全文获取类型
收费全文 | 74949篇 |
免费 | 836篇 |
国内免费 | 691篇 |
专业分类
电工技术 | 1437篇 |
综合类 | 47篇 |
化学工业 | 11191篇 |
金属工艺 | 3448篇 |
机械仪表 | 2642篇 |
建筑科学 | 1661篇 |
矿业工程 | 505篇 |
能源动力 | 1853篇 |
轻工业 | 6392篇 |
水利工程 | 846篇 |
石油天然气 | 2304篇 |
武器工业 | 41篇 |
无线电 | 7241篇 |
一般工业技术 | 16470篇 |
冶金工业 | 12524篇 |
原子能技术 | 2629篇 |
自动化技术 | 5245篇 |
出版年
2022年 | 576篇 |
2021年 | 909篇 |
2020年 | 695篇 |
2019年 | 782篇 |
2018年 | 1551篇 |
2017年 | 1563篇 |
2016年 | 1763篇 |
2015年 | 947篇 |
2014年 | 1565篇 |
2013年 | 3573篇 |
2012年 | 2365篇 |
2011年 | 2828篇 |
2010年 | 2379篇 |
2009年 | 2648篇 |
2008年 | 2625篇 |
2007年 | 2564篇 |
2006年 | 2186篇 |
2005年 | 1916篇 |
2004年 | 1842篇 |
2003年 | 1793篇 |
2002年 | 1709篇 |
2001年 | 1683篇 |
2000年 | 1671篇 |
1999年 | 1569篇 |
1998年 | 3684篇 |
1997年 | 2617篇 |
1996年 | 1955篇 |
1995年 | 1534篇 |
1994年 | 1345篇 |
1993年 | 1355篇 |
1992年 | 996篇 |
1991年 | 1056篇 |
1990年 | 1075篇 |
1989年 | 1052篇 |
1988年 | 944篇 |
1987年 | 880篇 |
1986年 | 877篇 |
1985年 | 935篇 |
1984年 | 780篇 |
1983年 | 771篇 |
1982年 | 680篇 |
1981年 | 695篇 |
1980年 | 663篇 |
1979年 | 651篇 |
1978年 | 620篇 |
1977年 | 775篇 |
1976年 | 936篇 |
1975年 | 583篇 |
1974年 | 555篇 |
1973年 | 544篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
O. P. Mikheeva A. I. Sidorov A. S. Khaiikina E. V. Chuguevets 《Technical Physics Letters》2002,28(1):48-49
Experimental data on the pulsed laser radiation confinement in compensated GaAs and ZnSe with deep impurity levels are reported for the laser wavelength λ=1.55 μm and a pulse repetition frequency of up to 100 kHz. It is demonstrated that an increase in the pulse repetition rate is accompanied by a decrease in the energy confinement threshold and by an increase in the radiation attenuation coefficient. These effects are explained by the accumulation of nonequilibrium charge carriers related to a dependence of the recombination time constant on the concentration of free impurity centers. 相似文献
152.
I. N. Polandov V. K. Novik O. K. Gulish B. P. Bogomolov V. B. Morozov 《Measurement Techniques》1989,32(9):888-890
Translated from Izmeritel'naya Tekhnika, No. 9, pp. 34–35, September, 1989. 相似文献
153.
A Symbolic Pole/Zero Extraction Methodology Based on Analysis of Circuit Time-Constants 总被引:1,自引:0,他引:1
O. Guerra J. D. Rodríguez-García F. V. Fernández A. Rodríguez-Vázquez 《Analog Integrated Circuits and Signal Processing》2002,31(2):101-118
This paper introduces a methodology for symbolic pole/zero extraction based on the formulation of the time-constant matrix of the circuits. This methodology incorporates approximation techniques specifically devoted to achieve an optimum trade-off between accuracy and complexity of the symbolic root expressions. The capability to efficiently handle even large circuits will be demonstrated through several practical circuits. 相似文献
154.
An audio recording/playback head using an amorphous (Fe-Co-Ru-Cr) 75(Si-B)25 alloy was developed. Compared with a commercial Sendust head, three excellent features were observed. The wear of the amorphous alloy head when used with γ-Fe2O 3 is two-thirds that of the Sendust head. The output level at high-frequency (14 kHz) is 5 dB higher than that of the Sendust head. The bias current for the amorphous alloy head is half that of the Sendust head 相似文献
155.
156.
A one-dimensional mesoscopic ring with one input and two output leads acts as a spintronic beam splitter. The spatial degree of freedom, i.e., the presence of two different possible output channels, gets intertwined with the spin direction as a consequence of quantum interference and spin-orbit interaction. We investigate this kind of spatial-spin correlation, and show that the output density operator contains no quantum entanglement in the important special case when the device polarizes a perfectly random input spin state. However, the correlations are in general not purely classical, we also present specific input states with maximal spatial-spin entanglement after the ring. 相似文献
157.
Occupational airway diseases are now receiving attention in industry, although study is hampered by a lack of readily-available data. The interpretation of the data that is available, and also of the root problems themselves, is itself a difficult problem. This paper has been written as a literature review which it is hoped that other researchers can take either as a starting point or as a refresher. 相似文献
158.
Evaluating and monitoring nucleation and growth in copper foil 总被引:1,自引:0,他引:1
Ye-Kun Lee Thomas J. O’Keefe 《JOM Journal of the Minerals, Metals and Materials Society》2002,54(4):37-41
The electrodeposition of copper foil for use in electronic materials applications is a complex and demanding process. The
specific aspects of producing and controlling the structure-property-performance requirements of the foil are important because
of the stringent demands placed on their use in printed circuit boards and similar products. In this paper, a brief review
of the electrodeposition process for raw copper foil is presented. Since electrolyte additives play such a significant role
in the copper-depositionprocess, the effects of two essential additives, chloride ion and an organic (e.g., glue or gelatine),
on the foil are described. Also, the influence of other operating parameters on the initial nucleation, growth, and subsequent
electrocrystallization are discussed. Selected characterization methods, such as polarization and scanning electron micrography
techniques, are described as a means of monitoring the process, but universally accepted methods of evaluating and controlling
the additives and foil quality during electrolysis are still being sought. 相似文献
159.
Tsujimura T. Tokuhiro O. Morooka M. Miyamoto T. Miwa K. Yoshimura Y. Andry P. Libsch F. 《Electron Devices, IEEE Transactions on》2002,49(4):576-583
The leakage mechanism for a top-gate thin-film transistor (TFT) produced using the fewest process steps in the industry is analyzed in order to achieve a high-contrast liquid crystal display (LCD). Using a T-shaped TFT structure, the OFF and ON channel lengths are defined independently, so that the leakage can be reduced with no ON current decrease 相似文献
160.