全文获取类型
收费全文 | 3820篇 |
免费 | 240篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 66篇 |
综合类 | 7篇 |
化学工业 | 870篇 |
金属工艺 | 90篇 |
机械仪表 | 98篇 |
建筑科学 | 143篇 |
矿业工程 | 3篇 |
能源动力 | 251篇 |
轻工业 | 356篇 |
水利工程 | 45篇 |
石油天然气 | 83篇 |
无线电 | 459篇 |
一般工业技术 | 730篇 |
冶金工业 | 160篇 |
原子能技术 | 13篇 |
自动化技术 | 703篇 |
出版年
2024年 | 14篇 |
2023年 | 140篇 |
2022年 | 258篇 |
2021年 | 318篇 |
2020年 | 210篇 |
2019年 | 205篇 |
2018年 | 248篇 |
2017年 | 198篇 |
2016年 | 199篇 |
2015年 | 126篇 |
2014年 | 163篇 |
2013年 | 312篇 |
2012年 | 192篇 |
2011年 | 218篇 |
2010年 | 151篇 |
2009年 | 149篇 |
2008年 | 116篇 |
2007年 | 78篇 |
2006年 | 86篇 |
2005年 | 77篇 |
2004年 | 58篇 |
2003年 | 38篇 |
2002年 | 47篇 |
2001年 | 34篇 |
2000年 | 35篇 |
1999年 | 35篇 |
1998年 | 45篇 |
1997年 | 26篇 |
1996年 | 35篇 |
1995年 | 19篇 |
1994年 | 22篇 |
1993年 | 27篇 |
1992年 | 22篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 17篇 |
1988年 | 17篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1974年 | 5篇 |
排序方式: 共有4077条查询结果,搜索用时 15 毫秒
41.
This article investigates the prediction of the crack growth angle of an existing internal crack under mixed mode loading at the crack tip for an unfilled ethylene propylene diene terpolymer rubber (EPDM). For the realization of mixed mode loading, the cracks of the uniaxial loaded specimens were oriented with different angles to the loading direction. The energy density factor was used as a potential criterion for determining the crack growth angle. The determination of the strain energy density factor was carried out simulatively in Abaqus. The second-order Ogden model was used to describe the rubber-like material behavior. The relative local minimum of the strain energy density factor provides the possible growth angle. The experimental investigations show that the initial cracks grow orthogonally to the loading direction for the different crack orientation angles. For the crack orientation angle parallel to the load direction, the crack growth was observed because the strong stretching of the specimen caused strong necking in the crack region. The crack growth for the remaining crack orientation angles were induced due to shear loading at the crack tip. The predictive angle of different crack orientation angles shows very good accordance to the measured crack growth angles. 相似文献
42.
Mohammed Alaeddine Abderrahim Mohammed Dib Mohammed El-Amine Abderrahim Mohammed Amine Chikh 《International Journal of Speech Technology》2016,19(2):229-236
As part of information retrieval systems (IRS) and in the context of the use of ontologies for documents and queries indexing, we propose and evaluate in this paper the contribution of this approach applied to Arabic texts. To do this we indexed a corpus of Arabic text using Arabic WordNet. The disambiguation of words was performed by applying the Lesk algorithm. The results obtained by our experiment allowed us to deduct the contribution of this approach in IRS for Arabic texts. 相似文献
43.
Design of a compact dual‐band folded‐waveguide bandpass filter using multilayer waveguide resonators 下载免费PDF全文
A novel compact dual‐band bandpass filter based on multilayer folded‐waveguide (FWG) structure is presented in this article.In this design, slots are used to realize direct coupling between adjacent resonators and apertures are adopted to implement cross coupling between non‐adjacent resonators.A new technique of external quality factor of FWG resonator and coupling coefficients between different resonators are studied using full‐wave simulator. In order to demonstrate the proposed technique, a four‐pole dual‐band bandpass filter is designed, fabricated and measured using vector network analyzer. Measurement results which are well agreed with simulation results are presented. Moreover, four‐pole substrate integrated folded waveguide SIFW dual‐band bandpass filter, using two layers of slotted folded waveguide resonators, is demonstrated. The proposed filter has a compact size and it is excellent candidate for the application of wireless communication systems. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:780–788, 2015. 相似文献
44.
45.
For many years, computer systems have emerged; they now occupy an important place in our daily lives. The growing needs and ever increasing use of computer systems have made application development more and more complicated, The complexity of these applications poses problems such as reuse, installation, administration and evolution of applications. The development of applications is related to the evolution of paradigms and approaches to developing them. This paper presents different approaches and paradigms of development starting with the procedural approach, coming up for service, through the component and object-oriented approaches. Also, for each of the approaches we determine the advantages and limitations. 相似文献
46.
