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961.
介绍了一种基于LabWindowsCVI测试软件启动口令的实现方法。这种方法简单有效,具有一定的实际应用价值。同时,还对这一方法所存在的问题及解决办法作了阐述。 相似文献
962.
Representing the reception condition directly, signal-to-noise ratio (SNR) is an important parameter in mobile propagation channels, and therefore is widely used in system performance evaluations and adaptive applications. Hence, this paper puts forward a frequency domain SNR estimator in mobile communications, where we exploit the signal model with the band-limited fading channel and the additive white Gaussian noise. With the above model, the noise power spectrum density can be estimated from the periodogram of channel-plus-noise signals, subsequently leading to our SNR estimation. Moreover, in order to degrade the intrinsic spectrum leakage of fast Fourier transform in periodogram calculation, the leakage expression is derived analytically and then an adaptive process is proposed to make a tradeoff between leakage reduction and noise smoothing. We verify our algorithm by simulations and observe high accuracy in a wide range of velocities and SNRs. Additionally, unlike the conventional work, the proposed estimator is not strictly based on the assumption of specific Doppler spectral shapes except for the requirement of the band-limited channel, hence it is robust to general mobile channels. 相似文献
963.
This paper focuses on the observer design for nonlinear discrete‐time systems by means of nonlinear observer canonical form. At first, sufficient and necessary conditions are obtained for a class of autonomous nonlinear discrete‐time systems to be immersible into higher dimensional observer canonical form. Then a method called dynamic observer error linearization is developed. By introducing a dynamic auxiliary system, the augmented system is shown to be locally equivalent to the generalized observer form, whose nonlinear terms contain auxiliary states and output of the system. A constructive algorithm is also provided to obtain the state coordinate transformation. These results are an extension of their counterparts of nonlinear continuous‐time systems to nonlinear discrete‐time systems (Syst. Control Lett. 1986; 7 :133–142; SIAM. J. Control Optim. 2003; 41 :1756–1778; Int. J. Control 2004; 77 :723–734; Automatica 2006; 42 :321–328; IEEE Trans. Automat. Control 2007; 52 :83–88; IEEE Trans. Automat. Control 2004; 49 :1746–1750; Automatica 2006; 42 :2195–2200; IEEE Trans. Automat. Control 1996; 41 :598–603; Syst. Control Lett. 1997; 31 :115–128). Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
964.
徐卫克 《网络安全技术与应用》2010,(9):75-77
LEACH协议是专门应用于无线传感器网络的层次路由协议,在无线传感器网络路由协议中占有重要地位。本文采用理论分析与仿真实验相结合的方法,对LEACH协议的性能进行了深入研究,指出了LEACH协议路由算法的不足,明确了进一步对LEACH协议进行改进的方向。 相似文献
965.
Shen Haiying Xu Cheng-Zhong 《Parallel and Distributed Systems, IEEE Transactions on》2010,21(2):242-256
Consistent hashing-based DHT networks have an inherent load balancing problem. The problem becomes more severe in heterogeneous networks with nonuniform and time-varying popular files. Existing DHT load balancing algorithms are mainly focused on the issues caused by node heterogeneity. To deal with skewed lookups, this paper presents an elastic routing table (ERT) mechanism for query load balancing, based on the observation that high-degree nodes tend to receive more traffic load. The mechanism allows each node to have a routing table of variable size corresponding to node capacities. The indegree and outdegree of the routing table can also be adjusted dynamically in response to the change of file popularity and network churn. Theoretical analysis proves that the routing table degree is bounded. The ERT mechanism facilitates locality-aware randomized query forwarding to further improve lookup efficiency. By relating query forwarding to a supermarket customer service model, we prove that a two-way randomized query forwarding policy should lead to an exponential improvement in query processing time over random walking. Simulation results demonstrate the effectiveness of the ERT mechanism and its related query forwarding policy for congestion and query load balancing. In comparison with existing "virtual-server”-based load balancing algorithms and other routing table control approaches, the ERT-based congestion control protocol yields significant improvement in query lookup efficiency. 相似文献
966.
