全文获取类型
收费全文 | 11167篇 |
免费 | 399篇 |
国内免费 | 1496篇 |
专业分类
林业 | 901篇 |
农学 | 900篇 |
基础科学 | 3361篇 |
2406篇 | |
综合类 | 3906篇 |
农作物 | 301篇 |
水产渔业 | 286篇 |
畜牧兽医 | 498篇 |
园艺 | 192篇 |
植物保护 | 311篇 |
出版年
2024年 | 112篇 |
2023年 | 232篇 |
2022年 | 406篇 |
2021年 | 370篇 |
2020年 | 391篇 |
2019年 | 473篇 |
2018年 | 342篇 |
2017年 | 535篇 |
2016年 | 622篇 |
2015年 | 494篇 |
2014年 | 602篇 |
2013年 | 676篇 |
2012年 | 936篇 |
2011年 | 884篇 |
2010年 | 680篇 |
2009年 | 698篇 |
2008年 | 606篇 |
2007年 | 789篇 |
2006年 | 575篇 |
2005年 | 515篇 |
2004年 | 365篇 |
2003年 | 323篇 |
2002年 | 208篇 |
2001年 | 166篇 |
2000年 | 160篇 |
1999年 | 135篇 |
1998年 | 135篇 |
1997年 | 103篇 |
1996年 | 92篇 |
1995年 | 92篇 |
1994年 | 64篇 |
1993年 | 68篇 |
1992年 | 52篇 |
1991年 | 34篇 |
1990年 | 43篇 |
1989年 | 29篇 |
1988年 | 28篇 |
1987年 | 16篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1979年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Wang XiaoruMi Linshu 《保鲜与加工》1990,(3)
Based on the experiment, magnetizing characteristic and its mathematical model of iron for the reactance transformer DKB has been studied in this paper. Its simulating calculation model has been achieved and implemented by program. The result of the simulation is satisfactory compared with that of the experiment. 相似文献
92.
Compared with the traditional full-bridge(FB)zero-voltage-switched(ZVS) pulsewidth-modulated(PWM) converter, the FB-ZVS-PWM converter with a saturable inductor has a wider load range with ZVS and smaller circulating energy as well as smaller duty cycle loss. By analyzing the operation principle of the converter, this paper studies design considerations of the parameter bringing about ZVS and dead time of the switch, and gives out the design method, finally simulation testing has been carried out. 相似文献
93.
This paper analyzes the structure and line current waveform of 3-phase AC voltage regulation circuit. As an application of 3-phase AC voltage regulation circuit, a high-frequency welding device's simulation model and harmonic analysis of line current are presented. Results of simulation are compared to field measurements. The two are in a good agreement, so this simulation model is correct. Two single-tuning filters and one second-order HPF are designed according to the device's harmonic condition. Simulation results of the circuit with filters indicate decrease of the harmonics in current of power supply, and the waveform is close to sinusoidal wave, which prove correctness of the solution to harmonics pollution. 相似文献
94.
REN Guang-sheng 《保鲜与加工》2001,(3):22-25
Characteristics of a tire are the foundation of vehicle dynamics studying, especially play a vital role in vehicle handling study. It is necessary to establish a tire model in the simulation for vehicle handling because the tire characteristics got by test can not be satisfied.The optimization of fitting to the tire test data curves by Magic Formula is discussed, included the digitalization of tire test data curves, designing objective functions and optimization processes,etc. Finally the parameters in Magic Formula tire model are obtained and they lay a foundation for the development of vehicle handling aftertime. 相似文献
95.
Tu Yaqing Huang Shanglian Li Zushu 《保鲜与加工》1993,(6):8-15
Based on the model of Human Simulation Intelligent Controller (HSIC)
presented briefly, a detailed algorithm was described for the servo system control by using the method of HSIC. Simulation results obtained proves the good performance of the control algorithm. 相似文献
96.
The aerodynamic characteristic of wind turbine is calculated by applying the Blade Element Momentum(BEM) theory.Also finite element mode analysis is done for the tower and the rotor.Then the multi-dynamic model of the wind turbine is built in Adams.Also the drive chain is calculated by applying state space method and programmed in Matlab/ Simulink.With that the combined simulation of vibration characteristics is carried out on the base of MATLAB/Simulink and ADAMS,in which the transmission effects and aero-elasticity coupling is fully considered.The results show that the method is able to simulate the vibration characteristic almost the same as software Bladed,which is well-known for analyzing performance and loads for the design and certification of wind turbines. 相似文献
97.
Bomsster is a key load-bearing part of railway lorry bogie.Because of its inherent defects casting-steel bomsster could not meet the demands of the heavy load,acceleration and security for lorry.So forging process is proposed to form it.The forming performance of forging-steel bomsster is analyzed.A forging technology is presented which realizes two forging-steel bomsster parts formed in one die.With the plastic forming simulation software DEFORM-3D,the simulation and optimization of the forming process of forging bomsster has been taken based on 3D rigid visco-plastic FEM theory.Optimized scheme has been used to direct the pilot product.The results of product's testing and application suggest that the new forging technology is feasible and the performance of the product is credibility and stabilization.The factory has realized large scale production of a series of forging-steel bomsster.Remarkable benefits of both economy and society have been achieved. 相似文献
98.
ANSYS/LS-DYNA is used to simulate the penetration process of B900FD - 1 bulletproof armor plate, Comparisons and analysis were made between numerical simulation and experiment results. The numerical simulations shows that the Johnson-Cook constitutive model could simulate the physical and mechanical behaviors of ductile materials under shock-loaded. The ultimate-thickness of B9OOFD-1 bulletproof armor plate under 500m/s impact velocity is analyzed by more numerical simulations. 相似文献
99.
With the development of circulating fluidized bed boiler(CFB),the study field of external heat exchanger(EHE) is greater in extent and degree.In order to research the working process of EHE,the model which deals with flow and heat transfer of EHE for 300MW CFB of Dong Fang Boiler Grou PCo.Ltd.is presented.Based on the cell modeling theory,the EHE is divided into several chamber by heating surfaces.The mass and energy conservation equations of each cell have been developed according to some reasonable assumption.The complete mathematical model has been compiled by Fortran and solved by classical Algorithm of Runge-Kutta.The static test and perturbation experiment of simulating model has been performed.The simulation results show that the model has been reached the steady state rapidly,the dynamic responses are reasonable and the modeling presented in the paper is reliable and appropriate. 相似文献
100.
Wu Chenbo Liang Xiaoping 《保鲜与加工》1997,(2):117-122
The flowfield and temperature field are numerically Simulated by the mathematical model of the fluid flow and heat transfer in circular combustion chamber widened suddenly. The distributions and influence factors of the flow field and temperature field are studied in it. The results have the guiding significance for the design of combustion chamber. The mathematical models can serve as the quantitative analysis methods for design. 相似文献