全文获取类型
收费全文 | 353043篇 |
免费 | 31966篇 |
国内免费 | 19907篇 |
专业分类
电工技术 | 30262篇 |
技术理论 | 57篇 |
综合类 | 44815篇 |
化学工业 | 37521篇 |
金属工艺 | 12505篇 |
机械仪表 | 21506篇 |
建筑科学 | 43426篇 |
矿业工程 | 18030篇 |
能源动力 | 14991篇 |
轻工业 | 18274篇 |
水利工程 | 17049篇 |
石油天然气 | 15647篇 |
武器工业 | 3617篇 |
无线电 | 25488篇 |
一般工业技术 | 25166篇 |
冶金工业 | 18465篇 |
原子能技术 | 3515篇 |
自动化技术 | 54582篇 |
出版年
2024年 | 1032篇 |
2023年 | 4113篇 |
2022年 | 7741篇 |
2021年 | 9279篇 |
2020年 | 9833篇 |
2019年 | 8287篇 |
2018年 | 7594篇 |
2017年 | 9276篇 |
2016年 | 11083篇 |
2015年 | 12318篇 |
2014年 | 21440篇 |
2013年 | 19658篇 |
2012年 | 25036篇 |
2011年 | 26264篇 |
2010年 | 20345篇 |
2009年 | 21222篇 |
2008年 | 19533篇 |
2007年 | 24595篇 |
2006年 | 22918篇 |
2005年 | 19715篇 |
2004年 | 16661篇 |
2003年 | 14796篇 |
2002年 | 12197篇 |
2001年 | 10296篇 |
2000年 | 8692篇 |
1999年 | 6950篇 |
1998年 | 5345篇 |
1997年 | 4660篇 |
1996年 | 4270篇 |
1995年 | 3599篇 |
1994年 | 3164篇 |
1993年 | 2324篇 |
1992年 | 2035篇 |
1991年 | 1561篇 |
1990年 | 1358篇 |
1989年 | 1184篇 |
1988年 | 914篇 |
1987年 | 617篇 |
1986年 | 467篇 |
1985年 | 390篇 |
1984年 | 366篇 |
1983年 | 272篇 |
1982年 | 249篇 |
1981年 | 187篇 |
1980年 | 145篇 |
1979年 | 126篇 |
1978年 | 73篇 |
1977年 | 79篇 |
1976年 | 57篇 |
1975年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The existing analytical average bit error rate (ABER) expression of conventional generalised spatial modulation (CGSM) does not agree well with the Monte Carlo simulation results in the low signal‐to‐noise ratio (SNR) region. Hence, the first contribution of this paper is to derive a new and easy way to evaluate analytical ABER expression that improves the validation of the simulation results at low SNRs. Secondly, a novel system termed CGSM with enhanced spectral efficiency (CGSM‐ESE) is presented. This system is realised by applying a rotation angle to one of the two active transmit antennas. As a result, the overall spectral efficiency is increased by 1 bit/s/Hz when compared with the equivalent CGSM system. In order to validate the simulation results of CGSM‐ESE, the third contribution is to derive an analytical ABER expression. Finally, to improve the ABER performance of CGSM‐ESE, three link adaptation algorithms are developed. By assuming full knowledge of the channel at the receiver, the proposed algorithms select a subset of channel gain vector (CGV) pairs based on the Euclidean distance between all CGV pairs, CGV splitting, CGV amplitudes, or a combination of these. 相似文献
62.
Yasoub Eghbali Mahmoud Ferdosizade Naeiny 《International Journal of Communication Systems》2020,33(14)
In this paper, an off‐grid direction of arrival (DoA) estimation method is proposed for wideband signals. This method is based on the sparse representation (SR) of the array covariance matrix. Similar to the time domain DoA estimation methods, the correlation function of the sources was assumed to be the same and known. A new measurement vector is obtained using the lower‐left triangular elements of the covariance matrix. The DoAs are estimated by quantizing the entire range of continuous angle space into discrete grid points. However, the exact DoAs may be located between two grid points; therefore, this estimation has errors. The accuracy of DoA estimation is improved by the minimization of the difference between the new measurement vector and its estimated values. Simulation results revealed that the proposed method can enhance the DoA estimation accuracy of wideband signals. 相似文献
63.
