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   369861篇
  免费   5130篇
  国内免费   1014篇
电工技术   7502篇
综合类   1629篇
化学工业   58069篇
金属工艺   12915篇
机械仪表   11209篇
建筑科学   10413篇
矿业工程   1568篇
能源动力   9408篇
轻工业   34293篇
水利工程   3277篇
石油天然气   4915篇
武器工业   20篇
无线电   46622篇
一般工业技术   69146篇
冶金工业   64023篇
原子能技术   6028篇
自动化技术   34968篇
  2022年   4697篇
  2021年   6263篇
  2020年   4600篇
  2019年   5852篇
  2018年   5112篇
  2017年   4492篇
  2016年   4446篇
  2015年   3352篇
  2014年   5360篇
  2013年   16077篇
  2012年   8801篇
  2011年   12867篇
  2010年   9950篇
  2009年   11226篇
  2008年   11143篇
  2007年   11071篇
  2006年   9988篇
  2005年   9311篇
  2004年   10254篇
  2003年   9815篇
  2002年   9648篇
  2001年   9384篇
  2000年   8445篇
  1999年   8630篇
  1998年   18917篇
  1997年   13867篇
  1996年   10887篇
  1995年   8555篇
  1994年   7970篇
  1993年   7541篇
  1992年   5835篇
  1991年   5453篇
  1990年   5387篇
  1989年   5337篇
  1988年   5120篇
  1987年   4268篇
  1986年   4489篇
  1985年   5188篇
  1984年   4616篇
  1983年   4463篇
  1982年   3993篇
  1981年   4070篇
  1980年   3681篇
  1979年   3673篇
  1978年   3548篇
  1977年   4203篇
  1976年   5192篇
  1975年   3079篇
  1974年   2892篇
  1973年   2844篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations.  相似文献   
2.
Clean Technologies and Environmental Policy - Food production and consumption is one of the major causes of global environmental degradation. One way to address environmental impacts in the food...  相似文献   
3.
Journal of Communications Technology and Electronics - Abstract—The article presents a rigorous numerical solution, using the Wiener–Hopf method, to the problem of plane wave...  相似文献   
4.

Surface integrity characterization of manufactured component is very important as it significantly affects the in-service performance of the component. Till now, surface integrity was evaluated using conventional measurement technique like microhardness tester, X-ray diffraction, optical microscopy and surface roughness tester. But, this technique being laboratory based cannot be used for in-service monitoring of the surface integrity. The present study focuses on the characterization of surface integrity upon electric discharge machined sample using non-destructive magnetic Barkhausen noise technique. Electric discharge machining was performed in die-sinking mode on die steel using copper–tungsten electrode (negative polarity). Experiment was performed by selecting different levels of peak current, gap voltage and pulse on time. Surface integrity characteristics like microhardness change, residual stress, microstructural alteration and surface roughness were analysed using microhardness tester, X-ray diffraction, optical microscopy and surface roughness tester, respectively, and were then correlated with magnetic parameter like root mean square value and peak value obtained from Barkhausen noise signal. The results show a good correlation between magnetic parameter (RMS and Peak value) of Barkhausen noise with the microhardness and surface roughness of the machined sample.

  相似文献   
5.
Russian Journal of Non-Ferrous Metals - Rolling bearing rings comprise a large reserve for expanding powder metallurgy production. This reserve is being incompletely implemented. The hot forging of...  相似文献   
6.
Metallurgical and Materials Transactions B - The process of obtaining titanium tetrachloride (TiCl4) from the quartz-leucoxene concentrate (QLC) from the Yaregskoe oil-titanium field was studied....  相似文献   
7.
Abstract

This article discusses different approaches to materiality and material expressions of cultural identity in contemporary Bahrain, a small Arab Gulf state. Various Islamic traditions have different understandings of materiality and its ontological qualities. In the contemporary Gulf this difference is often understood as a sectarian difference between Sunni and Shia Muslims, a division that has gained increasing political importance in recent years. In this article I discuss how these traditions view materiality in religion, in particular focusing on the role of material mediation for Shia Muslims, exemplified by the use and meaning of the turba prayer stone. With this as a point of departure I discuss two other forms of materiality—political graffiti and martyr images—that in the wake of the uprising in 2011 have also been imbued with sectarian meanings, but where this is less clear. I therefore argue that vernacular understandings of material culture show ambiguous identifications that challenge the clear dichotomies with which people—locally and analytically —often operate.  相似文献   
8.
9.
10.

Stability constants and formation enthalpies of supramolecular complexes of crown ethers and their cyclic and acyclic analogues are determined on the basis of experimental data obtained by different physicochemical methods in the terms of a general approach developed and implemented in the ChemEqui software package. The established regularities of variation of stability of complexes are discussed as dependent on the ligand structure, nature of the cation, solvent, and anion. The applicability of the suggested method of determining complexation selectivity is shown for multicomponent equilibria in solutions.

  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