In this paper, a novel structure is derived for efficient implementation of digital filters as well as minimizing the finite word length (FWL) errors. Such a structure is actually an improved version of that reported previously. The performance of this new structure and the famous normalized lattice structure are analyzed by deriving the corresponding expression for the roundoff noise gain. Design examples are presented to illustrate the behavior of the proposed structure and to compare it with some existing ones. It is shown that the proposed structure outperforms the others in terms of minimizing roundoff noise as well as implementation efficiency. 相似文献
967.
Dynamic spectrum sharing is a promising technology to improve spectrum utilization in future wireless networks. The flexible spectrum management provides new opportunities for licensed primary user and unlicensed secondary users to reallocate the spectrum resource efficiently. In this paper, we present an oligopoly pricing framework for dynamic spectrum allocation in which the primary users sell excessive spectrum to the secondary users for monetary return. We present two approaches, the strict constraints (type-I) and the QoS penalty (type-II), to model the realistic situation that the primary users have limited capacities. In the oligopoly model with strict constraints, we propose a low-complexity searching method to obtain the Nash Equilibrium and prove its uniqueness. When reduced to a duopoly game, we analytically show the interesting gaps in the leader–follower pricing strategy. In the QoS penalty based oligopoly model, a novel variable transformation method is developed to derive the unique Nash Equilibrium. When the market information is limited, we provide three myopically optimal algorithms “StrictBEST”, “StrictBR” and “QoSBEST” that enable price adjustment for duopoly primary users based on the Best Response Function (BRF) and the bounded rationality (BR) principles. Numerical results validate the effectiveness of our analysis and demonstrate the convergence of “StrictBEST” as well as “QoSBEST” to the Nash Equilibrium. For the “StrictBR” algorithm, we reveal the chaotic behaviors of dynamic price adaptation in response to the learning rates. 相似文献
968.
Space robotic systems are expected to play an increasingly important role in the future on-orbit service. The applications
include repairing, refueling or de-orbiting of a satellite, or removal of the space debris. The dynamical performances of
space robotic system result from the multi-physics interactions between mechanical, electrical, electronic, control, etc.
In this paper, we developed a unified multi-domain modelling and simulation system. The system is composed of the following
modules: the path planner, joint controllers, motor and its driver, gearing mechanism of the space manipulators, the Guidance,
Navigation, and Control (GNC) system, the actuators of the base, and the orbital environment, orbital dynamic and the multi-body
dynamic of the whole system, etc. Based on this system, the operation during different stages, including far range rendezvous,
close range rendezvous (is usually divided into two sub-phases: closing and final approach) and target capturing can be studied
from the view of multi-physics domains. The key algorithms, such as pose (position and attitude) measurement, GNC of the base,
path planning and control of the space manipulator, and so on, can be validated using the system. As examples, the capturing
processes of a moving target under free-floating and attitude-controlled modes are simulated and the simulation results are
given. 相似文献
969.
An approach for moving object recognition based on BPR and CI 总被引:1,自引:0,他引:1
A recognition and classification method of multiple moving objects in traffic based on the combination of the Biomimetic Pattern
Recognition (BPR) and Choquet Integral (CI) is proposed. The recognition process consists of three stages. At the first stage,
vehicles and pedestrians are detected in video images and the area, the shape and the velocity features are obtained by classical
methods. At the second stage, BPR is used to classify the Zernike moments extracted at the first stage. At the last stage,
CI is then adopted for multi-features fusion based on the output of BPR, and the area and the velocity features obtained at
the first stage to improve the recognition accuracy. Experiment results show that this approach is efficient. 相似文献
970.
QoS multicast routing is a non-linear combinatorial optimization problem. It tries to find a multicast routing tree with minimal cost that can satisfy constraints such as bandwidth, delay, and delay jitter. This problem is NP-complete. The solution to such problems is often to search first for paths from the source node to each destination node and then integrate these paths into a multicast tree. Such a method, however, is slow and complex. To overcome these shortcomings, we propose a new method for tree-based optimization. Our algorithm optimizes the multicast tree directly, unlike the conventional solutions to finding paths and integrating them to generate a multicast tree. Our algorithm also applies particle swarm optimization to the solution to control the optimization orientation of the tree shape. Simulation results show that our algorithm performs well in searching, converging speed and adaptability scale. 相似文献