全文获取类型
收费全文 | 347039篇 |
免费 | 3541篇 |
国内免费 | 797篇 |
专业分类
电工技术 | 6322篇 |
综合类 | 238篇 |
化学工业 | 50094篇 |
金属工艺 | 15835篇 |
机械仪表 | 10692篇 |
建筑科学 | 6794篇 |
矿业工程 | 2491篇 |
能源动力 | 7065篇 |
轻工业 | 22104篇 |
水利工程 | 4227篇 |
石油天然气 | 10503篇 |
武器工业 | 19篇 |
无线电 | 39778篇 |
一般工业技术 | 71900篇 |
冶金工业 | 69415篇 |
原子能技术 | 9834篇 |
自动化技术 | 24066篇 |
出版年
2021年 | 2658篇 |
2019年 | 2687篇 |
2018年 | 4797篇 |
2017年 | 4869篇 |
2016年 | 5191篇 |
2015年 | 3013篇 |
2014年 | 5273篇 |
2013年 | 13652篇 |
2012年 | 8273篇 |
2011年 | 10903篇 |
2010年 | 8868篇 |
2009年 | 10117篇 |
2008年 | 10547篇 |
2007年 | 10490篇 |
2006年 | 9309篇 |
2005年 | 8672篇 |
2004年 | 8462篇 |
2003年 | 8186篇 |
2002年 | 7941篇 |
2001年 | 8346篇 |
2000年 | 7852篇 |
1999年 | 8241篇 |
1998年 | 21441篇 |
1997年 | 14723篇 |
1996年 | 11189篇 |
1995年 | 8308篇 |
1994年 | 7237篇 |
1993年 | 7351篇 |
1992年 | 5354篇 |
1991年 | 5253篇 |
1990年 | 5305篇 |
1989年 | 5075篇 |
1988年 | 4819篇 |
1987年 | 4178篇 |
1986年 | 4288篇 |
1985年 | 4619篇 |
1984年 | 4250篇 |
1983年 | 3958篇 |
1982年 | 3680篇 |
1981年 | 3979篇 |
1980年 | 3646篇 |
1979年 | 3734篇 |
1978年 | 3845篇 |
1977年 | 4199篇 |
1976年 | 5514篇 |
1975年 | 3474篇 |
1974年 | 3458篇 |
1973年 | 3462篇 |
1972年 | 3081篇 |
1971年 | 2699篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
The results of the analysis of variations in the radiative recombination coefficient with varying doping level and concentration of excess electron-hole pairs are reported. It is shown that, along with the effect of narrowing of the band gap calculated in the many-electron approximation, the effect of screening of the Coulomb interaction responsible for the decrease in the excition binding energy should be taken into account. Both effects produce similar trends and decrease the radiative recombination coefficient with increasing levels of doping or injection. The contributions of excitonic radiative recombination and band-to-band radiative recombination to the total radiative recombination coefficient are separated from each other. It is shown that, in the region of room temperature, both contributions are comparable, while at liquid-nitrogen temperature, the excitonic component dominates over the band-to-band component. The results obtained by refined calculations of the limiting value of the internal quantum yield of electroluminescence for the silicon diodes and p-i-n structures are presented. It is shown that the internal quantum yield of electroluminescence can be as high as 14%. However, this values sharply decreases with increasing surface recombination rate and decreasing lifetime of excess charge carriers in the bulk. 相似文献
962.
963.
A. P. Vasil’ev V. P. Vasyukhno M. E. Netecha V. L. Vysotskii R. I. Kalinin A. A. Sarkisov A. Yu. Kazennov Yu. V. Sivintsev A. M. Chernyaev 《Atomic Energy》2006,101(1):506-511
The radioecological conditions which developed on the territory over the long operating time of the object of the naval fleet
in Guba Andreev are described. The results of an analysis of the sources of the real and potential danger and measures to
prevent dangerous effects for the environment and the workers at the time remediation work is performed are discussed.
__________
Translated from Atomnaya énergiya, Vol. 101, No. 1, pp. 49–55, July, 2006. 相似文献
964.
