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991.
Young-Ho Kim Won-Byong Bae Dong-Ju Lim Yun-Soo Suh 《Metals and Materials International》1998,4(4):852-858
A piston is an important component of the shock absorber which determines comfortable riding and handling. Conventional piston
is made of metal powder that is pressed in a mold, and then sintered at high temperatures below the melting point before machining
processes such as drilling, sizing and teflon banding. This study aims at cutting down cost and weight, and improving the
process by replacing the traditional sintering process used for manufacturing the shock absorber with the injection molding
process adopting engineering plastics as raw material. To analyze the injection molding process, we used the commercial program,
MOLDFLOW, and obtained an optimal combination of the process parameters. In addition, by comparing the engineering plastic
piston with the metal powder piston through the formability and the performance experiments, we confirmed the availability
of this alternative process suggested. 相似文献
992.
The effect of aging in air at 650°C for 100~1000 h on the tensile properties of superaustenitic stainless steel in the range
RT-750°C and the fatigue crack growth behaviour at RT and 650°C was studied. Yield strength and ultimate tensile strength
were almost the same between the as-received and the aged specimen. The fracture strain, however, decreased significantly
from aging, and the fracture surface of the aged specimen at RT test was intergranular. The fatigue crack growth rate at RT
is enhanced by aging at the high stress intensity factor range. This is due to the occurrence of an intergranular fracture
in the aged specimen. At 650°C the fatigue crack growth behaviour of both the as-received and the aged specimen was almost
same with no intergranular fracture. 相似文献
993.
A disturbance attenuation method in a control system, called the model-based disturbance attenuator (MBDA), is proposed, and its properties are studied. The MBDA makes the plant performs similarly to the nominal plant, as much as possible, using a compensator. Then, a controller is designed based on the nominal plant. It is shown that the MBDA is extremely robust with respect to large variations of load inertia. The MBDA is implemented in a position control system of a computer numerical control (CNC) machining center, where the velocity control system is composed of a servo-pack (PI controller), a servo motor, and a load. The MBDA attenuates external disturbances significantly in the cutting process containing high-frequency components, as well as the frictional forces containing large DC component. Several other controllers are also implemented in a position control system of a CNC machining center in a similar way as the MBDA, and the experimental results are compared with one another 相似文献
994.
A standard assumption in traditional (deterministic and stochastic) optimal (minimizing) linear quadratic regulator (LQR) theory is that the control weighting matrix in the cost functional is strictly positive definite. In the deterministic case, this assumption is in fact necessary for the problem to be well-posed because positive definiteness is required to make it a convex optimization problem. However, it has recently been shown that in the stochastic case, when the diffusion term is dependent on the control, the control weighting matrix may have negative eigenvalues but the problem remains well-posed. In this paper, the completely observed stochastic LQR problem with integral quadratic constraints is studied. Sufficient conditions for the well-posedness of this problem are given. Indeed, we show that in certain cases, these conditions may be satisfied, even when the control weighting matrices in the cost and all of the constraint functionals have negative eigenvalues. It is revealed that the seemingly nonconvex problem (with indefinite control weights) can actually be a convex one by virtue of the uncertainty in the system. Finally, when these conditions are satisfied, the optimal control is explicitly derived using results from duality theory 相似文献
995.
This paper presents some studies on partially observed linear quadratic Gaussian (LQG) models where the stochastic disturbances depend on both the states and the controls, and the measurements are bilinear in the noise and the states/controls. While the Separation Theorem of standard LQG design does not apply, suboptimal linear state estimate feedback controllers are derived based on certain linearizations. The controllers are useful for nonlinear stochastic systems where the linearized models include terms bilinear in the noise and states/controls and are significantly more accurate than if the bilinear terms are set to zero. The controllers are calculated by solving a generalized discrete time Riccati equation, which in turn has properties relating to well posedness of the associated LQG problem. 相似文献
996.
