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   5541篇
  免费   140篇
  国内免费   14篇
电工技术   131篇
综合类   6篇
化学工业   1100篇
金属工艺   138篇
机械仪表   97篇
建筑科学   139篇
矿业工程   27篇
能源动力   239篇
轻工业   291篇
水利工程   21篇
石油天然气   18篇
无线电   728篇
一般工业技术   1073篇
冶金工业   864篇
原子能技术   39篇
自动化技术   784篇
  2023年   50篇
  2022年   81篇
  2021年   124篇
  2020年   106篇
  2019年   104篇
  2018年   138篇
  2017年   134篇
  2016年   113篇
  2015年   91篇
  2014年   128篇
  2013年   355篇
  2012年   195篇
  2011年   261篇
  2010年   211篇
  2009年   212篇
  2008年   230篇
  2007年   192篇
  2006年   188篇
  2005年   185篇
  2004年   147篇
  2003年   130篇
  2002年   112篇
  2001年   112篇
  2000年   87篇
  1999年   97篇
  1998年   220篇
  1997年   162篇
  1996年   111篇
  1995年   80篇
  1994年   112篇
  1993年   106篇
  1992年   89篇
  1991年   67篇
  1990年   60篇
  1989年   48篇
  1988年   62篇
  1987年   54篇
  1986年   53篇
  1985年   73篇
  1984年   58篇
  1983年   48篇
  1982年   39篇
  1981年   49篇
  1980年   41篇
  1979年   38篇
  1978年   36篇
  1977年   45篇
  1976年   47篇
  1974年   33篇
  1973年   35篇
排序方式: 共有5695条查询结果,搜索用时 78 毫秒
1.
A series of studies of top European and other firms has revealed patterns of design management associated with commercial success. Firms that invest resources and professional expertise in product and industrial design in traditional and new industries have been commercially more successful than firms that pay less attention to these aspects of design. As an industry matures there is a shift in emphasis from design associated with technological innovation, to designs supporting technical improvements, and then to supporting user needs, fashion and product variants. These issues are illustrated through the history of the evolution of the bicycle.  相似文献   
2.
Sintering and grain growth of nano-crystalline undoped ZnO has been studied in detail over a wide range of temperature and holding time. Below 800 °C, sintering of over 70% theoretical density is not observed, irrespective of particle size. At 900 °C for 6 h, the nano-crystalline sample sinters to 99% of theoretical density whereas the density for as received sample is 93% of theoretical density. However, at 1300 °C or higher, the densification is found to be much faster and after a few hours becomes independent of holding time. Grain growth studies reveal a similar feature of attaining saturation over holding time. The average saturated grain size is found to be ∼1.5 and ∼2.2 μm at 800 and 900 °C, respectively, while at 1300 °C or higher, it is in between 12 and 13 μm.  相似文献   
3.
The term “color gamut” historically has been associated with color output such as optimal color stimuli and additive and subtractive imaging systems. Recently, this term has been used with input devices such as scanners and digital cameras. It is proposed that the term “color‐gamut rendering” should be used instead of input devices. This clarifies the distinction between input (analysis) and output (synthesis) color systems in terms of the effect of an input system on defining the colorimetric properties of an output system. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 334–335, 2007  相似文献   
4.
Tomato seed oil was extracted with supercritical carbon dioxide in a semibatch-flow extractor within the temperature range 313–343 K and the pressure range 10.8–24.5MPa. The extraction rates increased with pressure, but decreased with temperature increase because of the variation in solvent density and resultant differences in oil solubility. The fatty acid composition of the extracted oil was similar to that of soybean oil.  相似文献   
5.
Nickel molybdate catalysts used in several different upgrading reactions of coal-derived materials from low-rank Australian coals have been regenerated and their activity assessed using a number of physical and chemical techniques. Regeneration of spent coked catalysts for 20 hours in air at 450°C was sufficient to restore chemical hydrogenation activity to catalyst used for pre-asphaltene, asphaltene and oil upgrading, provided poisoning of the catalyst surface by other impurities, principally chlorine-containing molecules, had not occurred.  相似文献   
6.
7.
In reliability theory, lifetimes of systems and components are frequently studied through univariate concepts of ageing. By considering suitable multivariate generalizations of the univariate ageing properties, some multivariate ageing classes of life distributions are defined. Properties of these classes with their equivalent definitions and chain of implications are presented along with a few characterizing properties. These results are useful for obtaining reliability bounds (when component lives are independent) at the early stage of product design. Also for model selection, characterization results can be important. Moreover, the underlying mathematical treatment is univariate when viewed through conditional distributions  相似文献   
8.
Silicoaluminophosphate (SAPO-5) molecular sieves have been synthesised from reaction mixtures having a molar composition of: 0.7–1.0 Al2O3:0.7–1.0 P2O5:0.01–2.0 SiO2:xR:40 H2O (where R = (C2H3)3N or (C2H3)4NOH and x = 1.5–2.5 for (C2H5)5N and 0.5 for (C2H5)4NOH, at 473 K using various sources of alumina and silica. The effects of (i) varying the crystallinity of the alumina source (boehmite) and (ii) the use of different silica sources such as freshly prepared silica either from sodium silicate or paddy husk extract, silica gel from commercial water-glass, and tetraethyl orthosilicate have been studied. The crystallinity of boehmite has been found to have a strong effect on its reactivity towards the formation of SAPO-5. The activity of boehmite for SAPO-5 formation increased with a decrease in its crystallinity (or with increase in its moisture content). Any silica source devoid of sodium ions could be employed for the synthesis of SAPO-5. The process of crystallisation started as early as within 1.5 h of reaction and incorporation of silicon into the AlPO4 framework has been noted at this stage. Formation of some tridymite phase as impurity has been observed under conditions such as (i) SiO2 concentration > 1.7 mole and (ii) x > 2.0 when R = (C2H5)3N.  相似文献   
9.
This paper presents a new method, based on a multi-agent system and on a digital mock-up technology, to assess an efficient path planner for a manikin or a robot for an access and visibility task taking into account ergonomic constraints or joint and mechanical limits. In order to solve this problem, the human operator is integrated in the process optimization to contribute to a global perception of the environment. This operator cooperates, in real time, with several automatic local elementary agents. The result of this work validates solutions through the digital mock-up; it can be applied to simulate maintainability and mountability tasks.  相似文献   
10.
Reaction-induced phase separation (RIPS) of miscible blends of poly(?-caprolactone) (PCL) and an epoxy resin based on poly(propylene oxide) (PPO) was used to prepare thermoplastic vulcanizates (TPVs) with fine rubber dispersions. Scanning electron microscopy (SEM) confirmed the formation of cross-linked rubber particles dispersed in the thermoplastic matrix at PCL contents ≥20 wt%. The morphology development during phase separation was studied by optical microscopy (OM) and time-resolved small-angle light scattering (SALS). It was shown that higher curing temperatures lead to a decrease in rubber particle size, but at the same time lead to an increase in the extent of particle connectivity. In some cases, gelation of the PPO-rich phase limits full structure development, which leads to extensive connectivity between the dispersed rubber particles and a strong deterioration in tensile properties.  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