全文获取类型
收费全文 | 464862篇 |
免费 | 5149篇 |
国内免费 | 1273篇 |
专业分类
电工技术 | 8578篇 |
综合类 | 443篇 |
化学工业 | 71331篇 |
金属工艺 | 17783篇 |
机械仪表 | 13997篇 |
建筑科学 | 10965篇 |
矿业工程 | 2164篇 |
能源动力 | 11787篇 |
轻工业 | 42348篇 |
水利工程 | 4410篇 |
石油天然气 | 7714篇 |
武器工业 | 47篇 |
无线电 | 55348篇 |
一般工业技术 | 88787篇 |
冶金工业 | 89169篇 |
原子能技术 | 10097篇 |
自动化技术 | 36316篇 |
出版年
2021年 | 3975篇 |
2019年 | 3671篇 |
2018年 | 6264篇 |
2017年 | 6254篇 |
2016年 | 6641篇 |
2015年 | 4190篇 |
2014年 | 7307篇 |
2013年 | 20590篇 |
2012年 | 11538篇 |
2011年 | 15873篇 |
2010年 | 12693篇 |
2009年 | 14230篇 |
2008年 | 15051篇 |
2007年 | 15026篇 |
2006年 | 13356篇 |
2005年 | 11741篇 |
2004年 | 11335篇 |
2003年 | 11390篇 |
2002年 | 11009篇 |
2001年 | 11301篇 |
2000年 | 10599篇 |
1999年 | 10925篇 |
1998年 | 27387篇 |
1997年 | 19202篇 |
1996年 | 14782篇 |
1995年 | 11279篇 |
1994年 | 10038篇 |
1993年 | 9930篇 |
1992年 | 7314篇 |
1991年 | 6955篇 |
1990年 | 7010篇 |
1989年 | 6691篇 |
1988年 | 6396篇 |
1987年 | 5584篇 |
1986年 | 5552篇 |
1985年 | 6208篇 |
1984年 | 5808篇 |
1983年 | 5429篇 |
1982年 | 5102篇 |
1981年 | 5078篇 |
1980年 | 4911篇 |
1979年 | 4693篇 |
1978年 | 4497篇 |
1977年 | 5245篇 |
1976年 | 7022篇 |
1975年 | 3868篇 |
1974年 | 3746篇 |
1973年 | 3805篇 |
1972年 | 3241篇 |
1971年 | 2885篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
Dynamic Programming (DP) applies to many signal and image processing applications including boundary following, the Viterbi algorithm, dynamic time warping, etc. This paper presents an array processor implementation of generic dynamic programming. Our architecture is a SIMD array attached to a host computer. The processing element of the architecture is based on an ASIC design opting for maximum speed-up. By adopting a torus interconnection network, a dual buffer structure, and a multilevel pipeline, the performance of the DP chip is expected to reach the order of several GOPS. The paper discusses both the dedicated hardware design and the data flow control of the DP chip and the total array.This work was supported in part by the NATO, Scientific and Environmental Affairs Division, Collaborative Research Grant SA.5-2-05(CRG.960201)424/96/JARC-501. 相似文献
992.
Large signal analysis of the LCC-type parallel resonant converterusing discrete time domain modeling
A discrete time domain model for the LCC-type parallel resonant power converter has been derived. This model has been used to predict the large signal behavior of the power converter. The peak component stresses and the dynamic response of the key state variables, as obtained from the large signal analysis, using PRO-MATLAB software are plotted. SPICE results are included to verify the analytical results. Experimental results are also presented to verify the theory 相似文献
993.
Microfibre reinforced cement composites reinforced with high volume fractions of carbon, steel and polypropylene fibres were tested in uniaxial tension. Composites investigated included those with only one type of fibre (mono-fibre composites) and those with two or more types of fibres (hybrid-fibre composites) in the same mix. Considerable strengthening, toughening and stiffening of the host matrix due to microfibre reinforcement were observed. In the hybrid-fibre composites, different fibres appear to act as additive phases; i.e., they maintain their individual reinforcing capabilities. The composites were also impact tested in uniaxial tension using a newly designed instrumented impact machine. When compared with static test results, considerable sensitivity to stress rate was noted; composites were found to be stronger and tougher under impact and the improvements were more pronounced at higher fibre volume fractions. The potential of these composites for use in thin sheet products and other similar applications is recognized, and the need for continued research is stressed. 相似文献
994.
