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151.
提出了一种实现双数据通道DMA传输的新方法,并成功地应用于光子相关计中,得到了满意的实验结果。并以8237DMA控制器为例,详细地分析了工作在命令传输方式的8236与外设、CPU之间的操作时序,提出了实现双数据传输方式的逻辑设计,拓宽了DMA控制器的处理能力。 相似文献
152.
To develop simple traffic engineering rules for the downlink of a cellular system using Proportional Fairness (PF) scheduling, we study the “strict” and “approximate” insensitivity of a Processor Sharing (PS) system, specifically for the Egalitarian (EPS) and Discriminatory (DPS) variants of PS. Assuming homogeneous channel conditions, all concurrent flows are allocated an equal share of downlink transmission slots regardless of flow types and locations. The cell system is modeled as an EPS queue. We prove the performance insensitivity of EPS in a relevant new case that has not been studied in the literature. Considering heterogenous channel conditions, the system is modeled as the DPS queue in which each traffic type is divided into subclasses with different assigned weights. Asymmetric weights among the subclasses model the unequal channel sharing that occurs with PF scheduling. Our results show that the first-order performance of the DPS is largely insensitive to the input traffic characteristics, as long as the weights among subclasses are not highly skewed. Our findings, confirmed by the simulation of a cellular system, imply reduced complexity for traffic provisioning procedures. However, our study also shows that the first-order performance is sensitive to the traffic details when there is discrimination among different traffic types. This observation implies that the introduction of differentiated services may pose a great challenge to network provisioning in future cellular systems. 相似文献
153.
154.
155.
刘荣华 《东北电力学院学报》2007,27(5):95-100
关注大专学生的心理发展,加强心理健康教育,真正把他们培养成为德才兼备、情智并重、身心健康的社会主义建设者是高等教育面临的新课题。用Scl-90(症状自评量表)测试,对378名专科学生进行了心理健康状况的调查,目的是要了解和掌握大专学生的心理健康水平,分析影响大专学生心理健康的因素,寻找大专学生心理健康教育的主要途径。 相似文献
156.
The commonly used models for shadowed fading channels arise by compounding the Nakagami distribution with others such as the
log-normal and gamma distributions. A distribution that is more flexible than the Nakagami distribution is the well known
Weibull distribution. In this paper, we derive a collection of generalized models for shadowed fading channels by compounding
the Weibull distribution with other distributions belong to some fifteen flexible families. We also illustrate the superior
performance of these models over the standard Nakagami models. 相似文献
157.
m 《AEUE-International Journal of Electronics and Communications》2007,61(9):595-604
In this paper, a semi-deterministic propagation model for predicting short-term fading statistics in urban environments is presented. An approach to include surface scattering into deterministic ray-optical propagation models in urban scenarios is derived. This approach considers the coherent and incoherent components of the scattered signal. A statistical characterisation of the received signal at the received position permits to model the short-term fading for a local area around the mobile position using the Nakagami-m distribution. The parameters of the Nakagami-m distribution are obtained taking into account the real environment from a digital map information of the urban area. Computer simulation results and experimental data are compared. 相似文献
158.
Matthias Pätzold Bjørn Olav Hogstad Dongwoo Kim 《Wireless Personal Communications》2007,40(3):267-279
In this paper, we introduce a new technique for the design of high-performance Rayleigh fading channel simulators. The proposed
design method uses set partitioning – a technique, which plays a key role in the design of trellis-coded modulation schemes.
We show how set partitioning can be used to design multiple uncorrelated fading waveforms enabling the simulation of Rayleigh
fading channels. For the important case of isotropic scattering, we show that the sample average of the generated waveforms
results in a deterministic process, the autocorrelation function (ACF) of which tends to the zeroth-order Bessel function
of the first kind as the number of sample functions increases. The proposed procedure is completely deterministic. The comparison
with a stochastic procedure using Monte Carlo techniques will be made. A study of the performance shows clearly that the new
technique using set partitioning outperforms by far existing Monte Carlo methods. 相似文献
159.
The capacity-achieving coding scheme for the multiple-input multiple-output (MIMO) broadcast channel is dirty-paper coding.
With this type of transmission scheme the optimal number of active users that receive data and the optimal power allocation
strategy are highly dependent on the structure of the channel matrix and on the total transmit power available. In the context
of packet-data access with adaptive transmission where mobile users are equipped with a single receive antenna and the base
station has multiple transmit antennas, we study the optimal number of active users and the optimal power allocation. In the
particular case of two transmit antennas, we prove that the optimal number of active users can be a non-monotonic function
of the total transmit power. Thus not only the number of users that should optimally be served simultaneously depends on the
user channel vectors but also on the power available at the base station transmitter. The expected complexity of optimal scheduling
algorithms is thus very high. Yet we then prove that at most as many users as the number of transmit antennas are allocated
a large amount of power asymptotically in the high-power region in order to achieve the sum-capacity. Simulations confirm
that constraining the number of active users to be no more than the number of transmit antennas incurs only a marginal loss
in spectral efficiency. Based on these observations, we propose low-complexity scheduling algorithms with sub-optimal transmission
schemes that can approach the sum-capacity of the MIMO broadcast channel by taking advantage of multiuser diversity. The suitability
of known antenna selection algorithms is also demonstrated. We consider the cases of complete and partial channel knowledge
at the transmitter. We provide simulation results to illustrate our conclusions. 相似文献
160.
Liang Yang 《Wireless Personal Communications》2007,43(4):1717-1725
In this paper, we consider the multiple-input multiple-output (MIMO) wireless systems employing maximal ratio combining (MRC)
in the absence and presence of multiuser diversity. First, using the well-known moment generating function-based analysis
approach, we derive the error performance of the MIMO MRC systems without multiuser diversity over spatially correlated fading
channels. Second, we present the average capacity of MIMO MRC systems with multiuser diversity. Numerical results demonstrate
the accuracy of our analytical expressions. 相似文献