全文获取类型
收费全文 | 6470篇 |
免费 | 434篇 |
国内免费 | 775篇 |
专业分类
林业 | 552篇 |
农学 | 705篇 |
基础科学 | 505篇 |
748篇 | |
综合类 | 2718篇 |
农作物 | 535篇 |
水产渔业 | 289篇 |
畜牧兽医 | 895篇 |
园艺 | 429篇 |
植物保护 | 303篇 |
出版年
2024年 | 38篇 |
2023年 | 121篇 |
2022年 | 281篇 |
2021年 | 335篇 |
2020年 | 291篇 |
2019年 | 313篇 |
2018年 | 191篇 |
2017年 | 321篇 |
2016年 | 246篇 |
2015年 | 346篇 |
2014年 | 344篇 |
2013年 | 365篇 |
2012年 | 519篇 |
2011年 | 468篇 |
2010年 | 446篇 |
2009年 | 409篇 |
2008年 | 366篇 |
2007年 | 336篇 |
2006年 | 292篇 |
2005年 | 232篇 |
2004年 | 139篇 |
2003年 | 173篇 |
2002年 | 232篇 |
2001年 | 213篇 |
2000年 | 167篇 |
1999年 | 113篇 |
1998年 | 44篇 |
1997年 | 38篇 |
1996年 | 41篇 |
1995年 | 43篇 |
1994年 | 36篇 |
1993年 | 43篇 |
1992年 | 35篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 10篇 |
1988年 | 21篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1962年 | 2篇 |
1956年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有7679条查询结果,搜索用时 0 毫秒
71.
The high-precision displacement measuring technology of optic-measuring mechanics is, for the first time,successfully applied on the similar model of the model land-layer with a new-type variable modulus of elasticity. The angle of movement and the distributed displacement of upper and lower rock-layers are measured. The technology is a combination of laser's technology and the modern chemical sticker-it is called the sticking moire interferometry. Compared with the measured values, the result is very satisfactory. 相似文献
72.
Qian Zhenming Zhen Xu 《保鲜与加工》1993,(2):142-144
The .experimental system of differential Isodyne developed by authors is represented. The function and structure characteristic of the rotatable real-time loading device which is set in oil tank , the hydraulic scanning device and the device for synchronous movement of incident beam and Isodyne collector are mainly discussed. The fringe pattern of differential Isodyne in various characteristic directions and planes can be real-timely taken, by using this system. This system is able to apply to stress analyses of local effect .composite materials and structures. 相似文献
73.
Ran Li Ren Zhen Huang Wenying 《保鲜与加工》1993,(6):21-26
A new Monte Carlo Method for system reliability evaluation is proposed in this paper. The repeated sampling of system states with relatively great probabilities is avoided in the simulation,thus the sampling efficiency is significantly improved. Besides,the negative correlations used in different trials can further reduce the estimated varinaces. The sparse matrix technique is employed to reduce the memory requirement and to save the computer time. Comparative studies show that the method proposed is of great value and the application to the IEEE reliability test system (power system) is successful. 相似文献
74.
Zhang Wei Ren Zhen Qin Yihong Liao Qing 《保鲜与加工》1990,(1):56-62
A flexible mathematical model used for dynamic simulation studies of HVDC systems which is based on the stale variable method is presented, and the correspongding computer program has been implemented. Generality, easy to use, and suitable to run on microcomputers are the main features of the model and the computer program. Therefore the model is easy to be extended for application. An example is given in the paper to verily the coneclness of the model and the program. 相似文献
75.
Valuation based on the bill of quantifies will change the existing valuation mode of tender and bidding. For the standardized management of tender and bidding for power projects and the inteUigentized information management of power enterprises, it is an inevitable trend of reform to apply the valuation mode based on the bill of quantifies. According to the characteristics of power projects, this paper expounds the working process of the valuation mode based on the bill of quantities and analyzes the goal and function need of the tender and bidding management system. Considering the calculation procedure of the valuation and the quote strategy of quantities bill, the composition of fees for the valuation is settled and the calculation method is designed. To establish the management system of tender and bidding with a valuation based on the bill of quantities is beneficial for the costing reform of power projects and the perfection of the tender and bidding market. Therefore it is of great significance to spread the new management mode of project costing with a valuation based on the bill of quantities. 相似文献
76.
77.
78.
水分亏缺对覆膜玉米生长发育及产量的影响 总被引:1,自引:0,他引:1
通过系统的覆膜玉米亏水灌溉试验 ,研究了不同生育期内不同程度的水分亏缺对覆膜玉米生长发育、光合作用、产量及水分利用效率等的影响。结果表明 ,拔节期受旱对玉米株高及叶面积指数影响最大 ,抽雄后的水分亏缺对玉米生长发育影响不明显。各处理产量资料表明 ,覆膜春玉米的需水临界期为抽雄开花期 ,此期轻度的水分亏缺可造成产量大幅度下降 :灌浆期较抽雄开花期玉米产量对水分亏缺敏感程度低 ,但在这个阶段的水分亏缺也可使玉米减产 ;拔节期玉米产量对水分胁迫敏感程度较差 ,该阶段为对玉米进行水分亏缺处理的适宜时期 相似文献
79.
在稳流模拟试验台上,利用研制的柴油机试验缸盖、气门口三维流速测量装置,用热线风速仪测量了不同进气道布置方案下的进气门口三维流场,分析了进气门口三维流场产生的缸内空气动量矩流率,揭示了进气道的布置对柴油机进气门口空气运动影响的变化规律。进气道布置角度的变化对柴油机气门口流场及动量矩流率产生很大影响。各速度的大小和切向速度分布曲线发生较大变化,并随升程的增大而更加明显;对螺旋气道的动量矩流率影响较大,随升程的增加影响增大;对切向气道的动量矩流率影响更为明显,随着升程的增加影响减小。 相似文献
80.