全文获取类型
收费全文 | 305054篇 |
免费 | 18719篇 |
国内免费 | 9342篇 |
专业分类
电工技术 | 13146篇 |
技术理论 | 24篇 |
综合类 | 16010篇 |
化学工业 | 49334篇 |
金属工艺 | 17513篇 |
机械仪表 | 17304篇 |
建筑科学 | 19429篇 |
矿业工程 | 7910篇 |
能源动力 | 7441篇 |
轻工业 | 16799篇 |
水利工程 | 4772篇 |
石油天然气 | 16686篇 |
武器工业 | 1650篇 |
无线电 | 33545篇 |
一般工业技术 | 42224篇 |
冶金工业 | 15036篇 |
原子能技术 | 2483篇 |
自动化技术 | 51809篇 |
出版年
2024年 | 797篇 |
2023年 | 3599篇 |
2022年 | 6308篇 |
2021年 | 8922篇 |
2020年 | 6885篇 |
2019年 | 5856篇 |
2018年 | 19907篇 |
2017年 | 19773篇 |
2016年 | 15849篇 |
2015年 | 9336篇 |
2014年 | 11414篇 |
2013年 | 13385篇 |
2012年 | 17179篇 |
2011年 | 24309篇 |
2010年 | 21252篇 |
2009年 | 17860篇 |
2008年 | 18763篇 |
2007年 | 19279篇 |
2006年 | 12459篇 |
2005年 | 11903篇 |
2004年 | 8321篇 |
2003年 | 7338篇 |
2002年 | 5981篇 |
2001年 | 4977篇 |
2000年 | 5599篇 |
1999年 | 6462篇 |
1998年 | 5469篇 |
1997年 | 4448篇 |
1996年 | 4205篇 |
1995年 | 3491篇 |
1994年 | 2804篇 |
1993年 | 1956篇 |
1992年 | 1536篇 |
1991年 | 1232篇 |
1990年 | 924篇 |
1989年 | 726篇 |
1988年 | 539篇 |
1987年 | 325篇 |
1986年 | 265篇 |
1985年 | 190篇 |
1984年 | 130篇 |
1983年 | 98篇 |
1982年 | 119篇 |
1981年 | 98篇 |
1980年 | 68篇 |
1968年 | 47篇 |
1966年 | 43篇 |
1965年 | 48篇 |
1955年 | 64篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Squeeze-film effects of perforated plates for small amplitude vibration are analyzed through modified Reynolds equation (MRE).
The analytical analysis reckons in most important influential factors: compressibility of the air, border effects, and the
resistance caused by vertical air flow passing through perforated holes. It is found that consideration of air compressibility
is necessary for high operating frequency and small ratio of the plate width to the attenuation length. The analytical results
presented in this paper agree with ANSYS simulation results better than that under the air incompressibility assumption. The
analytical analysis can be used to estimate the squeeze-film effects causing damping and stiffness added to the system. Since
the value of Reynolds number involved in this paper is low (< 1), inertial effects are neglected. 相似文献
902.
Hua-Chieh Li 《Applicable Algebra in Engineering, Communication and Computing》2007,18(4):313-348
In this paper, we give a general criterion to determine when a complex space-time block code has a ring structure and then
we provide a complete list of complex space-time block codes which have ring structures up to size 4. 相似文献
903.
In this paper we consider A(θ)-stable finite difference methods for numerical solutions of dissipative partial differential equations of parabolic type.
Combining two rational approximation methods with different orders of accuracy, where the lower order method is applied n
0 times (n
0 fixed) at each time step, we prove the existence of a second order method which is contractive for all time steps. Moreover,
we shed light on the conditions on the lower order method which are sufficient (and sometimes necessary) to obtain the optimal
order of accuracy. For the one-dimensional heat equation we construct a family of numerical methods which are contractive
in the maximum norm for all values of the discretization parameters. We also present numerical examples to illustrate our
results.
Received: May 2002 / Accepted: January 2003 相似文献
904.
