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   40340篇
  免费   3325篇
  国内免费   1582篇
电工技术   3315篇
技术理论   2篇
综合类   3552篇
化学工业   3591篇
金属工艺   961篇
机械仪表   1953篇
建筑科学   7381篇
矿业工程   1466篇
能源动力   1460篇
轻工业   6380篇
水利工程   1811篇
石油天然气   1494篇
武器工业   313篇
无线电   1914篇
一般工业技术   3762篇
冶金工业   2426篇
原子能技术   496篇
自动化技术   2970篇
  2024年   198篇
  2023年   632篇
  2022年   1463篇
  2021年   1511篇
  2020年   1577篇
  2019年   1257篇
  2018年   1203篇
  2017年   1411篇
  2016年   1578篇
  2015年   1642篇
  2014年   3278篇
  2013年   2665篇
  2012年   3327篇
  2011年   3521篇
  2010年   2559篇
  2009年   2397篇
  2008年   1928篇
  2007年   2195篇
  2006年   1910篇
  2005年   1564篇
  2004年   1274篇
  2003年   1125篇
  2002年   879篇
  2001年   738篇
  2000年   572篇
  1999年   481篇
  1998年   390篇
  1997年   296篇
  1996年   228篇
  1995年   220篇
  1994年   175篇
  1993年   140篇
  1992年   132篇
  1991年   94篇
  1990年   86篇
  1989年   63篇
  1988年   61篇
  1987年   44篇
  1986年   31篇
  1985年   35篇
  1984年   30篇
  1983年   18篇
  1982年   24篇
  1980年   25篇
  1979年   26篇
  1965年   18篇
  1964年   23篇
  1963年   18篇
  1958年   16篇
  1957年   19篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
31.
A centrifugal partition chromatograph (CPC) was used as a liquid-liquid catalytic reactor for the isomerisation of hexen-3-ol into ethylpropylketone with a water soluble rhodium catalyst. Global mass transfer coefficients were measured and shown to depend on both the nature of the solute and the flow rate. Liquid-liquid partition isotherms were also determined with the CPC using elution chromatography. Finally, a reactor model was derived to account for the experimental results obtained both under stationary and transient (pulse) conditions. A parameter sensitivity evaluation is also presented.  相似文献   
32.
蒋大军 《烧结球团》1997,22(1):4-10
阐述了钒钛磁铁精矿的矿石特点,烧结特性及其与烧结矿质量之间的关系,并提出了强化烧结的措施。  相似文献   
33.
The paper addresses the design of two-level power system stabilizers using an optimal reduced order model whose state variables are torque angles and speeds. The reduced order model retains their physical meaning and is used to design a two-level linear feedback controller that takes into account the realities and constraints of electrical power systems. The two-level control strategy is used, and a global control signal is generated from the output variables to minimize the effect of interactions. The effectiveness of this controller is evaluated and a multimachine system is given as an example to illustrate the advantages of the proposed method. Responses of the system with a two-level scheme and an optimal reduced order scheme are included for comparative analysis.  相似文献   
34.
Learning a sequence of target locations when the sequence is uncorrelated with a sequence of responses and target location is not the response dimension (pure perceptual-based sequence learning) was examined. Using probabilistic sequences of target locations, the author shows that such learning can be implicit, is unaffected by distance between target locations, and is mostly limited to first-order transition probabilities. Moreover, the mechanism underlying learning affords processing of information at anticipated target locations and appears to be attention based. Implications for hypotheses of implicit sequence learning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
35.
小儿的心理状态与成人有着明显的差异,在其住院和接受医疗期间可出现严重的心理反应,导致植物神经功能紊乱,使机体低抗力下降,而削弱机体对麻药的耐受力,不利于麻醉诱导及管理,而且还会造成小儿的精神创伤。文章初步探讨了小儿麻醉心理学的有关问题。  相似文献   
36.
In a series of 10-day pair feeding experiments it was found that the nutritional value of diets containing beans was essentially the same for rats aged between 30 and 123 days. Thus net protein utilisation (NPU) values of 25–39 on diets containing Processor bean (35 g protein kg?1) + egg albumin (65g protein kg?1) were obtained. As food intakes were considerably reduced when rats were fed diets containing more than 35g protein kg?1 of Processor bean, the measurement of protein utilisation became increasingly more difficult. The severe disruption of the brush borders of duodenal and jejunal enterocytes, originally observed when bean-containing diets were fed to young (30-day-old) rats was also found with rats up to the age of 120 days on similar diets. Similarly, the development of circulating anti-lectin antibodies in the animals showed no age dependence within the age limits investigated. It was also shown that oral immunisation did not protect the rats from the effects of toxicity and that the immune response was a result of continuous absorption of lectin throughout the feeding period. Thus the extent and the mechanism of toxicity of Phaseolus vulgaris bean lectins were found not to be dependent on the age or maturity of the animal.  相似文献   
37.
Levels of benzaldehyde recovered from virginPseudaletia unipuncta (Haw.) males were not influenced by (1) the time hairpencils remained in the solvent (1-72 hr), (2) anesthetization or agitation of males prior to excision of hairpencils, or (3) the time (photophase or scotophase) that hairpencils were excised. Thus the interindividual variability observed is not a methodological artifact. Most males had similar concentrations in both hairpencils, although in some cases only one hairpencil contained pheromone. In one case, a male with partially extruded hairpencils had no benzaldehyde at all. Neither pupal weight nor hairpencil length proved to be reliable indicators of pheromone content.Contribution No. 373, Département de biologie, Université Laval.  相似文献   
38.
二维介质PBG结构的工程设计   总被引:7,自引:7,他引:0  
针对介质材料中按二维菱形周期排列空气圆孔的PBG结构,采用平面波展开法结合迭代技术的理论分析程序,对结构尺寸与介质参数的不同组合进行了批量计算,根据对计算结果的分析,归纳出阻带范围与结构参数之间的函数关系,经数据拟合得出一组准确而快捷的工程设计公式,还给出了根据预期的阻带范围设计PBG结构参数的简明步骤,实例验证了该组公式的实用性。  相似文献   
39.
本文对矩形光脉冲光电响应后沿拖曳的形成机制进行了详尽的实验研究和理论分析,认为形成该光电响应时滞后曳的主要根源在于光生电子与空穴的多声子慢态复合.我们给出了削减后沿拖曳、提高光电响应速度的有效措施,从而促进解决宽带光通讯的速度瓶颈问题.  相似文献   
40.
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