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   60968篇
  免费   6193篇
  国内免费   3362篇
电工技术   4094篇
技术理论   2篇
综合类   4494篇
化学工业   9440篇
金属工艺   3702篇
机械仪表   4264篇
建筑科学   5096篇
矿业工程   1882篇
能源动力   1636篇
轻工业   4242篇
水利工程   1389篇
石油天然气   3114篇
武器工业   619篇
无线电   7586篇
一般工业技术   6734篇
冶金工业   2892篇
原子能技术   717篇
自动化技术   8620篇
  2024年   297篇
  2023年   1141篇
  2022年   2205篇
  2021年   2934篇
  2020年   2229篇
  2019年   1751篇
  2018年   1828篇
  2017年   2203篇
  2016年   1939篇
  2015年   2851篇
  2014年   3488篇
  2013年   4132篇
  2012年   4393篇
  2011年   4887篇
  2010年   4278篇
  2009年   4160篇
  2008年   4074篇
  2007年   3596篇
  2006年   3302篇
  2005年   2654篇
  2004年   1700篇
  2003年   1355篇
  2002年   1273篇
  2001年   1155篇
  2000年   979篇
  1999年   981篇
  1998年   870篇
  1997年   703篇
  1996年   650篇
  1995年   566篇
  1994年   451篇
  1993年   365篇
  1992年   241篇
  1991年   217篇
  1990年   147篇
  1989年   120篇
  1988年   96篇
  1987年   59篇
  1986年   54篇
  1985年   33篇
  1984年   23篇
  1983年   27篇
  1982年   22篇
  1981年   16篇
  1980年   21篇
  1979年   12篇
  1977年   7篇
  1976年   7篇
  1975年   4篇
  1951年   6篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
141.
除沫器自动冲洗装置的设计及应用   总被引:1,自引:0,他引:1  
本文针对Ⅰ效二次蒸汽折流板式除沫器需定时冲洗的实际情况,设计了一套冲洗间隔灵活可调的自动冲洗装置,该装置结构简单、工作可靠,易于实现,有一定的实用价值。  相似文献   
142.
143.
LY-8602系列催化剂的失活原因及对策   总被引:2,自引:0,他引:2  
通过催化剂的评价及表征,对LY-8602系列催化剂在低硫裂解汽油加氢时的失活原因进行了研究,结果表明,其活性下降主要是催化剂的活性中心相Co-Mo-s遭到破坏,使催化剂表面的具有加氢活性的Mo^4 峰减小所致。采用新研制的高活性加氢催化剂LY-9702与LY-8602构成复合床催化剂,可以使加氢产品合格。  相似文献   
144.
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   
145.
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   
146.
We describe an optically modulated scatterer as an electric-field probe for measuring radio-frequency and microwave fields. It has a high spatial resolution and the ability to operate very close to conducting and dielectric objects without appreciable distortion of the field to be measured. Thus, it can scan close to antennas and diffracting metal structures. We describe how the electric field is deduced from the measurements and present gain measurements and far-field patterns deduced from near-field scans of antennas. The results are tested by comparing them with those obtained by established measurement techniques  相似文献   
147.
东海西湖凹陷探井钻井完井液技术   总被引:2,自引:2,他引:0  
介绍了东海西湖凹陷的储层特征。在分析探井储层损害原因的基础上,提出了优化的海水钻井完井液体系。两口井应用表明,储层保护效果明显。  相似文献   
148.
梁炳权 《建筑技术》1996,23(10):687-690
叙述我国中小型建筑构件厂最常用的预应力长线台座的建造过程,以及必须注意的事项及质量控制方法。  相似文献   
149.
水保种草有山地治理、改土开发、松林改造、封禁培育四种类型,是水土保持主要植物措施之一,见效快,效果好,效益显著。要提高认识,建立基地。做好草的转化利用.  相似文献   
150.
Responsiveness, the ability to detect meaningful clinical change, is a critical attribute of instruments used to evaluate outcomes of treatments. The authors hypothesized that self-administered symptom severity and functional status questionnaires are more responsive to clinical improvement after carpal tunnel release than traditional physical examination measures of strength and sensibility. Data were obtained from a randomized clinical trial of endoscopic versus open carpal tunnel release conducted in four university medical centers. Patients were evaluated before surgery and 3 months after surgery. Seventy-four patients indicating that they were more than 80% satisfied with the results of surgery were assumed to have clinically meaningful improvement and were the focus of the analysis. Evaluations included questionnaires assessing symptom severity, functional status, and activities of daily living as well as measurement of grip, pinch, and abductor pollicus brevis strength, and 2-point discrimination and Semmes-Weinstein pressure sensibility. Responsiveness was calculated with the standardized response mean (mean change/standard deviation of change) as well as the effect size (mean change/standard deviation of baseline values). The symptom severity scale was four times as responsive, and the functional status and activities of daily living scales were twice as responsive, as the measures of strength and sensibility. Self-administered symptom severity and functional status scales are much more responsive to clinical improvement than measures of neuromuscular impairment and should severe as primary outcomes in clinical studies of therapy for carpal tunnel syndrome.  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