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   212095篇
  免费   18083篇
  国内免费   9709篇
电工技术   12837篇
技术理论   20篇
综合类   15720篇
化学工业   34445篇
金属工艺   11569篇
机械仪表   13104篇
建筑科学   16514篇
矿业工程   5805篇
能源动力   5850篇
轻工业   17021篇
水利工程   3764篇
石油天然气   11164篇
武器工业   1690篇
无线电   24620篇
一般工业技术   24562篇
冶金工业   9679篇
原子能技术   2326篇
自动化技术   29197篇
  2024年   886篇
  2023年   3346篇
  2022年   6195篇
  2021年   8242篇
  2020年   6294篇
  2019年   5111篇
  2018年   5727篇
  2017年   6641篇
  2016年   5779篇
  2015年   8100篇
  2014年   10366篇
  2013年   12538篇
  2012年   13964篇
  2011年   15280篇
  2010年   13542篇
  2009年   13073篇
  2008年   13019篇
  2007年   12184篇
  2006年   12168篇
  2005年   10275篇
  2004年   7137篇
  2003年   6115篇
  2002年   5827篇
  2001年   5267篇
  2000年   4936篇
  1999年   5121篇
  1998年   4186篇
  1997年   3514篇
  1996年   3151篇
  1995年   2567篇
  1994年   2074篇
  1993年   1593篇
  1992年   1267篇
  1991年   974篇
  1990年   756篇
  1989年   635篇
  1988年   474篇
  1987年   367篇
  1986年   261篇
  1985年   203篇
  1984年   125篇
  1983年   105篇
  1982年   107篇
  1981年   81篇
  1980年   78篇
  1979年   41篇
  1978年   27篇
  1977年   26篇
  1976年   42篇
  1973年   12篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
A series of novel aliphatic poly(β‐thioether ester)s with various methylene group contents were prepared by direct lipase‐catalyzed polycondensation of the monomer with an acid‐labile β‐thiopropionate group. The polycondensation reaction using immobilized lipase B from Candida antarctica was carried out in diphenyl ether at 90 °C. Poly(β‐thioether ester)s with high molecular weights of 20 500–57 000 Da and narrow polydispersities in the range 1.40–1.48 were obtained. Thermogravimetric analysis, differential scanning calorimetry and wide‐angle X‐ray diffraction were used to investigate the thermal properties and crystal structures of these polyesters. All the poly(β‐thioether ester)s were semicrystalline polymers and thermally stable up to at least 200 °C. In vitro degradation studies showed that they can rapidly degrade under acidic conditions by the hydrolysis of the β‐thiopropionate groups, suggesting their potential as acid‐degradable polymeric materials. © 2019 Society of Chemical Industry  相似文献   
65.
Ionomics is a novel multidisciplinary field that uses advanced techniques to investigate the composition and distribution of all minerals and trace elements in a living organism and their variations under diverse physiological and pathological conditions. It involves both high-throughput elemental profiling technologies and bioinformatic methods, providing opportunities to study the molecular mechanism underlying the metabolism, homeostasis, and cross-talk of these elements. While much effort has been made in exploring the ionomic traits relating to plant physiology and nutrition, the use of ionomics in the research of serious diseases is still in progress. In recent years, a number of ionomic studies have been carried out for a variety of complex diseases, which offer theoretical and practical insights into the etiology, early diagnosis, prognosis, and therapy of them. This review aims to give an overview of recent applications of ionomics in the study of complex diseases and discuss the latest advances and future trends in this area. Overall, disease ionomics may provide substantial information for systematic understanding of the properties of the elements and the dynamic network of elements involved in the onset and development of diseases.  相似文献   
66.
Tricalcium silicate (C3S) and hydroxyapatite (HAp) composites were fabricated through the sol-gel process. The aim of this research is to improve the biocompatibility of C3S through HAp addition and study the potential of using this as coating materials. The composites (HAp/C3S) were characterised by Fourier transform infrared spectrometry, thermal gravity-differential thermal analysis and X-ray diffraction. The working and setting times of cement pastes were tested using Gillmore needle. Mechanical properties were examined by nanoindentation and material testing system. In vitro biocompatibility of the materials were studied by cell attachment and viability of L929 and MG-63 cells. HAp/C3S as a coating material on gelatin film were measured with the surface roughness and imaged by scanning electron microscope. With the addition of HAp, no undesirable free CaO was detected with the synthesis by the sol-gel preparation. The pH values of HAp added groups were between 7.54 and 8.76, which were much lower than pure C3S group (pH?=?11.75). For in vitro studies, the presence of HAp could effectively enhance the cell attachment and viability of both L929 and MG-63 cells grown in the extract or directly on the composites. However, the mechanical properties of the composites were impaired as compared to pure C3S. Lastly, HAp/C3S cement could be evenly coated on gelatin film. HAp is successfully demonstrated to improve C3S biocompatibility with this new composites HAp/C3S. C-75 (75% C3S and 25% HAp), in particular, has good biocompatibility, relatively high compressive strength and can be uniformly coated onto gelatin film. Thus, C-75 is a promising material for further investigation as a coating on other biopolymers.  相似文献   
67.
68.
69.
70.
电网的安全水平主要取决于其使用产品的质量是否过关。如果产品的质量较好,则能建造出优质的电网,电网的安全水平便会随之提高。因此,应加强对产品质量的监督管理,从而提高电网的安全水平。我们可建立质量监督管理系统,及时抽检出质量不过关的产品,从而消除电网运行过程中潜在的安全隐患。  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