64.
Geraint Johnes Swati Virmani 《International Transactions in Operational Research》2020,27(4):1869-1885
Data from the Young Lives study are used to evaluate the efficiency of education systems in four low and middle income countries: Ethiopia, India, Peru and Vietnam. A meta‐frontier variant of data envelopment analysis is used to assess the relative performance of each country's system, and, within each country, to evaluate the impact of public and private schooling, and of urban and rural location. Comparisons are drawn between the four countries; the results indicate that in no country does the educational system perform uniformly badly or well. Conditioning on the inputs available, rural areas are often indicative of higher levels of efficiency, thus suggesting a number of implications for policy. 相似文献
65.
66.
67.
Output feedback controller for polytopic systems exploiting the direct searching of the design space
This paper deals with the problem of designing a robust static output feedback controller for polytopic systems. The current research that tackled this problem is mainly based on LMI method, which is conservative by nature. In this paper, a novel approach is proposed, which considers the design space of the controller parameters and iteratively partitions the space to small simplexes. Then, by assessing the stability in each simplex, the solution space for design parameters is directly determined. It has been theoretically proved that, if there exists a feasible solution in the design space, the algorithm can find it. To validate the result of the proposed approach, comparative simulation examples are given to illustrate the performance of the design methodology as compared to those of previous approaches. 相似文献
68.
Most real-world vehicle nodes can be structured into an interconnected network of vehicles. Through structuring these services and vehicle device interactions into multiple types, such internet of vehicles becomes multidimensional heterogeneous overlay networks. The heterogeneousness of the overlays makes it difficult for the overlay networks to coordinate with each other to improve their performance. Therefore, it poses an interesting but critical challenge to the effective analysis of heterogeneous virtual vehicular networks. A variety of virtual vehicular networks can be easily deployed onto the native network by applying the concept of SDN (Software Defined Networking). These virtual networks reflect their heterogeneousness due to their different performance goals, and they compete for the same physical resources of the underlying network, so that a sub-optimal performance of the virtual networks may be achieved. Therefore, we propose a Deep Reinforcement Learning (DRL) approach to make the virtual networks cooperate with each other through the SDN controller. A cooperative solution based on the asymmetric Nash bargaining is proposed for co-existing virtual networks to improve their performance. Moreover, the Markov Chain model and DRL resolution are introduced to leverage the heterogeneous performance goals of virtual networks. The implementation of the approach is introduced, and simulation results confirm the performance improvement of the latency sensitive, loss-rate sensitive and throughput sensitive heterogeneous vehicular networks using our cooperative solution. 相似文献
69.
Fog computing has emerged to support the requirements of IoT applications that could not be met by today’s solutions. Different initiatives have been presented to drive the development of fog, and much work has been done to improve certain aspects. However, an in-depth analysis of the different solutions, detailing how they can be integrated and applied to meet specific requirements, is still required. In this work, we present a unified architectural model and a new taxonomy, by comparing a large number of solutions. Finally, we draw some conclusions and guidelines for the development of IoT applications based on fog. 相似文献
70.
The aim of this paper is to investigate the long and short-run relationship between spot and futures prices of the energy, precious metals, and base metals markets. We analyze daily data from January 1985 to February 2019. The empirical findings based on the cointegration test, which follows a nonlinear process, suggest that the spot prices of energy and metals assets have long-run relationships with their futures prices. Nonparametric Granger causality test results also indicate bi-directional causality among futures and spot prices. These findings indicate that the energy and metals markets are informationally efficient in the sense of Fama (1970). 相似文献