Sankaralingam K. Nagarajan R. Haiming Liu Changkyu Kim Jaehyuk Huh Burger D. Keckler S.W. Moore C. 《Micro, IEEE》2003,23(6):46-51
The Tera-op reliable intelligently adaptive processing system (TRIPS) architecture seeks to deliver system-level configurability to applications and runtime systems. It does so by employing the concept of polymorphism, which permits the runtime system to configure the hardware execution resources to match the mode of execution and demands of the compiler and application. 相似文献
905.
906.
Huiping Hu Qiyuan Chen Zhoulan Yin Pingmin Zhang Lusheng Ye 《Metallurgical and Materials Transactions A》2003,34(13):793-797
The thermal decompositions of mechanically activated and nonactivated galenas were studied by thermogravimetry analysis (TGA)
at the heating rate of 10 K min−1 in argon. Results indicate that the initial temperature of thermal decomposition (abbreviated as T
di) in the TGA curves for different galenas decreases gradually with increased grinding time. The specific granulometric surface
area (S
G), the structural disorder, and the content of elemental sulfur of mechanically activated galenas were analyzed by an X-ray
diffraction (XRD) laser particle-size analyzer, XRD analysis, and the gravimetric method, respectively, which shows that the
specific granulometric surface area of mechanically activated galenas remains almost constant after a certain grinding time,
but the lattice distortions (ε) rise, the crystallite sizes (D) decrease, and the elemental sulfur contents of mechanically activated galenas increase with increased grinding time. The
results imply that the decrease of the initial temperature of thermal decomposition in the TGA curves for mechanically activated
galenas is mainly caused by the increase of lattice distortions, and the formation of new dangling bonds resulted from the
production of elemental sulfur of mechanically activated galenas with increased grinding time. Finally, the differences in
the thermal-decomposition reactivity between nonactivated and mechanically activated galenas were also discussed. 相似文献
907.
908.
Mobile robots can be used in many applications, such as exploration, search and rescue, reconnaissance, security, and cleaning.
Mobile robots usually carry batteries as their energy source and their operational time is restricted by the finite energy
available from the batteries. Therefore, energy constraints are critical to the service time of mobile robots. This paper
investigates the minimum-energy control problem for translational trajectory generation, which minimizes the energy drawn
from the batteries. Optimal control theory is used to find the optimal velocity trajectory in analytic form. To demonstrate
energy efficiency obtainable, we performed simulations of minimum-energy velocity control and compared the results with loss-minimization
control and energy-optimal trapezoidal velocity profiles. Simulation results showed that significant energy savings can be
achieved, of up to 9% compared with loss-minimization control and up to 10% compared with energy-optimal trapezoidal velocity
profile. We also performed an actual robot experiment using Pioneer 3-AT platform to show the validity of the proposed minimum-energy
velocity control. The experimental results revealed that the proposed minimum-energy velocity control can save the battery
energy up to 10% compared with loss-minimization control.
Categories (3): Robot control, (5): RobotMotion Planning 相似文献
909.
Michael Fox Richard Hastings Scott Lovald Juan Heinrich 《Journal of Failure Analysis and Prevention》2007,7(3):165-174
A failure analysis case study is presented for a two-piece aerosol containing tetrafluoroethane, commonly referred to as Refrigerant
134a. A gentleman was preparing to recharge the air conditioning system of an automobile when the bottom exploded off the
aerosol container, propelling the body of the aerosol container like a rocket, which hit the man in the eye and blinded him
in that eye. The aerosol was never connected to the air conditioner, therefore backpressure from the air conditioner (AC)
compressor was ruled out as a cause for the explosion. The objective of the study was to determine why the aerosol exploded.
Several recently developed test methods were used, including two types of heat-to-burst tests and a puncture chamber to measure
the pressure-versus-temperature behavior of aerosols. More common test methods were also used, such as water bath pressure
tests, hydro pressure burst tests, pneumatic pressure burst tests, hardness measurements, weight measurements, metallography,
scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and an accident scenario recreation. A semi-empirical
correlation between the hardness and weights of the container bottoms was used to determine the explosion temperature and/or
pressure. This semi-empirical correlation agrees in principle with an analysis of the explosion pressures using finite-element
analysis (FEA). The root cause for the explosion was determined to be a lack of strength of the bottom of the two-piece aerosol
coupled with heating the aerosol to temperatures significantly above room temperature. 相似文献
910.