Sultan Aldirmaz Lutfiye Durak-Ata Aydin Akan Luis F. Chaparro 《Digital Signal Processing》2013,23(5):1747-1755
Discrete evolutionary transform (DET) has usually been applied to signals in a blind-way without using any parameters to characterize the signal. For this reason, it is not optimal and needs improvement by using some information about the signal. In this paper, we propose an improvement for the discrete evolutionary transform in order to obtain a sparse representation and redefine the generalized time-bandwidth product optimal short-time Fourier transform as a special case of it. In case of linear FM-type signals, the optimized kernel function of the transform is determined according to signal parameters including the instantaneous frequency. The performance of the adaptive-DET is illustrated on three distinct cases. In case of multi-component LFM signals, when the concentration of the proposed distribution is compared to the ordinary sinusoidal-DET, the improvement is computed as 28% in terms of the ratio of norms. Furthermore we define a new and a general class of distribution functions named as the short-time generalized discrete Fourier transform (ST-GDFT) which is a larger set of signal representations including the adaptive-DET. 相似文献
47.
Mohammed Chahim Ruud Brekelmans Dick den Hertog Peter Kort 《Optimization methods & software》2013,28(3):458-477
This paper determines the optimal timing of dike heightenings as well as the corresponding optimal dike heightenings to protect against floods. To derive the optimal policy, we design an algorithm based on the Impulse Control Maximum Principle. In this way, this paper presents one of the first real-life applications of the Impulse Control Maximum Principle developed by Blaquière. We show that the proposed impulse control (IC) approach performs better than dynamic programming with respect to computational time. This is caused by the fact that IC does not need discretization in time. 相似文献
48.
The position control system of an electro-hydraulic actuator system (EHAS) is investigated in this paper. The EHAS is developed by taking into consideration the nonlinearities of the system: the friction and the internal leakage. A variable load that simulates a realistic load in robotic excavator is taken as the trajectory reference. A method of control strategy that is implemented by employing a fuzzy logic controller (FLC) whose parameters are optimized using particle swarm optimization (PSO) is proposed. The scaling factors of the fuzzy inference system are tuned to obtain the optimal values which yield the best system performance. The simulation results show that the FLC is able to track the trajectory reference accurately for a range of values of orifice opening. Beyond that range, the orifice opening may introduce chattering, which the FLC alone is not sufficient to overcome. The PSO optimized FLC can reduce the chattering significantly. This result justifies the implementation of the proposed method in position control of EHAS. 相似文献
49.
Oil exploration in Egypt is a major contributor to the national Gross Domestic Product (GDP). With 50-65% of the oil resources located in the Gulf of Suez (GoS) region, the impact of such activity upon the region's water environment and its quality cannot be overlooked because of the volume of effluent generated. The objective of this study (September 2000-September 2001) was to assess the impact of a 650,000 barrels/day (bl/d) (100,000 m3/d) effluent arising from a major oil exploration site located south of GoS upon the local water environment. Another objective was to identify the pollutant contents amenable for reduction relative to the new Egyptian regulations. This was achieved by the characterization of the main contributing streams and the identification of the final effluent parameter constraints relative to the type of injection waters used. Subsequent investigations for the reduction of these contents were conducted on site and the results obtained are reviewed herewith. 相似文献
50.
Assessment of Sustainable Yield of Karst Water in Huaibei,China 总被引:2,自引:1,他引:1
Dan Yin Longcang Shu Xunhong Chen Zhenlong Wang Mokhatar Eisa Mohammed 《Water Resources Management》2011,25(1):287-300
This paper presents the assessment of sustainable yield in the Huaibei karst water area of Anhui province, China. A review
of sustainable yield definition is introduced first in this paper, and sustainable development in karst areas is more difficult
due to the complicated hydrogeologic conditions. General hydrogeology of the study area is provided to characterize hydraulic
connections between the karst aquifer and an overlying porous aquifer. Groundwater level declines continuously due to over-exploitation
of the karst groundwater, and two layers of groundwater dropping funnel were formed in Huaibei. These problems not only threaten
the eco-geo-environment, but also compromise the water utilization which depends on the shallow porous water. A “critical
water level” is proposed in this study to assess the sustainable yield, and it is determined by the historical exploitation
data which represent the relationship between the karst water and the shallow porous water uses. A three layer Artificial
Neural Network (ANN) model is used to understand the complex relationship of the karst water level and its influencing factors.
Precipitation, exploitation and water level of latest period are chosen as the input nodes, seasonal records of water level
are simulated by the ANN model. The sustainable yield is calculated by the trail-and-error adjusting method, and is equal
to the pumping rate when the “critical water level” is maintained. The rate of 30.05 MCM/a is the sustainable yield for the
Huaibei karst area in 2008, and it is less than the real pumping rate of 35.92 MCM/a. This assessment is meaningful to the
management for the Huaibei karst water. 相似文献