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   66833篇
  免费   5240篇
  国内免费   2637篇
电工技术   3767篇
技术理论   8篇
综合类   4255篇
化学工业   11235篇
金属工艺   3664篇
机械仪表   4155篇
建筑科学   5493篇
矿业工程   1872篇
能源动力   2043篇
轻工业   4204篇
水利工程   1174篇
石油天然气   4550篇
武器工业   453篇
无线电   7524篇
一般工业技术   8508篇
冶金工业   3134篇
原子能技术   798篇
自动化技术   7873篇
  2025年   5篇
  2024年   1134篇
  2023年   1257篇
  2022年   1804篇
  2021年   2603篇
  2020年   2177篇
  2019年   1911篇
  2018年   1924篇
  2017年   2158篇
  2016年   2032篇
  2015年   2418篇
  2014年   3264篇
  2013年   3691篇
  2012年   4088篇
  2011年   4435篇
  2010年   3885篇
  2009年   3693篇
  2008年   3618篇
  2007年   3516篇
  2006年   3568篇
  2005年   3088篇
  2004年   2095篇
  2003年   1881篇
  2002年   1651篇
  2001年   1603篇
  2000年   1654篇
  1999年   1774篇
  1998年   1383篇
  1997年   1170篇
  1996年   1054篇
  1995年   937篇
  1994年   770篇
  1993年   558篇
  1992年   436篇
  1991年   336篇
  1990年   315篇
  1989年   228篇
  1988年   177篇
  1987年   108篇
  1986年   107篇
  1985年   60篇
  1984年   41篇
  1983年   27篇
  1982年   34篇
  1981年   22篇
  1980年   13篇
  1979年   3篇
  1976年   1篇
  1975年   1篇
  1959年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
This paper introduced systematically the present situation of the research on theory andtechnology for hard roof control of coal face in Chinese collieries.  相似文献   
32.
液压凿岩设备在我国地下矿山的应用   总被引:1,自引:0,他引:1  
十多年来,我国液压凿岩设备的研制和使用进展很大。地下矿山除了使用我国自行设计、研制的产品外,还使用根据技术引进合同生产的产品,也有一些矿山直接从国外购买,本文着重介绍这些液压凿岩设备在金属矿山、黄金和化工等矿山的应用情况。  相似文献   
33.
This study mainly focuses on the formation of isotactic polypropylene (iPP) blend morphologies with microspheres and distinct bead–string spherulites. iPP microspheres have been prepared by a simple and convenient strategy through either an isothermal or a nonisothermal crystallization process based on the macrophase‐separated structure in molten state of iPP/olefin block copolymer (OBC) blend. The dimension of the iPP spheres can be adjusted easily from about 1 µm to >10 µm by controlling the compatibility and annealing conditions. It was found that any of the following three parameters, the molecular structure of OBC (particularly the octene content), molecular weight of iPP, and annealing condition can be rescaled with others in controlling the dimension of the iPP microspheres. The mechanism of the formation of iPP microspheres was studied in detail. Surprisingly, the typical spinodal decomposition morphology with interconnected or thin sheet structure is the precursor of these microspheres. During the subsequent annealing process, it breaks up and further coarsens into spherical structure. In addition, distinct spherulites with a bead–string substructure have been obtained during the isothermal crystallization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40863.  相似文献   
34.
大漆艺术在中国有着悠久的历史以及辉煌的成就,本文从漆艺的历史切入,阐述了大漆良好的性能对古代漆器的保护作用;重点对漆器工艺的木胎、竹胎、陶胎、金属胎、夹纻、脱胎等胎骨的器型、工艺、优缺点等进行分析;另外也对漆画、漆塑的胎骨进行了探索与革新。将整个漆工艺制胎技术进行梳理与对比。  相似文献   
35.
The first catalytic asymmetric construction of the cyclic enaminone‐based 3‐substituted 3‐amino‐2‐oxindole scaffold with potential bioactivity has been developed via chiral phosphoric acid‐catalyzed enantioselective addition reactions of cyclic enaminones to isatin‐derived imines, which afforded a series of cyclic enaminone‐based 3‐substituted 3‐amino‐2‐oxindoles in high yields and excellent enantioselectivities (up to 99% yield, 97% ee). The investigation of the reaction mechanism suggested that it was facilitated by a dual hydrogen‐bonding activation mode between the two substrates and the chiral phosphoric acid. Besides, this method could be utilized for a large‐scale synthesis with maintained enantioselectivity. This approach will not only offer a useful method for enantioselective construction of the cyclic enaminone‐based 3‐substituted 3‐amino‐2‐oxindole scaffold, but also enrich the research on catalytic asymmetric addition reactions of isatin‐derived imines by using electron‐rich olefins as nucleophiles. More importantly, a preliminary evaluation on the cytotoxicity of some selected products revealed that two of the enantio‐pure compounds exhibited moderate to strong cytotoxicity to A549, 786‐0, ECA109 and BT474 cancer cell lines.

  相似文献   

36.
Yu  Pei  Jiang  Junxiang  Chen  Can  Wang  Zhong  Wang  Da  Li  Guangci  Li  Xuebing 《Catalysis Letters》2022,152(10):3046-3057
Catalysis Letters - Catalytic selective hydrogenation of esterified malic acid to produce 1,2,4-butanetriol (1,2,4-BT) using H2 as the reducing reagent suffers from the low 1,2,4-BT selectivity....  相似文献   
37.
Jiang  Lu  Jia  Zhiqian  Xu  Xin  Chen  Yili  Peng  Wenjuan  Zhang  Jiamin  Wang  Huimin  Li  Suoding  Wen  Jianping 《Journal of Porous Materials》2022,29(4):1071-1081
Journal of Porous Materials - Activated carbon fiber (ACF) is often used as efficient adsorption material for removal of contaminants from water. However, the propagation of microorganism on ACF...  相似文献   
38.
Bulletin of Engineering Geology and the Environment - Full-face tunnel boring machines (TBMs) are widely used in tunnel engineering projects as an efficient, safe and economical tunneling method....  相似文献   
39.
A three-step chemical synthesis of SmCo_5/Co nanocomposites was developed. Firstly, the Co-Sm(OH)_3-Ca(OH)_2 precursors were prepared by co-precipitation.Secondly, SmCo_5 particles were obtained by reductive annealing of the precursors. At last, the SmCo_5/Co nanocomposites were achieved by chemical deposition based on SmCo_5 particles. The SmCo_5/Co nanocomposites contain hard magnetic phase of SmCo_5 with about 100 nm in size and soft magnetic phase of Co with about 8 nm in size,exhibiting independent two-phase structure without alloying. Compared to that of single-phase SmCo_5 particles, the saturation magnetization of SmCo_5/Co nanocomposites is increased by 27.5%. The synthesis provides a new route to fabricate SmCo-based nanocomposites.  相似文献   
40.
In this report, fluorescence detection coupled capillary electrophoresis (CE-FL) was used to detect Protein A. Antibody was first labeled with Cy5 and then mixed with quantum dots (QDs) to form QDs-antibody bioprobe. Further, we observed fluorescence resonance energy transfer (FRET) from QDs donor to Cy5 acceptor. The bioprobe was formed and brought QDs and Cy5 close enough to allow FRET to occur. After adding protein A, the FRET system was broken and caused the FRET signal to decrease. Thus, a new method for the determination of protein A was proposed based on the FRET signal changes. This study provides a new trail of thought for the detection of protein.  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