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   4620篇
  免费   292篇
  国内免费   7篇
电工技术   24篇
综合类   6篇
化学工业   1586篇
金属工艺   29篇
机械仪表   76篇
建筑科学   185篇
矿业工程   5篇
能源动力   92篇
轻工业   856篇
水利工程   44篇
石油天然气   17篇
无线电   218篇
一般工业技术   556篇
冶金工业   723篇
原子能技术   30篇
自动化技术   472篇
  2024年   10篇
  2023年   66篇
  2022年   346篇
  2021年   343篇
  2020年   159篇
  2019年   152篇
  2018年   151篇
  2017年   146篇
  2016年   151篇
  2015年   157篇
  2014年   191篇
  2013年   291篇
  2012年   259篇
  2011年   332篇
  2010年   244篇
  2009年   240篇
  2008年   241篇
  2007年   221篇
  2006年   159篇
  2005年   128篇
  2004年   131篇
  2003年   113篇
  2002年   98篇
  2001年   38篇
  2000年   53篇
  1999年   47篇
  1998年   51篇
  1997年   34篇
  1996年   38篇
  1995年   32篇
  1994年   36篇
  1993年   29篇
  1992年   20篇
  1991年   9篇
  1990年   19篇
  1989年   20篇
  1988年   24篇
  1987年   22篇
  1986年   18篇
  1985年   14篇
  1984年   7篇
  1983年   9篇
  1982年   14篇
  1981年   11篇
  1979年   11篇
  1978年   8篇
  1977年   3篇
  1973年   4篇
  1965年   2篇
  1955年   2篇
排序方式: 共有4919条查询结果,搜索用时 15 毫秒
41.
We demonstrate the non-uniqueness of proportional fairness prices, and show that the model of Kelly et al. [9] falls into the category of models that can be generalized to allow optimization of the link prices, with a view toward profit maximization. However, through this framework, we also show that the total revenue that can be obtained through proportional fairness pricing on a network is unique.  相似文献   
42.
成品率预测是可制造性设计(DFM)的基础之,但它还远不止于此。IBM系统和技术群300mm半导体运营副总裁DanArmbrust说:“我们精确预测成品率的能力就是我们的经济模式。”Armbrust是SEMICON West 2007成品率论坛讨论DFM现状的三位参与者之一。与他共同参加讨论的是Synopsys公司DFM解决方案副总裁Anantha Sethuraman和Photronics公司的CTO Chris Progler。  相似文献   
43.
Several message topic selection approaches propose that messages based on beliefs pretested and found to be more strongly associated with intentions will be more effective in changing population intentions and behaviors when used in a campaign. This study aimed to validate the underlying causal assumption of these approaches which rely on cross‐sectional belief–intention associations. We experimentally tested whether messages addressing promising themes as identified by the above criterion were more persuasive than messages addressing less promising themes. Contrary to expectations, all messages increased intentions. Interestingly, mediation analyses showed that while messages deemed promising affected intentions through changes in targeted promising beliefs, messages deemed less promising also achieved persuasion by influencing nontargeted promising beliefs. Implications for message topic selection are discussed.  相似文献   
44.
尽管互连尺寸在不断地等比例缩小,同时也会用到更加多孔的低k材料,工程师们还是在设法满足互连的可靠性规范。VLSI电路,特别是高性能逻辑器件的不断等比例缩小,推动着对低k材料和铜互连的需求,以降低RC延迟、串扰噪声和功耗。  相似文献   
45.
First‐order phase transitions, where one phase replaces another by virtue of a simple crossing of free energies, are best known between solids, liquids, and vapors, but they also occur in a wide range of other contexts, including even elemental magnets. The key challenges are to establish whether a phase transition is indeed first order, and then to determine how the new phase emerges because this will determine thermodynamic and electronic properties. Here it is shown that both challenges are met for the spin reorientation transition in the topological metallic ferromagnet Fe3Sn2. The magnetometry and variable temperature magnetic force microscopy experiments reveal that, analogous to the liquid–gas transition in the temperature–pressure plane, this transition is centered on a first‐order line terminating in a critical end point in the field‐temperature plane. The nucleation and growth associated with the transition is directly imaged, indicating that the new phase emerges at the most convoluted magnetic domain walls for the high temperature phase and then moves to self‐organize at the domain centers of the high temperature phase. The dense domain patterns and phase coexistence imply a complex inhomogenous electronic structure, which can yield anomalous contributions to the electrical conductivity.  相似文献   
46.
