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   54724篇
  免费   16079篇
  国内免费   948篇
电工技术   1834篇
综合类   1368篇
化学工业   19870篇
金属工艺   1215篇
机械仪表   1725篇
建筑科学   2749篇
矿业工程   410篇
能源动力   1639篇
轻工业   8472篇
水利工程   639篇
石油天然气   556篇
武器工业   101篇
无线电   8984篇
一般工业技术   13379篇
冶金工业   1727篇
原子能技术   237篇
自动化技术   6846篇
  2024年   45篇
  2023年   204篇
  2022年   456篇
  2021年   784篇
  2020年   1780篇
  2019年   3488篇
  2018年   3415篇
  2017年   3800篇
  2016年   4262篇
  2015年   4480篇
  2014年   4606篇
  2013年   5967篇
  2012年   3815篇
  2011年   3511篇
  2010年   3706篇
  2009年   3555篇
  2008年   3057篇
  2007年   2915篇
  2006年   2604篇
  2005年   2135篇
  2004年   2056篇
  2003年   2103篇
  2002年   2329篇
  2001年   1989篇
  2000年   1568篇
  1999年   834篇
  1998年   342篇
  1997年   325篇
  1996年   292篇
  1995年   186篇
  1994年   143篇
  1993年   141篇
  1992年   106篇
  1991年   111篇
  1990年   80篇
  1989年   87篇
  1988年   66篇
  1987年   49篇
  1986年   48篇
  1985年   42篇
  1984年   19篇
  1983年   28篇
  1982年   31篇
  1981年   35篇
  1980年   20篇
  1979年   20篇
  1978年   10篇
  1977年   22篇
  1976年   27篇
  1972年   8篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents.  相似文献   
102.
103.
陆东凹陷油气藏烃类组成非均质性及其意义   总被引:1,自引:1,他引:0  
陆东凹陷原油和油砂抽提物中烃类的宏观组成存在着明显的非均质性。在高孔隙度(>15%)储层单元中,饱和烃的含量高,占总组成的含量均大于40%,而极性化合物则相对较低,一般不足40%;相反,在低孔隙度(<15%)储层单元中,饱和烃的含量明显降低,而极性化合物则显著增加。此外,陆东凹陷原油和油砂抽提物中烃类成熟度亦存在着非均质性:在高孔隙度储层中,原油和油砂烃类的成熟度参数高,而在低孔隙度储层中原油和油砂烃类的成熟度参数低。根据原油和油砂抽提物中烃类的宏观组成特征和成熟度参数的变化规律,提出了陆东凹陷油气聚集模式。  相似文献   
104.
A route to synthesize ZSM‐5 crystals with a bimodal micro/mesoscopic pore system has been developed in this study; the successful incorporation of the mesopores within the ZSM‐5 structure was performed using tetrapropylammonium hydroxide (TPAOH)‐impregnated mesoporous materials containing carbon nanotubes in the pores, which were encapsulated in the ZSM‐5 crystals during a solid rearrangement process within the framework. Such mesoporous ZSM‐5 zeolites can be readily obtained as powders, thin films, or monoliths.  相似文献   
105.
义东油田大81-4块咸化湖泊生物礁储集层特征   总被引:2,自引:1,他引:1  
义东油田位于济阳坳陷沾化凹陷义东断裂带,该油田大81—4块沙四段成化湖泊生物礁复合体自下而上可分为5个小型礁体(2个藻礁,3个藻礁丘体)。根据岩心观察、镜下鉴定和钻井等资料,主要有3种岩石类型:白云岩类是下部藻礁的主体,灰岩类是礁丘相的主体,其它岩类(主要为碎屑岩类和盐岩)分布局限;储集空间主要有7种类型(粒间孔隙、粒内孔隙、铸模孔隙、生长骨架孔隙、角砾间孔隙、晶间孔隙和构造裂缝)。该生物礁复合体位于凸起边缘的断阶带平台,发育于有陆源碎屑供给的半清水水域,紧邻深水区。礁体形成后经历了深埋藏成岩期,对储集空间演化影响最大的成岩作用是白云石化作用、溶解作用、新生变形作用和胶结作用。预测大81—221井区及附近的2个枝管藻白云岩礁体为最有利的勘探目标,义东22井附近生物礁也有良好的勘探前景。  相似文献   
106.
The probing of the micromechanical properties within a two‐dimensional polymer structure with sixfold symmetry fabricated via interference lithography reveals a nonuniform spatial distribution in the elastic modulus “imprinted” with an interference pattern in work reported by Tsukruk, Thomas, and co‐workers on p. 1324. The image prepared by M. Lemieux and T. Gorishnyy shows how the interference pattern is formed by three laser beams and is transferred to the solid polymer structure. The elastic and plastic properties within a two‐dimensional polymer (SU8) structure with sixfold symmetry fabricated via interference lithography are presented. There is a nonuniform spatial distribution in the elastic modulus, with a higher elastic modulus obtained for nodes (brightest regions in the laser interference pattern) and a lower elastic modulus for beams (darkest regions in the laser interference pattern) of the photopatterned films. We suggest that such a nonuniformity and unusual plastic behavior are related to the variable material properties “imprinted” by the interference pattern.  相似文献   
107.
We analyze travel times for automated storage/retrieval systems. In particular, we apply our travel time model to turnover-based storage systems and determine the mean and variance of dual command travel times. We present detailed numerical results for selected rack shape factors and ABC inventory profiles. We then investigate the effect of alternative rack configurations on travel time performance measures. We also show how to determine the throughput of miniload systems with turnover-based storage and exponentially distributed pick times.  相似文献   
108.
Selective epitaxial growth (SEG) of silicon has attracted considerable attention for its good electrical properties and advantages in building microstructures in high‐density devices. However, SEG problems, such as an unclear process window, selectivity loss, and nonuniformity have often made application difficult. In our study, we derived processing diagrams for SEG from thermodynamics on gas‐phase reactions so that we could predict the SEG process zone for low pressure chemical vapor deposition. In addition, with the help of both the concept of the effective supersaturation ratio and three kinds of E‐beam patterns, we evaluated and controlled selectivity loss and nonuniformity in SEG, which is affected by the loading effect. To optimize the SEG process, we propose two practical methods: One deals with cleaning the wafer, and the other involves inserting dummy active patterns into the wide insulator to prevent the silicon from nucleating.  相似文献   
109.
110.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry  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