全文获取类型
收费全文 | 433491篇 |
免费 | 5746篇 |
国内免费 | 1391篇 |
专业分类
电工技术 | 7733篇 |
综合类 | 262篇 |
化学工业 | 68469篇 |
金属工艺 | 18257篇 |
机械仪表 | 12793篇 |
建筑科学 | 10714篇 |
矿业工程 | 2547篇 |
能源动力 | 10708篇 |
轻工业 | 39465篇 |
水利工程 | 4577篇 |
石油天然气 | 9332篇 |
武器工业 | 18篇 |
无线电 | 47656篇 |
一般工业技术 | 84406篇 |
冶金工业 | 79060篇 |
原子能技术 | 10602篇 |
自动化技术 | 34029篇 |
出版年
2021年 | 3231篇 |
2019年 | 3051篇 |
2018年 | 5510篇 |
2017年 | 5462篇 |
2016年 | 5812篇 |
2015年 | 3892篇 |
2014年 | 6539篇 |
2013年 | 18903篇 |
2012年 | 10738篇 |
2011年 | 14646篇 |
2010年 | 11898篇 |
2009年 | 13553篇 |
2008年 | 13913篇 |
2007年 | 13670篇 |
2006年 | 11950篇 |
2005年 | 11158篇 |
2004年 | 10431篇 |
2003年 | 10012篇 |
2002年 | 9995篇 |
2001年 | 9842篇 |
2000年 | 9398篇 |
1999年 | 9550篇 |
1998年 | 23361篇 |
1997年 | 17038篇 |
1996年 | 13265篇 |
1995年 | 10099篇 |
1994年 | 8912篇 |
1993年 | 8766篇 |
1992年 | 6597篇 |
1991年 | 6512篇 |
1990年 | 6254篇 |
1989年 | 6289篇 |
1988年 | 6192篇 |
1987年 | 5334篇 |
1986年 | 5304篇 |
1985年 | 6095篇 |
1984年 | 5756篇 |
1983年 | 5280篇 |
1982年 | 4973篇 |
1981年 | 5131篇 |
1980年 | 4862篇 |
1979年 | 4819篇 |
1978年 | 4895篇 |
1977年 | 5618篇 |
1976年 | 7220篇 |
1975年 | 4387篇 |
1974年 | 4193篇 |
1973年 | 4272篇 |
1972年 | 3703篇 |
1971年 | 3407篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
A. E. Lapshin Yu. F. Shepelev Yu. I. Smolin E. A. Vasil’eva 《Glass Physics and Chemistry》2008,34(2):182-186
The distribution and structure of tellurium nanoclusters synthesized in crystal channels of the porous silica ZSM-11 are investigated
using the maximum-entropy method and the Rietveld analysis. It is shown that the intercalated tellurium atoms are arranged
in channels of the ZSM-11 zeolite not randomly but in the form of scraps of infinite chains similar to those observed in massive
tellurium. The distances between the nearest neighbor tellurium atoms vary in the range 2.53(4)–2.70(3) ?. The clusters Te4 are formed at the intersections of channels in the structure. These clusters have the form of distorted tetrahedra in which
the tellurium atoms are separated by distances of 2.53(4) and 2.90(4) ?.
Original Russian Text ? A.E. Lapshin, Yu.F. Shepelev, Yu.I. Smolin, E.A. Vasil’eva, 2008, published in Fizika i Khimiya Stekla. 相似文献
992.
Hung-da Wan F. Frank Chen 《The International Journal of Advanced Manufacturing Technology》2008,38(9-10):995-1005
A Kanban system facilitates lean principles in a simple and effective way. While reportedly successful in many manufacturing firms, the conventional Kanban systems using physical cards suffer from human errors, limited tracking capability, and so on. To make the information flow leaner, software providers add new features to their existing programs for manufacturing systems to computerize Kanban activities. As Web-based technologies advance rapidly, developing an entirely Web-based Kanban system appears to be feasible and promising. This paper presents the advantages, limitations, and challenges of Web-based Kanban systems. An experimental program has been developed based on PHP+MySQL, a popular Web programming platform. The server-executed program features cross-platform compatibility, real-time tracking and performance monitoring, and greatly enhanced information contents compared to physical Kanbans. Human errors are minimized by the automated transactions; nevertheless, the interfacing and data maintenance require further research efforts. 相似文献
993.
Steensgaard J. Zhiqing Zhang Wenhuan Yu Sarhegyi A. Lucchese L. Dae-Ik Kim Temes G.C. 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(5):1289-1296
Incremental data converters (IDCs) are useful in instrumentation and measurement applications, where low-frequency analog signals need to be converted into digital form with high accuracy and low power dissipation. They are particularly well suited for applications where a single analog-digital converter is multiplexed between many channels. This paper proposes an exact design methodology for IDCs, which optimizes the signal-to-noise ratio of the converter under practical design constraints. The process also allows the designer to apportion the noise budget in an arbitrary manner between thermal and quantization noise. The design process is illustrated by an example which describes the optimization of a third-order multiplexed IDC. 相似文献
994.
