首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   10513篇
  免费   709篇
  国内免费   902篇
林业   813篇
农学   703篇
基础科学   351篇
  1080篇
综合类   5061篇
农作物   634篇
水产渔业   380篇
畜牧兽医   1694篇
园艺   934篇
植物保护   474篇
  2024年   70篇
  2023年   210篇
  2022年   529篇
  2021年   500篇
  2020年   487篇
  2019年   451篇
  2018年   310篇
  2017年   542篇
  2016年   359篇
  2015年   511篇
  2014年   552篇
  2013年   724篇
  2012年   974篇
  2011年   918篇
  2010年   928篇
  2009年   780篇
  2008年   784篇
  2007年   654篇
  2006年   525篇
  2005年   381篇
  2004年   244篇
  2003年   146篇
  2002年   140篇
  2001年   145篇
  2000年   112篇
  1999年   53篇
  1998年   15篇
  1997年   12篇
  1996年   18篇
  1995年   10篇
  1994年   7篇
  1993年   9篇
  1992年   8篇
  1991年   2篇
  1990年   4篇
  1988年   1篇
  1987年   2篇
  1984年   1篇
  1983年   1篇
  1981年   2篇
  1962年   2篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
Jointing of titanium alloy and stainless steel is very often in the fields like aviation, chemical plants etc. The combination of materials has the advantages of both titanium alloy and stainless steel and will reduce the consumption of titanium resource. The phase transformation diffusion bonding of TA17 titanium alloy to 0CriSNigTi stainless steel are carried out on Gleeble - 1500D. The effcet of maximum thermal cycle temperature, the tensile strength, the fracture surface and microstruture of the joints are investigated. The results show that TiFe and TiFe2 intermetallics and some solid solutions are formed along the interface, when maximum thermal cycle temperature increase, the area proportion of intermetallics in the fracture surface increase, which are detrimental to the mechanical properties of the transition joints.  相似文献   
102.
Based on the result of NiMH battery performance experiments, changing trend of maximal temperature and difference in temperature of HEV NiMH battery in different SOC and different charging current is analyzed. Considering the working situation of HEV NiMH battery and the theory of battery quick charging, a control strategy for NiMH battery quick charging is described which adapts to HEV regenerative braking system based on Mascc law. By Modeling and simulating the process of NiMH battery quick charging with this strategy, constant voltage charge method and constant current charge method, validates this control strategy.  相似文献   
103.
To the question that a meter is correspond with a set of lead and a sensor,this paper presents a design of data acquisition system for vehicle based on CAN bus.In this way,the combinatorial instrument is only connected by a bus unit.Author introduces the data acquisition structure chart and the CAN interface,analyzes the software by program flow chart,and shows it's application for vehicle virtual instrument.A method of calculating vehicle speed,engine rotate speed and the course of development mileage are also given.  相似文献   
104.
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   
105.
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   
106.
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   
107.
108.
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   
109.
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   
110.
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号