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   19190篇
  免费   834篇
  国内免费   25篇
电工技术   228篇
综合类   23篇
化学工业   3988篇
金属工艺   352篇
机械仪表   423篇
建筑科学   1054篇
矿业工程   50篇
能源动力   522篇
轻工业   1802篇
水利工程   122篇
石油天然气   57篇
武器工业   1篇
无线电   1692篇
一般工业技术   3256篇
冶金工业   3344篇
原子能技术   216篇
自动化技术   2919篇
  2023年   155篇
  2022年   216篇
  2021年   478篇
  2020年   354篇
  2019年   380篇
  2018年   440篇
  2017年   397篇
  2016年   515篇
  2015年   448篇
  2014年   542篇
  2013年   1106篇
  2012年   889篇
  2011年   1174篇
  2010年   810篇
  2009年   862篇
  2008年   917篇
  2007年   791篇
  2006年   739篇
  2005年   613篇
  2004年   512篇
  2003年   462篇
  2002年   442篇
  2001年   314篇
  2000年   333篇
  1999年   369篇
  1998年   843篇
  1997年   537篇
  1996年   427篇
  1995年   320篇
  1994年   294篇
  1993年   298篇
  1992年   196篇
  1991年   181篇
  1990年   159篇
  1989年   151篇
  1988年   140篇
  1987年   130篇
  1986年   133篇
  1985年   155篇
  1984年   156篇
  1983年   135篇
  1982年   105篇
  1981年   107篇
  1980年   104篇
  1979年   106篇
  1978年   91篇
  1977年   125篇
  1976年   165篇
  1975年   97篇
  1974年   84篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Labels in spreadsheets can be exploited for finding formula errors in two principally different ways. First, the spatial relationships between labels and other cells express simple constraints on the cells usage in formulas. Second, labels can be interpreted as units of measurements to provide semantic information about the data being combined in formulas, which results in different kinds of constraints.In this paper we demonstrate how both approaches can be combined into an integrated analysis, which is able to find significantly more errors in spreadsheets than each of the individual approaches. In particular, the integrated system is able to detect errors that cannot be found by either of the individual approaches alone, which shows that the integrated system provides an added value beyond the mere combination of its parts. We also compare the effectiveness of this combined approach with several other conceivable combinations of the involved components and identify a system that seems most effective to find spreadsheet formula errors based on label and unit-of-measurement information.  相似文献   
993.
The perception of duration is crucial when we make choices between immediate and delayed rewards. Immediate rewards are valued more than the same rewards if they are delayed. Preferences for earlier rewards become even stronger when the reward can be received within a subjectively proximate time frame. A “rational” decision to wait for a delayed reward may be overruled by an “impulsive” choice when the option for the closer reward falls within this proximate time range. Based on findings on circadian and circannual physiological rhythms, we suggest that there are 2 time units that are both biologically and culturally determined and have an impact on human experience and behavior: the day and the year. We highlight results of a neuroimaging study showing that rewards with delays up to 1 year are discounted differently than reward delays longer than 1 year. This duration-dependent discounting is associated with specific brain activation in the striatum. We present various conceptualizations of subjective time incorporated in parametric models of intertemporal decisions that may lead to a better understanding of human choice behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
994.
REIr2Si2 (RE = La, Ce, Pr and Nd) were found to be polymorphic compounds which can crystallize in two different tetragonal types of crystallographic structures (β-phase: CaBe2Ge2-type; α-phase: ThCr2Si2-type). Here we study the structural phase transitions (α- to β- and β- to α-) using thermal expansion, differential thermal analysis and neutron diffraction. Both phase transitions occur at temperatures lower than 1300 °C, have a hysteresis up to 300 °C, do not show any intermediate steps and are accompanied with the absorption/release of the latent heat. We conclude that these structural phase transitions are of the first order.  相似文献   
995.