Chaves R. Kuzmanov G. Sousa L. Vassiliadis S. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2008,16(8):999-1008
995.
It is shown that, at thermodynamic equilibrium, the release of charge carriers from the localized states of bistable amphoteric centers into quasi-free states depends on the degree of compensation. This brings about different functional dependences of the concentration of free charge carriers on temperature. It is found that, in uncompensated semiconductors, the concentration of free charge carriers follows the same dependence in the case of bistable amphoteric centers and bistable amphoteric U ? centers, although the distributions of charge carriers over the charge states and configurations are different for these types of centers. The results can be used for interpreting various experimental data insufficiently explained in the context of the traditional approach. 相似文献
996.
V. N. Jmerik A. M. Mizerov T. V. Shubina A. V. Sakharov A. A. Sitnikova P. S. Kop’ev S. V. Ivanov E. V. Lutsenko A. V. Danilchyk N. V. Rzheutskii G. P. Yablonskii 《Semiconductors》2008,42(12):1420-1426
Features of plasma-assisted molecular-beam epitaxy of AlGaN compounds at relatively low temperatures of the substrate (no higher than 740°C) and various stoichiometric conditions for growth of the nitrogen- and metal-enriched layers are studied. Discrete submonolayer epitaxy for formation of quantum wells and n-type blocking layers without varying the fluxes of components was used for the first time in the case of molecular- beam epitaxy with plasma activation of nitrogen for the nanostructures with the Al x Ga1 ? x N/Al y Ga1 ? y N quantum wells. Structural and optical properties of the Al x Ga1 ? x N layers in the entire range of compositions (x = 0–1) and nanostructures based on these layers are studied; these studies indicate that there is photoluminescence at room temperature with minimum wavelength of 230 nm. Based on the analysis of the photoluminescence spectra for bulk layers and nanoheterostructures and their temperature dependences, it is concluded that there are localized states in quantum wells. Using the metal-enriched layers grown on the c-Al2O3 substrates, heterostructures for light-emitting diodes with Al x Ga1 ? x N/Al y Ga1 ? y N quantum wells (x = 0.4–0.5, y = x + 0.15) were obtained and demonstrated electroluminescence in the ultraviolet region of the spectrum at the wavelength of 320 nm. 相似文献
997.
In this paper, a new method for detecting text regions in natural scene images is presented. The proposed algorithm is based on the segmentation of objects in a scene, followed by the identification of text objects by a support vector machine (SVM). First, to segment objects in the scene, the input image is separated into chromatic and achromatic regions according to the distribution of red, green and blue (RGB) elements, and different clustering algorithms are applied. Second, each object is transformed into the wavelet domain for multi-resolution analysis, and moment features of the wavelet coefficients are used in the SVM for the classification of text objects. The proposed approach provides robustness to non-uniform illumination by using different clustering algorithms according to the characteristics of the colour components in the segmentation. Also, moment features, used for classification, are invariant to the size, direction, shape and other properties of texts. Experimental results demonstrate the effectiveness of this approach. 相似文献
998.
The present work is aimed to extend the knowledge of mechanical properties of sandwich structures used for marine applications
focusing on the possibility to increase the performances of such structures by adding a bonder at the skin/core interface.
Therefore, three sandwich structures that are utilised in different structural components of a yacht were realised by manual
lay-up. The mechanical characterisation was performed by flatwise compressive, edgewise compressive and three point flexural
tests. The tests execution has allowed both to determine the mechanical performances and to understand the fracture mechanisms
that take place when the bonder is added in the stacking sequence of the samples. 相似文献
999.
1000.
Implementation of adaptive critic-based neurocontrollers for turbogenerators in a multimachine power system 总被引:1,自引:0,他引:1
Venayagamoorthy G.K. Harley R.G. Wunsch D.C. 《Neural Networks, IEEE Transactions on》2003,14(5):1047-1064
This paper presents the design and practical hardware implementation of optimal neurocontrollers that replace the conventional automatic voltage regulator (AVR) and the turbine governor of turbogenerators on multimachine power systems. The neurocontroller design uses a powerful technique of the adaptive critic design (ACD) family called dual heuristic programming (DHP). The DHP neurocontrollers' training and testing are implemented on the Innovative Integration M67 card consisting of the TMS320C6701 processor. The measured results show that the DHP neurocontrollers are robust and their performance does not degrade unlike the conventional controllers even when a power system stabilizer (PSS) is included, for changes in system operating conditions and configurations. This paper also shows that it is possible to design and implement optimal neurocontrollers for multiple turbogenerators in real time, without having to do continually online training of the neural networks, thus avoiding risks of instability. 相似文献