全文获取类型
收费全文 | 10366篇 |
免费 | 557篇 |
国内免费 | 1281篇 |
专业分类
林业 | 1175篇 |
农学 | 1660篇 |
基础科学 | 971篇 |
1929篇 | |
综合类 | 3129篇 |
农作物 | 640篇 |
水产渔业 | 395篇 |
畜牧兽医 | 1368篇 |
园艺 | 315篇 |
植物保护 | 622篇 |
出版年
2024年 | 29篇 |
2023年 | 122篇 |
2022年 | 262篇 |
2021年 | 362篇 |
2020年 | 373篇 |
2019年 | 359篇 |
2018年 | 247篇 |
2017年 | 333篇 |
2016年 | 360篇 |
2015年 | 439篇 |
2014年 | 439篇 |
2013年 | 553篇 |
2012年 | 576篇 |
2011年 | 678篇 |
2010年 | 634篇 |
2009年 | 614篇 |
2008年 | 553篇 |
2007年 | 579篇 |
2006年 | 564篇 |
2005年 | 439篇 |
2004年 | 237篇 |
2003年 | 320篇 |
2002年 | 395篇 |
2001年 | 350篇 |
2000年 | 294篇 |
1999年 | 276篇 |
1998年 | 262篇 |
1997年 | 207篇 |
1996年 | 216篇 |
1995年 | 217篇 |
1994年 | 159篇 |
1993年 | 165篇 |
1992年 | 134篇 |
1991年 | 105篇 |
1990年 | 89篇 |
1989年 | 86篇 |
1988年 | 59篇 |
1987年 | 40篇 |
1986年 | 22篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1963年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
大豆属Clycine亚属植物花粉形态研究 总被引:2,自引:0,他引:2
对大豆属Glycine亚属中0个种的花粉进行了光学显微镜和扫描电镜的观察。发现多倍体材料的花粉大于二倍体的。并发现Glycine亚属诸种花粉的形、萌发孔、外壁纹饰均存明显差异。 相似文献
123.
The existence of ettringite in sulphoaluminate cement hardened paste is mainly in the form of pole-like crystal,which causes unfavorable effect on the cement.In this paper the strength and microstructure of the sulphoaluminate cement containing ultra-fine CaCO_3 weze discussed.Experimet results show that the strength of sulphoaluminate cement was obviously improved by adding 3% of ultra-fine CaCO_3.After curing for 28d,the compressive strength of cement paste and mortar is 100.6MPa and 94.1MPa respectively,and the bending strength of the mortar reached 12.5MPa.SEM study on hardened paste of sulphoaluminate cement containing ultra-fine CaCO_3 showed that its structure was dense and homogeneous,there was hardly any massive crystall detected. 相似文献
124.
In TT&C system,unified spread spectrum framework and adaptive antenna digital beamforming technologies are used to track, telemetry and command objects. Constant modulus array (CMA) and adaptive signal canceller estimate the direction of arrival (DOA) of every signal and use the optimum weighted vector to form the beams. The phase weighted vectors estimated from DOA improve the processing gain as well as being utilized in the transmitting of tele command signal to form the beam of specified object. Its processing performance is researched and simulated in this paper. 相似文献
125.
In this paper, the application of reinforced earth technique, principle and calculation method, new reinforced materials developed and produced are introduced. A few of key technical problems in reinforced earth application is discussed, such as reinforced earth behavior, calculation method, durability of reinforced material, amendment and complement of the current standards. Then, the reinforced earth technique development and advancement were introduced. 相似文献
126.
The traditional scheduling for vehicle is option in the fixed network. But it can't satisfy the real time environment. The demand of order is changeable and uncertain in real environment. It is convenient for scheduling transforming it into static data, but can't get the advantage on time. This paper proposes a real time vehicle scheduling on the study of traditional scheduling and discusses the model structure and the key technology for the real time system that establishes the base for develop teal time system. 相似文献
127.
Aimed at soving the problem existing in the knowledge-acquisition directing-operation expert systems, a new method is proposed to acquire knowledge of expert-operation, excluding errors existed in examples and reinforce the accuracy of examples,the goal of knowledge acquisition can be achieved, the method presented in this paper solves the problem of self-enhancement of expert knowledge on line efficiently. 相似文献
128.
Along with the establishment of the constructor association,how to locate the constructor association is extremely important at present,which is not only related to the efficiency of the constructor trade management,but also related to the future development of the constructor trade.This paper launches the discussion on the constructor association's localization from three aspects,namely the legal localization,the profession localization and the relation localization with the government and its members,and puts forward some proposals and individual opinions. 相似文献
129.
Geogrid reinforced soil retaining wall(GRSRW) is composed of panel,geogrid and soil,its coupled hydromechanical structural characteristics are increasingly emphasized in practice.In this paper,based on the characteristics of the reinforcement-soil interaction,the grogrid and soil around it with a definite thickness were regarded as a kind of composite material with strain-compatible condition.A saturated porous media model was introduced to simulate the soil and reinforcement-soil composite material hereby and the mathematic model for numerical analysis on structural characteristics of GRSRW was built up.The FEM equations were deduced from the standard Galerkin procedure,resolving these equations,we can gain the relevant dynamic response of saturated GRSRW. 相似文献
130.
山羊卵泡卵母细胞的采集及体外成熟效果研究 总被引:2,自引:0,他引:2
为了获取高质量的卵泡卵母细胞,提高山羊体外胚胎生产的效率,采用切剖法与抽吸法采集卵泡卵母细胞,并对获得的可用卵母细胞进行了体外成熟培养。结果表明,切剖法能够获得较多的可用卵母细胞,可以明显增加用于体外成熟的卵母细胞数;卵母细胞的体外成熟率与卵泡直径密切相关,大卵泡与中卵泡的卵母细胞成熟率明显高于(P<0.05)小卵泡;山羊卵泡卵母细胞的体外成熟培养液中FCS的添加比例以10% ~ 15%为益。在一定范围内,提高FCS的浓度,并不能提高卵母细胞的成熟率。 相似文献