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   69183篇
  免费   6871篇
  国内免费   3698篇
电工技术   4642篇
技术理论   2篇
综合类   4982篇
化学工业   10888篇
金属工艺   4105篇
机械仪表   4718篇
建筑科学   5619篇
矿业工程   2060篇
能源动力   1967篇
轻工业   5027篇
水利工程   1529篇
石油天然气   3462篇
武器工业   683篇
无线电   8633篇
一般工业技术   7941篇
冶金工业   3010篇
原子能技术   827篇
自动化技术   9657篇
  2024年   318篇
  2023年   1246篇
  2022年   2427篇
  2021年   3256篇
  2020年   2479篇
  2019年   1997篇
  2018年   2068篇
  2017年   2471篇
  2016年   2234篇
  2015年   3153篇
  2014年   3970篇
  2013年   4663篇
  2012年   4943篇
  2011年   5540篇
  2010年   4862篇
  2009年   4656篇
  2008年   4566篇
  2007年   4056篇
  2006年   3688篇
  2005年   3059篇
  2004年   1967篇
  2003年   1618篇
  2002年   1559篇
  2001年   1426篇
  2000年   1168篇
  1999年   1134篇
  1998年   917篇
  1997年   763篇
  1996年   686篇
  1995年   639篇
  1994年   506篇
  1993年   404篇
  1992年   282篇
  1991年   240篇
  1990年   168篇
  1989年   138篇
  1988年   108篇
  1987年   64篇
  1986年   56篇
  1985年   37篇
  1984年   33篇
  1983年   36篇
  1982年   28篇
  1981年   28篇
  1980年   26篇
  1979年   14篇
  1976年   6篇
  1975年   5篇
  1972年   5篇
  1951年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
脉冲电镀最佳参数之探索和优化   总被引:3,自引:0,他引:3  
本文利用正交实验法对脉冲电镀各控制参数进行试验,对影响分散能力、镀层可靠性及外观质量的各种因素进行探讨,寻找影响外观质量的显著因子并加以控制,同时进一步优化脉冲电镀的工艺参数。  相似文献   
12.
A new integrated magnetic full wave DC/DC power converter that provides flexible transformer design by incorporating an independent output inductor winding is introduced. The transformer is implemented on a traditional three-leg magnetic core. The inductor winding can be separately designed to control the output current ripple. The cross-sectional area of the inductor core leg can be reduced dramatically. The operation and performance of the proposed circuit are verified on a 100 W prototype converter.  相似文献   
13.
文中严格地讨论了任意截面形状,任意模式的柱形谐振腔Q值与构成该谐振器的传输线衰减常数间的关系,给出了更一般的公式,推广了Davidson和Sim-monds^[1]、Barlow和Cullen^[2]以及Yeh和Shimabukuro^[3,4]的结果。  相似文献   
14.
本文涉及玻璃钢猎扫雷艇艇体材料的优选、铺层设计和工艺等内容。试验确定了以1629间苯聚酯树脂为基体、以900g/m2无碱无捻粗纱短切毡(M)和810g/m2无碱无捻粗纱方格布(R)为增强体以及(M+R)为基本铺层设计单元的方案。试验表明,按上述材料和铺层制作的层板,性能达到Lerici和MHC-51艇壳层板的指标要求。  相似文献   
15.
本文对动、静态下混凝土坍落度损失的规律进行了研究,并从流变学的角度分析了外加剂对动、静态下混凝土坍落度损失的影响坍落度损失存在差别的原因.  相似文献   
16.
This paper presents a method for multi-area power system total transfer capability (TTC) computation. This computation takes into account the limits on the line flows, bus voltage magnitude, generator reactive power, voltage stability, as well as the loss of line contingencies. The multi-area TTC problem is solved by using a network decomposition approach based on REI-type network equivalents. Each area uses REI equivalents of external areas to compute its TTC via the continuation power flow (CPF). The choice and updating procedure for the continuation parameter employed by the CPF is implemented in a distributed but coordinated manner. The proposed method leads to potential gains in the computational efficiency with limited data exchanges between areas. The developed procedure is successfully applied to the three-area IEEE 118-bus test system. Numerical comparisons between the integrated and the proposed multi-area solutions are presented for validation.  相似文献   
17.
18.
Four monoalkyl esters of isoalkylphosphonic acids have been studied for the chromatographic separation ofrare earths (RE).The relationship between distribution ratios and acid concentration of the eluants forsamarium and ytterbium has been explored.The characteristics of these extractants loaded onto macroreticularpoly (methyl methacrylate) resin beads for the separation of lanthanum,cerium,praseodymium and neodymiumhave been compared.Among the extractants studied,mono(1-methylheptyl) ester of isooctylphosphonic acidwas found to be the best for RE separation.The acidity for separation is lower than any known P-containingextractants for the same purpose.For instance,with 1.73 mol·L~(-1) nitric acid as eluent,thulium,ytterbium andlutetium can be separated quantitatively.The extractant-loaded resins possess high column efficiency with goodkinetic characteristics.The extraction mechanism was also explored.  相似文献   
19.
The previous discrete-model-based stability analysis of regional and national voting has been extended to a continuous-model-based analysis in the simultaneous presence of white and concentrated components of noise, reconfirming the previous conclusion that regional voting with smaller sized regions always demonstrates an improved stability over those with larger sized regions, including the national voting in its limiting case in particular. The conclusion remains valid as long as the weak distribution assumption is valid.  相似文献   
20.
A stability-indicating reversed-phase high performance liquid chromatographic method was developed for the detection of mitoxantrone HC1 and its degradation products under accelerated degradation conditions. The degradation kinetics of mitoxantrone HC1 in aqueous solution over a pH range of 1.18 to 7.20 and its stability in propylene glycol-or polyethylene glycol 400-based solutions were investigated. The observed rate constants were shown to follow apparent first-order kinetics in all cases. The pH-rate profile shows that maximum stability of mitoxantrone HC1 was obtained at pH 4.01. No general acid or base catalysis from acetate or phosphate buffer species was observed. The catalysis rate constants on the protonated mitoxantrone imposed by hydrogen ion water and hydroxy ion were determined to be 3.72 × 10 min-1 5.64 × 10-min-1 and 1.108 × 10-2min-1, respectively. The degradation rate constants of mitoxantrone affected by different ionic strength systems. Irradiation with 254 nm UV light at 25±0.5°C was found when canpared with the light-protected controls. Incorporation of nonaqueous propylene glycol or polyethylene glycol in the pH 4.01 mitoxantrone solution shows an increase in its stability at 502±0.5°C.  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