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   348419篇
  免费   2143篇
  国内免费   752篇
电工技术   5754篇
综合类   276篇
化学工业   52500篇
金属工艺   16353篇
机械仪表   11043篇
建筑科学   7542篇
矿业工程   2954篇
能源动力   7603篇
轻工业   24870篇
水利工程   4761篇
石油天然气   11386篇
武器工业   20篇
无线电   35787篇
一般工业技术   73045篇
冶金工业   61809篇
原子能技术   10595篇
自动化技术   25016篇
  2021年   3058篇
  2019年   3134篇
  2018年   5154篇
  2017年   5314篇
  2016年   5746篇
  2015年   3278篇
  2014年   5618篇
  2013年   14554篇
  2012年   8792篇
  2011年   11698篇
  2010年   9443篇
  2009年   10613篇
  2008年   10808篇
  2007年   10765篇
  2006年   9172篇
  2005年   8526篇
  2004年   8168篇
  2003年   7928篇
  2002年   7571篇
  2001年   7682篇
  2000年   7521篇
  1999年   7536篇
  1998年   17587篇
  1997年   12685篇
  1996年   9748篇
  1995年   7219篇
  1994年   6526篇
  1993年   6463篇
  1992年   5145篇
  1991年   5079篇
  1990年   4963篇
  1989年   4943篇
  1988年   4808篇
  1987年   4290篇
  1986年   4217篇
  1985年   4664篇
  1984年   4374篇
  1983年   4139篇
  1982年   3797篇
  1981年   4082篇
  1980年   3826篇
  1979年   4057篇
  1978年   4196篇
  1977年   4429篇
  1976年   5872篇
  1975年   3748篇
  1974年   3704篇
  1973年   3799篇
  1972年   3303篇
  1971年   2968篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
This article examines the history and future prospects of the production of iron powders by the atomizing high-carbon melts with compressed air. In terms of their properties, the iron powders obtained by this method are intermediate between water-atomized powders and reduced powders. They can be used to make anti-friction products or structural elements having a density within the range 6.3–6.9 g/cm3. The outlook for these powders is promising in Russia because they are needed for machine construction, especially in the auto industry.  相似文献   
993.
The DC and microwave properties of strained In0.65Ga 0.35As/In052Al0.48As HEMTs (high electron-mobility transistors) with double-heterojunction design are presented. The high sheet carrier density and good carrier confinement give rise to excellent device performance with very low output conductance. For 1×150-μm2 long-gate HEMTs, the measured cutoff frequency fT and maximum frequency of oscillation fmax are as high as 37 and 66 GHz, respectively  相似文献   
994.
Methods for cleaning commercial T-1500 dielectric oil with different adsorbents are studied. The oil is intended for impregnation of high-voltage pulse capacitors with film dielectric.  相似文献   
995.
The possibility of obtaining high laser output energies at a 1.32-μm wavelength using thin LiNdLa phosphate glass slabs with a high Nd3+ concentration is discussed. In the experiments, 3×14×125-mm slabs were prepared from LiNdLa phosphate glass with a Nd-concentration of 1.2×1021 cm-3. The facets of the slabs were not antireflection-coated. They were tested in a silver-coated quartz tube reflector of 25-mm diameter and pumped by 450-μs pulses from a flash lamp with a 120-mm arc length. In this construction the light, which passes through the slab, returns to it after reflection from the tube surface. Most of the radiation falls on the wider side of the slab at large angles of incidence, thus maximizing its path inside the slab. The quartz reflector was water cooled. The 150-mm laser resonator was formed by two flat mirrors. At 1.32-μm lasing wavelength an output mirror of r=95% reflectivity was used with less than 10% reflectivity at 1.32 μm  相似文献   
996.
997.
Whether tolerance develops to the "anorexia" induced by haloperidol (HAL) was determined. Rats were given HAL (2.5 or 5 mg/kg) either before or after access to milk for 53 days. Controls were given injections of saline. On Day 54, when all groups received pretest injections of the drug, only rats previously given posttest injections of HAL were tolerant. The absence of tolerance in rats previously given pretest injections suggests that tolerance is suppressed when rats are given access to food in the drugged state. It is concluded that tolerance develops to HAL as a result of pharmacological exposure but is suppressed by the "anhedonic" effect of the drug. The relevance of these findings to the role of reinforcement in behavioral tolerance is briefly discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
998.
999.
1000.
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