首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   250420篇
  免费   1747篇
  国内免费   268篇
电工技术   4062篇
综合类   92篇
化学工业   40714篇
金属工艺   15162篇
机械仪表   10092篇
建筑科学   4223篇
矿业工程   3765篇
能源动力   3918篇
轻工业   9815篇
水利工程   4098篇
石油天然气   13016篇
武器工业   28篇
无线电   20305篇
一般工业技术   63005篇
冶金工业   32302篇
原子能技术   11162篇
自动化技术   16676篇
  2021年   2796篇
  2019年   2775篇
  2018年   5474篇
  2017年   5756篇
  2016年   6100篇
  2015年   3096篇
  2014年   5375篇
  2013年   10193篇
  2012年   7390篇
  2011年   9018篇
  2010年   7351篇
  2009年   8179篇
  2008年   8236篇
  2007年   7903篇
  2006年   6400篇
  2005年   5607篇
  2004年   5513篇
  2003年   5329篇
  2002年   5163篇
  2001年   4969篇
  2000年   4949篇
  1999年   4262篇
  1998年   7200篇
  1997年   5845篇
  1996年   4440篇
  1995年   3670篇
  1994年   3440篇
  1993年   3634篇
  1992年   3224篇
  1991年   3364篇
  1990年   3484篇
  1989年   3377篇
  1988年   3277篇
  1987年   3268篇
  1986年   3161篇
  1985年   3320篇
  1984年   3261篇
  1983年   3150篇
  1982年   3004篇
  1981年   3051篇
  1980年   3076篇
  1979年   3263篇
  1978年   3497篇
  1977年   3467篇
  1976年   3920篇
  1975年   3217篇
  1974年   3303篇
  1973年   3347篇
  1972年   2991篇
  1971年   2763篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
991.
Problems of Information Transmission - A new problem of transmitting information over the adversarial insertion-deletion channel with feedback is introduced. Assume that the encoder transmits $$n$$...  相似文献   
992.
The field and temperature dependence of the transverse magnetoresistivity and the Hall coefficient for single-crystal tungsten with a resistivity ratio 293K/4.2K varying from 780 to 80800 are measured at temperatures between 4.2 K and 50 K in magnetic fields up to 150 kOe. The role of the static skin effect and the temperature breakdown in the galvanomagnetic properties of the compensated metals is evaluated through experiments with tungsten. The experimental data shows that the galvanomagnetic properties of the compensated metals in the high magnetic fields are not dependent only on the Fermi surface geometry. A substantial role in their formation is played by the processes of the electron-surface and the intersheet electron-phonon scatterings.  相似文献   
993.
Direct data have been obtained for the creep of high- and medium-strength aluminum alloys in the stress range of O.6–1.2 of the nominal yield strength 0.2 in laboratory air and in aqueous NaCl solution at room temperature. On this basis using known theories approximating functions have been determined for the creep curves. Stress 0.2 serves as a natural boundary for the macroelastic and macroplastic regions in the first of which creep is only transient, and in the second there are transient, quasisteady-state, and accelerated stages. Extrapolated estimates of creep strain in the macroelastic region from data measured in the macroplastic region are not physically competent. However, a tendency towards an increase in ductility with an increase in time to failure at stresses greater than o.2 makes it possible to estimate by extrapolation the time for onset of the accelerated creep stage with low test stresses from measured values at greater stresses in the macroplastic region. Fractographic and strain indices revealed the harmful effect of moist atmospheres on the deformation and failure resistance of alloys with prolonged loading.Translated from Problemy Prochnosti, No. 1, pp. 50–58, January, 1990.  相似文献   
994.
The article presents results of a study of the strengthening of threaded connections M6 and M8 of alloys ÉI698, VT16, and VTZ-1 by thermovibration treatment to raise their creep resistance. Treatment regimes and empirical formulas for determining the index of strengthening (for the ÉI698 alloy) are discussed. Data on long-term strength of threaded connections in initial and post-treatment states, and on the effect of aging on retention of the strengthening effect, are presented along with some mechanical and fatigue characteristics.Translated from Problemy Prochnosti, No. 9, pp. 98–103, September, 1990.  相似文献   
995.
The article presents the results of the investigation of the mechanical properties and microinhomogeneity of deformation of steel in dependence on its structure. A dependence of the characteristics of ductility and of impact toughness on the level of the microinhomogeneity of deformation is established. The change of ultimate (tensile) strength u corresponds to the change of microhardness which serves as indirect characteristic of the strength properties of microvolumes. It is shown that impact toughness is a characteristic sensitive to the manifestation of microinhomogeneity of deformation, and that it changes in dependence on its level more than the static characteristics. The obtained results make it possible to choose the optimal structure of the metal.Translated from Problemy Prochnosti, No. 1, pp. 120–122, January, 1990.  相似文献   
996.
1.  The algorithm for the integration of the reactor kinetics equations, based on Gear's numerical methods, provides an efficient means of calculating critical-assembly accidents, in which the assembly rapidly goes into prompt-neutron supercriticality and then slowly cools down.
2.  The maximum temperature in the assembly zones, and the energy released during the burst, are not appreciably affected by the positive reactivity insertion rate.
3.  Accident damage is significantly reduced (the assembly remains operational) only in cases of rapid scram-rod dumping (0.3 sec delay), provided the temperature coefficient of reactivity equals or exceeds the rated value.
Translated from Atomnaya énergiya, Vol. 69, No. 1, pp. 47–49, July, 1990.  相似文献   
997.
Translated from Poroshkovaya Metallurgiya, No. 8(332), pp. 6–9, August, 1990.  相似文献   
998.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 32–35, February, 1990.  相似文献   
999.
1000.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 5, pp. 17–20, May, 1990.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号