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   208291篇
  免费   2309篇
  国内免费   597篇
电工技术   3539篇
综合类   155篇
化学工业   32336篇
金属工艺   10316篇
机械仪表   7057篇
建筑科学   4079篇
矿业工程   2166篇
能源动力   4682篇
轻工业   13088篇
水利工程   2940篇
石油天然气   7730篇
武器工业   22篇
无线电   21721篇
一般工业技术   45556篇
冶金工业   34525篇
原子能技术   6632篇
自动化技术   14653篇
  2021年   2116篇
  2019年   2027篇
  2018年   3755篇
  2017年   3803篇
  2016年   4110篇
  2015年   2307篇
  2014年   3882篇
  2013年   8894篇
  2012年   5844篇
  2011年   7340篇
  2010年   5987篇
  2009年   6610篇
  2008年   6744篇
  2007年   6599篇
  2006年   5678篇
  2005年   5195篇
  2004年   4704篇
  2003年   4613篇
  2002年   4420篇
  2001年   4502篇
  2000年   4204篇
  1999年   4228篇
  1998年   10220篇
  1997年   7216篇
  1996年   5521篇
  1995年   4148篇
  1994年   3612篇
  1993年   3850篇
  1992年   2990篇
  1991年   3001篇
  1990年   2897篇
  1989年   2857篇
  1988年   2871篇
  1987年   2514篇
  1986年   2577篇
  1985年   2859篇
  1984年   2697篇
  1983年   2561篇
  1982年   2307篇
  1981年   2280篇
  1980年   2357篇
  1979年   2362篇
  1978年   2388篇
  1977年   2494篇
  1976年   2882篇
  1975年   2192篇
  1974年   2070篇
  1973年   2169篇
  1972年   1941篇
  1971年   1756篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
111.
The effect of the composition of sensitizing–activating solutions on the activation efficiency and the chemical coppering of diamond powders is studied. The results demonstrate that stabilizing additives improve the stability of the solutions, influence the average coppering rate, and play a key role in determining the morphology and quality of the resultant coatings. The most effective stabilizing additive is synthamid-10, which ensures the deposition of high-quality copper coatings.  相似文献   
112.
The structure and mechanical properties of nanocrystalline aluminum alloy 1570 obtained by means of severe plastic deformation have been studied. Being tested in a temperature range from 300 to 400°C, the alloy exhibits high-strain-rate superplasticity. At 400°C, the superplasticity is manifested in a very broad range of strain rates, extending from 5 × 10?3 to 1 s?1.  相似文献   
113.
114.
115.
The biochemical composition can be seen as a good indicator of both the biodegradability and the methane potential of a given waste. The work presented here is an attempt to elaborate a typology of wastes and to compare it to the anaerobic degradation characteristics. The first data indicate that there is a link between the ligno-cellulosic content of the waste and the biodegradability. When dealing with application to anaerobic digestion processes, having a tool to predict the ability of the waste to be degraded could be of the greatest interest for preventing failures, estimating biogas production, methane content, or for the management of co-digestion processes.  相似文献   
116.
A combination of concept (the product portfolio and the product life cycle) and empirical research (the PIMS study) can aid in clarifying the key issues involved in the selection of a firm's core strategies. Strategy control is multistage: periodic re-evaluation of strategy alternatives by use of the marketing audit; an analytical framework for control of chosen strategies by breaking down components and reporting their performance variances; and 'marketing segment' analysis for control of the detailed marketing plan.?  相似文献   
117.
In the present work 316LN as well as 316 stainless steel (SS) coupons each of dimensions (0.025 × 0.018 × 0.006 m3) in well-polished condition were used as two nominal electrodes which were immersed in the aerated solution of 0.5 M NaCl. Correlated current and potential electrochemical noise (EN) signals were collected at 1 Hz sampling frequency for 1 h daily over a period of 30 days. The detrended EN data were used to calculate the noise resistance (R N) as well as the spectral noise resistance at zero frequency (R SNo) values and other statistical parameters. To study the nature of pits and distribution of their diameters as well as depths, extensive observations of the pitted and the blank specimens were carried out using Confocal Laser Scanning Microscopy (CLSM). The current and the potential records of the two alloys showed distinct differences in their corrosion behavior. It was observed that within less than 4 h of immersion, 316SS showed signals indicative of unstable pitting and onset of stable pitting was noticed after 48 h of exposure. However, until about 24 h, 316LN showed just the random signals and unstable pitting was observed after 28 h. The signals clearly indicated continuous growth of the stable pits in 316SS as against the repassivation of the unstable pits in 316LN after 7 days exposure. It was observed that R N values showed a continuous decrease in the case of 316SS, but were quite stable in the case of 316LN over the exposure period. Concurrent to these observations it was observed that 316SS specimen was extensively pitted. The frequency distributions of pit diameters as well pit depths were observed to be highest at 10-20 μm and 5-10 μm, respectively. However, pits with as large as 70-80 μm diameter and as deep as 20-25 μm too were observed. No pits were observed in case of 316LN even after 30 days of exposure, an observation that corroborates well with the stable R N values. Thus, in the present investigation, the long-term tests using EN technique coupled with CLSM studies conclusively prove that many unstable pits initiated in 316SS turn into stable ones resulting in insidious localized corrosion attack whereas the unstable pits initiated in 316LN get passivated in the simulated coastal environment.  相似文献   
118.
Filled fibrous sorbents modified with transition metal ferro- and ferricyanides capable to recover americium(III) and rare-earth metals(III) from nitric acid solutions were prepared. The most complete and rapid recovery is attained on complex-forming and cation-exchange sorbents (as filled fibrous materials) saturated with nickel ions. The sorbents are characterized by good kinetic properties and can be used for recovery of the above metals.  相似文献   
119.
Production methods used to prepare graphite crucibles with high operating properties are considered: use as a filler of good graphitizing acicular coke, vibration molding of the original coke mix, use of production cycles for impregnation with medium temperature coal-tar pitch — firing, firing of compacted billets in metal containers, graphitization of fired billets in graphite cylinders. The last two production methods make it possible to reduce the temperature drop throughout the volume of a billet during heat treatment, and as a consequence to reduce crack development to a minimum as a result of reducing thermal stresses. All of the production methods recommended may be entirely accomplished in existing electrode plants and may be used to increase markedly the quality crucible graphite. It is possible to achieve a quality for these materials at the best world level. Translated from Novye Ogneupory, No. 8, pp. 28–33, August 2008.  相似文献   
120.
Technology is developed for preparing refractory components made of partially stabilized zirconium dioxide using an isostatic compaction press. Technology is provided for manufacturing dispensing nozzles using combined and separately stabilized zirconium dioxide, and also indices of the refractories obtained and imported materials are compared. __________ Translated from Novye Ogneupory, No. 3, pp. 127–131, March 2008.  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