Conductive anodic filament (CAF) formation has been studied for a number of years, but the mechanism of its formation has not previously been defined. In 2002, Ready identified CAF as atacamite, Cu2(OH)3Cl. Electrochemical studies have shown that both CuCl and CuCl 2 ? participate in the formation of Cu2(OH)3Cl, with the predominating species being CuCl. This paper proposes a mechanism for CAF formation based on x-ray photoelectron spectroscopy. The data show that CuCl is the precursor to the formation of Cu2(OH)3Cl in the presence of oxygen and water. Earlier, Meeker and Lu Valle had proposed that CAF failure is best represented by two competing reactions: the formation of a copper chloride corrosion compound (now identified as Cu2(OH)3Cl) and the formation of innocuous trapped chlorine compounds. Since no evidence of any trapped chloride compounds has been found, we propose that the formation of CAF is best represented by a single nonreversible reaction.  相似文献   
47.
A protein-free formation of bone-like apatite from amorphous precursors through ball-milling is reported. Mg2+ ions are crucial to achieve full amorphization of CaCO3. Mg2+ incorporation generates defects which strongly retard a recrystallization of ball-milled Mg-doped amorphous calcium carbonate (BM-aMCC), which promotes the growth of osteoblastic and endothelial cells in simulated body fluid and has no effect on endothelial cell gene expression. Ex situ snapshots of the processes revealed the reaction mechanisms. For low Mg contents (<30%) a two phase system consisting of Mg-doped amorphous calcium carbonate (ACC) and calcite “impurities” was formed. For high (>40%) Mg2+ contents, BM-aMCC follows a different crystallization path via magnesian calcite and monohydrocalcite to aragonite. While pure ACC crystallizes rapidly to calcite in aqueous media, Mg-doped ACC forms in the presence of phosphate ions bone-like hydroxycarbonate apatite (dahllite), a carbonate apatite with carbonate substitution in both type A (OH) and type B (PO43−) sites, which grows on calcite “impurities” via heterogeneous nucleation. This process produces an endotoxin-free material and makes BM-aMCC an excellent “ion storage buffer” that promotes cell growth by stimulating cell viability and metabolism with promising applications in the treatment of bone defects and bone degenerative diseases.  相似文献   
48.
新加坡特许半导体制造有限公司的J.B.Tan不久将推出五大成品率及可靠性问题的解决方案,结合多层互连结构及铜和低k介质集成。工程师们在互连工艺向批量生产过渡之前对这些问题进行了验证,并在6月5-7日在加州Burlingame举行的“国际互连技术会议”中推出研究成果。  相似文献   
49.
The management of small cell is considered a key point in next‐generation cellular networks for providing higher data rates, and the relay nodes are expected to be useful to improve the coverage area. Moreover, multicast services have gained importance to disseminate common data to subscribers. The use of buffer‐aided relay for multicast communications is analysed in the paper, and different policies to perform the optimal link selections are compared. These policies are based on the knowledge of the instantaneous link quality indicators as well as the status of the relay buffer and dynamically select the better link according to a suitable probabilistic criterion by improving the aggregate multicast flows. The parameters of these multicast policies are optimized via a Markov chain theoretical framework. The performance for all the proposed methods is analytically derived and validated through computer simulations conducted in different multicast scenarios. The advantages of the proposed schemes are pointed out in terms of multicast throughput, buffer occupancy for different buffer and multicast group size. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
50.
The relationship between exposure to sexually objectifying music television, primetime television programs, fashion magazines, and social networking sites and the internalization of beauty ideals, self‐objectification, and body surveillance was examined among adolescent girls (N = 558). A structural equation model showed direct relationships between sexually objectifying media and the internalization of beauty ideals, and indirect relationships between sexually objectifying media and self‐objectification, and body surveillance through the internalization of beauty ideals. The direct relationships between sexually objectifying media and the internalization of beauty ideals, self‐objectification, and body surveillance differed across the types of sexually objectifying media. The discussion focuses on the implications of these findings to explain self‐objectification among girls.  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