Moh Lim Sim Gunawan E. Boon-Hee Soong Cheong-Boon Soh 《Vehicular Technology, IEEE Transactions on》1999,48(3):911-921
Performance of a reverse link code-division multiple-access (CDMA) system with fast close-loop power control algorithms is studied. It is found that if the fast close-loop power control algorithm functions effectively, the speed of the mobile unit is in the range such that its Doppler frequency is less than one tenth of the power control updating rate. This paper also proposes a new predictive power control algorithm with better performance in terms of system capacity than the conventional and adaptive step size algorithms. An increase in system capacity as high as 22% compared with the conventional algorithm can be achieved depending on the mobile velocity 相似文献
997.
A power-factor controller for single-phase PWM rectifiers 总被引:1,自引:0,他引:1
Jee-Woo Lim Bong-Hwan Kwon 《Industrial Electronics, IEEE Transactions on》1999,46(5):1035-1037
A novel power-factor controller for single-phase pulsewidth modulated rectifiers is proposed. The unity power-factor controller for a sinusoidal input current is derived using the feedback linearization concept. Two active switches and two diodes are utilized for AC-to-DC power conversion. Experimental results obtained on a 4 kW prototype are discussed 相似文献
998.
Joonho Lim Dong-Gyu Kim Soo-Ik Chae 《Solid-State Circuits, IEEE Journal of》1999,34(6):898-903
In this paper, we describe an energy-efficient carry-lookahead adder using reversible energy recovery logic (RERL), which is a new dual-rail reversible adiabatic logic. We also describe an eight-phase, clocked power generator that requires an off-chip inductor. For the energy-efficient design of reversible logic, we explain how to control the overhead of reversibility with a self-energy-recovery circuit. A test chip was implemented with a 0.8 μm CMOS technology, which included two 16-bit carry-lookahead adders to allow fair comparison: an RERL one and a static CMOS one. Experimental results showed that the RERL adder had substantial advantages in energy consumption over the static CMOS one at low operating frequencies. We also confirmed that we could minimize the energy consumption in the RERL circuit by reducing the operating frequency until adiabatic and leakage losses were equal 相似文献
999.
Sangcheol Kim Won Ho Jo Junkyung Kim Soon Ho Lim Chul Rim Choe 《Journal of Materials Science》1999,34(1):161-168
In an effort to investigate the effect of the crystalline morphology of a poly(butylene terephthalate) (PBT) phase on the toughening of PBT/epoxy blends, the blends, having different degrees of perfectness of the PBT crystalline phase, were prepared by blending PBT and epoxy at various temperatures ranging from 200 to 240 °C. As the blending temperature decreases, the degree of perfectness of the PBT crystalline phase increases as a result of the increase of crystal growth rate. For PBT/epoxy blends, the change in crystalline morphology induced by processing may be the most important cause for the dependency of the fracture energy on blending temperatures. It has been found that PBT phases with a well-developed Maltese cross are most effective for epoxy toughening. This dependency reveals the occurrence of a phase transformation toughening mechanism. Also, the higher relative enhancement of fracture energy of a higher molecular weight epoxy system is further indirect evidence for a phase transformation toughening mechanism. Some other toughening mechanisms observed from the fracture surfaces, such as crack bifurcation, crack bridging, and ductile fracture of PBT phases, have been found to also be affected by the blending temperatures. 相似文献
1000.
Development of Expert System for Concurrent Product Design and Planning for Assembly 总被引:5,自引:3,他引:2
X. F. Zha S. Y. E. Lim S. C. Fok 《The International Journal of Advanced Manufacturing Technology》1999,15(3):153-162
This paper addresses the development of an expert system for concurrent product design and assembly planning (CDAPFAES) including
conceptual design, detailed design, assemblability analysis and design for assembly, assembly system design, assembly process
planning and stimulation, and technical–economics justification. This approach is implemented through an agent-based framework
with concurrent integration of multiple cooperative knowledge sources and software. This intelligent system can offer systematic
assistance for assembly design and planning in the early stage of product development and facilitate, as far as possible,
the use of flexible assembly equipment, including robots. Finally, this new design methodology is illustrated with a successful
implementation of a switch product design. 相似文献