. 相似文献
50.
Based on the content of enterprise culture and enterprise credit, it is pointed out that the enterprise culture related to the enterprise core competitive force.In this paper, from the viewpoint of combining theory with practice, the intension, function and mutual relations between them are described and their significance in the market competition as well.The potential things,which the enterprise staffs are seeking for, from its inherent mind and the enterprise theory are the enterprise culture which becomes the enterprise core competitive force in its actual sense.The enterprise credit, as the enterprise culture in its ideological sphere, is an essential factor, which greatly affects the enterprise core competitive force.At last the authors provide some good suggestions on how to cultivate enterprise credit and to build enterprise culture. 相似文献