全文获取类型
收费全文 | 1294篇 |
免费 | 83篇 |
国内免费 | 344篇 |
专业分类
林业 | 122篇 |
农学 | 198篇 |
基础科学 | 45篇 |
84篇 | |
综合类 | 628篇 |
农作物 | 171篇 |
水产渔业 | 184篇 |
畜牧兽医 | 253篇 |
园艺 | 11篇 |
植物保护 | 25篇 |
出版年
2024年 | 10篇 |
2023年 | 19篇 |
2022年 | 14篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 20篇 |
2018年 | 14篇 |
2017年 | 20篇 |
2016年 | 33篇 |
2015年 | 18篇 |
2014年 | 57篇 |
2013年 | 70篇 |
2012年 | 88篇 |
2011年 | 111篇 |
2010年 | 107篇 |
2009年 | 46篇 |
2008年 | 43篇 |
2007年 | 27篇 |
2006年 | 50篇 |
2005年 | 39篇 |
2004年 | 48篇 |
2003年 | 126篇 |
2002年 | 278篇 |
2001年 | 232篇 |
2000年 | 138篇 |
1999年 | 49篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1989年 | 4篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有1721条查询结果,搜索用时 15 毫秒
101.
The relationship between abrasive concentration, length of oscillating chamber, standoff distance and cutting depth, erosion rate as well as cutting specific energy was investigated by experiments in the submerge and surface conditions. The cutting and erosion capabilities of the pre-mixed abrasive water jet and the pulsed abrasive water jet were analyzed in contrast. It is shown that the maximum cutting depth and erosion rate of the pulsed abrasive water jet are respectively 1.67,1.72 and 1.39, 1.47 than the pre-mixed abrasive water jet in submerge and surface conditions. These results attained from the research are useful to increase the cutting efficiency, decrease the energy ratio and expand the application domains of the abrasive water jet. 相似文献
102.
103.
To be effectively heated in incinerator for MSW is very important for stabilization and completeness combustion, the smaller produce of the PCDD/Fs. At the same time, the transient heat transfer characteristics of the MSW lump decides the stay time of the MSW in incinerator and effects on the operation feature of the combustion equipments. All of these would lead to design the reasonable and clean combustion project, the optimum incinerator and recover energy system. The component, shape, dimension, property, the hardly and inner structure feature of the MSW lump are taken in account, and the effective conduct heat coefficient has been adopted. And then, the physical model is setup with different shape(ball, cylinder, squareness), and the 3-D mathematical model and conduct heat efficient with porous feature for transient heat transfer of MSW lump are presented, at the same time, the simulation tests are gotten in various boundary and the interesting conclusions are gotten: The center stable temperature of the MSW lump is mostly decided by the inner gas temperature of the incinerator and the heated area of the lump. The transient heat transfer characteristics is variously effected by the shape of the MSW lump in incinerator. The transient process becomes longer and the center stable temperature decreases, the volatile can't be easily separated out and the combustion efficiency decreases because of the increasing of the lump feature dimension. 相似文献
104.
浅析了贵州茶叶加工业与国内外比较的现状、存在问题、茶叶产业发展优势和加工生产潜力,提出了贵州茶叶加工业发展的对策建议和主要措施,通过确立发展目标和规划,建立优势区域原料生产基地和地方特色茶产业,以达到加快发展贵州茶叶加工业的目的。 相似文献
105.
The lighting for city night scenes became a hot spot of urban construction.It is quite necessary for building designers to understand the relationship between the facade fabric design and the facade lighting design of a building and know the design method as well.This paper analyses the relationship between the facade fabric design and the lighting design,and proposes the factors that should be considered in the facade fabric design process. 相似文献
106.
YANG Chen yu 《保鲜与加工》2001,(5):56-60109
Based on the field data of berthing velocity for the ship (10000t-50000t), the berthing velocities have been numerically simulated by using Monte Carlo method in this paper. After statistical tests, it shows that the maximum values of the berthing velocity follow a Gumber distribution and the probability curves of failure for the means of maximum values are also obtained. The present results have been compared with the ones determined by specification of harbor engineering both at home and abroad. 相似文献
107.
In this paper from the view point of sociology, the main factors of community formation and the sociological connotations of the community are analyzed. Finally, the objects of realization of sociological elements for a community are presented. 相似文献
108.
109.
Parallel immune clone algorithm is proposed based on population coevolution theory and parallel computing affinity of individual at multiple compute nodes. Introducing the immune memory mechanism, the evolution processes of antibody population and memory units are conducted simultaneously, meanwhile, it improves mutual cooperation among antibodies, and ensures solution set approaching optimal solution from the inside of feasible region or infeasible region border. Clone proliferation, high frequency variation and operation of crossover operators increase the chance that better individuals gain affinity maturation by the operation of clone expansion, improve diversity of antibody population distribution, achieve the balance of optimization between depth and range, and ensure the convergence of the algorithm and the diversity of the search range. A computational study for a standard data set is carried out to test the validity of the algorithm, and the effect of algorithm parameters on the results is analyzed. The simulation results show that the global search capability, local search capability, algorithm stability and computing speed of the algorithm are all superior to conventional optimization algorithms such as normal immune clone optimization algorithm, genetic algorithm, etc. 相似文献
110.
A new algorithm based on gradient optimization is proposed for optical flow estimation of video images with different motion ranges. The original video images are transformed by using Loggabor filtering on phases and measures,and then the spatio-temporal gradient is calculated by using the obtained feature images. The optical flow is calculated with the spatio-temporal gradient. The video images are layered and processed with coarse-to-fine image pyramid method. The theoretical analysis and experimental results show that the algorithm is suitable for the video optical flow motion estimation of the significant range. It can not only obtain the video images following the human visual resolution characteristics, but also optimize the spatio-temporal gradient, while the optical flow calculation is more accurate. Besides, the time complexity of this algorithm is equivalent to that of the traditional optical flow method, and the accuracy of the algorithm is superior to the methods suggested by Horn-Schunck, Duan,et al. 相似文献