全文获取类型
收费全文 | 19022篇 |
免费 | 1021篇 |
国内免费 | 1507篇 |
专业分类
林业 | 1650篇 |
农学 | 1455篇 |
基础科学 | 787篇 |
1742篇 | |
综合类 | 8785篇 |
农作物 | 1101篇 |
水产渔业 | 709篇 |
畜牧兽医 | 3065篇 |
园艺 | 1450篇 |
植物保护 | 806篇 |
出版年
2024年 | 85篇 |
2023年 | 247篇 |
2022年 | 712篇 |
2021年 | 732篇 |
2020年 | 688篇 |
2019年 | 688篇 |
2018年 | 443篇 |
2017年 | 756篇 |
2016年 | 561篇 |
2015年 | 838篇 |
2014年 | 894篇 |
2013年 | 1260篇 |
2012年 | 1644篇 |
2011年 | 1675篇 |
2010年 | 1678篇 |
2009年 | 1449篇 |
2008年 | 1401篇 |
2007年 | 1274篇 |
2006年 | 1007篇 |
2005年 | 799篇 |
2004年 | 510篇 |
2003年 | 328篇 |
2002年 | 378篇 |
2001年 | 371篇 |
2000年 | 304篇 |
1999年 | 188篇 |
1998年 | 108篇 |
1997年 | 83篇 |
1996年 | 71篇 |
1995年 | 74篇 |
1994年 | 53篇 |
1993年 | 59篇 |
1992年 | 54篇 |
1991年 | 33篇 |
1990年 | 28篇 |
1989年 | 23篇 |
1988年 | 17篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1963年 | 1篇 |
1962年 | 2篇 |
1956年 | 4篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Reference efficiency of a pair of gear drive without planetary motion is the base to calculate efficiency of the whole planetary gear train. The authors find reference efficiency for speed increase is higher than that of the same drive used for speed reduction. This is different from the earlier viewpoint. New equations are derived for correctly calculating the reference efficiency of spur gear and helical gear with internal conjugate and external conjugate either in the state of speed increase or speed reduction respectively. The equations are also used to calculate efficiency of 2K-H planetary gear train. 相似文献
182.
183.
In this paper, the selection of type, function and technological requirements of EMCS for Shenzhen Underground has been introduced.Based on the investigation for EMCS's worldwide applications and the analysis of practice in Shenzhen Underground, the comparison and selection of PLC and DDC have been done completely.At the same time,the introduction of EMCS is organized by the center level, station level and the spot level. 相似文献
184.
In this paper the inevitable trend of constructing open ecosystem in modern settlement environment was discussed through the history of the settlement environment and the characters of modern settlement environment.The ecological crisis,change of the modern life and the citizens' needs and the ecological system character show,that it is important for sustainable development of the settlement environment to construct open ecosystem.The construction of modern habitation and the city room embodies the concept of open ecosystem.Then,in construction and research of modern settlement,the ecological viewpoint and method should be applied. 相似文献
185.
186.
The process of actin polymerization and depolymerization have some relation with its function,the activation of such process is compatible to its functions. The polymerization progress is divided into four steps: The first step is the activation of the monomer actin. The nucleation of actin nucleus forms in the second step which limits the polymerization speed. The elongation of the F-actin filaments happens in the following step. In the last step, a steady-state is attained, the length of the filament does not change because the polymerizing rate in the barbed end is the same with the depolymerizing rate in the pointed end. Some factors which affect the polymerizing process, such as nucleotide, actin related proteins are discussed. The aim is to know more about how to assemble the complicated system with biomacromolecule and what to function. 相似文献
187.
Knowledge sharing is the important way in which enterprises create organizational knowledge and obtain competition advantage.Scholars always have difference viewpoints about the motivators in knowledge sharing.This paper(analyzes) the incomplete information game and the choice of the motivators in knowledge sharing.If the knowledge(acceptant) offers motivators to the knowledge owner,knowledge sharing might make the participants obtain knowledge-sharing incomes.If knowledge-sharing incomes can make up the participants' costs,knowledge sharing can be caught through.Because the information of knowledge's value is incomplete,enterprises need knowledge managers and organizational additional motivators promote knowledge sharing. 相似文献
188.
The electrocardiogram (ECG) signal is a recording of the electrical activity on the body surface generated by the heart frequency of which is weak and low. Many researchers devote themselves to get more perfect ECG in many ways. This article introduces the characterize of an ECG signal , then discusses the requirements for the sampling circuit of an ECG. Since there are some shortcoming in common design means, the authors give an effective circuit. The system is composed of a low-cost , low-power and high-performance MCU C8051F020 , amplifier AD620 , right-leg drive circuit ,communication circuit and power management circuit. Then software design is given which is used to sampling and filtering ECG signal. Levkov filter arithmetic and smooth filter arithmetics are used in this design. In the end , the authors advance a distributing and networking ECG monitor system. 相似文献
189.
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
190.
Frequency refining is an important spectrum analyzing tool, and is one of the main function of signal processing and the virtual instrument. This paper introduces several typical frequency refining analysis methods including DFT and multiple modulation and so on. It also probes into their advantages and disadvantages, and proposes a new frequency refining method combining subband decomposing DFT and multiple modulation, which inherits the advantages of multiple modulation, needs not to design a specific filter, reduces the amount of calculation, and is fit for real-time refining analysis. At last, it exhibits several frequency refining algorithm and their effects with applications in virtual instruments. 相似文献