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   37594篇
  免费   3990篇
  国内免费   2495篇
电工技术   879篇
综合类   1861篇
化学工业   8553篇
金属工艺   3233篇
机械仪表   1118篇
建筑科学   2276篇
矿业工程   727篇
能源动力   2109篇
轻工业   1439篇
水利工程   259篇
石油天然气   269篇
武器工业   474篇
无线电   4151篇
一般工业技术   13766篇
冶金工业   2002篇
原子能技术   358篇
自动化技术   605篇
  2024年   168篇
  2023年   913篇
  2022年   964篇
  2021年   1397篇
  2020年   1629篇
  2019年   1428篇
  2018年   1306篇
  2017年   1409篇
  2016年   1345篇
  2015年   1342篇
  2014年   1972篇
  2013年   2164篇
  2012年   2340篇
  2011年   3238篇
  2010年   2328篇
  2009年   2460篇
  2008年   2208篇
  2007年   2510篇
  2006年   2169篇
  2005年   2010篇
  2004年   1600篇
  2003年   1421篇
  2002年   1151篇
  2001年   833篇
  2000年   758篇
  1999年   523篇
  1998年   494篇
  1997年   345篇
  1996年   293篇
  1995年   226篇
  1994年   232篇
  1993年   165篇
  1992年   133篇
  1991年   134篇
  1990年   122篇
  1989年   99篇
  1988年   47篇
  1987年   29篇
  1986年   28篇
  1985年   21篇
  1984年   34篇
  1983年   19篇
  1982年   28篇
  1981年   7篇
  1980年   10篇
  1979年   3篇
  1976年   3篇
  1963年   2篇
  1955年   4篇
  1951年   7篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
The fabrication of functional textiles able to provide thermal regulation and comfort for the body has attracted increasing interest in recent years. This research investigated fabric coatings containing energy absorbing, temperature stabilizing, phase‐change material microcapsules (PCMMcs), and their methods of application. Specifically, a coated fabric was directly prepared by a dual‐type coating method, in which the PCMMcs were dispersed in a polyurethane coating solution with no binder. The thermal performances of the dual‐coated samples were evaluated by differential scanning calorimetry, and their physical characteristics were examined by scanning electron microscopy, thermal vision camera, porosity, water vapor transmission rate (WVTR), and water entry pressure (WEP) analyses. Furthermore, the microclimate characteristics of the thermally enhanced fabrics were investigated under experimental conditions using a human‐clothing‐environment (HCE) simulator system. The study results confirmed the superior performance of the dual‐coated fabrics in terms of thermal regulation and body comfort, compared with those coated by the dry or wet coating method, because of the improved WEP, WVTR, and thermal performance. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   
102.
103.
104.
The flexural and shear rigidity of pultruded composite sheet pile panels consisting of E-glass fiber-reinforced polyester are studied in this paper. The analysis consists of an experimental investigation and an analytical modeling to determine the resistance of the sheet pile panels to the deflections for design of composite sheet pile walls. Timoshenko’s beam theory was used to experimentally determine the flexural rigidity (EI) and shear rigidity (kAG) of the panel. Three- and four-point bending tests were performed on six different span lengths and the results were self-compared from the two independent tests. Analytical expressions for the flexural and shear rigidities were derived to allow the prediction based on the layered structure of pultruded shapes. The values computed from the analytical expressions were examined with the experimental results.  相似文献   
105.
The paper provides details on the current approach to multi-scale modeling and simulation of advanced materials for structural applications. Examples are given that illustrate the suggested approaches to predicting the behavior and influencing the design of nanostructured materials such as high-performance polymers, composites, and nanotube-reinforced polymers. Primary simulation and measurement methods applicable to multi-scale modeling are outlined. Key challenges including verification and validation are highlighted and discussed.  相似文献   
106.
107.
Al-SBA-15 of varying Si/Al ratios in the range 11.4–78.4 was synthesized using tri-block copolymer P123. The calcined materials were examined by XRD, pore size distribution, surface area, 27Al NMR spectroscopy. The acidity and acid strength distribution were studied using microcalorimetric adsorption of NH3. The acidic properties were also examined by cumene cracking reaction as a function of Si/Al ratios. Systematic variation of acidity and activity was observed as a function of Si/Al ratio. The initial heats of NH3 adsorption correlated well with activity indicate that acid sites with ΔH > 100 kJ/mole is responsible for cumene cracking activity. Linear correlations were obtained with total acidity and cumene cracking activities. The tetrahedral aluminum was found to be responsible for the observed acidities and catalytic activities.  相似文献   
108.
The aim of this article is to develop an experiment and a procedure to investigate the restoration of water-damaged paper and archival materials using freeze drying in order to allow a reproducible test and comparison of the influence of different operating conditions on drying time and restored paper quality. Firstly, a reproducible method for the preparation of soaked samples simulating water-damaged paper has been developed. Then, the samples have been freeze-dried in a laboratory-scale apparatus that allowed monitoring the temperature as well as the weight of the samples. The technique of evaporative freezing, which reduces the drying time required, has been used in this case. An innovative procedure for the visualization of the progress of the drying process has been validated, thus allowing the validation of a simple phenomenological model of the time evolution of the ice core volume; in addition, data on the residual moisture of the dried paper sheets in different zones have been given. Finally, optimization of this particular drying process by using simple or more sophisticated approaches has been discussed.  相似文献   
109.
In this work the synergistic effects of microwave (MW) irradiation induced oxidation processes and CoFe2O4 were studied for the degradation of brilliant green (BG) from aqueous solutions. Under the optimum condition, the ratio of solid to liquid was 1:167 (0.3 g CoFe2O4 mixed with 50 mL of 20 mg L−1 BG solution), MW power 600 W, and the time of the irradiation 2 min. And the decolorization rate could reach up to 100%. Further investigation showed that BG was degraded by MW-induced oxidation combined with CoFe2O4 surface adsorption. The CoFe2O4 could increase the efficiencies of MW degradation and be used repeatedly. The experimental results indicated that the method of MW degradation BG in the presence of CoFe2O4 could reduce reaction time and increase product yield.  相似文献   
110.
The effect of rare earth elements on eutectic carbide‘s morphology of low chromium semi-steel in as-cast state and after heat treatment was investigated, and accordingly, the thermal fatigue property of this material was studied. The results show that RE can improve the eutectic carbide‘s morphology, inhibit the formation and propagation of thermal fatigue cracks, therefore, promote the thermal fatigue property, which is more noticeable in case of the RE modification in combination with heat treatment. The optimal thermal fatigue property can be obtained when treated with 0.2% RE modification as well as normalization at 950℃ for 3h.  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