With the growth of competition between nations in our knowledge-based world economy, excellence programs are becoming a national agenda item in developing as well as developed Asian countries. The main purpose of this paper is to compare the goals, funding policies and selection criteria of excellence programs in China, Japan, Korea and Taiwan and to analyze the academic achievement of their top ranked universities in three areas: research output, internationalization, and excellence, by using data from the Shanghai Jiao Tong, QS, and HEEACT rankings. The effectiveness of Taiwan??s ??Development Plan for World Class Universities and Research Centers of Excellence?? was assessed as a case study in the paper via a survey targeting on 138 top administrators from 11 Taiwan??s universities and 30 reviewers. The study found that more funding nations had, the more outputs and outcomes they would gain, for example China. The Taiwan case demonstrates that world-class universities and research centers are needed in Asian nations despite the concerns for inequality which they raise.  相似文献   
996.
By triangulating analyses of content and reception with a focus on production, this article attempts to understand the dynamics of and underlying reasons for the media stigmatisation of place. The research described contributes to a body of work examining how mass media and other social forces factor in the creation of negative stereotypes that damage the reputations of the places in which the poor reside. The overarching framework of understanding, provided by Goffman’s theory of stigma, is complemented by two further inter-related theoretical approaches, namely Social Exclusion and Political Economy. Combining analyses of media production (practices), media content (discourses) and audience reception (beliefs, attitudes), we analyse the representation of one of Ireland’s most deprived public housing estates in the print and broadcast media. Having established the stigmatising character and impact of national and local media content via this tripartite methodology, we focus on identifying and explaining the media practices that serve to (re)produce the estate’s ‘spoiled identity’. Our analysis of journalists’ explanations for these practices identifies the commercial realities, which progressively influence media production, as directly impacting media producers’ relationships with, and depictions of, poor places. We conclude by examining debates regarding the potential for rehabilitating a spoiled identity.  相似文献   
997.
We present a new epoxy-based negative-tone dry film photoresist (DFR) for fabricating multilayer microfluidic devices using a lamination process combined with a standard photolithography technology. As proof-of-concept, a complex 3D-hydrodynamic focusing device was produced via a six-layer lamination process of 33 µm-thick DFR layers. The bonding strength of the new DFR was tested on silicon, glass, and titanium substrates, respectively. A maximum bonding strength of 37 MPa was obtained for the dry film photoresist laminated on glass. No leakage was found, and burst tests proved excellent robustness and sealing reliability of the microchannels.  相似文献   
998.
Polyurethane–siloxane thermoset copolymers were obtained from Isophorone diisocyanate trimer, Polycaprolactone triol and 10% of hydroxy terminated Polydimethyl siloxane. The copolymers showed a phase separated structure that depended on the conversion of the reaction and casting temperature. The different samples obtained had water contact angles higher than 90°. Moreover the contact angle values presented a maximum at intermediate reaction conversion. Although FTIR measurements showed that siloxane concentration at the surface increased with reaction time, the maximum contact angle value was related to the higher roughness calculated from AFM images. DMTA results confirmed that the phase separation was higher at intermediate conversions.  相似文献   
999.
A method to print two materials of different functionality during the same printing step is presented. In printed electronics, devices are built layer by layer and conventionally only one type of material is deposited in one pass. Here, the challenges involving printing of two emissive materials to form polymer light‐emitting diodes (PLEDs) that emit light of different wavelengths without any significant changes in the device characteristics are described. The surface‐energy‐patterning technique is utilized to print materials in regions of interest. This technique proves beneficial in reducing the amount of ink used during blade coating and improving the reproducibility of printed films. A variety of colors (green, red, and near‐infrared) are demonstrated and characterized. This is the first known attempt to print multiple materials by blade coating. These devices are further used in conjunction with a commercially available photodiode to perform blood oxygenation measurements on the wrist, where common accessories are worn. Prior to actual application, the threshold conditions for each color are discussed, in order to acquire a stable and reproducible photoplethysmogram (PPG) signal. Finally, based on the conditions, PPG and oxygenation measurements are successfully performed on the wrist with green and red PLEDs.  相似文献   
1000.
The wireless industry is currently undergoing a major transition from second generation (2G) to third generation (3G) wireless technologies. The paper attempts to assess wireless technology migration options using the real options approach (ROA) to support the wireless network operators’ strategic decisions: to migrate or not, if so, which migration path to take. The preliminary result shows that the evolution of wireless network technologies between generations is desirable, but not within generations. Finally, from a strategic perspective, we should consider the possible challenges that may hinder migration. By identifying these challenges, we can be more watchful of transition pitfalls and can choose a better alternative.  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