A neural network-based power system stabilizer (neuro-PSS) is designed for a generator connected to a multi-machine power system utilizing the nonlinear power flow dynamics. The use of power flow dynamics provides a PSS for a wide range of operation with reduced size neural networks. The neuro-PSS consists of two neural networks: neuro-identifier and neuro-controller. The low-frequency oscillation is modeled by the neuro-identifier using the power flow dynamics, then a generalized backpropagation-through-time (GBTT) algorithm is developed to train the neuro-controller. The simulation results show that the neuro-PSS designed in this paper performs well with good damping in a wide operation range compared with the conventional PSS 相似文献
995.
Abstract: Maintainability problems associated with traditional software systems are exacerbated in rule-based systems. The very nature of that approach — separation of control knowledge and data-driven execution — hampers maintenance. While there are widely accepted techniques for maintaining conventional software, the same is not true for rule-based systems. In most situations, both a knowledge engineer and a domain expert are necessary to update the rules of a rule-based system. This paper presents, first, an overview of the software engineering techniques and object-oriented methods used in maintaining rule-based systems. It then discusses alternate paradigms for expert system development. The benefits of using case-based reasoning (from the maintenance point of view) are illustrated through the implementation of a case-based scheduler. The main value of the scheduler is that its knowledge base can be modified by the expert without the assistance of a knowledge engineer. Since changes in application requirements can be given directly to the system by the expert, the effort of maintaining the knowledge base is greatly reduced. 相似文献
996.
We propose a new principle for a low temperature semiconductor detector of charged particles with possibly submicron lateral resolution based on point contacts formed in the 2-dimensional electron gas (2DEG) of a GaAs-AlxGa1-xAs heterostructure using split-gates. The detector operates up to liquid nitrogen temperatures. Impinging particles excite locally extra donors in the doping layer of the heterostructure. By measuring simultaneous increase in the conductances of 3 point contacts due to the impacts of charged particles the position of penetration is calculated using the Thomas-Fermi approximation for screening in 2DEG. 相似文献
997.
998.
R Gouider E LeGuern J Emile S Tardieu F Cabon M Samid J Weissenbach Y Agid P Bouche A Brice 《Canadian Metallurgical Quarterly》1994,44(12):2250-2252
Fistulas secondary to Crohn's disease occur in about 33% of patients. A colobronchial fistula complicating Crohn's disease is very rare, having been reported only twice previously. We present an unusual fistula secondary to Crohn's colitis that originated from the splenic flexure and crossed the diaphragm to involve the bronchial tree. 相似文献
999.
E. C. Kirby 《Fullerenes, Nanotubes and Carbon Nanostructures》1994,2(4):395-404
The possibility of toroidal cages of carbon with repeating five and seven membered ring pairs (azulene units) upon their surfaces is briefly discussed. Some of the difficulties in recognising possible fullerene cage shapes are pointed out. 相似文献
1000.
Investigates adaptive digital notch filters for the elimination of powerline noise from biomedical signals. Since the distribution of the frequency variation of the powerline noise may or may not be centered at 60 Hz. Three different adaptive digital notch filters are considered. For the first case, an adaptive FIR second-order digital notch filter is designed to track the center frequency variation. For the second case, the zeroes of an adaptive IIR second-order digital notch filter are fixed on the unit circle and the poles are adapted to find an optimum bandwidth to eliminate the noise to a pre-defined attenuation level. In the third case, both the poles and zeroes of the adaptive IIR second-order filter are adapted to track the center frequency variation within an optimum bandwidth. The adaptive process is considerably simplified by designing the notch filters by pole-zero placement on the unit circle using some suggested rules. A constrained least mean-squared algorithm is used for the adaptive process. To evaluate their performance, the three adaptive notch filters are applied to a powerline noise sample and to a noisy EEG as an illustration of a biomedical signal 相似文献