M. I. Surin V. E. Keilin S. M. Miklyaev S. A. Shevchenko 《Instruments and Experimental Techniques》2008,51(4):634-637
Within the framework of the “International Thermonuclear Experimental Reactor” (ITER) program, a prototype of a superconducting magnet for a 170-GHz gyrotron has been developed, manufactured, and tested. The operating induction value (7.1 T at the center of a 219-mm-diameter cold hole and 8.1 T on the winding) is reached at a current of 185.2 A. In the final version of the magnet, the required induction value was reached without aging. Special requirements are imposed on the distribution of the magnetic field along the axis, including an abrupt field decrease on both sides of the magnet. Axial forces are additionally taken by a special device. The magnet’s sections are wound with multifiber conductors based on niobium-tin and niobium-titanium alloys. Seventeen resistive shunts are provided for protecting sections during their transition to the normal state. The magnet is equipped with a device for removing a part of energy from the sections. Mechanical stresses in the magnet’s sections and the structure’s power elements have been measured during tests. 相似文献
965.
M. E. Borodyanskii I. M. Borodyanskii T. A. Martyshchenko 《Instruments and Experimental Techniques》2008,51(3):392-395
A device for measuring the active resistance of a direct current energized circuit section is described. Owing to the use of up-to-date electronic components, an iteration measurement algorithm, and a sinusoidal signal as a test one, the following performance characteristics have been obtained: the measurement time is <1 s, and the error varies from 0.3 to 2.0% in a 100-Ω to 1-MΩ range and ≤25% in 10-to 100-Ω and 1-to 10-MΩ ranges. 相似文献
966.
E. M. Zobov M. E. Zobov F. S. Gabibov I. K. Kamilov F. I. Manyakhin E. K. Naimi 《Semiconductors》2008,42(3):277-280
The results of the effect of ultrasonic treatment of ZnSe crystals on the structure of the energy spectrum of electronic states of centers with deep levels forming photoelectric and luminescent properties of this compound are presented. It is for the first time proved experimentally that the climb of edge dislocations under the effect of ultrasound leads to regrouping and generation of defects forming deep levels, which manifest themselves in phenomena of photosensitivity and radiative recombination. 相似文献
967.
V. F. Ivanov A. A. Nekrasov K. V. Tcheberiako A. V. Vannikov A. S. Posed'ko S. I. Lishik Yu. V. Trofimov 《Journal of the Society for Information Display》2003,11(1):11-14
Abstract— An all solid‐state photoelectrochromic element (PECE) was developed on the basis of electrochromic layers of WO3 and polyaniline with a layer of polymer electrolyte placed on a base of polyamidosulfoacid, in which a thin‐film CdSxSe1?x photoresistor was used as an electronic key. The dependence of the sensitometric characteristics of the PECE on the applied voltage was studied. 相似文献
968.
Polyacrylate gels containing Ag+ and TiO2 nanoparticles are shown to swell under UV light and shrink under visible light in water. In work reported by Tetsu Tatsuma and co‐workers on p. 1249, the TiO2 absorbs UV light and reduces the Ag+, whereas the deposited Ag absorbs visible light and dissolves itself. These redox reactions change the interactions between the polymer chains and eventually the volume of the gel, as shown on the cover. 相似文献
969.
Viktor G. Khizhnyak Vitalii I. Korol' Alexei D. Kostenko 《Powder Metallurgy and Metal Ceramics》2003,42(11-12):644-648
Wear resistance measurements have been made with U8A steel bearing protective coatings based on the carbides of titanium, vanadium, and chromium or iron borides, for various forms of wear. The carbide and boride coatings raise the wear resistance considerably (by factors of 6-30 in accordance with the type of wear). Measurements have been made on the microhardness, microbrittleness, and adhesion of the coating to the substrate, which are effective characteristics that quite fully reflect the effects of the microhardness and state of stress, structure, and defectiveness on the wear resistance. 相似文献
970.
In this time of flat, team-based and technology-enabled organizations the effectiveness of communication and team leadership practices will be more important than ever before. Therefore, we believe that some of the earlier, time-tested classic works on group dynamics and leadership are worthy of re-reading. We are particularly impressed by how relevant one of the oldest classics, Benne and Sheats' (1948) article on functional roles of group members, remains to this day. 相似文献